Conductive Keratoplasty Hyperopia and Presbyopia 

Updated: Mar 15, 2016
Author: Manolette R Roque, MD, MBA, FPAO; Chief Editor: Hampton Roy, Sr, MD 



Although nonsurgical correction (ie, glasses, contact lenses) for patients with low-level hyperopia and presbyopia has been widely successful throughout the world, the surgical correctional procedures have been somewhat less accepted. (See History of the Procedure.) Conductive keratoplasty (CK), an advanced method for vision correction using controlled-release radiofrequency energy to gently reshape the cornea and to provide long-lasting vision correction, is now available for these patients. See the video below for an introduction to conductive keratoplasty.

Video introduction to conductive keratoplasty.


History of the Procedure

Laser and laserlike surgical procedures for the correction of hyperopia have a checkered history.[1, 2, 3, 4, 5, 6] For this article, the discussion is limited to CK.

The history of CK for hyperopia began with Svyatoslav Fyodorov, MD, the inventor of radial keratotomy (RK). Fyodorov inserted a hot needle (nickel-chromium probe) at the peripheral cornea to induce shrinkage. This procedure was called hot needle keratoplasty; others referred to it as hot needle in the eye or HNE. Fyodorov encountered problems with consistency and maintenance of the temperature because the temperature (heated to as high as 600° C) went down as the hot needle entered the cornea (to a desired depth of up to 90% of corneal thickness). A scorching sound was produced each time the needle was applied on the cornea. The procedure resulted in an uneven application of heat, with the external cornea receiving more heat than the inner cornea.

Summit Laser then introduced its holmium:YAG laser, first successfully used by Theo Seiler, MD, in 1990 for contact laser thermal keratoplasty (LTK) for the correction of hyperopia of up to 5 diopters (D), which also eventually failed.

In 1995, Sunrise Technologies introduced its noncontact holmium laser (Hyperion LTK System) for hyperopic correction via LTK. The problems that beset this particular technology were also related to the regression associated with the unequal distribution of energy from the base to the apex.

Nonholmium types (CO2 lasers and diode lasers) of laser thermokeratoplasty options appeared in the market, also resulting in positive but transient effects.

Early attempts with hyperopic photorefractive keratectomy (HPRK) were besieged by haze and regression.

The aforementioned procedures were successful in correcting some degree of hyperopia; however, long-term stability, vision quality, and patient comfort were not properly addressed. They were all instrumental as building blocks for the success of hyperopic laser in situ keratomileusis (LASIK), which currently provides excellent outcomes for low levels of hyperopia; low levels of hyperopia are classified as +3.00 D in the United States and up to +5.00 D in Canada.[7, 8, 9]

Mendez then discovered CK. This revolutionary procedure presents convincing advantages over hyperopic LASIK and hyperopic correction via LTK.[10] CK uses high radiofrequency energy that is delivered with a thin metal tip in concentric rings of multiple spots around the corneal periphery, shrinking collagen and steepening the central cornea. Refractec manufactures and markets this technology.[11, 12, 13, 14]

See related CME at LASIK Mostly Effective in Long-Term for Myopia of More Than -10 Diopter.


The central problem in the correction of hyperopia and presbyopia is the pressing challenge of steepening the central cornea.[15]

Current treatment modalities include excimer laser ablation of the corneal periphery via either photorefractive keratoplasty (PRK) or LASIK and shrinkage of collagen in a circular pattern in the corneal periphery (eg, LTK).[16] Hyperopic LASIK has been described as widely successful for low levels of hyperopia; however, the risk of flap-related complications cannot be overlooked. Thermal keratoplasty alters corneal curvature by heating the stromal tissue and causing the shrinkage of collagen. An optimal collagen shrinkage profile is currently acceptable. Previous experience has shown that too low of a heat causes minimal effect, while excessive heat causes remodeling and regression of effect. Two methods of collagen shrinkage are available: application of laser energy (ie, LTK) and application of radiofrequency energy (ie, CK).[17]


The Food and Drug Administration (FDA) Phase III clinical trials for CK included the following investigators: Asbell, McDonald, Maloney, Davidorf, Hersh, Manche, and Durrie.[18] The study was a prospective multicenter clinical trial to evaluate both the safety and the effectiveness of the ViewPoint CK system for the correction of hyperopia using the CK procedure. The study design was consistent with FDA guidance for refractive surgery lasers and draft American National Standards Institute (ANSI) guidance regarding laser systems for corneal reshaping.

The aim of the study was for a full correction of spherical hyperopia (ie, target of plano). All the treatments were based on preoperative cycloplegic refraction spherical equivalent (CRSE). Eligible patients for the study included those in the range of +0.75 D to +3.25 D of spherical hyperopia, with -0.75 D or less of refractive cylinder, yielding +0.75 D to +3.00 D cycloplegic spherical equivalent.

The effective parameters included improvement in uncorrected visual acuity (UCVA), predictability, stability, and patient satisfaction.


The FDA Phase III clinical trials for presbyopic application of CK included the following investigators: McDonald, Durrie, Asbell, Maloney, and Nichamin.[19] The study was a prospective multicenter clinical trial to evaluate CK for the treatment of presbyopic symptoms in emmetropic and hyperopic eyes.



Although numerous figures are reported in publications, the exact number of hyperopes in the world is unknown. Generally, hyperopia is believed to affect millions of persons in the United States and hundreds of millions of individuals around the world.

Of those individuals older than 50 years, 100% of them need corrective lenses for presbyopia.


Errors in refraction may be inherited, and hyperopia may run in families. Presbyopia is a natural part of the aging process and affects everyone.


In CK, a controlled release of radiofrequency energy is delivered intrastromally via a probe tip (450 µm X 90 µm). Impedance of the corneal tissue results in a thermal effect.[20, 21] Thermal profile is homogeneous to approximately 80% of the depth of the cornea. The CK footprint has an average width of 405 µm and an average depth of 509 µm, as measured with ultrasonic biomicroscopy.


At some point, most, if not all, patients with hyperopia complain of a reduction in vision. The degree of blur depends on the amount of refractive error present. Both near vision and distance vision may be affected. Age may affect the reduction in visual performance. Patients with mild hyperopia, who function well prior to the presbyopic years, begin to experience difficulty with near work once their age approaches 40 years. Visual improvement is excellent with appropriate correction.


Hyperopic indications

The basis for the initiation of CK as a surgical procedure includes hyperopia. Hyperopia, commonly referred to as farsightedness, is an error of refraction (EOR) in which an individual may not have any difficulty seeing objects that are distant but may have problems focusing on objects that are near. In some instances, farsighted individuals can see all objects clearly, but they notice the need to strain the eyes, albeit unnecessarily, to maintain focus.

This type of EOR occurs when the eyeball is too short or when the cornea is too flat. In hyperopia, rays of light focus behind the retina instead of on it. This results in poor vision because the focus of light is not directly on the retina where it should be for normal vision. This anatomical structure induces a constant physiologic attempt to make up for the problem and to focus images. Symptoms of hyperopia involve asthenopia, which can include eyestrain, blurred vision, or headache (especially when reading or at the end of the day). These symptoms can increase over time.

Farsightedness (hyperopia) is often confused with presbyopia, which is a normal development of the aging process. Presbyopia occurs when the lens inside the eye loses flexibility, thereby preventing accurate focusing on nearby objects. This condition is common in individuals by the age of 40 years, and all persons older than 50 years experience presbyopia. People with this condition may experience eye strain/fatigue when reading in poor lighting conditions or at the end of the day, have trouble (slow) in changing focus from distance to near, or need to constantly reposition (move away) reading material in an attempt to find the correct focus.[22, 23]

CK hyperopic indications for use, as approved by the FDA, are as follows[18] :

  • CK treatment for the reduction of spherical hyperopia in the range of +0.75 D to +3.25 D of cycloplegic spherical hyperopia, with -0.75 D or less of refractive astigmatism, yielding +0.75 D to +3.00 D cycloplegic spherical equivalent

  • CK treatment in patients with less than or equal to 0.50 D difference between preoperative manifest and cycloplegic refractions

  • CK treatment in patients aged 40 years and older

Presbyopic indications

FDA supplemental approval of Refractec ViewPoint® CK System is for the temporary induction of myopia (-1.00 D to -2.00 D) to improve near vision in the nondominant eye of presbyopic hyperopes or presbyopic emmetropes, as follows[19] :

  • Via spherical hyperopic treatment of 1.00 D to 2.25 D

  • In patients 40 years or older with a documented stability of refraction for the prior 12 months

  • As demonstrated by a change of less than 0.50 D in spherical and cylindrical components of the manifest refraction

  • With less than or equal to 0.75 D of cycloplegic refractive cylinder and with a successful preoperative trial of monovision or history of monovision wear (ie, dominant eye corrected for distance vision and nondominant eye corrected for near vision)

Other Indications

In 2015, Sy et al reported that combined astigmatic keratotomy and conductive keratoplasty is safe and effective for correcting high corneal astigmatism after surgery or trauma.[24]

CK is an elective procedure with the alternatives including, but not limited to, the following:

  • Reading glasses

  • Bifocal eyeglasses

  • Multifocal contact lenses

  • Monovision contact lens wear

  • Other refractive surgeries

Additional selection criteria

Suggested additional initial patient selection criteria for CK are as follows:

  • Healthy, virgin cornea[25, 26, 27]

  • Corneal pachymetry at least 560 µm at 6 mm

  • Corneal curvature between 41-44 D

  • Patient tolerance for monovision

  • Accurate determination of eye dominance

  • Good corrected binocular vision

  • No implanted regulating medical devices

  • Patient understanding that presbyopia is progressive, with the probability of requiring additional treatments in the future

Relevant Anatomy

In hyperopia, the axial length (measurement of the most anterior part of the cornea to the most posterior part of the sclera) of the eyeball is generally shorter than normal and/or the corneal diopteric strength is weaker (flatter curvature).

A transparent avascular tissue, the cornea is continuous with the opaque sclera and the semitransparent conjunctiva. The cornea is covered by tear film on its anterior surface and bathed by aqueous humor on its posterior surface.

In adults, the cornea measures 11-12 mm horizontally and 9-11 mm vertically. The average corneal thickness is 0.5 mm (500 µm) centrally and 0.7 mm (700 µm) peripherally.


Patients must meet the inclusion criteria to be considered a good candidate for CK. A few relative contraindications (exclusion criteria) exist for CK, as follows:

  • Younger than 21 years

  • Drastic changes in vision or eyeglass prescription within the past year.

  • Ophthalmoscopic signs of progressive or unstable hyperopia

  • Eye conditions, including the following: (1) anterior segment pathology, including +2NS cataracts; (2) residual, recurrent, active ocular or uncontrolled eyelid disease, or any corneal abnormality (ie, recurrent corneal erosion, severe basement membrane disease); (3) recurrent history of herpes zoster or herpes simplex keratitis; (4) glaucoma (steroid responsiveness, ocular hypertension, risk for angle closure, or with potentially occludable angles); (5) intractable keratoconjunctivitis sicca; (6) known hypersensitivity to concomitant medications; and (7) peripheral pachymetry reading of less than 560 µm (at 6 mm optical zone).

  • Patient who underwent strabismus surgery or may develop strabismus after the CK procedure

  • Physical conditions, including the following: (1) diabetes, diagnosed autoimmune disease, connective tissue disease, or clinically significant atopic syndrome; (2) pregnancy, breastfeeding, or plans of pregnancy; and (3) keloid formation history

  • Use of systemic medications with significant ocular adverse effects

  • Use of chronic systemic corticosteroid or other immunosuppressive therapy that may affect wound healing

  • Any immunocompromised patients

  • Patients who are using ophthalmic medications other than artificial tears for treatment of any ocular pathology

  • Patients with implantable electrical devices (eg, pacemakers, defibrillators, cochlear implants)

Patient Education

Conductive keratoplasty is a safe procedure that inevitably regresses. Regression is usually complete at around 2 years after surgery. Because of this, conductive keratoplasty is no longer considered the procedure of choice for hyperopia or presbyopia management.[28, 29, 30]



Imaging Studies

Corneal topography development provides surgeons with effortlessly understood color-coded maps of corneal curvature, in addition to quantitative indexes of irregular astigmatism that correlate with potential visual acuity.[31] Modern instrumentation produces a videokeratograph (generally a color-coded contour map).[14] The use of keratography in preoperative and postoperative evaluation of all refractive surgery patients is valuable. Different manufacturers use different methods (eg, Placido, 40 scanned slits, combination Placido and 40 scanned slits, phase modified laser holography, raster stereography).

The pachymeter (eg, optical, ultrasonic) is used to measure corneal thickness. Accurate determination of corneal thickness preoperatively allows the surgeon to set the depth of incision to two thirds of the measured result. Orbscan II by Orbtek uses both 40 scanned slits and Placido methods to provide data on anterior and posterior corneal curvature and corneal thickness.

Ultrasonic biomicroscopy is used to measure corneal thickness (where available). Typically, it is used in clinical studies.



Medical Therapy

Medical therapy is limited to broad-spectrum topical antibiotics and corticosteroids for uncomplicated cases (see Postoperative details).

Surgical Therapy

See Intraoperative details for the surgical procedure.

Preoperative Details

The procedure for CK can be performed with a local (topical) anesthetic in the form of eye drops to numb the eye. Patients who are nervous and/or have a high level of anxiety may be given a mild sedative to assist them in relaxing for the procedure.

The operative field is prepared, and the patient is prepared in the usual sterile fashion for ophthalmic surgery. A lid speculum, as shown below, is used for globe exposure.

Hyperopia, conductive keratoplasty. Speculums. Pub Hyperopia, conductive keratoplasty. Speculums. Published with permission from Refractec.

This procedure may be performed inside the clinic.

Intraoperative Details

After appropriately preparing the patient, a lid speculum is used to hold open the eye during the CK procedure; it also serves as a return path for the radiofrequency energy applied via the instrument. CK is performed using a pen-shaped instrument to apply controlled radiofrequency energy in a ring pattern on the cornea. In performing CK, the conductive tip should be placed perpendicularly to the corneal surface prior to activation. This placement of the conductive tip ensures appropriate application of the conduction marks. The procedure is considered painless and typically requires only a few minutes (approximately 5 min) to perform. See the images below.

ViewPoint conductive keratoplasty device. Publishe ViewPoint conductive keratoplasty device. Published with permission from Refractec.
Hyperopia, conductive keratoplasty. Suture. Publis Hyperopia, conductive keratoplasty. Suture. Published with permission from Refractec.
Hyperopia, conductive keratoplasty. Corneal markin Hyperopia, conductive keratoplasty. Corneal markings. Published with permission from Refractec.
Hyperopia, conductive keratoplasty. ViewPoint with Hyperopia, conductive keratoplasty. ViewPoint with radiation. Published with permission from Refractec.
Hyperopia, conductive keratoplasty. Change in corn Hyperopia, conductive keratoplasty. Change in corneal curvature. Published with permission from Refractec.

LightTouch technique

LightTouch is a corneal compression technique in which surgeons should apply minimal pressure to the cornea. The application of the tip is similar to the initial procedure identified above, except that after the tip is completely implanted into the cornea, it is retracted slightly until there is minimal to no indentation of the cornea, followed by application of the radiofrequency energy. See the images below.

NearVision conductive keratoplasty with LightTouch NearVision conductive keratoplasty with LightTouch technique.
Conductive keratoplasty conventional pressure tech Conductive keratoplasty conventional pressure technique.

Postoperative Details

Following the procedure, the lid speculum is removed. Postoperatively, antibiotic-corticosteroid combination drops and/or ointment are used. Antibiotic-corticosteroid combination drops are used 4 times daily for 1 week. The eye may be covered overnight with a shield.


Certain precautions should be taken following the CK procedure and are similar to those that are required with any other type of vision procedure where the cornea is altered.

Patients should take the following precautions for at least 1 week after surgery:

  • Avoid getting contaminated water (eg, fountains, swimming pools, spas, lakes, ocean, rivers) in the eyes.

  • Keep the eyes closed while showering or taking baths to avoid getting soap and dirty water into them.

  • When exercising, keep sweat out of the eyes.

  • For females, avoid applying eye makeup.

Patients should avoid vigorously rubbing the eyes for 2 weeks after the surgical procedure.

Patients are seen postoperatively on day 1; week 1; and months 1, 3, 6, and 12. Vision begins to improve within a week's time. The surgeon should monitor patients for postoperative complications; an observation timeline is outlined in Complications.

For patient education resources, see the Eye and Vision Center, as well as Vision Correction Surgery and Contact Lenses.


See the list below:

  • Preservation of best spectacle corrected visual acuity (BSCVA)[32, 33, 34]

    • Loss of greater than 2 lines BSCVA in less than 5% of eyes

    • Decrease from 20/20 preoperative to worse than 20/40 postoperative in less than 1% of eyes

  • Induced cylinder[35]

    • Induced cylinder greater than 2.00 D in 5% of eyes (< 1% of eyes per draft ANSI guidance)

    • Induced cylinder greater than 1.00 D reported in labeling for all comparable products for hyperopia treatment

    • Induced cylinder greater than or equal to 1.00 D reported at request of FDA

    • Effect of induced cylinder and axis shift on UCVA eyes treated with current nomogram

    • Approximately 1 line impact on mean UCVA at 12 months in the following:

      • Eyes with greater than 1.00 D and greater than or equal to 1.00 D induced cylinder

      • Eyes with greater than 1.00 D and greater than or equal to 1.00 D induced vector cylinder

      • Eyes with greater than 0.75 induced cylinder and 30° axis shift

    • Correcting for residual sphere using regression models, difference in UCVA not statistically significant (P=0.82)

  • Induced cylinder summary

    • Meets FDA safety guideline (< 5%, < 1% proposed)

    • Frequency and magnitude diminish over time.

    • No effect on BSCVA

    • When induced cylinder is present, UCVA is affected by approximately 1 line at 6 months and improves over time as induced cylinder resolves.

    • level of persistent induced cylinder is low (>1.00 D is 6.4% at 12 mo)

  • Endothelial cells

    • Endothelial cell loss is no more than 10%.

    • No change (within ±1%) in endothelial cell density over the course of follow-up in any region (central, midperipheral, and peripheral cornea)

    • No polymegathism or polymorphism

    • Radiofrequency energy can be safely delivered to the cornea with no effect on the endothelium.

  • Patient symptoms

    • Increase of greater than or equal to 5% in moderate-to-severe symptoms

    • Subjective questionnaire was administered at baseline and at 1, 3, 6, 9, and 12 months. Patients were asked to rate the following symptoms as none, mild, moderate, marked, or very severe: light sensitivity, headaches, pain, redness, dryness, excessive tearing, burning, foreign body sensation, glare, halos, blurred vision, double vision, fluctuation of vision, variations of vision with change in lighting, and night driving vision problems.

    • Symptoms with greater than or equal to 5% increase from baseline in moderate, marked, or very severe, at months 6, 9, and 12, included dryness, glare, halos, double vision, fluctuation of vision, and variations of vision with change in lighting.

  • Complications and adverse events[32, 36]

    • Adverse events to occur in no more than 5% of eyes; any single adverse event to occur in less than 1% of eyes

    • Recurrent corneal erosions in both eyes of 1 patient (< 1%), resolved by 3 months

    • Foreign body sensation in 1 eye of 1 patient (< 1%), reported at 9 months and resolved by 12 months

    • Pain in both eyes of 1 patient (< 1%), reported at 3 months and resolved by 6 months

    • Double/ghost images in 13 eyes of 9 patients (3%), complaint resolved in most eyes (10 out of 13 eyes)

    • Keratitis and corneal melting occurred in a single case report of conductive keratoplasty enhancement.[37]

    • Keratitis and corneal melt associated with nonsteroidal antiinflammatory topical medications occurred in a post-CK patient.[38]

    • Other complications occurring at a rate of less than 1% include blepharitis, external hordeolum, viral conjunctivitis, allergic conjunctivitis, bacterial conjunctivitis, meibomianitis, subconjunctival hemorrhage, central striae, central stromal defects, lash loss, ecchymosis, blurry vision, starbursts, headaches, film over eye, glare, halos, and light sensitivity.[39]

  • Adverse events related to device/procedure

    • Corneal perforation in 1 eye of 1 patient (< 1%)[40, 41]

      • Resulted from detachment of Teflon stop

      • Healed uneventfully; CK procedure successfully completed 2 weeks later

      • Preoperative - UCVA 20/40, mean refractive spherical equivalent (MRSE) +2.00 D

      • 12-month outcome - UCVA 20/16, MRSE 0.0 D

      • Corrective actions implemented

    • No radiofrequency energy delivered during treatment in 2 eyes of 2 patients (< 1%)

      • Resulted from poor solder joint

      • One eye successfully treated 3 weeks later

      • Preoperative - UCVA 20/200, MRSE +2.00 D

      • Twelve-month outcome - UCVA 20/32, MRSE +0.50 D

      • Second eye determined to be ineligible because of previously undetected narrow angles

      • Corrective action validated, implemented, and reviewed by FDA

  • IOP greater than 25 mm Hg in 3 eyes of 2 patients (< 1%)[42]

    • One eye of 1 patient had baseline IOP of 25 mm Hg and ineligible for enrollment

    • Two eyes of 1 patient had increased IOP that resolved without treatment or sequelae

  • Mild iritis in 1 eye of 1 patient at 7 days (< 1%), resolved without sequelae[43]

  • Decrease of BSCVA of greater than 2 lines, inferior altitudinal hemianopsia, and optic atrophy secondary to spinal surgery in 1 eye of 1 patient

  • Retinal break in 1 eye of 1 patient

    • Occurred 18 months after CK procedure

    • Successfully treated with argon laser

  • Nonophthalmic events included terminal cancer, heart attack, breast cancer, temporal arteritis, hospitalization for tonsillectomy, and nasal septum repair.

  • Maloney reported that out of 50 cases of CK, no single patient complained of dryness or haziness.[32, 36]

Outcome and Prognosis

In 2001, McDonald and Maloney presented the interim results of the FDA Phase III clinical trial during the American Society of Cataract and Refractive Surgery (ASCRS) meeting in San Diego. Maloney reported that at 9-month follow-up, the UCVA was found to be 20/20 or better in 60% of the eyes treated and 20/40 or better in 96% of the eyes treated. In addition, 60% of the eyes were within 0.5 D of planned correction, whereas 80% of the eyes were within 1 D of planned correction. Maloney reported the absence of adverse events or complications after 9 months. McDonald reported that at 12-month follow-up, the UCVA was found to be 20/20 for 51% of the eyes treated, 20/25 for 73% of the eyes treated, and 20/40 or better for 91% of the eyes treated.[18, 44, 45, 19, 34, 36, 15, 46, 47, 48, 49, 50, 51, 52]

  • Presentation of results

    • Effectiveness was reported for eyes treated with current nomogram.

    • Safety and stability were reported for all eyes treated.

  • Effectiveness parameters[53]

    • Improvement in UCVA

      • UCVA 20/40 or better in greater than or equal to 85% of the eyes with preoperative BSCVA 20/20 or better

      • Postoperative UCVA equal to or better than preoperative BSCVA for 32% of the eyes

      • Postoperative UCVA within 1 line of preoperative BSCVA for 63% of the eyes

    • Predictability

      • MRSE within ±0.50 D for 50% of the eyes

      • MRSE within ±1.00 D for 75% of the eyes

    • Stability[54]

    • Patient satisfaction

In 2004, McDonald, Durrie, Asbell, et al, published the 6-month results of a 1-year clinical trial evaluating CK for the treatment of presbyopic symptoms in emmetropic and hyperopic eyes.[19]

  • Presentation of results

    • Of the eyes treated for near, 77% had uncorrected near vision of J3 or better at 6 months postoperatively.

    • A total of 85% of all patients had binocular distance UCVA of 20/25 or better along with J3 or better near, a combination that represents functional acuity for a presbyope.

    • Of eyes treated for near, 66% had the MRSE within ±0.50 D of intended at 6 months.

    • In 89% of eyes, the MRSE changed 0.05 D or less between 3 and 6 months postoperatively. After month 1, the incidence of variables associated with safety was 1% or lower.

    • Of patients treated, 76% were very satisfied or satisfied with their procedure.


  • Patients with previous LASIK or PRK showed a greater treatment response to CK but regressed at a similar rate as those eyes without prior LASIK or PRK. Overall, CK is a safe procedure that inevitably regresses.[55, 56, 57]

Future and Controversies

Conductive keratoplasty is demonstrated to be safe for the treatment of presbyopia in post-LASIK patients as well as in non-LASIK patients, although longer observation in terms of factors affecting predictability is suggested. It is understood that LASIK affects the biomechanical properties and strength of the cornea, and this may be the reason for the lesser, albeit statistically insignificant, predictability.[58]

Topography-guided conductive keratoplasty may be effective in reshaping corneal configuration in eyes with keratoconus. Although the reported follow-up time is short, it theoretically may avoid or delay corneal transplantation in some cases.[59, 60]

Studies have been conducted for the safe application of conductive keratoplasty for astigmatism.[35, 61, 62, 63] Other surgical methods for the correction of hyperopia include phakic intraocular lenses (implantable contact lenses). Bifocal intraocular lenses and scleral-relaxing incision with collagen plug implantation are among the other surgical methods for the correction of presbyopia.