Epikeratophakia for myopia correction

Cataract surgery following refractive surgery: Principles to achieve optical success and patient satisfaction

A growing number of patients with prior refractive surgery are now presenting for cataract surgery. Surgeons face a number of unique challenges in this patient population that tends to be highly motivated to retain or regain functional uncorrected acuity postoperatively. Primary challenges include recognition of the specific type of prior surgery, use of appropriate intraocular lens (IOL) power calculation formulas, matching IOL style with spherical aberration profile, the recognition of corneal imaging patterns that are and are not compatible with toric and/or presbyopia-correcting lens implantation, and surgical technique modifications, which are particularly relevant in eyes with prior radial keratotomy or phakic IOL implantation. Despite advancements in IOL power formulae, corneal imaging, and IOL options that have improved our ability to achieve targeted postoperative refractive outcomes, accuracy and predictability remain inferior to eyes that undergo cataract surgery without a history of corneal refractive surgery. Thus, preoperative evaluation of patients who will and will not be candidates for postoperative refractive surgical enhancements is also paramount. We provide an overview of the specific challenges in this population and offer evidence-based strategies and considerations for optimizing surgical outcomes.

Clinical outcomes in post-epikeratophakic eyes after removal of epikeratoplasty lenticule

Background

Assessment of the optical outcome and adverse events in post-epikeratopathic eyes after removal of the epikeratoplasty lenticule (EKPL).

Methods

This was a retrospective case-series study of patients who underwent EKPL removal between 2002 and 2020. Ten eyes were included in the analysis. We compared the clinical characteristics of the patients before surgery, 6 months after surgery, before lenticular removal, and after removal, and reported optical or ocular surface complications.

Results

We removed EKPL due to the lenticular opacity in five eyes (50%), intraocular lens (IOL) insertion (n = 4, 40%) after cataract surgery (n = 3) or in aphakic eyes (n = 1), and lenticule-induced irregular astigmatism in one eye (10%). After EKPL removal, the mean refractive power of the cornea (Km) revealed a tendency to increase. Out of nine cases, six cases showed corneal steepening and three cases revealed corneal flattening. When the keratometric readings of pre-epikeratoplasty and post-lenticular removal were compared within the same case, the average difference was 5.1 D ± 4.0 (n = 8). Complications were observed in 3 of 10 cases (excessive corneal flatness, ectatic change, and abnormal epithelial cell ingrowth) after removal.

Conclusions

The surgeon should expect the corneal refractive power to steepen or flatten in some cases with abnormal astigmatism and irregularity. Epikeratophakic eyes may exhibit serious ectatic changes, and abnormal epithelial cell ingrowth after removal of epikeratophakic lenticules.

Advances in Corneal Surgical and Pharmacological Approaches to the Treatment of Presbyopia

The purpose of this article is to review the current status of presbyopia amelioration with surgical and pharmacologic procedures that partially compensate for loss of accommodation in advance of cataract surgery and lens replacement. Over the last few years, several corneal surgical and topical pharmacological approaches for the treatment of presbyopia have been introduced to the marketplace or are in the developmental pipeline. The approaches vary in invasiveness, duration of effect, reversibility, risk/benefit ratio, and clinical results. The advantages and disadvantages for each are discussed. Corneal surgical interventions aim to provide improved near and intermediate vision in patients with presbyopia through refractive means that extend ocular depth of focus through shape modification. The use of miotic drops or corneal lamellar implants extend depth of focus with the "pinhole" aperture size reduction effect. Unlike in adults younger than 40 years, the refractive status of the patient with presbyopia is not stable. Hence, procedures that provide a permanent refractive change may not provide long-term full correction; eye drops or other treatments that are self-reversing in time or are easily reversible may be used as needed. On the horizon, procedures are being explored that may add years of functional lens accommodation by preserving the deformable gel properties of the lens. [J Refract Surg. 2021;37(6 Suppl):S20-S27.].

Long-term follow-up of epikeratophakia

We report a 28-year follow-up of epikeratophakia surgery after extracapsular extraction of a congenital cataract. The patient's ocular history included the diagnosis of bilateral cortical congenital cataracts at 2 years of age, which was more severe in the right eye than in the left. One year later, the visual acuity in the right eye progressively worsened, and extracapsular cataract extraction without intraocular lens implantation was performed. After contact lens fitting failed, an epikeratophakia procedure was performed in the right eye. Twenty-eight years after the procedure, the patient was referred to Bascom Palmer Eye Institute for progressive loss of visual acuity in the left eye. It was discovered that the right eye had remained stable; the corrected distance visual acuity was 20/30 with a manifest refraction of -8.75 + 0.50 × 105.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Epikeratoplasty for adult and pediatric aphakia, myopia, and keratoconus: the Massachusetts Eye and Ear Infirmary experience

Between February, 1985 and February, 1987, 49 eyes of 47 patients underwent epikeratoplasty for one of the following indications: adult aphakia (21 eyes; 20 patients), pediatric aphakia (10 eyes; 10 patients), myopia (7 eyes; 6 patients), and keratoconus (11 eyes; 11 patients). Follow-up at least 12 months (average = 18 months) is available for all 49 eyes. Of 49 eyes, 44 (90%) were anatomically successful with an intact, clear lenticule at least 12 months post-operatively, with no significant difference between the four groups (adult aphakia = 90%, pediatric aphakia = 90%, myopia = 86%, and keratoconus = 91%). The functional success rate, however, was 91% for keratoconus, 81% for adult aphakia, 80% for pediatric aphakia, and only 43% for myopia. We conclude that epikeratoplasty can be an effective tool in the treatment of carefully selected patients with adult or pediatric aphakia and keratoconus, but has only limited applicability in the management of myopia.

Ten-year follow-up of epikeratophakia for the correction of high myopia

OBJECTIVE

To determine the long-term functional results of epikeratophakia for myopic patients.

DESIGN

Retrospective, noncomparative, interventional case series.

PARTICIPANTS

Twenty-two patients (32 eyes; average age, 43+/-6 years) who underwent epikeratophakia surgery for high myopia. Mean preoperative myopia was -18.74+/-9.16 diopters (D; range, -7 D to -49 D). Follow-up was 12+/-2 years.

MAIN OUTCOME MEASURES

Uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), change in mean keratometry, visual acuity under glare conditions, BCVA versus potential acuity meter reading, and patient satisfaction with the visual outcome.

RESULTS

Mean preoperative UCVA increased from 20/800+/-20/400 (range, counting fingers-20/400) to 20/80+/-20/200 (range, 20/250-20/32) in 24 eyes. Mean preoperative BCVA of 20/32+/-20/64 increased only in five eyes, whereas six eyes had no change and 18 eyes had a more than one line loss of Snellen BCVA. Mean preoperative keratometry reading decreased from 43.67+/-0.90 D (range, 41.0-46.25 D) to 37.40+/-2.92 D (range, 29.43-47.68 D). In the presence of glare, mean BCVA decreased to 20/100+/-20/100 (range, counting fingers-20/32). Potential acuity meter (PAM) readings were significantly (P<0.05) higher than BCVA. Mean PAM reading was 20/25+/-20/100 (range, 20/100-20/16). Seven patients (11 eyes) were extremely satisfied with the operative result more than 10 years after the operation, whereas four patients (four eyes) were not satisfied at all.

CONCLUSIONS

Epikeratophakia for the correction of myopia improved UCVA significantly, but BCVA decreased. The removal of the lenticules in patients who were not satisfied with their visual acuity was uncomplicated, and acceptable vision could be achieved with either contact lenses or intraocular lens implantation.

A review of the development of a synthetic corneal onlay for refractive correction

A synthetic corneal onlay, or implantable contact lens, could obviate the need for spectacles or conventional contact lenses in patients who seek convenient, reversible correction of refractive error. Several research groups have attempted to develop such a product in the past but much of the data from these studies remains unpublished due to commercial interests. This article reviews relevant papers and patents in the corneal implant field and discusses our efforts to develop a synthetic corneal onlay using a perfluoropolyether-based polymer.

Advances in refractive surgery: 1975 to the present

PURPOSE

To review the major advances in the field of refractive surgery occurring over the past 25 years.

METHODS

Literature review.

RESULTS

The major developments in refractive surgery over the past 25 years are reviewed.

CONCLUSIONS

The past 25 years have witnessed great changes in refractive surgery. As a result of advancements in technology, instrumentation, and technique, we have seen improvements in the treatment of all types of ametropias. In this article, we review some of the successes and failures of the past quarter-century.

Long-term outcome of epikeratophakia

PURPOSE

To assess the long-term outcome of epikeratophakia.

SETTING

National center for pediatric ophthalmology (The Children's Hospital) and ophthalmology department in a regional general hospital (Waterford Regional Hospital), Republic of Ireland.

METHODS

A retrospective clinical review was carried out of 25 eyes (20 patients) with epikeratophakia performed over 10 years. Eyes were assigned to a children's group (Group 1) or an adult group (Group 2), depending on patient age at the time of surgery, and assessed with respect to indication for surgery, visual acuity, condition of the implanted lenticule, complications, refraction, and corneal topography. Histological analysis was performed on 1 removed lenticule.

RESULTS

Mean follow-up of all patients was 7.3 years (median 6.8 years; range 4.0 to 10.0 years). Most eyes (n = 18) were contact lens intolerant. Freeze-dried lenticules were implanted in all cases, and all but 1 had stable visual acuity from the early postoperative period to last follow-up. In Group 1 (n = 10), most eyes had a visual acuity of 6/36 or worse preoperatively with an improvement of 1 or more lines in 4 eyes. In Group 2 (n = 14), at last follow-up most eyes retained good or improved visual acuity by 1 or more lines. Most grafts were clear or had insignificant opacities outside the visual axis. The overall complication rate was 12%, with the most serious complication being significant induced astigmatism requiring removal of 1 epigraft. Mean induced astigmatism was 2.50 diopters (D) (median 2.00 D; range 1.00 to 6.00 D), which was accurately predicted within +/- 1.00 D by corneal topography in 14 of 19 eyes. Histology demonstrated infiltration of the implanted lenticule by host keratocytes.

CONCLUSION

Epikeratophakia, a reversible procedure with a low complication rate, resulted in stable visual acuity with good lenticule condition and minimal induced regular astigmatism after long-term follow-up.

Laser in situ keratomileusis to correct high myopia

PURPOSE

To evaluate the effectiveness, predictability, and safety of laser in situ keratomileusis (LASIK) in 143 eyes with myopia from 8.00 to 20.00 diopters (D).

SETTING

Alicante Institute of Ophthalmology, University of Alicante School of Medicine, Alicante, Spain.

METHODS

This prospective study comprised 143 eyes (94 patients) that had LASIK with the Chiron Automated Corneal Shaper and the VISX 20/20 excimer laser using a multizone profile and a sutureless hinged corneal flap technique.

RESULTS

Uncorrected visual acuity of 20/40 or better in 45.0% of eyes 3 months postoperatively and in 46.4% at 6 months. Best corrected visual acuity (BCVA) improved by 0.07 at 3 and 6 months and was stable after 3 months. Mean spherical equivalent was -13.19 diopters (D) +/- 2.89 (SD) preoperatively and +0.51 +/- 1.63 D at 3 months and +0.18 +/- 1.66 D at 6 months postoperatively. At 3 months, spherical equivalent was within 1.00 D of emmetropia in 57.5% of all eyes, 71.0% of eyes with a baseline refraction from -8.00 to -11.99 D (n = 59), 44.4% with a baseline refraction from -12.00 to -15.99 D (n = 54), and 53.0% of eyes with a baseline refraction from -16.00 to -20.00 D (n = 30). The respective 6 month percentages were 60.0, 72.4, 46.0, and 50.0%. The regression of effect was similar in all groups (approximately 0.50 D) between 1 and 3 months, although the high myopia group had further regression. Significant corneal steepening and an increase in corneal thickness occurred between 1 and 3 months. Flap thickness was always less than predicted with both the 130 microns plates, and achieved laser ablation was deeper than programmed. The relationships between postoperative refraction and preoperative keratometry and postoperative refraction and the difference in achieved versus programmed ablation were significant. Complications at 6 months included epithelial ingrowth, corneal flap melting, decentered ablation, and irregular astigmatism with loss of BCVA, although none was vision threatening.

CONCLUSION

In this study, LASIK was effective and predictable in the correction of high myopia but was more accurate for myopia up to 12.00 D. Current surgical algorithms must be modified to improve predictability in higher corrections. Longer follow-up is necessary to evaluate long-term incidence of vision-threatening complications.

Randomized Clinical Trial of Topical Sodium Hyaluronate After Excimer Laser Photorefractive Keratectomy

BACKGROUND

Sodium hyaluronate (Healon) has been reported to promote corneal epithelial healing following severe eye burns in humans and rabbits. Endogenous hyaluronate has been shown to be significantly increased in the corneal tissue following extracapsular lens extraction, anterior segment trauma, and radial keratotomy. The authors report the use of topical sodium hyaluronate administration on the cornea of eyes which have been treated by photorefractive keratectomy for myopia.

METHODS

Forty eyes of 40 patients undergoing excimer laser photorefractive keratectomy for myopia were studied to evaluate the effect of topical sodium hyaluronate versus placebo (Healon buffer) instillation on pain and corneal epithelial healing in an observer blind randomized clinical trial.

RESULTS

There was no significant difference between patients whose eyes were treated with sodium hyaluronate and those treated with a placebo (Healon buffer), with regard to the amount of postoperative pain or the rapidity of corneal epithelial healing.

CONCLUSIONS

Topical sodium hyaluronate administration showed no effect on pain or corneal epithelial healing following photorefractive keratectomy in this study.

Improved preservation of human corneal basement membrane following freezing of donor tissue for epikeratophakia

Current methods for the production of lenticules for epikeratophakia involve rapid freezing, cryolathing, and slow warming of the donor cornea. We have found that this procedure causes structural damage to the epithelial basement membrane in the donor cornea which may subsequently contribute to poor postoperative re-epithelialisation of the implant, leading to graft failure. Endeavouring to overcome these problems, the effects of cryoprotection of donor cornea were investigated, using dimethyl sulphoxide, in conjunction with different cooling and warming rates as part of the protocol for cryolathing. The structural integrity of the epithelial basement membrane zone (BMZ) was then assessed by electron microscopy and by immunofluorescence microscopy using antibodies to types IV and VII collagen, components of the basal lamina and anchoring fibrils respectively, and an antibody to a component of the anchoring filaments. No differences in the pattern of immunostaining for these components were detected, indicating that the composition of the BMZ was unaltered by the different treatment regimens applied. However, electron microscopy showed that preservation of basement membrane ultrastructure was markedly improved when cornea was warmed rapidly rather than slowly, both in cryoprotected and non-cryoprotected tissue. Epithelial cell retention and preservation of stromal architecture appeared superior in cryoprotected samples, while keratocyte structure was heterogeneous throughout the experimental groups. Further work is in progress to assess the efficacy of these protocols in the preservation of keratocyte viability in association with improved basement membrane structure in donor tissue for epikeratophakia.

Ultrasound biomicroscopy in refractive surgery

The need for improved methods of assessing corneal topography arose from the advent of refractive surgery. Ultrasound biomicroscopy (UBM) is a high-resolution technique that uses high-frequency transducers to evaluate the cornea. We conducted a pilot study to assess the cornea after refractive surgery using UBM. Six patients who had prior epikeratophakia, radial keratotomy, or photorefractive keratectomy were examined with a 50 MHz transducer. Ultrasound biomicroscopy provided a striking image of the epigraft after epikeratophakia. Imaging after radial keratotomy and photorefractive keratectomy was less helpful. However, the corneal refractive power computed from the UBM data for the photorefractive keratectomy was close to the optical keratometry values. The study indicates UBM has some applications in analyzing the cornea after refractive surgery.

Long-term results of myopic epikeratoplasty

Twenty-three eyes of 20 patients who had had myopic epikeratoplasty were evaluated and the mean 21-month postoperative results (range: 12 to 47 months) tabulated. Average preoperative myopia was -16.7 diopters (D) spherical equivalent (range: -10 to -33 D), and average postoperative refractive correction was 13 D. Of 22 eyes, 17 eyes (77%) were within 4 D of emmetropia. Preoperative visual acuities without correction were between 2/200 and 20/100 (average = 2/40); postoperative acuities were between 2/200 and 20/20 (average = 20/40). Average preoperative best corrected visual acuity was 20/30. Best corrected visual acuities were unchanged or improved in 82% of cases. Re-epithelialization was complete within an average of seven days (range: three to 16 days) postoperatively except in one case in which the lenticule was removed because re-epithelialization did not occur. Five cases showed progressive loss of lenticular power.

Epikeratophakia for keratoconus. Long-term results using fresh, free-hand made lamellar grafts

Epikeratophakia using fresh, free-hand made corneal grafts was done in 16 patients with keratoconus. The follow-up period averaged 27.8 months (range 13-45 months). A significant improvement of visual acuity was obtained (p = 0.002), and 14 of the 16 eyes (87.5%) achieved a corrected visual acuity greater than or equal to 6/12. The spherical equivalent and the cylindrical refractive error were reduced (p less than 0.05), and a significant flattening of the central corneal curvature was obtained (p less than 0.002). The mean postoperative central corneal astigmatism was 4.25 D. Postoperatively, the mean central corneal thickness was 0.670 mm, and the mean central thickness of the epithelialized graft was 0.336 mm. Six patients reported some postoperative glare or blurring of vision, despite a visual acuity greater than or equal to 6/9 on the Snellen chart. No significant subjective or objective changes were noticed after the 6-month postoperative follow-up visit.

Epikeratoplasty for keratoglobus associated with blue sclera

Patients with keratoglobus and blue sclera as part of a generalized connective tissue disorder are at a high risk of developing corneal perforations either spontaneously or after mild trauma. Six patients (6 eyes) between the ages of 2 and 16 years of age (mean, 7.5 years) with keratoglobus, blue sclera, hypermobile joints, and consanguineous parents were treated by epikeratoplasty, using commercially prepared 12.5-mm lenticules. Surgery was performed for tectonic support and/or visual improvement and was successful in five of six patients with a follow-up period of 11 to 27 months (mean, 21 months). One lenticule was removed because the epithelium did not heal. Peripheral interface opacities occurred in three patients.

Bilateral phakic hypermetropic epikeratoplasty for accommodative esotropia

Optical correction of high hypermetropia with glasses is the primary treatment for accommodative esotropia. These glasses are often poorly accepted by adolescents and young adults for they are cosmetically undesirable, heavy, and esotropia occurs with their removal. We report an 11 1/2-year-old, physically mature female with high hypermetropia and accommodative esotropia corrected to orthophoria with glasses who was unable to be weaned from her glasses. She became intolerant to glasses wear, refused contact lenses, and was treated successfully with bilateral phakic hypermetropic epikeratoplasty. Two years postepikeratoplasty her visual acuity is 20/40 and 20/20 uncorrected and the vision in the amblyopic right eye has remained at its maximum preoperative level. She is orthophoric at distance and has a 2 prism diopter monofixational esophoria at near without glasses. Epikeratoplasty is an option in the treatment of accommodative esotropia for patients who are past the amblyopia forming age, have a stable angle of strabismus, and who require their full hypermetropic optical correction to maintain orthophoria.

One year follow-up of epikeratoplasty for myopia

Eighteen surgeons performed 166 consecutive epikeratoplasty procedures to correct myopia in 103 patients. Of this total, 147 (89%) were first surgeries and 19 (11%) were repeat surgeries. First surgery patients were divided into three subpopulations based on preoperative spherical equivalents (low -5.00 diopters [D] to -9.49 D, medium -9.50 D to -14.00 D, and high greater than -14.00 D). The percentage of eyes with 20/40 or better best corrected visual acuity before surgery was 93% for the low group, 89% for the medium group, and 57% for the high group. The percentage of eyes with 20/40 or better uncorrected visual acuity at 12 months after surgery was 58% for the low group, 42% for the medium group, and 17% for the high group. The average and median spherical equivalent after one year was -1.40 D (2.45 SD) and -1.00 D, respectively; 41% of the eyes were within one diopter of emmetropia, 65% within two diopters, and 76% within three diopters. Clinically significant regression was only noted in low and medium myope groups under 25 years of age. Repeat surgery outcomes were equivalent to those in first surgery patients who had a single procedure.

Corrective measures for myopia

Many myopic people, expressing dissatisfaction with traditional methods of optical correction, are interested in a permanent correction of their refractive error which would alleviate dependence on corrective lenses. Although much effort has been put forth in the last century, there is still no method of correcting myopia which is broadly acceptable as safe and effective. The nonsurgical procedures of orthokeratology and the topical use of cycloplegics have not been well proven. Surgical measures are the current vectors of hope. Surgical procedures on parts of the eye other than the cornea have proven to be difficult. Surgery which alters the refractive power of the cornea (refractive keratoplasty) has been used frequently in the past decade. These procedures include keratomileusis, epikeratophakia and radial keratotomy. The latter is currently the most often performed method for the correction of myopia. This paper critiques the major methods, explains their historical development and basic procedures, lists major published studies and discusses their problems and promise for their future.

Epikeratophakia after ocular trauma

Five patients with long-standing monocular traumatic aphakia and contact lens intolerance underwent epikeratophakia. This procedure was chosen to rehabilitate the visual function in those eyes that exhibited distorted anterior segment anatomy after trauma. Three of the patients had corneal scars associated with their old perforation wounds, and all of them had undergone an intracapsular cataract extraction soon after their original injuries. Best-corrected visual acuity was 20/50 or better in all cases before surgery. Postoperative best-corrected visual acuity improved to within two lines of the best-corrected preoperative visual acuity, after a minimum follow-up period of six months. No intraoperative complications were noted. One cornea developed late-onset partial scarring of the interface in the area of the original scar, but the process arrested spontaneously.

The surgical management of overcorrection in myopic epikeratophakia

Three patients underwent myopic epikeratophakia that resulted in overcorrection. The surgical management of these cases involved resuturing the myopic lenticule to flatten the peripheral curvature and reduce the amount of minus power. A reduction in the overcorrection was achieved in all cases.

Epikeratoplasty. The surgical correction of aphakia, myopia, and keratoconus

Thirty-five patients have had 39 consecutive epikeratoplasty procedures (12 adult aphakic, 9 pediatric aphakic, 12 myopic, and 6 keratoconic eyes) by the same surgeon, using commercially prepared lenticules. The lenticule remained totally clear in 85% of eyes. Two lenticules were removed due to infection and scarring; four lenticules had minimal scarring and did not require removal. Spectacle-corrected acuity was worse than one line from the preoperative spectacle-corrected acuity in 58% of the adult aphakic eyes; however, 75% were 20/50 or better postoperatively. Fifty percent were within 2 diopters (D) of emmetropia and 92% within 3 D. All pediatric aphakic patients showed an improvement in best-corrected acuity, and 83% of eyes at 6 months were within 2 D of emmetropia; by 1 year a 3.4-D average myopic shift had occurred. Two of the six eyes (33%) using the original myopia technique were within 2 D of emmetropia, whereas five of the six eyes (83%) with the current technique are within this range. Spectacle-corrected acuity in the entire current myopia group has either improved by one or more lines or has remained unchanged. Five of the six keratoconic eyes had 20/40 or better spectacle-corrected and 20/25 contact lens-corrected acuity postoperatively; average corneal flattening was 6 D. Persistent epithelial defect and irregular astigmatism were the principal factors in delay in visual recovery.

Clear lens extraction for axial myopia. An appraisal

Optional surgery requires a higher degree of safety than that performed for medical necessity. This ethical principle is particularly applicable to axial myopes, who have higher-than-normal rates of operative and postoperative complications if they undergo lens extraction. Moreover, several noninvasive, extraocular, and reversible techniques now exist for the correction of myopia. Currently, it would appear that the possible optical benefits of clear lens extraction in axial myopia are usually outweighed by the severity of the risks and by the availability of safer alternatives.

The nationwide study of epikeratophakia for myopia

In the nationwide study of epikeratophakia, 116 ophthalmic surgeons performed 352 procedures for the correction of myopia; 256 of the eyes had 30 or more days of follow-up after suture removal. Of 204 eyes, 153 (75%) were within 30% of emmetropia after surgery. Of 208 eyes, 202 (97%) had postoperative best corrected visual acuity within two Snellen lines or better of their preoperative visual acuity. All but one patient improved uncorrected visual acuity. Of the 120 patients who equaled or improved their preoperative best corrected visual acuity, 116 (97%) were within two Snellen lines of their preoperative measurement between 30 and 60 days after suture removal. Corneal astigmatism changed from a preoperative mean (+/- S.D.) of 1.4 +/- 0.8 diopters to a postoperative mean of 2.6 +/- 2.1 diopters. Of 352 tissue lenses, 36 (10%) were removed, largely as a result of inaccurate power, decay, or failure to reepithelialize, and 17 of these eyes underwent a second successful epikeratophakia procedure.

Corneal topography in myopic patients undergoing epikeratophakia

We analyzed the corneal topography of eight eyes in seven patients who had undergone myopic epikeratophakia, using a 1.5-mm graft/host disparity. Topographic maps of corneal power generated by computer analysis of keratoscope photographs disclosed a central spherical optical zone smaller in diameter than was predicted by the preoperative lathing measurements. Outside this optical zone, the dioptric power of the graft surface increased steadily, indicating a progressive steepening of the corneal slope as the graft/host interface is approached. This pattern occurred in patients with accurate and inaccurate refractive results. The center of the graft was noted in some cases to be decentered from the patient's visual axis. The corneal topography analysis system has made clear the need to maximize the diameter of the effective optical zone.

The nationwide study of epikeratophakia for aphakia in children

In the nationwide study of epikeratophakia, 97 surgeons performed a total of 335 procedures in 314 eyes for the correction of aphakia in children under the age of 8 years 1 month. Fifteen children underwent bilateral surgery. Thirty-six tissue lenses were removed and 21 of these eyes underwent a second epikeratophakia procedure. Overall, the success rate for procedures was 89%, and with repeated surgery it was 95% for eyes. Seventy-three percent of the patients were within 3 diopters of emmetropia after surgery. Visual acuity results in patients able to provide verbal responses to the illiterate E, Allen card, or Snellen line chart testing showed improvement in most cases. The safety of epikeratophakia makes it a desirable option for the correction of aphakia in children who are spectacle or contact-lens intolerant, and the permanence of the correction eliminates the problem of optical noncompliance.

The nationwide study of epikeratophakia for aphakia in adults

In the nationwide study of epikeratophakia, 154 ophthalmic surgeons who had attended a training course performed 519 procedures for the correction of aphakia in adults: 310 of the eyes had 30 or more days of follow-up after suture removal. Of 229 eyes, 172 (75%) were within 3 diopters of emmetropia after surgery. Of 259 eyes, 245 (95%) demonstrated improved uncorrected visual acuity; 138 (53%) improved by four or more Snellen lines. Of 265 eyes, 209 (78%) achieved within two lines or improved their best corrected visual acuity. Of the 119 patients who achieved or improved their preoperative best corrected visual acuity, 110 (92%) were within two Snellen lines or better by 30 to 60 days after suture removal. Of the 127 patients with more than three months of follow-up after suture removal, 124 (98%) of those between 18 and 70 years of age but only 13 of 23 (54%) of those between 81 and 87 years of age achieved within two lines or better of their best corrected visual acuity. Corneal astigmatism measured by keratometry changed from a preoperative mean (+/- S.D.) of 2.1 +/- 1.8 diopters to a postoperative mean of 2.7 +/- 2.6 diopters. Of the 519 tissue lenses, 22 (4%) were removed, and one third of these patients underwent a second, successful epikeratophakia procedure.

Nonfreeze epikeratophakia for the correction of myopia

We developed a procedure for preparing epikeratophakia tissue lenses for the correction of myopia from unfrozen tissue using a newly developed artificial anterior chamber and the BKS-1000 (Barraquer-Krumeich-Swinger) refractive set. The results of 23 clinical cases involving tissue that was not frozen or lyophilized demonstrate a correlation coefficient of 0.90 in terms of accuracy of correction and good visual acuity results.

Postoperative astigmatism

With the numerous significant advances in surgical methodology--e.g., microinstrumentation, the operating microscope, the surgical keratometer, and intraocular lenses--that have been developed over the past two decades, both surgeons and patients have become increasingly aware of the final optic result of any surgical intervention. This is especially so since the development of refractive surgery, where good uncorrected vision is frequently the final arbiter of success. We have progressed to the stage where the optic manipulation of the cornea, whether intentional or otherwise, can be understood in terms of a number of variables. These include the preparation and closure of the surgical wound, the choice of suture material, and both intraoperative and postoperative manipulations. Where these have failed and postoperative astigmatism still occurs, a number of surgical procedures are available to reduce the astigmatic error to an acceptable level.

Histological study of epikeratophakia tissue lenses for myopia removed from two patients

Epikeratophakia tissue lenses for the correction of myopia were removed from two patients as a result of postoperative complications such as stromal folds, complaints of glare, and decreased visual acuity. Light and electron microscopic analysis showed protrusions in Bowman's membrane and the anterior stroma corresponding to corneal folds that had been observed clinically. The epithelial cells in these areas contained many vacuolations and a thickened basement membrane. Hemidesmosomes were decreased in number. The tissue lenses had been cut 1.5 mm larger in diameter than the trephined recipient bed into which they were placed. Excess tissue lens material in the central area may have been thrown into folds by mechanical pressure, resulting in the histological changes, clinical signs, and optical distortion that necessitated removal of these grafts. Recently, the surgical technique has been modified, in an attempt to eliminate this problem.

Five year follow-up of epikeratophakia in children

Epikeratophakia alters the anterior curvature of the cornea by the addition of a machine-carved donor lenticule. Since March 1980, 88 patients under eight years of age have had epikeratophakia, with at least six months of follow-up. Eighty percent of the original surgeries were successful; some failed grafts were replaced successfully, so that in all, 89% of the patients had successful grafts. The average increase in curvature of the cornea was 14.7 diopters, and the average spectacle overcorrection was +0.56 diopters. In these growing eyes, we documented a myopic shift of 1.5 diopters per year. Visual acuity results varied with the timing of refractive surgery, density of the amblyopia, and the parents' ability to maintain the patching schedule. The largest group of children were those who had unilateral traumatic cataracts. In this group, 7 of 15 patients who had surgery under 4 years of age had final verbal acuities of 20/40 or better. Long-term follow-up has demonstrated that epikeratophakia safely and successfully corrects refractive errors in aphakic children either as a primary procedure, or as a secondary procedure after cataract extraction.