Small optical zones, subepithelial persistent haze, and problematic night vision are symbols and relics of the first phase of photorefractive keratectomy (PRK). In this issue, Fagerholm provides a review of our current knowledge of corneal wound healing. Comprehension of this complex subject is being stimulated by clinical need in the wake of corneal laser surgery advancements.
Now, the laser in situ keratomileusis (LASIK) revolution is upon us. Several aspects of LASIK surgery are discussed in this issue. On the Internet society mailboxes and chat lines, LASIK queries abound as this revolution unveils the pitfalls that may ruin the hopes and expectations of ophthalmologist and patient alike. For many LASIK practitioners, PRK is deemed to be obsolete because invoking anterior corneal wound-healing responses not only creates some uncertainty of outcome, but the delay in stability coupled with postoperative discomfort seem to be inferior to the LASIK process.
We speak of LASIK as though the procedure were performed in a universal manner. However, as Leung and coauthors report, microkeratomes differ, creating flaps of variable thickness, diameter, and hinge location. Additionally, clinical excimer lasers may use broad beams, narrow beams, or small beams. Computer-controlled delivery systems attenuate the shutters, rotating slits, and scanning beams to facilitate optimum delivery of ablative energy in the dozen excimer lasers in world-wide clinical use. That each variant on the LASIK theme should be considered as one is patently absurd. Therefore, discussion of LASIK problems must always relate to particular hardware and software.
Schwiegerling and Snyder's study of eye movement in relation to ablation centration on the optical zone suggests that a high-frequency, active tracking laser delivery system will avoid potential pitfalls, even from physiological eye movement, however brief the exposure time.
Chuck et al. found that corneal flap creation involves sectioning the corneal nerve fibers with inevitable alteration of superficial corneal sensation. This has a probable consequence of reduced blinking and relative dry-eye problems.
Post-LASIK fluctuation of refraction and regression of effect requires a deeper understanding of corneal stromal wound healing, for there appears to be a variable ability to lift the flap days, weeks, months, or even years after the initial flap is created.
The major issue to emerge from the mass application of LASIK is the potential for corneal ectasia—limited base corneal thickness, variable intraocular pressure, individual corneal collagen properties, and eye rubbing could contribute to a plague of iatrogenic keratoconus. This concern has parallels with the Y2K bug, a potential problem unforeseen despite the imminent arrival of a new millennium. Prevention is always better than cure, but the urgent appeal of applying a new modality may overlook inherent dangers.
Limiting corneal thinning would seem to be advisable by resisting the temptation to apply LASIK beyond modest levels of myopia. It could be argued that PRK has a continuing role because of predictable results with low levels of myopic correction, but implantable Intacts® with their indirect influence on the cornea's optical zone may have more appeal. Treatment of higher levels of myopia, from which LASIK is precluded by limited corneal thickness, should only be considered for PRK application if and when corneal wound healing and subepithelial adverse responses are reliably controlled. The discomfort and delayed recovery of PRK when compared with LASIK will nevertheless be a price to be paid. Fisher and coauthors suggest that bilateral simultaneous treatment is also unacceptable for these reasons.
The natural design of the cornea has many purposes, one of which is to limit optical aberrations. By changing the shape from prolate to oblate, the effect of optical zone ablation, some of the optical properties are sacrificed. In the present state of the art, sacrificing a degree of optical quality, which is difficult if not impossible to quantify, is offset by the dramatic improvement in uncorrected visual acuity that patients enjoy. As corneal refractive surgery matures, these issues will have to be considered.
Such is the weight of information provided by current ophthalmic literature and meetings that it is easy to forget that corneal refractive surgery is complemented by a lenticular approach to the solution of many refractive errors. Major refractive errors may be best treated by lenticular methods, reserving corneal refractive methods for fine-tuning the outcome. Refractive surgery should always be considered a process rather than a single treatment. In this way, patient expectations will be more realistic and refractive surgeons will avoid the embarrassment of unwanted outcomes.
Laser in situ keratomileusis is performed as a bilateral simultaneous process in most major centers, for it is perceived that patient rehabilitation deserves this approach. Yet LASIK is an invasive procedure, with an incidence of unpredictable infection and noninfectious inflammatory responses. This bilateral simultaneous surgery on a wide scale contrasts with the uniocular application of cataract and intraocular lens surgery and refractive lensectomy. The Consultation Section in a 1997 issue considered the advisability of bilateral simultaneous lens surgery.1 The issue produced significant condemnation, even though the safety of such rapid closed-eye surgery is self-evident. The question therefore arises, Why is bilateral surgery of the cornea with all its attendant risks so different from lens surgery?
1. Masket S. Consultation section. J Cataract Refract Surg 1997; 23:1437-1448