Phakic Intraocular Lens (IOL) for Myopia Correction 

Updated: Sep 22, 2016
Author: Arun Verma, MD; Chief Editor: Hampton Roy, Sr, MD 

Overview

Background

Myopia can be corrected by 3 different means, as follows:

  • Optical devices (ie, glasses, contact lenses)

  • Corneal refractive procedures (ie, radial keratotomy [RK], automated lamellar keratoplasty [ALK], photorefractive keratoplasty [PRK], laser-assisted in situ keratomileusis [LASIK])

  • Intraocular procedures (ie, clear lens extraction with or without lens implantation and the use of phakic intraocular lens [IOL] implants)

The important facets of each procedure are the ease of application, the accuracy, the period of recovery, the quality of vision, the long-term stability of the results, and the minor or major complications. Also important are the possibilities of the reversal of the procedure and the successful management of complications.

Each intraocular procedure has its advantages, in terms of ease of implantation and tissue reactions causing change of position, inflammation, degeneration, and rise of intraocular pressure (IOP).

LASIK is currently the most popular type of refractive surgery. It is safe and effective, and technology advances such as femtosecond bladeless LASIK have further improved visual outcomes. However, not all patients are good candidates for LASIK surgery, including patients with severe myopia, patients who have hypermetropia or astigmatism, patients with an unusually thin or irregularly shaped cornea, and patients with eye conditions such as keratoconus, pellucid marginal dystrophies, or dry eye.

Phakic IOL is preferable over LASIK surgery in most patients with severe myopia. In such patients, outcomes of phakic IOLs are superior to those of LASIK surgery in terms of both postoperative visual acuity and contrast sensitivity.

All the various phakic IOLs, whether angle supported, iris supported, or placed in the posterior chamber, provide good immediate postoperative results. However, frequent change in the designs of the angle-supported and the posterior chamber lenses makes conclusions about long-term stability difficult. The design of the iris claw lens has practically remained unchanged in the past 15 years.

Note the images below.

Phakic myopia lens of -20.0 diopters, 7 years post Phakic myopia lens of -20.0 diopters, 7 years postoperatively, in a 30-year-old man. There is slight upward decentration. The lens appears well tolerated.
Phakic myopia iris claw lens, 11 years postoperati Phakic myopia iris claw lens, 11 years postoperatively. The claws of the lens are shifted upwards. This configuration makes iris fixation in the claws easier at the time of surgery. It reduces the chances of pressure by the lens haptics and the optic on the natural lens and the iris, in case a bigger knuckle of iris is drawn inside the claw.
Anterior segment fluorescein angiography in a case Anterior segment fluorescein angiography in a case of iris claw lens (Artisan lens) in a phakic myope. There is no dye leakage. Courtesy of Professor Jan J. F. Worst, MD.

Compared to the corneal procedures, the intraocular procedures suffer from one glaring handicap, that is, patients with the lens implants have to be under careful supervision of the ophthalmic surgeon throughout their lives to prevent or treat any adverse development. The role of microtrauma or macrotrauma as a result of blinking, squeezing, and minor rubbing during the waking hours and involuntary hard rubbing during some phases of sleep, in producing tissue changes, cannot be overemphasized.

The future of phakic IOLs shall be determined by the newer techniques of corneal refractive surgery, especially the wave-guided ablations. Phakic IOLs cannot take care of preexisting astigmatism. Surgery might introduce astigmatism of its own. Also, with the passage of months and years, patients with phakic IOLs tend to miss detailed follow-up examinations. Situations do exist where phakic IOLs and corneal procedures can be combined to provide the best refractive results. Whether a phakic myopia IOL in a young patient will be a problem in future decades is still unknown.

Phakic Intraocular Lens Types

Various phakic IOLs are available.

The Visian implantable collamer lens (ICL), marketed by Staar Surgical, is a posterior-chamber phakic IOL, meaning it is positioned behind the iris and in front of the crystalline lens. It received FDA approval in 2005 for correcting myopia ranging from -3.00 to -20.00 D. The Visian ICL is made of a soft biocompatible collagen copolymer. Owing to its flexibility, the lens can be folded during implantation, requiring only a small surgical incision.

The Verisyse (Abbott Medical Optics) is an anterior-chamber phakic IOL, meaning it is positioned in front of the iris. In 2004, the Verisyse phakic IOL received FDA approval for correcting moderate to severe myopia ranging from -5.00 to -20.00 D. The Verisyse lens is made of medical-grade plastic (polymethylmethacrylate [PMMA]) and is rigid in form. In Europe, it is approved and marketed under the trade name Artisan. Verisyse IOLs are not typically noticeable in the eye, although they may be visible to patients upon close inspection with a mirror.. This iris claw lens has been in use in India by Professor Dr. Daljit Singh by the name of Singh's modification of Jan Worst's lens since the late 1970s. Dr. Singh has implanted this lens in more than 100,000 eyes over the past 30 years.

The Visian ICL and Verisyse phakic IOL are FDA approved to correct myopia only.

History of the Procedure

The phakic myopia lens was introduced by Strampelli and later popularized by Barraquer in the late 1950s. The design was a biconcave angle-supported lens. These lenses were abandoned following serious angle- and endothelium-related complications. In the mid 1980s, Dveli restarted phakic myopia lenses with 4 soft angle-supported loops. Baikoff introduced a myopia lens with Kelman-type haptics. This design had many problems, leading to its design modification a number of times. Fyodorov introduced the concept of a soft phakic lens in the space between the iris and the anterior surface of the crystalline lens. Earlier, the material used was silicone; now, the material used is collamer. Note the image below.

This phakic intraocular lens is fixated to the mid This phakic intraocular lens is fixated to the midperiphery of the iris.

Worst, who introduced the iris claw lens in 1977, implanted an opaque iris claw lens in the phakic eye of a patient who had unbearable diplopia in 1979. Fechner and Worst introduced a phakic myopia lens of iris claw design in 1986. According to Ophthec, the maker of this lens (now called Artisan), more than 16,000 such lenses have been implanted worldwide in phakic myopes. During the same period, more than 250,000 iris claw lenses have been implanted in aphakes, which suggested that the design is well tolerated by the iris, where the lens is fixated.

Note the images below.

5-mm optic Artisan lens. Courtesy of Professor Jan 5-mm optic Artisan lens. Courtesy of Professor Jan J. F. Worst, MD.
6-mm diameter optic, Artisan lens. Courtesy of Pro 6-mm diameter optic, Artisan lens. Courtesy of Professor Jan J. F. Worst, MD.

During the past 20 years, the coauthor has implanted more than 160,000 iris claw lenses (ie, Artisan lenses) in his hospital (ie, Daljit Singh Eye Hospital, Amritsar, India); during this same period, the author has implanted approximately 20,000 lenses. In India, also during this same period, approximately 100,000 lenses have been implanted. Ophthec reports that more than 15,000 lenses are implanted in Europe every year.[1]

Problem

Myopia is a common refractive error, which exists from a young age. A unilateral myopia, with or without amblyopia, might remain undiscovered for a long time. The treatment of unilateral myopia is not easy. Since the vision is very good in the other emmetropic eye, the child is not impressed by the glass or the contact lens for the affected eye because the child prefers to use the nonaffected eye. Most parents give up all efforts out of sheer frustration, and the magnitude of wasted sight is immense.

While there is some experience with such modalities as the excimer laser for use as PRK or LASIK and the newly designed phakic IOLs, they have been used in adult patients, and there is little or no experience in the group of young patients who need the treatment.[2, 3] Slight or moderate myopia is hardly a problem as far as the vision is concerned. These patients do extremely well with glasses or contact lenses. However, high myopes do experience serious handicaps, both cosmetic and visual, for which surgery becomes a matter of importance.

Myopia is not merely a refractive problem. The importance of regular retinal examination should not be overlooked.

Etiology

Much remains unknown about the developing eye. It is known that myopia results when the refracting optics of the eye focus parallel rays from infinity to a point in front of the retina (relative to the length of the eyeball).

Newborns are moderately hyperopic, but they have a broad distribution of refractive errors. As the eye grows, there is a shift toward emmetropia. Perhaps, myopia represents an extension of the emmetropization process.

Pathophysiology

The pathophysiology differs in the 3 types of IOLs, the angle-supported, the iris-fixated, and the precrystalline varieties.

Angle-supported lenses

Two types of angle-supported lenses for use in phakic eyes are available. One has a Kelman-type haptic design, the other has a somewhat different design. The optic is biconcave. The lens is vaulted at 20°. The effective optic diameter is 4 mm in one design and 5 mm in the other design. Both are polymethyl methacrylate (PMMA) lenses. Note the image below.

Phakic minus iris claw lens, 12 years postoperativ Phakic minus iris claw lens, 12 years postoperatively, in a 36-year-old patient shown in 3D. The lens is seen to sit on top of the iris cone. This picture helps to understand why the much larger angle-supported lenses have to be vaulted by 20° to keep clear of the iris.

The angle-supported lens becomes fixated somewhere in the angle structures. There cannot be a perfect size of the IOL. A well-fixed lens is supposed to rest its haptics on the scleral spur. In actuality, the haptics press against the corneoscleral trabeculae and the Schlemm canal and, sometimes, the blood vessels in the vicinity that overlie the scleral spur. The haptics impinge on the nerve endings in the angle of the anterior chamber. However, nothing is known about this interaction. The haptics press on the segmental blood supply of the iris, leading to ischemia and iris atrophy, which results in progressive ovalization of the pupil. The haptics can erode through the angle tissues and become lodged in the ciliary body.

A loose angle-supported lens can move around and damage the corneal endothelium. Tissue reactions and damage to the angle of the anterior chamber can cause breakdown of the blood-aqueous barrier, uveitis-glaucoma-hyphema (UGH) syndrome.[4] Anterior segment inflammatory pathology may find an echo in the development of cystoid macular edema.[5] Microtrauma and macrotrauma of any nature can accelerate the pathological changes in the angle.

Iris-supported lenses

Iris claw lenses also are made of PMMA; the overall length of the implant varies from 7.2-8.5 mm, the size of the optic varies from 5-6 mm. The optic is convexo-concave, with a maximum height of 0.96 mm. The lens also is vaulted at the haptic to clear the natural vault of the iris.

The haptics become fixed to the midperiphery of the iris through the medium of the claws, located on either side of the lens. The amount of iris engaged into the claw depends on the judgment of the surgeon at the time of surgery.

The size of the IOL precludes all angle-related complications. No pupil- or posterior pigment epithelium–related problems occur because at no time does the lens come into contact with either of them. The author and the coauthor have used these lenses extensively, and they are very satisfied with the results. A concern does exist regarding chronic inflammation as a result of continued compression of the iris tissue in the claws. The inclusion of excessive iris tissue in the claws during surgery can push the lens against the iris and the crystalline lens. This can interfere with the free circulation of the aqueous through the pupil, possibly resulting in the formation of posterior synechia and inflammation.

Micromovements, such as blinking and squeezing, do not bring together the endothelium of the cornea and the optic of the IOL. However, forcible rubbing for any reason has the potential to damage the endothelium.[6]

Posterior chamber lenses

The phakic posterior chamber lens or the precrystalline lens is made of a soft material, such as silicone or collamer. The overall length varies from 11-13 mm. The central biconcave optical zone varies from 4.5-5.5 mm. The average thickness of the haptic is 60 µm. In an ideal lens implant situation, it is supposed to remain clear of the crystalline lens by 100-200 µm. The posterior chamber lens is sized empirically by adding 0.5 mm from the white-to-white corneal diameter.

The vaulting of the lens is produced by the elastic single piece lens getting lifted from the ciliary body. This puts some constant pressure, however small, on it. The vaulting may let it stay clear of the crystalline lens, but it physically pushes the iris anteriorly, a tissue normally in touch with the crystalline lens in the central part. This unnatural constant contact pressure and friction might lay the foundation for ciliary body reactions and shedding of posterior pigment epithelium. It also may prevent free passage of aqueous across the pupil. A mistakenly larger sized lens will put more pressure on the iris and push it forward by what may be called the spinnaker effect (blowing sail of a sail boat).

The optimal size remains a matter of conjecture. A mistaken small size allows the lens to rub against the natural crystalline lens (causing cataract) and knock against the ciliary body (setting up uveal reaction) and the posterior surface of the iris (releasing the pigment). The free volume of the restricted posterior chamber space is encroached upon by the implanted IOL and an increase in the size of the natural crystalline lens with age. If the peripheral iridectomy becomes blocked, iris bombé and consequent angle-closure glaucoma will occur. Some of the developments occurring behind the iris cannot be visualized clinically. They can only be speculated.

During blinking, squeezing, and rubbing, the results of pressure and friction between the IOL and the surrounding tissues are unknown. Even if the frictional force is very small, it is bound to continue for life. When shed from the iris and ciliary processes, the pigment may lead to glaucoma. Patients with diabetes can have problems. This disease causes changes in the posterior pigment epithelium of the iris, which may cause excessive shedding of pigment. An inflammatory process can bind the lens to the iris, the ciliary body, or even the crystalline lens. An intermittent or a continuous touch with the anterior lens capsule can produce lens opacification. Sometimes, the presence of the artificial lens in the posterior chamber can crowd the angle of the anterior chamber, leading to glaucoma.

In all phakic IOLs, increased crystalline lens size with increasing age and cataract formation leading to a decrease in the depth of the anterior chamber and crowding in the posterior chamber tend to exaggerate the pathologic processes. While the results of phakic IOLs are highly predictable, long-term data are limited.

Frequency

The prevalence of myopia is approximately 20% in the United States. This incidence rate frequently varies with age, sex, race, ethnicity, occupation, environment, and other factors in various sampled populations. The condition is more common in central and eastern Europe than in northern Europe, Britain, and the United States.

Incidence

The incidence of simple myopia is quite high since it occurs as a normal chance variant in the biological series, which include emmetropia and hypermetropia. In comparison, high and degenerative myopia are relatively rare. It has been estimated that myopia of more than -6.00 diopters (D) represents 27-32% of the myopic population and more than -8.00 D represents 6-18% of the myopic population.

Mortality/morbidity

Unilateral high myopia (more than about -6.00 D) of early onset can cause severe amblyopia. Severe symmetric refractive error (isometropia) may cause bilateral amblyopia of mild-to-moderate degree. However, myopia, even when extreme, rarely causes bilateral amblyopia because the sharply focused images of objects held close to the eyes support normal visual development.

Race

Race exercises a considerable influence over myopia. High degrees with degenerative changes are very common in certain races, such as Chinese, Japanese, Arab, and Jewish persons. Myopia is uncommon in black, Nubian, and Sudanese persons. The variation probably is due more to heredity than habit.

Sex

Sex appears to have an influence on the incidence. Although in the lower degrees of myopia, the sexes seem to be affected equally, with a probable excess in males; females are more prone to the higher degrees and to degenerative changes. Surgical correction of myopia in girls assumes significance in certain societies where wearing of glasses and/or contact lenses is not looked upon kindly.

Age

Age at which surgery is performed is of great importance. The ideal age should be at around age 18 years when the refraction stabilizes. However, in specific circumstances, in the interest of the minor patient, the parents and the surgeon can opt to perform phakic lens implantation at an earlier age.

Presentation

Clinical manifestations are as follows:

  • Defective uncorrected vision

  • Defective corrected vision - Myopic retinal degeneration and deprivation amblyopia

  • Strabismus

  • Nystagmus

Clinical findings are as follows:

  • The eyeball may be normally placed, prominent, or deeply set.

  • The cornea may have a normal diameter, or some degree of microcornea or megalocornea may be present.

  • Axial length - 20 mm to greater than 30 mm

  • Keratometry reading - 38-50 D

  • Depth of the anterior chamber - 2.5-4 mm

  • Myopia may be moderate or severe, even going beyond -20.0 D.

  • IOP should be normal, and the patient should not be under treatment for any kind of glaucoma.

  • Strabismus

  • Nystagmus

  • Fundus examination may show various degrees of lattice degeneration, with or without one or more holes. The macular area may show disturbed macular reflex, chorioretinal atrophy, or posterior staphyloma.

  • Visual field defects of myopia may be present.

History findings are as follows:

  • Deteriorating vision

  • Difficulty in handling glasses or contact lenses; intolerance to contact lenses

  • Optical problems in daily life, especially during driving

  • Cosmetic concerns of the patient

  • Problems in such professions as sports, stage, and service regulations

Physical findings are as follows:

  • All patients should undergo a complete ophthalmic examination.

  • Manifest and cycloplegic refraction

  • Uncorrected visual acuity

  • Spectacle and/or contact lens corrected visual acuity

  • Slit lamp examination of the anterior segment and ocular adnexa

  • IOP

  • Pupil size measurement under scotopic conditions

  • Corneal endothelial cell count with specular endothelial microscopy

  • Biometry to calculate axial length of the eyeball and the anterior chamber

  • White-to-white corneal diameter measurement, if contemplating angle-supported or posterior chamber implants

  • Videokeratography and keratometry

  • Fundus examination by indirect ophthalmoscopy

  • Field charting

Indications

Indications include unilateral or bilateral, moderate or severe myopia; cosmetic needs; and professional and service requirements.

The current practical options for the cornea are PRK and LASIK; for intraocular implantation procedures, an angle-supported lens, an iris-supported lens, or a posterior chamber lens are practical options. Surgeons in different parts of the world may have differing opinions about these 3 lenses.

When planning for an IOL implant in phakic myopes, consider the following:

  • What is the minimum age at which the lens is to be implanted?

  • What is the minimum or the maximum refractive error to be treated?

  • What should be the lowest limit for anterior chamber depth?

  • What is the lowest corneal diameter at which lens implantation will be refused?

  • How accurate is the white-to-white diameter on the basis of which the length of an implant lens is to be derived?

  • What is the smallest size of the lens available?

  • How can the risk of complications be minimized? What are those complications? What are the chances of occurrence?

The final decision to do lens implantation comes after careful contemplation and detailed consultations and discussions.

The author and the coauthor are very interested in amblyopia and, to date, have helped more than 10,000 children and young adults with various forms of amblyopia, including those with amblyopia due to high myopia (unilateral and bilateral).

A new study by Alio et al shows promise in treating anisometropic amblyopia with phakic IOLs in adults.[7] The study reported a mean gain in vision of 3 lines, with a range of 0-7 lines. No patient lost any vision. PRK and LASIK have previously been studied to correct anisometropic amblyopia. In comparison to these studies, the visual results were similar after phakic IOL implantation for amblyopia. However, phakic IOL implantation may be a better option than LASIK or PRK because this study’s population had a much higher initial spherical equivalent. While effective in adults, phakic IOLs—in the right size—might work even better in children.

These IOLs may now have a new niche in the correction of amblyopia in adults. Alio et al evaluated the use of phakic IOLs to correct amblyopia in an adult population, with surprisingly good results.[7]

According to Alio et al, "This improvement is accounted for by the magnification on the retina caused by the intraocular lens, as opposed to the minimization induced by optical correction at the spectacle plane and the decrease in the spot size resulting from optical aberrations. This improvement was related to optical factors involved in the correction of the high myopia with a phakic IOL."

PRK and LASIK have previously been studied to correct anisometropic amblyopia and have had some success. According to Alio et al, "If excimer laser procedures can improve amblyopia in adults, phakic IOLs should be capable of doing so as well. This, along with the advantages of phakic IOLs regarding better quality of vision and lack of induction of aberrations resulting from corneal laser ablation, makes them an excellent alternative for the treatment of anisometropic amblyopia."

Fifty-nine eyes of 48 patients with anisometropic amblyopia underwent analysis by Alio and colleagues. They received angle-supported phakic IOLs (Domilens-Chiron, Lyon, France). Thirty-seven patients were unilaterally implanted, and 11 patients were bilaterally implanted.

According to Alio et al, "After implantation of a phakic IOL, the visual acuity of myopic patients with anisometropic amblyopia showed a significant increase. This improvement is accounted for by the magnification on the retina caused by the intraocular lens, as opposed to the minimization induced by optical correction at the spectacle plane and the decrease in spot size resulting from optical aberrations."

Specifically, the mean gain in visual acuity was 3 lines, with a range of 0-7 lines. No eyes lost vision. Further, 54 eyes (91.5%) gained at least 1 line of visual acuity.

According to Alio et al, "Our analysis … does not show evidence of neuroprocessing related to underlying mechanics in the rehabilitation of amblyopia in these anisometropic adult patients; instead, this improvement was related to optical factors involved in the correction of the high myopia with a phakic IOL."

Comparing these results with those from LASIK or PRK for amblyopia, the advantages of phakic IOLs are evident. As stated by Alio et al, "We obtained visual outcomes in our study group similar to those reported with other refractive procedures. Mean preoperative spherical equivalent was much higher in our series; thus, phakic IOL implantation was a better surgical option than LASIK or PRK."

Karl Stonecipher, MD, Medical Director, TLC Carolina, Greensboro, NC, agreed that phakic IOLs have a role to play in amblyopia correction but suggested better results could be obtained if they are implanted earlier in life prior to the development of the amblyopia.[8]

"I agree totally with the findings of Dr. Alio’s group and other reports of success with LASIK and refractive lensectomies that have been presented and published. Those studies show that improving the optics, as the study suggests, improves the overall visual function. I think it would be great if we could just interrupt the process earlier. Most older studies show you’re not going to significantly change the course of the problem after nine years of age. Yet, in these anisometropic amblyopic patients, any benefit can add to the functionality of the patient."

Unfortunately, current phakic IOLs are too large for young children. So other more conventional methods, such as glasses, contact lenses, atropine, and patching, may have to do in the meantime. Additionally, reports of LASIK for anisometropia in children have appeared and shown successful outcomes.

Stonecipher noted, if phakic IOLs were made for children to treat anisometropic amblyopia, that would probably be a relief for parents who have to deal with contact lenses, patching, and the use of atropine drops. Parents often get tired of these methods to correct amblyopia because of their child’s complaints.

However, one potential problem with a smaller phakic IOL would be the fact that it would have to be explanted at some point and a larger IOL fitted or another refractive procedure performed as the eye grows. Further, putting kids to sleep to perform the phakic IOL procedure is also a risk, Stonecipher said.

Alio et al noted in their study that there is indeed room for improvement in amblyopia correction for children. Success rates of conventional methods, such as atropine and occlusion, range from 63-83%, respectively.

Relevant Anatomy

Important anatomical features for phakic posterior chamber lens implantation

The following anatomical features involved in phakic posterior chamber lens implantation are important: the space available for the implanted lens, the structures with which the lens will intimately contact, and the effect of age on the dimensions of various involved structures.

The pupillary margin normally rests on the crystalline lens. The contact is maximum in a middilated condition. The posterior chamber, which has a volume of 65 µL, is a triangular space on cut section. The base is toward the periphery, and the apex is toward the pupillary margin (where the chamber depth is zero). Nothing is known about the variations of this space and its relationship with age, the depth of the anterior chamber, or with refraction.

Anteriorly, there is a floppy iris about 0.5 mm in thickness; the thickness does not change throughout life. Posteriorly, there is the firm crystalline lens, which has a volume of 140 µL at birth. The volume increases to 163 µL in the 30s and to 240 µL in the 80s, a change of 100 µL.

The anterior chamber depth decreases by 7% every decade. It is the increasing size of the crystalline with age that causes shallowing of the anterior chamber. At the same time, it is not unreasonable to assume that the restricted posterior chamber space is also progressively encroached upon by the increasing volume of the crystalline lens. By the time the patient is in the seventh decade, the space is nothing more than a mere slit. In the case of a posterior chamber lens, the thickest part of the implant, the optic, occupies the shallowest or the zero space.

If a plate haptic lens has to stay clear of the crystalline lens, it should vault in the central area. This can happen only if the haptic rests strongly on the ciliary processes and bows forward. Staying clear of the crystalline lens can lead to rubbing against the posterior pigment epithelium. It also means impinging on the ciliary epithelium of the ciliary processes. If the ciliary epithelium sheds, then the implanted lens will further touch the ciliary vasculature. The ciliary capillary endothelium has fenestrations of 30-100 µm, which are permeable to plasma proteins and tracer elements.

Lying between the crystalline lens and the iris, the phakic posterior chamber lens produces resistance to the flow of aqueous. The increasing volume of the crystalline lens with age encroaches on the posterior chamber volume. The crystalline lens volume increases greatly, from 150 µL to 240 µL, in a matter of 60 years.

The average anterior chamber depth is 3.15 mm (2.6-4.4 mm). The volume of the anterior chamber is 250 µL, which decreases by 7.5% per decade.

Important anatomical features for iris claw and angle-supported lenses

The iris is 0.5 mm thick at the root and 0.6 mm at the collarette. An iris claw lens is attached to the peripheral anterior surface of the iris by pushing a fold of the iris into the 2 claws of the lens. Consider the following 3 points: the space available around the lens and the distance from the corneal endothelium and the crystalline lens; the anatomy of the iris, especially the vasculature, as it is fixed in the claws of the lens; and the pupil movements and the friction between the iris and the phakic iris claw lens.

The posterior surface of the IOL is concave and cannot touch the crystalline lens. There is a respectable distance between the various parts of the lens and the corneal endothelium. The maximum height of the optic, which is in the center, is less than 1 mm. The haptic of the lens in the periphery is 0.18 mm. With age, the growth of the crystalline lens tends to reduce the depth of the anterior chamber. The maximum width of the implant lens is 8.5 mm, which allows it to remain away from the structures of the angle of the anterior chamber.

The vasculature of the iris is peculiar. The vascular endothelium of the human iris is not fenestrated. The endothelial cells of the iris vessels are joined by 2 types of intercellular junctions, the zonular tight junctions and the gap junctions. The vessels are covered in layers in the following order:

  • Pericytes

  • 0.5-3 µm wide basal lamina

  • 7-µm zone of sparse, longitudinally directed collagen fibers

  • Granular ground substance

  • Another 10 µm-wide connective tissue layer

Vessels that are located in the more cellular parts of the stroma (eg, anterior border layer) are invested in thicker and more cellular adventitia. These vascular peculiarities explain why the claw lens can grip the iris fold so well. Friction between the iris claw lens and the anterior surface of the iris is possible at the immediate vicinity of the 2 claws as well as along the edge of the lens. As observed during the past 25 years, an iris claw lens is well tolerated in aphakic eyes. Phakic eyes are different, and surgeons must be aware of any degenerative or inflammatory response. Furthermore, phakic lenses are being implanted in younger patients, and these patients will need to be observed beyond the lifetime of many of their surgeons.

Important anatomical features for angle-supported lenses

The angle of the anterior chamber is another place where phakic angle-supported lenses are made to rest their footplates. The tissues involved are the corneoscleral trabeculae, the ciliary body, and the periphery of the iris. In the depth of the trabecular meshwork, there is the Schlemm canal, stray blood vessels in its vicinity, and the scleral spur. The scleral spur is deeper to the Schlemm canal, and it ends at a few micrometers wide tip under the posterior part of the corneoscleral trabeculae. The recess of the angle does not end at the level of the scleral spur but further posteriorly.

The major arterial circle is situated in the anterior part of the ciliary body. From this circle arise branches that go to the root of the iris anteriorly and the ciliary processes posteriorly. The endothelium of the capillaries in the ciliary body and the processes has fenestrations of 30-100 µm, which are permeable to plasma proteins and tracer elements. The arteries to the iris arise along with the branches to the ciliary processes. The vessels travel toward the pupillary margin without anastomosing, that is, they are more or less end arteries.

Contraindications

Contraindications include the following:

  • Myopia other than axial

  • Evidence of nuclear sclerosis or developing cataract

  • History of uveitis

  • Presence of anterior or posterior synechiae

  • Corneal dystrophy

  • Glaucoma or IOP higher than 20 mm Hg

  • Personal or family history of retinal detachment

  • Diabetes mellitus

  • Anterior chamber depth less than 2.75 mm

Some of the above contraindications are relative on the discretion of the surgeon and the needs of the patients.

Relative contraindications include the following:

  • The patient should not rub the eye. Young children who cannot follow these instructions should not be implanted with a phakic IOL.

  • The smallest available posterior chamber phakic lens is of 11 mm. The length of the lens is calculated by adding 0.5 mm to the white-to-white limbal diameter. The minimum white-to-white diameter should be 11 mm. Any degree of microcornea from this size is a contraindication. In the case of an iris claw lens, it is possible to have customized, smaller lenses. While the normal phakic lens is 8.5 mm wide, the iris claw lens may be made as small as 6 mm, thus greatly extending its application.

The presence of amblyopia should not be a contraindication for the following purposes:

  • To reduce the power of the glasses

  • To provide a greater freedom of movement

  • Later, to attempt to improve the eyesight with pleoptic exercises

Anterior chamber depth is an important consideration for all 3 types of lenses, whether it is angle-supported, iris claw, or posterior chamber lenses. A depth of less than 2.75 mm is a contraindication. The angle-supported or the posterior chamber lens may cause crowding of the angle, but the iris claw lens will encroach on the central depth of an already shallow anterior chamber.

 

Workup

Other Tests

Determination of the lens formula is as follows:

  • Van der Heijde's nomogram for iris claw lens power calculation

  • Feingold's formula (proprietary) for a precrystalline lens implant

  • Matrix formula for phakic anterior chamber intraocular lens (AC IOL) power calculation

  • Binkhorst 2 formula for posterior chamber intraocular lens (PC IOL) power calculation

 

Treatment

Medical Therapy

Medical therapy is as follows:

  • Perform both manifest refraction and cycloplegic refraction.

  • Conjunctival swab is taken for culture 2 days before surgery, after which topical antibiotics (tobramycin 0.3%) are started, 6 times a day.

  • Preoperative drops: Preoperative eye preparation depends on the type of IOL to be implanted.

  • Angle-supported lens and iris claw lens: Contract the pupil with 1% pilocarpine drops, instilled at 15-minute intervals, starting 45 minutes before surgery.

  • Precrystalline lens: Dilate the pupil with homatropine (2%) and phenylephrine (5%), instilled 3 times at 15-minute intervals, starting 1 hour before surgery.

  • Nonsteroidal anti-inflammatory drug (NSAID) drops are instilled 2 times before surgery.

Surgical Therapy

Nd:YAG laser peripheral iridectomy may be performed 1-2 weeks prior to a phakic lens implantation. This procedure prevents pupillary block in the postoperative period. The other alternative is to perform a manual iridectomy at the time of the phakic lens implantation.

Every phakic IOL demands meticulous care in the performance of the finest detail of implant surgery. There should be minimal surgical trauma. The incision lines should be meticulously closed. The protection of the endothelium with viscoelastics is of the utmost importance as is the complete removal of viscoelastics at the end of the surgery. Making the incision as well as closing the incision should be meticulous and should preferably not introduce an astigmatic error.

Preoperative Details

Preparation and anesthesia need detailed attention.

Anesthesia is as follows:

  • By mutual consultation, the patient and the surgeon can choose the type of anesthesia, whether topical, intraocular, local, or general.

  • Surface anesthesia leading to intraocular anesthesia: Use preservative-free, 2% intraocular lidocaine.

  • Local anesthesia: Use 2% lidocaine with adrenaline (1:200,000) and 7.5 U/mL hyaluronidase. It may be used as a peribulbar anesthesia or for facial nerve block and retrobulbar block. The local anesthesia is given 10 minutes before surgery. Apply orbital compression to make the eye soft and to reduce orbital pressure.

  • General anesthesia: A phakic lens implantation surgery only takes a few minutes. General anesthesia makes the surgery more comfortable for the surgeon, who can concentrate better on the steps of the surgery.

Preparation of the surgical field is as follows:

  • 5% povidone: Paint the periorbital skin with povidone iodine, then apply the same solution 2-3 times to the lid margin and the conjunctival fornices. Then, the eye is washed with saline.

  • Exposure of the surgical field: An eye speculum may be used.

  • The upper and lower lid sutures and the superior rectus suture are applied in place of the speculum. Adhesive plastic drape, applied to the surface of the eyelids, is used to pull the eyelashes away from the surgical field.

Intraoperative Details

Angle-supported lens is as follows:

  • A 6.00-mm corneoscleral incision is made in the steepest meridian, attempting to correct the preoperative astigmatism. A smaller incision is needed for a foldable lens.

  • A 1-mm tunnel incision is placed at the limbus or in the clear cornea, depending on the preoperative astigmatism.

  • The anterior chamber is irrigated with acetylcholine and then filled with a viscoelastic material.

  • A 5.00-mm silicone Sheets glide is introduced into the anterior chamber, and more viscoelastic material is injected over the glide.

  • The phakic IOL is held at the optic with a Kelman-McPherson forceps, and the inferior haptic is slipped into the anterior chamber.

  • With the forceps pushing the superior edge of the optical zone, the IOL is carefully slid over the silicone Sheets glide until both ends of the inferior haptics are in contact with the angle. Then, the glide is removed from the anterior chamber.

  • The upper haptic is pushed gently into the anterior chamber and under the posterior lip of the wound using a double-tip nucleus manipulator.

  • The phakic IOL is rotated, using a Sinskey or Lester hook, to the horizontal meridian where the white-to-white distance is measured. During this maneuver, special care is taken to prevent damage to the angle structures. If a temporal or nasal incision is performed, this rotating maneuver is not required.

  • A peripheral iridectomy, 0.5-1 mm in length, is performed.

  • If the pupil is not round, the Sinskey hook is used to push the haptic away from the angle; then, it is released.

  • Verifying that the lens is well centered, the pupil is completely round, and no traction forces from the haptic footplate are present on the iris is important.

  • A 2- to 3-bite running 10-0 nylon suture is used to close the incision, but before the knot is tied, all the viscoelastic material is removed carefully with balanced salt solution. Finally, the suture is tied.

  • If a limbal incision is used, a nylon suture is used to close the conjunctival flap.

  • After the incision is closed, gonioscopic evaluation is performed to visualize the haptic ends and to verify that they are in a good position and that there is no iris tuck.

Iris claw lens is as follows:

  • Two pocket-type side incisions, one 1-mm wide and one main incision 5- to 6-mm wide, at the 12-o'clock position, are made in the form of a pocket. A foldable version of the lens needs a smaller incision.

  • The anterior chamber is filled with viscoelastic material.

  • The iris claw lens is slipped into the anterior chamber vertically. Once inside the anterior chamber, the lens is rotated horizontally.

  • A vertically holding lens forceps, which enters the anterior chamber through the main incision, centers the optic on the pupil and holds it steadily. A thin forceps is introduced from the side incision that grasps a fold of iris under the haptic and passes it through the claw, thereby fixing it. Both instruments are withdrawn, and the surgeon changes hands for holding each tool.

  • The anterior chamber is again filled with viscoelastic material, and the lens-fixation instruments are reintroduced.

  • The second claw-fixation maneuver is performed through the incision on the opposite side.

  • A peripheral iridectomy is performed.

  • Viscoelastic material is washed out thoroughly.

  • The incision line is closed with 1 or 2 very superficial sutures.

  • Note the image below.

    The drawing shows the relation of the phakic iris The drawing shows the relation of the phakic iris claw lens to the surrounding structures. Courtesy of Professor Jan J. F. Worst, MD.

Posterior chamber lens is as follows:

  • One 0.6-mm side port is made. It is needed to inject viscoelastic material in the anterior chamber.

  • For a precrystalline lens, a 3.2-mm clear corneal incision is made on the steep meridian.

  • The lens is introduced with angled-suture forceps, then it is positioned behind the iris on a horizontal axis with a cyclodialysis spatula.

  • The lens is manipulated to center the optic on the pupil.

  • The viscoelastic material is removed from the anterior and posterior chambers with an aspiration syringe (24-gauge cannula) or by copious irrigation with saline.

  • The pupil is contracted with intraocular acetylcholine 1%, carbachol 0.01%, or pilocarpine 0.5% solution.

  • The incision is closed by hydrating the corneal incisions. A suture rarely is needed.

End of surgery is as follows:

  • Subconjunctivally inject 20 mg of gentamicin and 2 mg of dexamethasone.

  • Apply a sterile pad and a protective shield.

Postoperative Details

Note the following postoperative details:

  • Monitor the patient as with any other IOL surgery. In particular, carefully look at the incision line and be watchful of IOP and any inflammation.

  • The first dressing is completed 8-12 hours after the surgery.

  • Protecting the eye from injury: Patients should use protective goggles during the day and a protective shield at night. Do not bump the eye when applying eye drops.

  • Cleaning the eye: The corners of the eye and the surrounding area may be cleaned with sterile cotton swabs.

  • Patients should be careful when bathing, so as not to spill bathing water into the eye.

  • Using the eye: No restrictions for such activities as watching television or reading are indicated.

Postoperative physical activity is as follows:

  • No restriction on walking is indicated.

  • Patients should avoid heavy exercise for 2 weeks.

  • Contact sports should be avoided for 2 months.

  • Swimming is allowed after 2 months, but diving should be avoided.

  • Rubbing of the eye should be avoided throughout life regardless of the lens design.

  • Patients can drive a car after 1-2 days.

Follow-up

Early postoperative care: On postoperative days 1, 2, 3, and 7, perform slit lamp examination and record any uncorrected or corrected visual acuity and IOP. Note the image below.

Slit lamp photograph of optical section of the ant Slit lamp photograph of optical section of the anterior segment showing a gap between the anterior surface of the crystalline lens and the posterior surface of the implanted myopia iris claw lens. Courtesy of Professor Jan J. F. Worst, MD.

Longer follow-up care is as follows:

  • Patients should receive follow-up care after 1 month, 6 months, and once every year.

  • The pupil is dilated at every visit.

  • Use slit lamp examination to find evidence of inflammation, pigment dispersion, adhesion formation with the uveal tissues, and touch to the anterior lens capsule.

  • Look for any opacification of the crystalline lens.

  • Perform a careful refraction.

  • Regularly monitor the endothelial cell density with specular endothelial microscopy.

  • Gonioscopy is mandatory in angle-supported or posterior chamber lenses. Look for peripheral anterior synechia formation, growth of uveal tissues on the footplates of the lenses, and the presence of pigment that is derived from the iris and the ciliary body.

  • Observe for any crowding of the angle that is due to the IOL behind the iris.

Complications after phakic lens implantation

General

The early problems are related to the design of the lens and the meticulous details of surgery. The late postoperative complications are related to the interaction of the IOL and the intimate ocular tissues during the lifetime of the patient. Lifelong, regular follow-up care is essential in all cases.

Explantation of the lens may ameliorate some of the complications. Later in life, if the patient develops a cataract, it should be possible to do an atraumatic explantation, followed by cataract extraction and implantation of another appropriate IOL. Development of a newer, safer technology to correct myopia may necessitate explantation of the IOL.

Anterior chamber IOLs

The anterior chamber lens has 2 features; it lies completely in front of the pupil, and it is supported by the delicate tissues of the angle of the anterior chamber. The anterior chamber lens can be safe, if the following occur:

  • Minimum contact with the drainage angle

  • No micromovement or macromovement and erosion in the angle

  • No adverse effect on the integrity of the iris

  • No endothelial touch

At present, no single anterior chamber lens can guarantee all 4 of these requirements. A lens has to be somewhat oversized to stay in place; otherwise, it will rotate or move anteroposteriorly. If perforce, it is oversized, it is impossible to avoid erosion of the angle tissues, occurring over a period of time. An endothelial touch can occur if the eye is rubbed even moderately, especially if the flexible and the semiflexible haptics become vaulted due to size mismatch.

Operative complications

If the lens is longer, it may be forced into the ciliary body, leading to severe intraoperative hemorrhage. Hemorrhage from iridectomy site may occur.

Postoperative complications

A lens may press upon the ciliary body and cause tenderness, which is accentuated with the slightest touch, especially if the lens has been placed vertically.

The pressure on the ciliary body can cause low-grade UGH syndrome. Cystoid macular edema may occur.

An undersized lens can rotate in the angle or move anterior-posteriorly and, thus, injure the corneal endothelium. Unmanaged, it leads to corneal decompensation. A mismatched oversized lens or undersized lens can decenter, causing many optical problems, such as reduced vision, prism effect, glare, or diplopia.

An oval pupil can occur, regardless of all the precautions that might have been taken at the time of surgery. Round pupils at the time of surgery and the confirmation of the correct placement of the feet by intraoperative gonioscopy may not prevent the occurrence of pupil ovalization later on. An oval pupil as such produces no symptoms. However, if the process of ovalization continues to increase optical problems, low-grade uveitis and decentration can occur. The late ovalization of the original round pupil is caused by callous formation where the feet of the implant impinges on the iris. The callous formation can contract, causing a progressive pupillary distortion.

Iris overgrowth of the loop can occur. Other postoperative complications include erosion of the uveal tissue in the angle, peripheral iris synechia formation and glaucoma, and neovascularization of the angle. Corneal decompensation may be caused by intermittent touch by rubbing the eye or by size mismatch.

Iris claw lens

Operative complications

Operative complications include off center fixation, pull on the iris root causing hyphema, and hyphema during peripheral iridectomy. Clumsy efforts at iris enclavation can cause a crystalline lens injury.

Postoperative complications

Early dislocation is caused by inadequate fixation. Early or late anterior uveitis can occur.[9] Late dislocation is caused by trauma, leading to momentary opening of the claw through which the iris may wriggle out. The iris tissue in the claw may atrophy and cause dislocation.

Corneal decompensation can be produced by forcible rubbing. Corneal decompensation may occur if a dislocated phakic lens is not corrected or explanted well in time. Cystoid macular edema may occur.

Precrystalline phakic posterior chamber implant

Operative complications

Operative complications include trauma to the lens, which may or may not manifest later.

Early postoperative complications

Pupillary block glaucoma may develop due to the blockage of previous laser iridotomies or viscoelastic material residue in the posterior chamber. It shows itself within the first 24-48 hours. The vasovagal response causes pain, blurred vision, and systemic symptoms. Red eye, corneal edema, shallow anterior chamber, dilated pupil, and a marked rise in IOP also occur. If the condition does not respond to systemic therapy with acetazolamide, hyperosmotic agents, local miotics, and beta-blockers, surgery may be needed to control this serious problem.

Transciliary filtration in such a case should be performed under general anesthesia. A Fugo blade is used for this surgery. With a 600-µm Fugo blade tip, the sclera is ablated 1 mm behind the surgical limbus until the anterior part of the ciliary body becomes visible. The next step uses a 100-µm Fugo blade tip. An ablation path is made through the anterior part of the ciliary body and into the posterior chamber. Drainage of the posterior chamber deepens the anterior chamber and allows the possibility to save the eye as well as to keep the phakic lens in place. This filtration is recommended once medical management is clearly not working. A delay in surgery means damage.

Explantation of the posterior chamber phakic lens may be performed as either a first resort or a last resort, preferably as the latter.

Delayed management or mismanagement can cause variable degrees of visual loss.

Specular endothelial microscopy in these cases may reveal a substantial loss of endothelial cells. The closure of peripheral iridotomies and pupillary block glaucoma can occur after one or more weeks. Such cases may be treated by a repeat laser iridotomy, surgical peripheral iridectomy, transciliary filtration, or lens explantation.

Late complications

An anterior subcapsular cataract may form because of contact with the natural lens. This complication is being observed frequently. Many patients develop cataract within 2 years. However, the offending phakic lens can be explanted, with the cataract being removed at the same time. The long-term incidence of cataract is not yet known. A small IOL has greater chances of having direct contact with the crystalline lens. Uveitis can occur in acute or chronic form. Pigment dispersion may be seen on the artificial lens or the natural lens. Late glaucoma may occur because of crowding of the angle and pigment deposits in the angle. In some cases, the pupil may become partially dilated and not respond to the usual miotics.

This 64-year-old patient had an iris claw lens imp This 64-year-old patient had an iris claw lens implanted in his aphakic eye on the posterior surface of the iris, 10 years ago. The white line represents the pupil in its normal state. Note fine pigment on the surface of the intraocular lens in this area. Bigger pigment granules are seen in the periphery. It seems that the pigment dispersed as a result of friction between the anterior surface of the intraocular lens and the posterior surface of the iris, over a very long time. This happened in spite of the fact that the posterior chamber was very roomy due to aphakia. Courtesy of Kiranjit Singh, MD.
Gonioscopy in the same patient as in Image 9 with Gonioscopy in the same patient as in Image 9 with iris claw lens fixed to the back of the iris. The angle shows severe pigmentation of the angle of the anterior chamber. Only the very finely pulverized pigment is deposited in the angle. Courtesy of Kiranjit Singh, MD.
Gonioscopy in 3D of the other eye of the same pati Gonioscopy in 3D of the other eye of the same patient as in Image 9 that received anteriorly fixed iris claw lens in the aphakic eye, 11 years ago. There is total absence of pigmentation in the angle of the anterior chamber. Courtesy of Kiranjit Singh, MD.

Outcome and Prognosis

Good results are obtained as much by surgical skill as by the lens design chosen. The best vision is achieved within 1-2 days. No line is lost. In fact, a sizable percentage of patients experience improvement in visual acuity, possibly due to increase in the image size.

Glare and edge effects may be produced by small optic posterior chamber, angle-supported, and iris claw lenses. The 6-mm optic iris claw lenses give minimum problems of this nature. These effects are less in people with dark iris, since the pupil size is small and it does not dilate much in the dark.

The first few days after surgery are crucial and a careful follow-up examination is essential to ward off serious problems, such as pupil block glaucoma and anterior uveitis. A regular detailed follow-up examination is essential for all operated cases to detect and treat any untoward problem early, so that no damage occurs. The crystalline lens, IOP, and endothelial cell status are important guides to the continued good health of the eye.

The operated eye needs to be protected from rubbing and trauma because they tend to upset the delicate balance between the implanted IOL and the adjacent ocular tissues.

Yearly fundus examination by indirect ophthalmoscopy is an essential ingredient of myopia care, the importance of which is not reduced (actually, it is increased by phakic lens implantation).

An oversized or undersized lens may decenter. This does not apply to an iris claw lens, if it has been fixed at the right place. An angle-supported phakic lens may develop problems related to the tissues in the angle of the anterior chamber. An iris claw lens should be monitored at the points of claw fixation to detect and manage loosening or weak fixation before dislocation of the lens.

Besides producing optical problems, a decentered p Besides producing optical problems, a decentered phakic intraocular lens, by taking the haptics closer to the limbus, makes the eye vulnerable to intermittent endothelial touch whenever the eye is forcibly rubbed. It can be prevented by a careful fixation during surgery. The decentered lens can be managed by opening the claws and refixation at the right place. Courtesy of Professor Jan J. F. Worst, MD.

A posterior chamber phakic lens can develop problems in relation with the tissues that it comes into contact with and rubs against. The most important problem is the development of early cataract. Such a problem does not happen with an iris claw lens or an angle-supported lens. The treatment of cataract is not difficult; however, patients do not expect this development. An iatrogenic cataract in a young patient is a serious matter. Pigment shedding from the posterior surface of the iris is unavoidable, no matter how slow the process may be. If the patient develops diabetes mellitus, the problem is compounded.

In the event of recurrent iritis, glaucoma, and size-mismatch, explanting a phakic lens may be necessary. When such a course is indicated, an early explantation should be performed.

Myopes do develop posterior segment problems, which might include retinal detachment. Development of adhesions between the implanted lens and the adjacent tissues (eg, a posterior chamber lens developing adhesions with the iris and the crystalline lens) will interfere with the visualization process.

The increasing size of the crystalline lens with age and the formation of cataract, especially of an intumescent type, will greatly disturb the tissue relations. An early management of cataract, including the explantation of the implanted phakic lens, will be needed.

Implantation of a phakic lens in a myopic eye ought to be a small event for the operated eye; unfortunately, it is not so. Therefore, lifelong regular follow-up care is essential.

Long-term follow-up care results with a final design of a lens type are available only with the iris claw (Artisan) lens, up to 14 years. However, it remains to be seen if this and the other lenses will be tolerated for the next 4-6 decades.

Postmortem appearances in an eye with an iris claw Postmortem appearances in an eye with an iris claw lens showing the ciliary body and the posterior surface of the iris. There is a total lack of inflammatory or degenerative changes. Courtesy of Professor Jan J. F. Worst, MD.
Eleven years after phakic minus iris claw lens imp Eleven years after phakic minus iris claw lens implantation in a 35-year-old patient, the pupil has been dilated for fundus examination. Iris claw lens does not affect the movements of the iris and the pupil, except at the point where the iris passes through the claw. The crystalline lens is not affected since the implanted lens remains far away from it.

Looking at both the early results and the late results of laser refractive surgery in cases of high myopia is important. PRK plus wave-guided ablation can prove to be a good alternative for a phakic lens in certain cases. The additional advantage is the possibility of correcting preexisting astigmatism. Beyond a certain period, the only follow-up is for myopia fundus problems.

Future and Controversies

IOL implantation for phakic eyes is only one of many modalities to alleviate myopia. Several attractions for implanting phakic lenses include the following:

  • Surgical injury to the ocular tissues is minimal, even though it means opening the eye and closing it after making a few manipulations.

  • Viscoelastic materials make lens implantation easy and safe, although they should be removed thoroughly from the eye at the end of the surgery.

  • As long as surgical quality is not compromised, the results are highly predictable, immediate, and hopefully lasting.

  • No big investment is involved for beginning this kind of refractive surgery, even in the remote corners of the world.

The ocular tissues may tolerate and survive the presence of an IOL in a phakic eye for a patient's lifetime. However, it will survive only if the lens implantation occurs as a 1-time event and not the beginning of a process, which initially may appear innocuous. Thus, every new modality, especially an IOL, has to prove itself over a long period of time. It has been repeatedly proven that pressure or friction between the IOL and the ocular tissue will damage the latter.

Posterior chamber phakic lens

A posterior chamber phakic lens suffers from certain flaws. The sizing of the posterior chamber lens is a matter of controversy. It commonly is advised to add 0.5 mm to white-to-white diameter, while some authors advise adding 1 mm. The rationale of the size selection in phakic implants is difficult to understand, when it is considered that in hyperopia, the lens is sized 0.5 mm smaller than white-to-white diameter. The IOL is thickest in the central area. It is this area where normally there is no space as the iris rests on the crystalline lens.

It is not possible for the IOL to remain there without rubbing against the posterior pigment epithelium of the constantly moving iris, with the movements of the pupil. Years and decades of friction, no matter how soft and minor, between the pigment epithelium and the highly polished implanted lens, can only result in the attrition of the former. If the patient is diabetic or develops diabetes later on, the problem is compounded.

When discussing phakic posterior chamber lenses, only 2 structures (the iris and crystalline lens) usually are mentioned. There also should be a safety concern for the delicate ciliary body, ciliary processes, its epithelia, and its vasculature. If a plate haptic oversized posterior chamber phakic lens (this is what it normally is) has to stay clear of the crystalline lens, it should vault all the way from the periphery to the center. This is brought about by vaulting in design and by a forward lift of the oversized lens from the ciliary processes.

A foldable posterior chamber lens is fairly firm in consistency and is not to be compared with soft contact lenses. A normally fixed lens impinges hard on the ciliary body, ciliary epithelium, and ciliary processes. If the ciliary epithelium sheds, then the implanted lens will further affect the ciliary vasculature. The ciliary capillary endothelium has fenestrations of 30-100 µm, which are permeable to plasma proteins and tracer elements. A breakdown of the blood-aqueous barrier is seen clinically as inflammation and adhesion formation.

According to Trindade, the thickest part of the posterior chamber phakic lens is approximately 0.3 mm and is in the region of optic-haptic junction.[10] The ultrasound biomicroscopy cannot for sure demonstrate that there is no contact between the implanted lens and the crystalline lens, since the resolving power of the instrument is up to 0.04 mm. Centrally, there is separation between the implanted lens and the crystalline lens, whereas there is frequent contact with the natural lens in the area of optic-haptic junction as revealed by ultrasound biomicroscopy.

The ideal vaulting of the posterior chamber phakic lens is yet to be known in each individual case. According to Zaldivar, low vaulting of the lens may induce subcapsular cataract formation by mechanical irritation or by obstruction of aqueous circulation to the crystalline lens.[11] In contrast, excessive vaulting may lead to iris chafing and pigment loss. An oversized overvaulted lens would release pigment and cause pigmentary glaucoma as a late complication. This is of special concern because high myopes are at increased risk for glaucoma. Having a perfect vault is an ideal that is difficult to achieve in practice. If later ultrasound biomicroscopy reveals oversizing or undersizing, then another appropriate vaulting must be determined.

Reports have emphasized the accuracy of correction and the improvement of uncorrected visual acuity. However, a much larger issue, long-term tissue tolerance, is more significant than any short-term benefits, which some cite as justification for proliferating use.

In aphakic eyes, posterior chamber lens implantation in the sulcus was abandoned in favor of a more difficult, in-the-bag implantation. The reason is that sulcus fixation leads to many unacceptable complications as a result of tissue erosion, which are produced even in the roomy aphakic compartments. It is difficult to perceive that sulcus-supported phakic lenses will fare any better in a more restricted space (ie, the normal posterior chamber). Another responsibility is saving the crystalline lens from inadvertent damage, which leads to cataract formation.

In a group of patients who are prone to angle-closure glaucoma, nothing prevents the plate haptics of the phakic posterior chamber lens from pushing forward the iris periphery and crowding the angle. A precrystalline lens with its optic abutting against the iris surrounding the pupil produces some resistance to the normal free flow of aqueous through the pupil. The increasing volume of the crystalline lens with age further encroaches on the posterior chamber volume. The crystalline lens volume increases by almost 70%, from 140 µL to 240 µL, in a matter of 60 years. The normal posterior chamber volume is about 65 µL.

Undersizing and oversizing are common, and both lead to lens decentration. Unfortunately, the discovery is made only in the postoperative period when most surgeons are hesitant of exchanging the lens to a size that might perhaps be correct. The explantation of a posterior chamber foldable lens is not easy, since it is quite tough in its unfolded state.

Angle-supported lens

The angle-supported lens is not without bright and dark spots. The lens is supposed to be easiest to implant. Unlike a posterior chamber phakic lens, an angle-supported lens does not cause the development of cataract or the release of pigment from the posterior surface of the iris. The length of the IOL is calculated by adding 0.5 mm to the white-to-white diameter. It may not be the most correct way of sizing, since there are many reports of lens rotation, indicating undersizing. The tenderness and pain after phakic minus lenses is indicative of oversizing. Since the exact size of the lens cannot be defined preoperatively, it cannot be known which lens is the smaller sized, which lens would rotate, and which lens is the bigger sized and would impinge on the tissues.

There is no way to ensure that the feet of the implant will come to lie on the scleral spur. The feet lie on the corneoscleral trabeculae or on the ciliary body. In that position, the pressure of the feet may erode the angle or the uveal tissues, leading to a number of problems. The ovalization of the pupil is a much more serious problem, which tends to be overlooked in the beginning, in hopes that the process will stop on its own. However, the history of angle-supported lenses does not support this rosy picture. The sectorial nature of end arteries of the iris appears to be at the root of this malady. There is no way to bypass the anatomy of the iris.

The occurrence of UGH syndrome is a distinct possibility at any time.

Explantation may not be as easy as implantation. The reason is that the haptics have to be brought out of the angle. The haptics might be covered by the uveal tissues, which might bleed at the time of disengagement. Further, the explantation involves much pushing and pulling that causes trauma to the uvea.

Iris claw lens

The iris claw lens has many plus and minus points. The iris claw lens is a pure iris support lens. The lens is smaller than the area where it is fixed. The ocular tissues cannot catch this lens (unlike the posterior chamber lens and the angle-supported lens), so the lens is designed to catch the tissues (the anterior surface of the iris).

The centration and fixation of the lens is completed by the surgeon. The lens position is permanent, unless it dislocates due to poor fixation or injury. The principle of iris fixation inside the claws was tested clinically on thousands of aphakic eyes over 9 years, before the lens was redesigned for phakic eyes. These changes help the implanted lens to stay clear of the natural crystalline lens and the corneal endothelium. However, the principle of claw fixation remains unchanged.

The lens design permits it to stay far from the angle of the anterior chamber and allows freedom to the pupillary movements. The lens floats in the aqueous humor, while it remains fixated at 2 points. It totally avoids the posterior chamber.

The iris claw lens fixation has proved itself for a long time, both in aphakic (nearly 250,000 implantations in over 20 y) and in 16,000 myopia phakic eyes (over 14 y). Postmortem studies performed on many eyes have shown no signs of inflammation in or behind the iris. Iris claw lens implantation is not easy to perform. It requires bimanual dexterity and familiarity with the functioning of the claws.

The presence of iris tissue inside the claw and the close contact and minor friction of the haptic with the iris tissue close to the claw may potentially cause a subclinical inflammatory response. This response may be responsible for unexplained endothelial loss in certain cases.

Role of microtrauma and macrotrauma in phakic lens

One has only to examine a postoperative implanted patient on the operating table to observe that microtrauma and macrotrauma can influence the results after phakic lens implantation. After applying a local anesthetic, if the area of the limbus and the ciliary body and the equator are pressed gently with a blunt-tipped instrument or a sponge, one can see how easily the ocular tissues move. The limbus moves centrally with the greatest ease.

An angle-supported lens in such a created situation appears to be a risky device. However, there is nothing to prevent a similar or more severe form of deformation when the patient rubs the eye, for whatever reason. The tenderness of the eye on pressure may act as a preventive signal. It is well known that patients rub their eyes during sleep. Pressure on the eyeball at similar places is less transmitted to the iris-haptic junction of the iris claw lens. A determined pressure can bring the corneal endothelium and the IOL together. The same holds true of the angle-supported lenses.

The effect of pressure on the outside of the globe is difficult to gauge in relation to the posterior chamber phakic lens. It is inconceivable to suggest that some friction is not produced between the 3 important ocular tissues (crystalline lens, iris, and ciliary body) and the rather stout posterior chamber phakic lens.

When the role of microtrauma and macrotrauma are considered, one has to think in terms of many decades. The phakic IOLs have started making a mark after a long time because the limitations and complications of the corneal laser refractive surgeries have become glaring. The postoperative dry eye, diffuse lamellar keratitis, and keratoconus are quite unnerving to both the patient and the surgeon. These problems do not occur with phakic IOLs. However, phakic lens patients need meticulous lifelong attention.

Developments on the laser refractive front might improve results and minimize complications. The possibility of improved visual acuity results (sometimes even beyond 20/20 in a good percentage of cases) with the use of wave-guided ablations is well accepted today. Laser refractive procedures also may correct astigmatic errors.

Patients with extreme refractive errors cannot be treated fully with only phakic IOLs or with only corneal refractive surgery. In such cases, the 2 modalities play a complementary role. These patients are treated best if a phakic lens is implanted first to correct a large part of the refractive error, while the laser refractive surgery accurately finishes the residual error.

Unfortunately, endothelial cell counting is neglected. This important examination should be mandatory for all kinds of phakic lens implants. The endothelial cells are shed, even in cases of lenses in the posterior chamber. The mechanism of the loss of endothelial cells, beyond the mechanical trauma, is not understood.

Conclusion

Phakic IOLs have made tremendous progress over the past 20 years in terms of safety and efficacy. With proper attention to details, including postoperative care, the risk-to-benefit ratio becomes very acceptable for the individual who desires refractive surgery. By following the above principles for phakic IOL postoperative care, in addition to the surgeon’s experience with postcataract surgery care, patients should do well in the long run. Phakic IOL surgery is coming of age and becoming a mainstream option for patients who seek quality surgical vision correction.

According to Kohnen, the highly myopic patient's choices for surgical refractive correction are implantation of a phakic IOL and clear lens extraction with IOL implantation.[12] Considering the high rate of retinal detachment over time after clear lens extraction in myopic eyes and the loss of accommodation, phakic IOL implantation will be considered more and more by surgeons around the world.

Current options of phakic IOLs include anterior chamber lenses (angle-supported or iris claw) or posterior chamber lenses. Several potential advantages have been ascribed to the use of phakic IOLs to correct refractive errors (ie, myopic, hyperopic), including excellent refractive accuracy, preservation of accommodation, compatibility with proven cataract and phakic IOL implantation procedures, correction of higher levels of myopic and hyperopic refractive errors, and reversibility.

The immediate effect following phakic IOL implantation in highly myopic patients is dramatic: improvement in uncorrected visual acuity, including magnification of the visual image and increase in best corrected visual acuity. However, the list of complications is long and includes endothelial cell loss, pupil ovalization, induced astigmatism, glaucoma, and chronic subclinical inflammation for anterior chamber IOLs; for posterior chamber IOLs, complications include cataract formation, pupillary block, pigment dispersion, and glaucoma. It is necessary to report the long-term outcome of these lenses for the correction of refractive errors.

Pérez-Santonja et al reported 2-year data of a polymethylmethacrylate (PMMA) phakic IOL (ZSAL, Morcher) and concluded that fourth-generation phakic IOLs are an effective, predictable, and stable option to correct severe myopia, with minimal endothelial cell loss and a lower rate of night halos than with previous models.[13] However, haptic-related problems (eg, pupil ovalization, IOL rotation, low-grade postoperative uveitis) were found. Allemann et al demonstrated similar results with good efficacy for the correction of high myopia using the NuVita 4.5-mm optic phakic IOL, but the authors were concerned about iris retraction and endothelial loss.[14]

In a study of 263 phakic IOLs, Alio et al demonstrated that a potential risk of earlier nuclear cataract development after implantation of this phakic IOL exists in patients older than 40 years with axial lengths longer than 30 mm.[15] This occurrence should be discussed with the patient before surgery because it has not been reported with this type of phakic IOL. The authors also showed that bilensectomy (explantation of angle-supported anterior chamber phakic IOLs and phacoemulsification with posterior chamber lens implantation) successfully resolved the complication.

Whether the perfect angle-supported anterior chamber phakic IOL for the correction of myopia has been found is an unanswered question. For all types of phakic IOLs, another question that remains unanswered and will not be known until a statistically based prospective study comparing the different phakic IOLs reports the long-term results, is whether the perfect phakic IOL design and material as well as the perfect anatomical position for the phakic IOL have been found.

The development of phakic IOLs is an ongoing process, and these lenses should be used with caution. Many patients currently have no good option for correcting their refractive error other than phakic IOLs. In some patients, the procedure is successful and the patients are overwhelmed by the optical outcome. The problems must still be addressed. Experience with these lenses will increase our understanding of them, and the results will then continuously improve. After looking at the reported complications with phakic IOLs, it has been concluded that the perfect phakic IOL has not yet been developed. This remains a goal for the next decade of refractive surgery.

Medical/legal pitfalls

Refractive surgery by phakic IOLs among myopes is not as popular as corneal refractive procedures. Phakic IOL has one advantage; the procedure is reversible, if necessary. If myopic patients agree to a refractive correction, they should know about all the available options (ie, laser refractive procedures, various types of phakic IOLs). To bear the responsibility of treating patients with phakic IOLs, surgeons should consider their personal training, experience, and surgical facilities.

A detailed informed consent is important. Problems can arise under many circumstances, as follows:

  • Failure to calculate the proper IOL power and to inform the patient about the planned refractive goals

  • Failure to perform a preventive iridectomy, either before surgery with a laser or a manual iridectomy during operation

  • Failure to warn the patient about the possibility of some serious problems, such as pupil block glaucoma and inflammation

  • Failure to advise a surgical management of severe complications by iridectomy or lens explantation at an early opportunity

  • Failure to reposition, explant, or exchange an IOL when there is evidence of decentration, rotation, endothelial touch, tissue erosion, and subluxation

  • Failure to inform about the possibility of late occurrence of inflammation, cataract formation, and glaucoma

  • Failure to insist on lifelong, regular checkups about the transparency of the media, the IOP, fundus examination by indirect ophthalmoscopy, and anterior segment examination with a slit lamp microscope

  • Failure to advise regular gonioscopy for angle-supported and posterior chamber lenses to exclude angle crowding

  • Failure to advise specular endothelial cell counting on an annual basis