Opinions on excimer laser photorefractive keratectomy and radial keratotomy vary as much as the surgical modalities themselves.
Proponents of the excimer claim photorefractive keratectomy will replace radial keratotomy in this decade. They cite poor predictability, progressive hyperopic shift, and structural weakening of the cornea as major deficiencies of radial keratotomy.
Radial keratotomy advocates express concern over removing Bowman's layer, ablating corneal tissue in the central visual axis, and the subepithelial reticular haze that occurs with photorefractive keratectomy.
The strengths and weaknesses of both procedures were debated during two panels at the 1991 American Academy of Ophthalmology meeting in Anaheim, Calif. Refractive and Corneal Surgery has compiled a composite of the opinions expressed:
Richard A. Villasenor, MD: "There is no doubt that serious complications have been reported with radial keratotomy, but the majority of these were in early cases where primitive instrumentation such as metal blades, optical pachymetry, and too many incisions were performed. The reality is that serious complications are rare using current conservative techniques."
Denis M. OTDay, MD: "Unfortunately, complications of radial keratotomy are frequently permanent or difficult to treat. An example is the fluctuating vision, which in my experience has persisted in some patients for as long as a decade."
Villasenor: "A combined series of over 1600 eyes by the PERK group revealed only three cases of vision threatening complications, all related to contact lens bacterial keratitis, all recovering 20/40 vision or better. This is a low complication rate of 0.19%."
O'Day: "In essence, radial keratotomy is empirical and changes in technique are made with a lack of sound scientific basis for their validity. Hence, results do not really improve, although some surgeons may learn to avoid those patients likely to have anomalous results. Importantly, the race of science is passing radial keratotomy by as laser technology is explored in the search for effective refractive surgery. Radial keratotomy has nowhere to go in the future."
Villasenor: "While the Air Force has used the weakened eye as a reason for exclusion, law enforcement agencies and fire departments do not. Hundreds of thousands of them perform their daily duties with the knowledge that limited vision will no longer threaten their lives."
O'Day: "Unfortunately radial keratotomy doesn't come even come close to qualifying as a deserving procedure since it really cannot help the thickglasses group. Are we concentrating on the fact that 25% of adults in Western countries are myopic because it indicates the extent of a serious blinding disease, or because it is of real significance to a profession beset by a serious economic threat?
"No one doubts that the need to wear glasses, especially thick ones, can be a disability to some, but to expend so much of our energy [on radial keratotomy] and so much of our fimi ted resources raises serious questions about our sanity, not to mention our ability to act responsibly as physicians."
Larry W. Piebenga, MD: "Early (photorefractive keratectomy) results are not perfect, but in the perspective of an investigational study of a new modality, they are impressive, as is the lack of complications. Infections will occur, but the risk is small and the infections superficial... The excimer is essentially astigmatism-negative."
Alan L. Stern, MD: "Very little information is available as to the long-term problems of glare, contrast sensitivity, and stable refractive errors. When you think of it from a perspective of visual acuity, we're not amazed at how well photorefractive keratectomy works for myopia - we are amazed that it works at all.
"Can we so easily dismiss any mutagenic effects of ultraviolet radiation? Can we transfer the results of highly committed investigators with significant technical support and adapt them to a variety of more clinical settings? Can we so easily dismiss decentration of an ablated area as clinically insignificant?"
Piebenga: "Unlike radial keratotomy, we haven't made cuts 500 μ into the cornea, leaving only 58 μ, if we are lucky, of normal tissue to achieve this result. We have no risk of perforation and the strength of the globe is virtually unaltered."
Stern: "With photorefractive keratectomy, the fixation of the eye and centration of the beam are manual and visual, with decreasing effectiveness as the procedure progresses and the epithelium is removed. This can allow for significant decentration of the ablation."
Richard L. Lindstrom, MD: "The major advantage of radial keratotomy is the patient gets instant gratification. On day 1, they come back much improved. For the 1st 3 months, radial keratotomy is the clear winner over photorefractive keratectomy. At 1 year, you have your radial keratotomy patients coming in, and they have star bursts. Maybe 20% to 30% will have a compressive hyperopic change.
Maybe 5% will have a progressive myopic change." Marguerite B. McDonald, MD: "If the data continues to look as good as it does, eventually incisional techniques will be replaced by the excimer. They will coexist for a few years, however."
Stern: "This procedure (photorefractive keratectomy) involves the most costly equipment venture to date, more than an ambulatory surgery unit. If treatment indications are few, the cost may be extraordinary."
Piebenga: "Ultimately, after deliberate and cautious improvement, the excimer offers a procedure that does not require a super specialist's skill. They can be performed by general ophthalmologists with average surgical ability."
Stern: "The results of photorefractive keratectomy for low myopia appear to be as effective as radial keratotomy; however, data published to date often combines or deletes series or patients done without steroids and may be difficult to compare directly."
Keith P. Thompson, MD: "It is unlikely, based on what we know about wound healing, that there will be a shift towards hyperopia, as there is with radial keratotomy. Everything we've learned about wound healing tells us that the cornea wants to steepen, both through epithelial hyperplasia and through regeneration of the stroma. This appears to stabilize sometime between 6 and 12 months."
Steven Trokel, MD: "The ultraviolet fight we use in the excimer laser approaches the cornea as if it were a brick wall.. .It appears that the amount of secondary UV light, which is the only UV light that can penetrate the eye, is 1000 times below the most pessimistic damage threshold for UV damage for the retina or the lens.
George O. Waring, MD: "I know of no evidence that Bowman's layer is the keeper of the shape of the front of the cornea. Removing Bowman's layer is not associated with keratoconus. There are 500 µm of corneal fibrils that stretch from one side of the limbus to the other. They form a very tight mesh that maintains the shape of the cornea."
Trokel: "I am more concerned about sneaking in some patients with keratoconus into a photorefractive keratectomy situation without being aware that it's there than I am about developing keratoconus in later years."
McDonald: "We have found that somewhere between 5% and 10% of our patients have a very early form of keratoconus (preoperatively) that you can't pick up by refraction or with a keratometer or at the slit lamp that show definitely on a map. Anyone in the future who will engage in this will have to do preop screening... There are still a few people who will sneak by your detection if you don't have a color-coded map."
Waring: "As we do micron surgery, we also will have to start doing micron diagnostics, in a sense, and have much more sensitive ways to weed out these people, who really we think should not have corneal refractive surgery because they are progressing."
Stern: "An ophthalmic community that has yet not wholeheartedly embraced the concept of refractive myopic surgery via radial keratotomy should evaluate photorefractive keratectomy further."