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Refractive Surgery
EDITORIAL Refractive Surgery Herbert E. Kaufman Refractive surgery is a confusing subject be cause it involves two disparate issues: safety and necessity. On one hand is the group of patients for whom spectacles are functional but undesirable; for these patients, the risks of refractive surgery must be exceedingly low. On the other hand is the group of patients who are blind without some sort of surgery, for exam ple, adults and children who are unilaterally aphakic and contact-lens intolerant, and pa tients with keratoconus. For this group, sur gery with a higher risk is acceptable. The intraocular lenses of Ridley, Binkhorst, and Choyce were the beginning of a kind of surgery done because spectacles were not total ly satisfactory. Our discovery of the endothelial damage caused by these lenses and our use of protective agents (initially polyvinyl pyrrolidone and methylcellulose) as well as the development of posterior chamber lenses by Shearing have made intraocular lens implanta tion a safe and generally accepted procedure. Today, it is the exception when a plastic lens is not inserted into an eye at the time of cataract extraction. Yet, originally there was great de bate about the justification for such surgery, because it was difficult to balance the severe curtailment of lifestyle caused by poor vision against unknown potential risks. Now, the in sertion of intraocular lenses has become rou tine, and the safety of the procedure has brought widespread acceptance. In the category of surgery useful for patients who may otherwise be blind is epikeratophakia. Although epikeratophakia surgery is more time consuming and requires more elabo rate postoperative care than an operation such as radial keratotomy, it was designed for a different group of patients, whose visual prob lems are more complex. The monocularly apha kic pediatric patients who are contact-lens in tolerant would be functionally blind without the surgery or would require high risk, often sight-threatening intraocular lens insertion. The monocularly aphakic adults without an intact posterior capsule who are contact-lens intolerant require potentially hazardous sur
©AMERICAN JOURNAL OF OPHTHALMOLOGY
103:355-357,
gery that can carry with it permanent loss of vision, especially if the endothelium is abnor mal, chronic iritis is present, or vitreous is in the anterior chamber. In this supplement of THE JOURNAL, Durrie and associates compare their experience with secondary intraocular lenses and epikeratophakia. Additionally, pa tients with keratoconus who lose the ability to wear contact lenses require some form of sur gery, and the severely myopic who are intoler ant to contact lens wear can suffer severe limi tation of their lifestyle with the distorted vision provided by spectacles. These were the groups for which epikeratophakia surgery was initially developed. This supplement of THE AMERICAN JOURNAL OF OPHTHALMOLOGY includes what I consider to be a series of unique studies of epikerato phakia. This surgery evolved from the early work of Barraquer and was developed by me originally with Werblin and then made practical by McDonald. It evolved to avoid the need for each physician to lathe tissue lenses for pa tients and to avoid the hazards and irreversible difficulties of microkeratome incisions. The tis sue lenses used in epikeratophakia were not originally considered to be devices requiring regulation by the Food and Drug Administra tion, and yet the manufacturer of the tissue lenses, Allergan Medical Optics, and our group undertook to conduct a prospective nationwide study of the risks and benefits of the proce dure, so that surgeons inexperienced with this procedure could have some basis for estimating potential gain and possible risks. The Prospective Evaluation of Radial Keratot omy (PERK) study and the nationwide study of epikeratophakia were designed differently. The PERK study asked the question, "How good can this operation be?" It included only corneal surgeons or experienced radial keratotomy sur geons. It required special training and trial operations with assistance from expert teachers and it eliminated the first ten cases with their potential complications for each investigator. Conversely, the epikeratophakia study was de veloped primarily by McDonald and is a proMARCH,
1987
355
356
AMERICAN JOURNAL OF OPHTHALMOLOGY
spective study that includes every case of every surgeon. No learning cases were eliminated, and all complications were included. Investiga tors attended a two-day laboratory training session, and all cases performed thereafter were required to be reported and included in the database. To my knowledge, this is the first instance of a new surgical modality undergoing a large scale study, not in the hands of experts alone, but primarily in the hands of those learning the procedure, before widespread dis semination of the procedure and materials was permitted or encouraged. For the future of epikeratophakia, the possibility of cutting the tissue lenses without freezing and the use of agents to stimulate healing may make this al ready relatively safe and effective procedure even simpler and safer, as may new edge de signs for the lenses, and other promising devel opments. For this form of refractive surgery, this is just the beginning. Radial keratotomy has been considered con troversial, not because it is refractive surgery, but because the myopia it is meant to correct is generally low myopia which, with the aid of spectacles, is not the handicap to functional living that other more severe refractive errors can be. Additionally, radial keratotomy is an essentially irreversible procedure, unlike epi keratophakia in which the tissue lens can be removed, usually restoring the eye to its preoperative state. A number of serious complica tions have been reported after radial keratoto my, some of which, such as optic atrophy after retrobulbar injection, could perhaps have been avoided, since retrobulbar injections are not generally indicated with this procedure. De layed bacterial ulcers, perforations of the cor nea, and other problems have also been report ed; however, iri my practice I have seen many of these complications caused by contact lens es, and it is not clear that the incidence of such complications is higher with surgery than with long-term contact lens wear. I think that the major problem with radial keratotomy is its unpredictability, and the like lihood, in my opinion, that it will remain un predictable. For low refractive errors, the pre dictability is relatively good, but above 6 or 8 diopters, the probability of a given patient achieving the desired correction and being able to go without spectacles is much lower. In this supplement, Deitz and others report the results of a prospective study of radial keratotomy. Even though the dropout rate is high (about 29%), and even though Dr. Deitz
March, 1987
does such a large volume of radial keratotomies that he has been able to develop his own formu las and software, in the group of myopic indi viduals with high refractive errors, the predict ability remains suboptimal. Other surgeons using these techniques may not achieve the results that he achieves, and the overcorrections and undercorrections remain a significant problem. Some look at the problem of predictability as a question of having sufficiently precise instru ments to make optimal cuts. To me, the lack of predictability represents the differences in healing among patients, and I suspect that this will follow a normal distribution curve and carry with it an inherent variability for the procedure. It seems likely that healing after other incisional operations, such as relaxing incisions and the Ruiz procedure, will suffer from the same lack of predictability for the same reasons. Pharmacologic attempts have been made to control healing after radial kera totomy, for example, antimetabolites and colla gen cross-linkage inhibitors reduce scar forma tion, and substances such as epidermal growth factor speed up collagen formation. However, to my knowledge, there is no evidence that they make this procedure more predictable. There is a considerable question about whether it should be attempted in patients with more than 6 or 8 diopters of myopia. The status of synthetic lenses implanted within the cornea is still largely experimental. Hydrogel implants require a keratomileusislike lamellar dissection made with a microkeratome, which, in my opinion, introduces a risk of irreversible damage. Additionally, I believe these compressible hydrogels may give varia ble corrections with variations in patient heal ing and scar contraction of the cornea over the implant. Impermeable polysulfone implants, if placed deep enough and made small enough, may permit sufficient oxygen and metabolites from the endothelium to reach the anterior cornea by diffusion around the implant or through holes in the implant, but this assumes that the keratocytes immediately over the im plant require no nutrition and I think that this is not true. My own guess is that a significant incidence of basement membrane deposition, vascularization, and other problems will per sist, and complications of this procedure are not easily reversible. A new modality on the horizon for refractive surgery is the excimer laser, which was pio neered for use in ophthalmology by Trokel.
Vol. 103, No. 3, Part II
Although there may be other mechanisms of action, most believe that this laser, with emis sions in the near ultraviolet range (193 nm appears to be the most effective wavelength), disrupts bonds between atoms, tearing mole cules apart and vaporizing tissue with a mini mal thermal effect. It may be that this laser will be minutely controllable, and that a patient may some day be able to sit in front of a laser for 30 seconds or so and obtain a predictable change in corneal shape so that eyeglasses become unnecessary. The excimer laser has the potential to serve as a surgical knife, and to make radial keratotomy incisions, but the re shaping of the cornea to provide a totally new refractive surface is its most exciting possibili ty. What hazards may accompany such new procedures remain to be seen, and whether good vision can be achieved by an eye without Bowman's layer is uncertain. Some types of refractive surgery, which now have a defined and often acceptable risk, are of great potential benefit to some patients, espe
Editorial
357
cially those who cannot see without surgery. I predict that progress in this field will be rapid, and will be enhanced by related research such as the research, which has been stimulated by the National Eye Institute, on corneal healing through the use of fibronectin, growth factors, and other substances. Progress in refractive surgery may eclipse the progress already made in intraocular lens sur gery and this surgical modality may become a progressively more important part of our pro fession. At the same time, I urge readers to think of the political consequences that may ensue if, indeed, a patient can receive a brief laser treatment, and safely and permanently be rid of refractive error and the need for eye glasses.
Reprint requests to Herbert E. Kaufman, M.D., LSU Eye Center, 2020 Gravier St., Suite B, New Orleans, LA 70112.
©AMERICAN JOURNAL OF OPHTHALMOLOGY
103:355-357,
gery that can carry with it permanent loss of vision, especially if the endothelium is abnor mal, chronic iritis is present, or vitreous is in the anterior chamber. In this supplement of THE JOURNAL, Durrie and associates compare their experience with secondary intraocular lenses and epikeratophakia. Additionally, pa tients with keratoconus who lose the ability to wear contact lenses require some form of sur gery, and the severely myopic who are intoler ant to contact lens wear can suffer severe limi tation of their lifestyle with the distorted vision provided by spectacles. These were the groups for which epikeratophakia surgery was initially developed. This supplement of THE AMERICAN JOURNAL OF OPHTHALMOLOGY includes what I consider to be a series of unique studies of epikerato phakia. This surgery evolved from the early work of Barraquer and was developed by me originally with Werblin and then made practical by McDonald. It evolved to avoid the need for each physician to lathe tissue lenses for pa tients and to avoid the hazards and irreversible difficulties of microkeratome incisions. The tis sue lenses used in epikeratophakia were not originally considered to be devices requiring regulation by the Food and Drug Administra tion, and yet the manufacturer of the tissue lenses, Allergan Medical Optics, and our group undertook to conduct a prospective nationwide study of the risks and benefits of the proce dure, so that surgeons inexperienced with this procedure could have some basis for estimating potential gain and possible risks. The Prospective Evaluation of Radial Keratot omy (PERK) study and the nationwide study of epikeratophakia were designed differently. The PERK study asked the question, "How good can this operation be?" It included only corneal surgeons or experienced radial keratotomy sur geons. It required special training and trial operations with assistance from expert teachers and it eliminated the first ten cases with their potential complications for each investigator. Conversely, the epikeratophakia study was de veloped primarily by McDonald and is a proMARCH,
1987
355
356
AMERICAN JOURNAL OF OPHTHALMOLOGY
spective study that includes every case of every surgeon. No learning cases were eliminated, and all complications were included. Investiga tors attended a two-day laboratory training session, and all cases performed thereafter were required to be reported and included in the database. To my knowledge, this is the first instance of a new surgical modality undergoing a large scale study, not in the hands of experts alone, but primarily in the hands of those learning the procedure, before widespread dis semination of the procedure and materials was permitted or encouraged. For the future of epikeratophakia, the possibility of cutting the tissue lenses without freezing and the use of agents to stimulate healing may make this al ready relatively safe and effective procedure even simpler and safer, as may new edge de signs for the lenses, and other promising devel opments. For this form of refractive surgery, this is just the beginning. Radial keratotomy has been considered con troversial, not because it is refractive surgery, but because the myopia it is meant to correct is generally low myopia which, with the aid of spectacles, is not the handicap to functional living that other more severe refractive errors can be. Additionally, radial keratotomy is an essentially irreversible procedure, unlike epi keratophakia in which the tissue lens can be removed, usually restoring the eye to its preoperative state. A number of serious complica tions have been reported after radial keratoto my, some of which, such as optic atrophy after retrobulbar injection, could perhaps have been avoided, since retrobulbar injections are not generally indicated with this procedure. De layed bacterial ulcers, perforations of the cor nea, and other problems have also been report ed; however, iri my practice I have seen many of these complications caused by contact lens es, and it is not clear that the incidence of such complications is higher with surgery than with long-term contact lens wear. I think that the major problem with radial keratotomy is its unpredictability, and the like lihood, in my opinion, that it will remain un predictable. For low refractive errors, the pre dictability is relatively good, but above 6 or 8 diopters, the probability of a given patient achieving the desired correction and being able to go without spectacles is much lower. In this supplement, Deitz and others report the results of a prospective study of radial keratotomy. Even though the dropout rate is high (about 29%), and even though Dr. Deitz
March, 1987
does such a large volume of radial keratotomies that he has been able to develop his own formu las and software, in the group of myopic indi viduals with high refractive errors, the predict ability remains suboptimal. Other surgeons using these techniques may not achieve the results that he achieves, and the overcorrections and undercorrections remain a significant problem. Some look at the problem of predictability as a question of having sufficiently precise instru ments to make optimal cuts. To me, the lack of predictability represents the differences in healing among patients, and I suspect that this will follow a normal distribution curve and carry with it an inherent variability for the procedure. It seems likely that healing after other incisional operations, such as relaxing incisions and the Ruiz procedure, will suffer from the same lack of predictability for the same reasons. Pharmacologic attempts have been made to control healing after radial kera totomy, for example, antimetabolites and colla gen cross-linkage inhibitors reduce scar forma tion, and substances such as epidermal growth factor speed up collagen formation. However, to my knowledge, there is no evidence that they make this procedure more predictable. There is a considerable question about whether it should be attempted in patients with more than 6 or 8 diopters of myopia. The status of synthetic lenses implanted within the cornea is still largely experimental. Hydrogel implants require a keratomileusislike lamellar dissection made with a microkeratome, which, in my opinion, introduces a risk of irreversible damage. Additionally, I believe these compressible hydrogels may give varia ble corrections with variations in patient heal ing and scar contraction of the cornea over the implant. Impermeable polysulfone implants, if placed deep enough and made small enough, may permit sufficient oxygen and metabolites from the endothelium to reach the anterior cornea by diffusion around the implant or through holes in the implant, but this assumes that the keratocytes immediately over the im plant require no nutrition and I think that this is not true. My own guess is that a significant incidence of basement membrane deposition, vascularization, and other problems will per sist, and complications of this procedure are not easily reversible. A new modality on the horizon for refractive surgery is the excimer laser, which was pio neered for use in ophthalmology by Trokel.
Vol. 103, No. 3, Part II
Although there may be other mechanisms of action, most believe that this laser, with emis sions in the near ultraviolet range (193 nm appears to be the most effective wavelength), disrupts bonds between atoms, tearing mole cules apart and vaporizing tissue with a mini mal thermal effect. It may be that this laser will be minutely controllable, and that a patient may some day be able to sit in front of a laser for 30 seconds or so and obtain a predictable change in corneal shape so that eyeglasses become unnecessary. The excimer laser has the potential to serve as a surgical knife, and to make radial keratotomy incisions, but the re shaping of the cornea to provide a totally new refractive surface is its most exciting possibili ty. What hazards may accompany such new procedures remain to be seen, and whether good vision can be achieved by an eye without Bowman's layer is uncertain. Some types of refractive surgery, which now have a defined and often acceptable risk, are of great potential benefit to some patients, espe
Editorial
357
cially those who cannot see without surgery. I predict that progress in this field will be rapid, and will be enhanced by related research such as the research, which has been stimulated by the National Eye Institute, on corneal healing through the use of fibronectin, growth factors, and other substances. Progress in refractive surgery may eclipse the progress already made in intraocular lens sur gery and this surgical modality may become a progressively more important part of our pro fession. At the same time, I urge readers to think of the political consequences that may ensue if, indeed, a patient can receive a brief laser treatment, and safely and permanently be rid of refractive error and the need for eye glasses.
Reprint requests to Herbert E. Kaufman, M.D., LSU Eye Center, 2020 Gravier St., Suite B, New Orleans, LA 70112.