Ophthalmic Procedures Assessment*

Keratophakia and Keratomileusis: Safety and Effectiveness American Academy of Ophthalmology * The purpose of the Committee on Ophthalmic Procedures Assessment is to evaluate on a scientific basis new and existing ophthalmic tests, devices, and procedures for their safety, efficacy, clinical effectiveness and appropriate uses. Evaluations include examination of available literature, epidemiological analyses when appropriate, and compilation of opinionsjrom recognized experts and other interested parties. After appropriate review by all contributors, including legal counsel, assessments are submitted to the Academy's Board of Directors for consideration as official Academy policy.

Keratophakia (corneal lens) and keratomileusis (corneal carving) are extraocular lamellar keratoplasty procedures that alter the refractive state of the eye, potentially reducing the need for spectacles, contact lenses, and intraocular lenses. Both procedures involve the reshaping of parallel-faced corneal discs to produce tissue lenses capable of correcting myopia and hyperopia, including aphakia. These techniques were developed by Jose Barraquer, who first reported results in 1964. 1 The surgery is technically complex and difficult to perform. These techniques were performed in England by Ainslie 2 in the early 1970s and were introduced into the United States in 1977 by Troutman and Swinger. 3 Over two-hundred American ophthalmologists have received training in these techniques; however, a significant commitment of time and expense is required to become proficient. These factors, coupled with surgeon reservations about the engineering tolerance of the instruments used to perform the procedures, ,account for the fact that only 15-25 surgeons actively perform them.

Procedure Types and Techniques Keratophakia Keratophakia is a procedure restricted to the correction of hyperopia and aphakia. 2- 24 A fresh or preserved donor cornea undergoes a lamellar keratectomy, and its epithe-

Prepared by the Committee on Ophthalmic Procedures Assessment and revised and approved by the Academy's Board of Directors on February 15, 1992

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lium, Bowman's layer, and stroma are removed in a controlled manner to produce a stromal tissue lens approximately 6.0 mm in diameter and 0.20 mm in thickness. The stromal lens can be preserved fresh by refrigeration in tissue culture medium, by freezing at sub-zero temperatures, or by freeze-drying. The stromal lens, thickest centrally, is shaped as a converging meniscus lens and is capable of correcting hyperopia and aphakia. It is implanted within the patient's corneal stroma. A lamellar keratectomy is performed on the recipient's cornea; the tissue is placed intrastromally and the anterior lamellar cap is sutured in place (Figure 1). The shape of the stromal lens induces a steepening of the patient's anterior corneal surface and increases the refractive power of the cornea.

Keratomileusis Keratomileusis is a procedure that may correct either myopia or hyperopia. 1- 3•6 •8 • 14- 19 •23 - 44 A lamellar keratectomy is performed on the patient's cornea. The patient's resected corneal disc (autoplastic keratomileusis) or a corneal disc obtained from an eye bank eye (homoplastic keratomileusis) is modified by either the Barraquer cryolathe or the Barraquer-Krumeich-Swinger (BKS) system. Hyperopic correction requires removal of relatively more tissue from the peripheral portion of the disc resulting in a secondary steepening of the central cornea, thereby increasing refractive power (Figure 2). Myopic correction results from removal of more tissue from the central portion of the disc, resulting in flattening of the central cornea and a decrease in the cornea's refractive power (Figure 3). Following modification, the lenticule is sutured onto the patient's lamellar keratectomy bed. Commercially

AAO

Keratophakia and Keratomileusis

A

the best refractive and visual acuity results. 50 Results of epikeratoplasty for myopia are more disappointing. Fairly severe corneal irregularity can occur even in patients who obtain good Snellen visual acuity. 51 Refractive regression and visual aberration are common, and refractive accuracy is poor. 6·39

Surgical Methodology B

c

Equipment The equipment necessary for performing keratophakia and keratomileusis is technically complex and expensive (cost is about $50,000-$75,000). The microkeratome performs a circular lamellar keratectomy of defined depth and diameter. The diameter of the resected tissue is determined by choosing a suction ring (which the surgeon places on the eye to act as a guide for the microkeratome) of appropriate height. Depth of incision is determined by choice of the base plate inserted into the micro keratome head. Keratectomy depth is accurate to within 5% of planned depth 49 in most cases, but even experienced surgeons can inadvertently enter the anterior chamber in 12% of cases. 1·25 ·40·41 ·49 The accuracy of keratectomy diameter is more problematic. Even experienced surgeons can fail to obtain disc tissue of proper diameter in up to 2-3% of cases.Z 5 The size of the suction ring apparatus

D Figure 1. Keratophakia. Following a lamellar keratectomy on the donor cornea (A), the resected disc is modified by removing the anterior membrane complex (cross-hatched) (B), resulting in the stromallenticule (C) that, when placed into the patient's cornea following a lamellar keratectomy, results in steepening of the central cornea.

A precarved homoplastic tissue obviates the need for lathing devices and simplifies the procedure. Homoplastic keratomileusis should be distinguished from the procedure of epikeratophakia (or 'epikeratoplasty'). 6·11 ·16·38 ·39·45 -48 The epikeratoplasty procedure avoids the use of the microkeratome on the host cornea.11·49 Host cornea preparation requires de-epithelialization of the surface and the preparation of a mid-stromal circular grooved incision peripheral to the apical cap. A Barraquer lathe or BKS device produces a pre-carved homoplastic lenticule. The surgeon secures the edge of the lenticule in this groove (Figure 4). Homoplastic keratomileusis differs from epikeratoplasty in that the donor tissue is sewn onto the bed of the lamellar keratectomy performed with the microkeratome (Table). The epikeratoplasty procedure does not have the risk of injury from the micro keratome to the recipient eye, 11 but the added thickness of tissue in epikeratoplasty can sometimes cause problems with epithelial healing and graft clarity or result in visual loss in a small percentage of cases. 47·48 Epikeratoplasty shows promise in the correction of aphakia. Secondary lens implantation provides better refractive accuracy and visual acuity and limits epikeratoplasty to contact lens-intolerant patients at high risk for intraocular procedures. Topography studies show moderate degrees of corneal irregularity in patients who obtain

B

c

D Figure 2. Hyperopic keratomileusis. Following a lamellar keratectomy (A), the resected disc is modified on its stromal side (B), resulting in a hyperopic lenticule (C) that, when placed on the bed (D), results in steepening of the central cornea.

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A

B

c

Keratophakia or keratomileusis surgery is usually performed on an outpatient basis under local anesthesia, with operating times varying from 30 to 90 minutes. The tissue resected with the microkeratome, whether from the patient's cornea or from a donor cornea, is placed into a solution of0.25% light green dye in either water or buffer. Some surgeons add a cryoprotectant to this mixture. 28•52 The tissue is then frozen on the cryolathe for one to two minutes for the reshaping process or modified without freezing on the BKS device. 12•53- 59 Autoplastic lenticules are immediately replaced on the patient's eye, whereas homoplastic lenticules may be used immediately or preserved by refrigeration in tissue culture media, freezing or freeze-drying.

Clinical Applications Aphakia

D Figure 3. Myopic keratomileusis. Following a lamellar keratectomy (A), the resected disc is modified on its stromal side (B), resulting in a myopic lenticule (C) that, when placed on the bed (D), results in flattening of the central cornea.

precludes use of the system on small eyes and limits its application in the pediatric population to those older than 4 years of age. The original microkeratome apparatus requires the surgeon to manually pass the instrument over the cornea. Equipment failure or improper surgical technique can lead to irregular cuts and even inadvertent anterior chamber entry. Automated microkeratomes are under development which may reduce the effect of surgeon error.

Tissue Modification Two devices are available to modify the harvested corneal discs. The original apparatus is the Barraquer cryolathe. The device is a spherical contact lens lathe that is modified to allow the corneal tissue to be frozen prior to the lathing process. A calculator or microcomputer uses an algorithm to determine the appropriate spherical surface to lathe on the stromal surface of the corneal disc to obtain the desired refractive correction. The Barraquer-Krumeich-Swinger (BKS) non-freeze refractive set distorts the anterior curvature of the tissue lens by placing it in a suction device of defined curvature and uses a microkeratome to perform a planar cut on the posterior stromal surface of the disc. 18.45 It does not require tissue freezing and avoids temperature-induced tissue injury. Microkeratome-induced tissue injury can occur.

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The need for secondary refractive procedures after cataract extraction is infrequent, because most patients receive an intraocular lens implant at the time of cataract extraction. Patients with aphakia usually tolerate secondary lens implantation, but long-term complications can occur and visual acuity results are worse than with primary lens implantation. Keratorefractive procedures are restricted to aphakic patients with contact lens intolerance and at high

A

B

c Figure 4. Epikeratophakia. After removal of the central epithelium, a circumferential keratotomy is made, or wedge of tissue resected (A). A refractive lenticule (B), prepared from a donor cornea, is then placed on top of the patient's cornea (C), thereby altering the central curvature.

AAO · Keratophakia and Keratomileusis Table.

Variable Equipment Surgical Skill Post-op Course Reversibility Reported Results Optic Correction Accuracy (% > 3 D) Astigmatism Rehabilitation Stability-myopia -hyperopia Complications Keratectomy Abn. AC Perforation BKS/Cryolathe Abn. Subjective SXs Failed Lenticule Delayed Epithelialization Epithelium in Interface Irregular Astigmatism Reduced Acuity

AutoKM* BKS/Cryolathe Microkeratome

HomoKM Microkeratome

KF Microkeratome

High Mild 12 mo

Moderate Moderate 12 mo

Moderate Easy 24mo

Moderate Moderate Indefinite

16 D 10-20 Low Rapid Moderate Good

25 D 10-20 Low Moderate Moderate Unknown

20D 25 Low Slow N/A Good

30D 25 Low Slow Poor Good

2% 1-2% 1% 20-30% Rare 0-2% 1-5% Frequent 10%

2% 1-2% N/A 20-30% 5% 5% 1-5% Frequent 10%

2% 1-2% N/A 5% Rare 0% 1-5% Frequent Up to 60%

N/A 1-2% N/A 20-40% 7% 5-10% Rare Frequent Up to 60%

EPI

• Abbreviations used: Auto KM = autoplastic keratomileusis; Homo KM = homoplastic keratomileusis; KF = keratophakia; EPI = epikeratophakia. Adapted from: Barker BA and Swinger CA: Complications of corneal refractive surgery. In Schwab IR (ed). Refractive Keratoplasty. New York: Churchill Livingstone, 1987, pp. 227-271.

risk for secondary intraocular procedures because visual recovery is prolonged, the quality of visual performance is often reduced, and refractive accuracy is not as good as with secondary intraocular lens implants or contact lenses. 15 Epikeratoplasty, because it is technically simpler, is performed much more often than keratophakia and keratomileusis in these patients.

Myopia The development of contact lens intolerance in a patient with high myopia can have serious effects on the patient's functional visual capacity. These patients often have considerable difficulty adapting to optical aberrations induced by spectacle correction. Barrel distortion and minification effects are particularly bothersome in patients with myopia-related macular disease. When attempts to reinstate contact lens wear are unsuccessful, consideration must be given to keratorefractive surgery since procedures involving intraocular surgery (removal of the crystalline lens-anterior chamber lens implants in phakic patients) carry considerably more risk. 46 The problems related to epikeratoplasty for myopia and the inability of radial keratotomy to correct high myopia make myopic keratomileusis a reasonable option for this select group of highly myopic patients. 6·14.4°·41

Clinical Efficacy Overview 17 The capability of keratophakia 16 and keratomileusis to correct high hyperopia, and the capacity of keratomileusis to correct high myopia, 41 ·42 are well-documented in the literature. Keratophakia has corrected up to 15 diopters of hyperopia at the corneal plane and more than 20 diopters when the preoperative cornea is flat. 16 Reports of correction of up to 12 diopters at the corneal plane have been reported with hyperopic keratomileusis. 17 Standard myopic keratomileusis techniques have been reported to correct up to 14 diopters of myopia at the corneal plane and up to 20 diopters if thick resections and smaller optic zones are utilized. 41 The highest myopic correction achieved with homoplastic keratomileusis was 25 diopters.42 These isolated reports suggest the absolute refractive limits of these procedures but a closer look at the limited number of large surgical series is necessary to determine safety and efficacy. Questions regarding the consistency of refractive accuracy for a given degree of refractive error must be evaluated. The optical consequences of surgically-induced irregular astigmatism must also be evaluated as well as the

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incidence of complications that may induce serious functional visual impairment or require the need for secondary procedures such as penetrating keratoplasty or repeat homoplastic keratomileusis. 60 The following sections review these data-procedure by procedure.

Homoplastic Keratomileusis for Myopia A study of 10 eyes (only 5 with 6-month followup and only 4 with preoperative visual acuity of 20/40) found half within 10 and all patients within 3 diopters of em42 metropia at the time of the most recent visit. No human study using exclusively homoplastic tissue has been published since the advent of the corneal tissue press which eliminates donor tissue edema prior to lathing. Homoplastic tissue has been used by a number of authors when cryolathe malfunctions preclude the use of the patient's own corneal button. 37

BKS Keratomileusis for Myopia The only published paper reporting results of the BKS non-freeze system for myopic keratomileusis is the report of Colin and colleagues. 6 The paper reports on 26 eyes of 18 patients with followup ranging from 6 to 20 months. Refractive results are reported in terms of proximity of refractive error to emmetropia, but no information is provided regarding refractive stability or the relation between anticipated and achieved result. Only 61% of patients were within 3 diopters of emmetropia. Six months after surgery, 31% of patients lost 2 or more lines of Snellen acuity and 15% improved 2 or more lines, compared to preoperative vision. Visual recovery was described as "slow" and the authors had the clinical impression that it continued to improve for at least a year after surgery. Small interface opacities were noted in 80% of cases. One patient had delayed epithelial healing and one developed an epithelial inclusion cyst.

Standard Keratomileusis for Myopia Information on refractive accuracy is difficult to extract from recent large studies of myopic keratomileusis (MKM) where the patient's own tissue was modified on the Barraquer cryolathe. The only prospective study of myopic keratomileusis to date is an early one by Swinger. 41 Forty-two cases were attempted, of which 38 were analyzed. Two cases were aborted because of too thin a resection (prior to advent of homoplastic keratomileusis which would have allowed completion), and two cases had a lamellar keratoplasty for complications. Nineteen patients were followed for a year or more. The mean refractive correction was 94.1% + 24%, and 82% of eyes were within 3 diopters. No patient followed for a year or more lost spectacle acuity, whereas 63% of eyes experienced an improvement in spectacle acuity, up to 5 lines in one case. The authors stated that it took the refraction 3-6 months to stabilize, and no longterm data on stability were available. Complications con-

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sisted of inadequate microkeratome resections in 3 cases, with no visual sequelae and 4 eyes with epithelial problems or focal necrosis of Bowman's layer. There is only one report by Barraquer on the longterm stability of MKM evaluating 23 eyes with a mean follow-up of 9.3 years. 14 The mean refractive correction showed a decay of 1.870 between postoperative years 1 and 9.3. However, the fellow unoperated eyes showed a shift of 1.420 toward myopia, presumably because of progressive myopia. In 1986 Nordan reported on the one-year results of only 74 of 80 nonamblyopic patients undergoing myopic 54 keratomileusis followed for one year. Some of the patients had standard keratomileusis and others had homoplastic keratomileusis. One of the 74 patients experienced inadvertent entry of the anterior chamber, and repeat keratomileusis was performed in three others for persistent irregular astigmatism. Nine percent of patients manifested irregular astigmatism. Although only 8% of patients had residual refractive error greater than 3 diopters from emmetropia, this was achieved only after reoperations on three patients. Maxwell reported on his initial consecutive series of 23 MKM patients. 37 Seventeen had at least 6 months' followup. Of the patients with 20/40 vision preoperatively (n= 19), none lost more than one line of visual acuity and only one patient was more than 3 diopters from emmetropia. No information is presented by Maxwell on refractive stability. A later study of 100 consecutive patients from the Barraquer group published in 1990 had a 3% rate of complications related to the micro keratome. 25 One patient had inadvertent entry of the anterior chamber and two others had a smaller than predicted lamellar disc harvested which precluded lathing of the tissue. The report follows only 60 of the 100 patients for 90 days. A mean "81% refractive correction" was obtained in this subgroup but no information on residual ametropia is reported.

Keratophakia for Hyperopia Only a handful of reports are available in peerreviewed journals regarding keratophakia. Troutman and colleagues22 attempted 32 operations. The operation was combined with cataract extraction in 29 and was a secondary procedure in the remaining 3. Three cases were aborted because of "irregular resection" of the lamellar discs. Two patients developed wound dehiscences which required secondary procedures. Two patients developed postoperative corneal edema. The report states that improved instrumentation and software improved refractive results in those patients operated on after August of 1978. Twenty-five percent of patients in the improved technology group had a postoperative refraction more than 3 diopters from emmetropia, and it is unclear how many patients were in this group. A report on 41 eyes operated by Barraquer between 1967 and 1978 (a mix of primary and secondary procedures) provides no information on the relation between preoperative refractive error and postoperative accuracy,

AAO · Keratophakia and Keratomileusis refractive stability, or change in best corrected visual acuity. 17 Friedlander and colleagues reported on 14 patients (8 ICCE + keratophakia, 6 secondary keratophakia). 8 Inadvertent entry into the anterior chamber requiring penetrating keratoplasty occurred in one patient. Epithelial nests occurred in the interface in 2 cases. Two patients lost more than 2 lines of best corrected acuity. Eleven of fourteen patients were within 3 diopters of emmetropia. No information is presented on refractive regression. Taylor presented 10 patients with at least 6 months of followup. 43 Two patients developed filamentary keratitis that persisted for months. One graft was decentered. Keratoscope photographs show obvious corneal distortion at the graft-host interface similar to that seen after epikeratoplasty for aphakia. No information is presented on refractive regression.

Keratomileusis for Hyperopia The largest series on keratomileusis for hyperopia, in the American literature, was published by Jose Barraquer in 1983. 32 Keratomileusis was combined with cataract extraction in 107 of 111 eyes. Of the 111 eyes, one was excluded because of entry into the anterior chamber by the microkeratome, and two because of malfunction of the lathe. Four of the remaining 107 patients developed poor vision because of decentration of the microkeratome cut, 3 secondary to severe optical distortion in the graft, one secondary to interface opacities, and 6 secondary to "epitheliopathy." These figures reflect a complication rate of 14%. No information is presented on refractive stability. All results are presented in terms of most recent refraction, and followup varies widely. The report states that recovery of visual acuity continues for at least 18 months. Eightyeight percent of patients had best-corrected vision of at least 20/40. Forty-nine percent were more than 3 diopters from emmetropia.

Assessment of Safety Vision-threatening complications related to procedures requiring use ofmicrokeratomes and cryolathes are welldocumented in the section on clinical efficacy and have been reviewed elsewhere. 60 Information regarding severe permanent visual loss is difficult to obtain from the literature. The application of the suction ring prior to the micro keratome causes transient elevation of intraocular pressure to as much as 60 mmHg and could potentially cause retinal arterial occlusion. Inadvertent penetration of the optic nerve or retina with a retrobulbar needle is possible especially in patients with high myopia. Since there are very few studies with long-term followup, the long-term risk of bacterial keratitis is unknown, although it has never been reported. Delayed bacterial keratitis has been observed after radial keratotomy in the PERK study. None of the patients had infection during the first year of followup, but 1% had at least one episode within four years of surgery. Any operation that uses a microkeratome presents the risk of entry into the anterior chamber. Large series by

the most experienced keratomileusis surgeons show this complication to occur in 1-2% of cases. Decentration of the microkeratome cut relative to the entrance pupil reduces optical resolution and causes glare. Unacceptably small corneal buttons may also occur. These three complications can leave the patient with permanent visual disability unless they resort to a penetrating keratoplasty and its attendant risks. Cryolathe malfunctions may occur. These may cause the surgeon to abort the case or force the surgeon to rely on homoplastic tissue. Inappropriate lathing techniques can induce irregular astigmatism. We know little about the degree of cryolathe-induced irregular astigmatism in these patients because most of the papers in this field were performed prior to the availability of computer-based corneal topography systems. Reports in the epikeratoplasty literature show that Snellen visual acuity information is an insensitive measure of corneal irregularity. 50 One isolated report on the topography of a patient with visual aberration after myopic keratomileusis has shown that severe corneal irregularity can occur even when keratoscope rings appear circular. 36 Postoperative complications include delayed epithelialization of the graft, persistent superficial punctate keratopathy, filamentary keratitis, corneal edema, epithelial ingrowth in the graft-host interface, dellen, interface debris, and irregular astigmatism related to epithelial wound healing effects, among others. 60 Delayed return of bestcorrected visual acuity, reduction in best corrected vision, and refractive inaccuracy have been discussed in the CLINICAL EFFICACY section. Refractive stability is difficult to analyze since there are no large series of consecutive cases that report changes in refraction between defined postoperative intervals. More severe complications have also been reported following keratophakia such as corneal edema, iritis, vitritis, and cystoid macular edema. 15 However, most such complications have been in patients undergoing combined cataract surgery and keratophakia, and thus, these complications cannot be attributed to the keratophakia alone. Although reportedly low, there have been no prospective studies of endothelial cell loss following keratophakia or keratomileusis.

Research and Development Although there have been clinical reports of hyperopic keratomileusis in the United States, 8• 17·27•29 most of the relatively few studies have been restricted to keratophakia and myopic keratomileusis. 3·7- 10·14- 17·21 - 24·37·40•41 ·43 Clinical results have been described above. In addition, there has also been extensive laboratory investigation of these techniques.61-67 Such studies have documented destruction of the keratocytes by the freezing process and then repopulation of the damaged stroma within several months, except in the case of keratophakia, where the lenticules remain unpopulated. 56 Although the collagen framework of the stroma appears to be maintained following freezing, it is frequently less organized than normal. 56 ·64 At the present time, a limited number of clinical in-

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vestigations are in progress. Both autoplastic and homoplastic surgery continue to be evaluated to determine the correction obtainable, the complication rates, the visual results, and the frequency of symptoms. A number of variants of the basic procedures have been presented, but they have not undergone sufficient evaluation. These include lathe shaping at room temperature using freezedried tissue, 12 establishment of tissue banks to provide pre-carved lenticules for keratophakia and keratomileusis,42 a modified cryolathe to freeze the tissue slowly, which increases keratocyte survival, 57 and use of a high-speed air turbine handpiece to provide finer lenticule surface quality. 54 At the present time, these procedures continue to be refined. Although they have been shown to be efficacious, they continue to be technically cumbersome and difficult. There are currently 3 approaches to improvement: nonfreeze surgery, 6·18·59·67 hydrogel keratophakia, 3·68- 73 and excimer laser photoablation. 74- 87 Improvement of the nonfreeze BKS technique, which produces tissue lenses with viable keratocytes is being evaluated at several centers. In addition, a second non-freeze approach, called 'keratomileusis-in-situ,' has been developed but not yet published. In this approach, a second microkeratectomy is performed on the keratectomized bed within the confines of the primary microkeratectomy. The second is smaller in diameter and, after replacing the anterior lamellar cap, causes a compensatory change in the anterior cornea. The technique eliminates the BKS device and cryolathe, and is further simplified by using a vertically adjustable suction ring, to effect concentric resections, and an automated microkeratome (Steinway Instrument Co., San Diego, CA), both of which might also be ofbenefit for performing classic keratomileusis and keratophakia. However, it is technically difficult and less reversible than the classic keratomileusis approach where the cap, and not the bed, is modified. A second avenue of development is synthetic corneal inlay. In hydrogel keratophakia, soft contact lens material, shaped appropriately, is implanted within the cornea following keratectomy. The lenses appear to be well-tolerated and the procedure is quite reversible. However, early results with myopic lenses have given less than satisfactory results. 69 A topographic study of the first seven patients in the trial shows disturbing degrees of irregular astigmatism in most of the patients studied. 88 Rigid synthetic corneal implants have also been evaluated with less than satisfactory results. Choyce pioneered the use of such lenses, which can be made quite thin because they are manufactured from high refractive index polysulfone. Choyce has shown that high myopia and hyperopia can be corrected in humans, with maintenance of a clear cornea and stability for up to 5 years in some cases. 89 In a controlled study on cats, however, severe limitations with this technique were demonstrated. Significant complications such as lens extrusion (up to 29%), anterior corneal necrosis (up to 12.5%), and stromal opacification (up to 71%) were noted. 89 Investigators continue to search for synthetic inlays with greater biocompatibility. A third area of research would eliminate all mechanical cutting and alloplastic materials with techniques using

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the 193 nm excimer laser, which can accurately ablate corneal tissue. The procedure is termed 'photorefractive keratectomy' or laser keratomileusis in which the excimer laser beam is applied perpendicularly to the patient's cornea to ablate tissue. A moving diaphragm or ablatable mask allows greater energy to be applied to certain locations, thereby selectively altering corneal curvature. Preliminary results in a blind eye study were encouraging. 81 Currently, however, hyperopic and aphakic corrections are difficult to obtain, and high myopic corrections may be unstable or accompanied by greater than usual haze. Using the excimer laser, unlike the other methodologies described, the corneal epithelium and Bowman's layer are destroyed, the long-term consequences of which remain to be seen. 74·75 To preserve the anterior corneal structures, the excimer laser might be used in conjunction with the BKS device in lieu of mechanical cutting to ablate the corneal bed following an initial keratectomy.

Qualifications for the Treating Ophthalmologist All of these keratorefractive procedures are technically demanding. Before performing keratophakia and keratomileusis, an ophthalmologist should obtain formal training. Time should then be spent in a practice laboratory in order to gain familiarity with the instrumentation prior to beginning human surgery. The surgeon must be well-versed with the indications, contraindications, and the management of postoperative complications, and should observe the procedures performed by surgeons skilled in these procedures. Even skilled surgeons may have visually significant complications in 1-14% of cases. Thus far, few surgeons have made the commitment to learn the autoplastic techniques. Simplification, through the use of pre-carved tissue, hydrogel lenses, or the excimer laser, may allow these techniques to become widely practiced.

Conclusions Keratophakia and keratomileusis have a small well-defined role to play in the surgical management of high refractive errors, whether hyperopic or myopic. Although a large number of cases have been performed, there have been few well-controlled studies. The complication rates reported are significant in some series. The major problems include the complexity of the procedure and equipment, the delayed visual rehabilitation, the potential for minor to severe visual loss, decrease in the quality of vision from glare, loss of contrast sensitivity, inaccuracy of refractive results, and postoperative complications principally involving re-epithelialization and wound healing. Well designed prospective studies are needed to objectively evaluate these techniques and to compare other surgical alternatives including intraocular lens implantation and epikeratoplasty. Current research is directed toward nonfreeze techniques, synthetic materials, and photoablation using the excimer laser.

AAO · Keratophakia and KeratomUeusis Preparation was coordinated by the Committee on Ophthalmic Procedures Assessment, with the help of the following: Original draft: Reviewers:

Casimir A. Swinger, MD Perry S. Binder, MD Richard Elander, MD Miles H. Friedlander, MD Kenneth R. Kenyon, MD Andrew 0. Lewicky, MD Marguerite B. McDonald, MD Leo J. Maguire, III, MD Anthony B. Nesburn, MD Daniel M. Taylor, MD Richard A. Villasenor, MD Richard L. Lindstrom, MD Thomas D. Lindquist, MD, PhD Jennifer Clelland Board of Directors 1986 Board of Directors February 15, 1992

Edited by: Managing Editor: Approved by: Revised and Approved by:

Proprietary Interests* p Ccl Cc8 N N N N

Cc2, Cc5, Cc7, Cc8

N N N N N N

* Proprietary Interests Stated: CATEGORY

Investor

ABBREV p Pc I

Consultant

c_

Product

Ic

Cc

C1 or Ccl C2 or Cc2 C3 or Cc3 C4 orCc4 C5 or Cc5 C6 or Cc6 C7 or Cc7 C8 or Cc8 None

N

SPECIFIC FINANCIAL INTERESTS

Financial interest in equipment, process, or product presented. Such interest in potentially competing equipment, process, or product. Financial interest in a company or companies supplying the equipment, process, or product presented. Such interest in a potentially competing company. Compensation received within the past 3 years for consulting services regarding the equipment, process, or product presented. Such compensation received for consulting services regarding potentially competing equipment, process, or product. EXAMPLES OF COMPENSATION RECEIVED INCLUDE: 1. 2. 3. 4. 5. 6. 7.

Retainer Contract payments for research performed Ad hoc consulting fees Substantial non-monetary perquisites Contribution to research or research funds Contribution to travel funds Reimbursement of travel expenses for presentation at meetings or courses 8. Reimbursement of travel expenses for periods of direct consultation

No financial interest. May be stated when such interests might falsely be suspected.

References 1. Barraquer JI: Keratomileusis for the correction of myopia. Ann Inst Barraquer 1964;5:209-229. 2. Ainslie D: The surgical correction of refractive errors by keratomileusis and keratophakia. Ann Ophthalmol1976;8: 349-367. 3. Troutman RC, Swinger C: Refractive keratoplasty: Keratophakia and keratomileusis. Trans Am Ophthalmol Soc 1978;76:329-339. 4. Barraquer JI: Keratophakia. Trans Ophthalmol Soc UK 1972;92:499-516.

5. Barraquer JI: Keratophakia. Japan J Ophthalmol 1974;18: 199-212. 6. Colin J et al: The surgical treatment of high myopia: Comparison of epikeratoplasty, keratomileusis and minus power anterior chamber lenses. Refract Corn Surg 1990;6:245251. 7. Friedlander MH eta!: Keatophakia using preserved lenticules. Ophthalmology 1980;87:687-692. 8. Friedlander MH et a!: Clinical results of keratophakia and keratomileusis. Ophthalmology 1981 ;88:716-720. 9. Friedlander MH et al: Update on keratophakia. Ophthalmology 1983;90:365-368.

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Ophthalmology

Volume 99, Number 8, August 1992

10. Goldstein MT, Troutman RC, Swinger CA: Keratophakiaevaluation of accuracy. Invest Ophthalmol Vis Sci (Suppl) 1980;19:51 (ARVO Abstract). II. Kaufman HE: The correction of aphakia. XXXVI Edward Jackson Memorial Lecture. Am J Ophthalmol 1980;89:110. 12. Maguen E et al: Keratophakia with lyophilized cornea lathed at room temperature: New techniques and experimental surgical results. Ophthalmic Surg 1983;14:759-762. 13. Rich LF, Haraguchi KH, Louiselle 1: Stimulation of keratocyte repopulation in keratophakia lenticules by mesodermal growth factor. J Refract Surg 1988;4: 169-172. 14. Swinger CA: Refractive surgery for the correction of myopia. Trans Ophthalmol Soc UK 1981;101:434-439. 15. Swinger CA: Comparison of results obtained with keratophakia, hypermetropic keratomileusis, intraocular lens implantation, and extended-wear contact lenses. Int'l Ophthalmol Clin 1983;23(3):59-74. 16. Swinger CA: Lamellar refractive keratoplasty. In: Englestein JM (ed). Cataract surgery-Current options and problems. Orlando, Grune & Stratton, Inc., 1984;225-244. 17. Swinger CA, Barraquer JI: Keratophakia and keratomileusis-Clinical results. Ophthalmology 1981 ;88:709-715. 18. Swinger CA, Krumeich J, Cassiday D: Planar lamellar refractive keratoplasty. J Refract Surg 1986;2:17-24. 19. Swinger CA et al: Corneal endothelium in refractive surgery: A microscopic study of cat endothelium after keratophakia and myopic keratomileusis. Invest Ophthalmol Vis Sci (Suppl) 1983;24: 127. 20. Swinger CA, Troutman RC, Forman J: KeratophakiaPostoperative astigmatism. Cornea 1987;6:202-206. 21. Troutman RC: Indications, techniques, and complications ofkeratophakia. Int'l Ophthalmol Clin 1983;23:11-23. 22. Troutman RC, Swinger C, Goldstein M: Keratophakia update. Ophthalmology 1981 ;88:36-38. 23. Troutman RC, Swinger CA, Kelly RJ: Keratophakia: A preliminary evaluation. Ophthalmology 1979;86:523-533. 24. Villasenor RA: Keratophakia-Long-term results. Ophthalmology 1983;90:673-675. 25. Barraquer C, Gutierrez AM, Espinosa A: Myopic keratomileusis: short-term results. J Refract Surg 1989;5:307-313. 26. Barraquer JI: Keratomileusis. Int Surg 1967;48(2): 103-117. 27. Barraquer JI: Keratomileusis for the correction of aphakia. In: Symposium on Medical and Surgical Diseases of the Cornea. Transactions of the New Orleans Academy of Ophthalmology. StLouis, CV Mosby Co, 1980;450-479. 28. Barraquer Jl: Queratomileusis y queratogaquia. Bogota: Instituto Barraquer de America, 1980. 29. Barraquer JI: Keratomileusis for myopia and aphakia. Ophthalmology 1981 ;88:70 1-708. 30. Barraquer JI: Keratomileusis for the correction of myopia. Arch Soc Am Oftal Optom 1982;16:221-232. 31. Barraquer JI: Long term results of myopic keratomileusis1982. Arch Soc Am Oftal Optom 1983;17:137-148. 32. Barraquer JI: Results of hypermetropic keratomileusis. Int'l Ophthalmol Clinics 1983;23(3):25-44. 33. Buchbinder M, York KK, Villasenor RA: Postoperative management of myopic keratomileusis. J Refract Surg 1986;2:256-257. 34. Kommehl EW et al: Comeascope evaluation of myopic keratomileusis. Invest Ophthalmol Vis Sci (Suppl) 1985;26: 203. 35. Krumeich JH: Indications, techniques, and complications of myopic keratomileusis. Int'l Ophthalmol Clin 1983;23(3): 75-92.

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36. Maguire U et al: Visual distortion after myopic keratomileusis: Computer analysis of keratoscope photographs. Ophthalmic Surg 1987; 18:352-356. 37. Maxwell WA, Nordan LT: Myopic keratomileusis: Early experience. J Refract Surg 1985; 1:99-103. 38. Neumann AC: High myopia: which operation should we do? J Refract Surg 1988;4:76-79. 39. Neumann AC, McCarty G, Sanders DR: Delayed regression of effect in myopic epikeratophakia vs myopic keratomileusis for high myopia. J Refract Surg 1989;5:161-6. 40. Nordan LT, Failor MK: Myopic keratomileusis: 74 consecutive non-amblyopic cases with one year of follow-up. J Refract Surg 1986;2:124-128. 41. Swinger CA, Barker BA: Prospective evaluation of myopic keratomileusis. Ophthalmology 1984;91 :785-792. 42. Swinger CA, Villasenor RA: Homoplastic keratomileusis for the correction of myopia. J Refract Surg 1985;1:219223. 43. Taylor DM et al: Keratophakia-Clinical evaluation. Ophthalmology 1981;88:1141-1150. 44. Villasenor RA et al. Preliminary study ofkeratomileusis in primates (Macaca speciosa). Ophthalmology 1981 ;88:724728. 45. Krumeich JH, Swinger CA: Nonfreeze epikeratophakia for the correction of myopia. Am J Ophthalmol1987;103:397403. 46. Waring GO: Opportunities for more rational assessment of refractive corneal surgery. Refract Com Surg 1990;6:240244. 47. Werblin TP: Lamellar refractive surgery: where have we been and where are we going? J Refract Surg 1989;5:167176. 48. Werblin TP et al: Epikeratophakia: The surgical correction of aphakia. III. Preliminary results of a prospective trial. Arch Ophthalmol 1981;99:1957-1960. 49. Binder PS et al: Refractive keratoplasty: Microkeratome evaluation. Arch Ophthalmol 1982; 100:802-806. 50. Maguire U: Corneal topography of patients with excellent Snellen visual acuity after epikeratophakia for aphakia. Am J Ophthalmol 1990; 109:162-167. 51. Maguire U et al: Corneal topography in myopic patients undergoing epikeratophakia. Am J Ophthalmol 1987;103: 404-416. 52. Binder PS et al: Refractive keratoplasty: Tissue dyes and cryoprotective solutions. Arch Ophthalmol 1983; 101:15911596. 53. Barrett G, Moore MB: A new method of lathing corneal lenticules for keratorefractive procedures. J Refract Surg 1988;4:142-147. 54. Hill RA, Kratz K, Schanzlin DJ: A new method of cutting frozen corneal tissue for cryorefractive surgery. Refractive Surg 1986;2:80-82. 55. Safir A et al: The corneal press: Restoring donor corneas to normal dimensions and hydration before cryolathing. Ophthalmic Surg 1983;14:327-331. 56. Schanzlin DJ, Jester JV, KayE: Cryolathe corneal injury. Cornea 1983;2:57-68. 57. Schanzlin DJ et al: Keratocyte survival following a controlled-rate freeze. Invest Ophthalmol Vis Sci (Suppl) 1985;26:203. 58. Wisnicki J, Swinger C, Kommehl E: A modified corneal press to restore normal corneal dimensions. Invest Ophthalmol Vis Sci (Suppl) 1985;26: !50. 59. Zavala EY, Krumeich J, Binder PS: Laboratory evaluation of freeze versus non-freeze lamellar refractive keratoplasty. Arch Ophthalmol 1987;105:1125-1128.

AAO · Keratophakia and Keratomileusis 60. Barker BA, Swinger CA: Complications of corneal refractive surgery. In: Schwab IR (ed.). Refractive Keratoplasty. New York, Churchill Livingstone 1987;227-271. 61. Binder PS, Beale JP Jr, Zavala EY: The histopathology of a case of keratophakia. Arch Ophthalmol 1982; 100: 101105. 62. Breaux BE, Villasenor RA: Myopic keratomileusis: Histopathology and clinical correlation. Cornea 1982;1:65-69.58. 63. Hoffman F: The fate of corneal stromal cells in keratophakia. Arch Am Ophthalmol Optom 1981;15:183-196. 64. Koch P et al: Ultrastructure of human lenticules in keratophakia. Arch Ophthalmol 1981 ;99: 1634-1639. 65. Pokorny KS et al: Histopathology and ultrastructure of human keratorefractive surgery. Invest Ophthalmol Vis Sci (Suppl) 1983;24: 127. 66. Yamaguchi T et al: The ultrastructure of well-healed lenticules in keratomileusis. Ophthalmology 1983;90: 14951506. 67. Zavela EY, Krumeich J, Binder PS: Clinical pathology of non-freeze lamellar refractive keratoplasty. Cornea 1988;7: 223-230. 68. McCarey BE: Alloplastic refractive keratoplasty. In: Sanders DR, Hofmann RF, Salz JJ (eds). Refractive Corneal Surgery. Thorofare, NJ: Slack Inc., 1986;531-548. 69. McCarey BE: Current status of refractive surgery with synthetic intracorneal lenses: Barraquer lecture. Refract Corn Surg 1990;6:40-46. 70. McCarey BE et a!: Refractive predictability of myopic hydrogel intracorneallenses in nonhuman primate eyes. Arch Ophthalmol 1990; I 08:1310-1315. 71. van Rij G: Alloplastic corneal lenses. J Refract Surg 1989;5: 148-149. 72. Werblin TP, Patel AS: Myopic hydrogel keratophakia: improvements in lens design. Cornea 1987;6:197-201. 73. Werblin TP, Peiffer RL, Patel AS: Synthetic keratophakia for the correction of aphakia. Ophthalmology 1987;94:926934. 74. Del Pero RA eta!: A refractive and histopathologic study of excimer laser keratectomy in primates. Am J Ophthalmol 1990;109:419-429. 75. Fantes FE et a!: Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys. Arch Ophthalmo11990;108:665-675.

76. Food and Drug Administration. Draft clinical guidance for the preparation and contents of an investigational device exemption (IDE) application for excimer laser devices used in ophthalmic surgery for myopic photorefractive keratectomy (PRK). Refract Corn Surg 1990;6:265-269. 77. Gaboy S, Slomovic A, Jares T: Excimer laser-processed donor corneal lenticules for lamellar keratoplasty. Am J Ophthalmol 1989;107:47-51. 78. Gaster RN eta!: Corneal surface ablation by 193 nm excimer laser and wound healing in rabbits. Invest Ophthalmol Vis Sci 1989;30:90-98. 79. Goodman MT et al: Corneal healing following laser refractive keratectomy. Arch Ophthalmol1989;107:1799-l803. 80. L'Esperance FA, Taylor DM, Warner JW: Human excimer laser keratectomy: short-term histopathology. J Refract Surg 1988;4:118-124. 81. McDonald MB et a!: Central photorefractive keratectomy for myopia: the blind eye study. Arch Ophthalmo11990; 108: 799-808. 82. McDonald MB et al: One-year refractive results of central photorefractive keratectomy for myopia in the nonhuman primate cornea. Arch Ophthalmol 1990; 108:40-4 7. 83. Renard G et a!: Excimer laser experimental keratectomy: ultrastructural study. Cornea 1987;6:269-272. 84. Taylor DM et a!: Human excimer laser lamellar keratectomy. Ophthalmology 1989;96:654-664. 85. Taylor DM et al: Experimental corneal studies with the excimer laser. J Cataract Refract Surg 1989;15:384-389. 86. Trokel S: Evaluation of excimer laser corneal surgery. J Cataract Refract Surg 1989; 15:373-383. 87. Tuft SJ, Zabel RW, Marshall J: Corneal repair following keratectomy: A comparison between conventional surgery and laser photoablation. Invest Ophthalmol Vis Sci 1989;30: 1769-1777. 88. Abde!Megeed MA et al: Postoperative corneal topography of aphakic human eyes with hydrogel intracorneal implants. Invest Ophthalmol Vis Sci 1990;3 (suppl) 101. 89. Lane SS, McCarey BE, Lindstrom RL: Alloplastic corneal lenses. In: Schwab IR (ed), Refractive Keratoplasty. New York: Churchill Livingstone 1987;95-124.

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