eMedicine Specialties > Ophthalmology > Refractive Disorders
Myopia, Phakic IOL: Follow-up
Updated: May 16, 2008
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.
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.
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.3 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.4 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.5 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.6 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.7In 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.8 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
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Further Reading
Keywords
intraocular contact lens, internal contact lens, ICL, implantable contact lenses, angle supported phakic lens, iris fixated phakic lens, Artisan lens, iris claw lens
