Refractive surgery is one of the fastest growing surgical specialties in the world today, however, there are a paucity of long-term data in the literature. Even as phenomenal growth has occurred in the number of commercial clinics performing this surgery, there is a marked lack of interest shown by academic clinics. Many unanswered questions remain regarding long-term efficacy of refractive surgery and on many of the problems concerning quality of vision. There is a need for prospective multicenter studies to answer these questions.
Although refractive surgery has been practiced for 40 years, only a very few ophthalmic centers1 performed it until radial keratectomy gained popularity. The introduction of the excimer laser and its application to the corneal surface in PRK2,3 — and subsequently in LASIK — has made it the most popular and widely performed surgery in the world. It is now a major focus of interest at most international meetings, in peer-reviewed journals and in the popular press.
Encouragingly, PRK has shown long-term stability for up to 12 years.4 Despite removal of Bowman's membrane, the corneas have remained transparent. Patients have obtained good results in terms of visual acuity, but significant problems regarding quality of vision remain.
LASIK is the world's most popular surgery because it is pain-free and provides patients with rapid visual rehabilitation. Only a few studies have reported longer-term data. Sekondo et al5 reported that 66% of patients with an unaided vision of ?0.4 LogMAR and 46% of all patients were within ±1.00 D of attempted correction. They reported that 75% of patients had nighttime visual problems. Jaycock et al6 reported that 71% of eyes treated for +1.00 D to +3.00 D of hyperopia were within ±1.00 D of intended correction, whereas 37% of those between +3.50 D and +6.00 D of hyperopia were within ±1.00 D of intended correction. O'Doherty et al,7 in their 5-year LASIK follow-up study, reported that 60% of eyes were within ±0.50 D and 83% were within ±1.00 D of attempted correction. They concluded that LASIK surgery is predictable for mild-to-moderate myopia, however, beyond -6.00 D its efficacy decreases with a trend toward myopia over 5 years. Twenty-four percent of their patients had halos and glare. Although this is less than Segundo's study, it is still a significant finding. Overall, findings are encouraging in that they report good unaided vision and good safety with a 98% patient satisfaction rate. These investigators should continue to monitor their patient cohort and report 10-year follow-up results.
None of these studies obtained results on patients with keratoconus. Nevertheless, keratoconus has emerged as a significant risk in some patients who undergo LASIK. In a review of the literature, Binder8 reported 85 cases of progressive post-LASIK keratectasia that were not associated with preoperative forme fruste keratoconus. What has yet to be properly established is whether patients who present with keratoconus following laser surgery have preexisting forme fruste keratoconus or if LASIK disturbs the organization of collagen fibers. The latter case would result in compromised corneal strength and thereby induce keratoconus in a previously normal cornea.9,10 This possibility has stimulated development of new approaches to preoperative corneal assessment. One technique involves analysis of a corneal biomechanical property known as hysteresis, which measures the viscoelastic properties of the cornea.
Instruments are now available for use in clinical practice, but as of yet no peer-reviewed data on the significance or benefit of corneal hysteresis measurement are available. The present rule of thumb (ie, leaving 250 µm of undisturbed stromal bed beneath the treated area of LASIK) is now generally accepted by most surgeons. Casebeer11 considered that ectasia could be avoided, provided that the ablation or incision did not go below 70% of depth of the cornea.
Do Not Address Certain Concerns
Despite its popularity and the high volume of refractive surgeries performed, good short- and long-term data on patient outcomes are lacking. There are no prospective, large, multicenter studies that address concerns such as: Is regression age-related or influenced by the degree of myopia, tear secretion, medication and occupation? Do patients undergo natural myopic shift over time, regardless of laser surgery and is this related to age, degree of myopia or occupation?
Myopic eyes undergoing surgery are probably the most vulnerable of all eyes and have a higher risk of retinal problems. Yet, we do not have any definitive answers as to the effect of refractive surgery on the vitreous or retinal status, either in the short- or long-term. There is also the issue of visual quality outcome post-laser, in particular the problem of halos and glare, which has been highlighted in many 5-year studies. Do customized laser procedures reduce these? Are they related to the pupil size? Do they decrease or disappear over time? These questions remain to be answered by long-term studies.
Contrast sensitivity can be poor in the presence of good visual acuity and should be a component of evaluation. The methods available for measurement of contrast sensitivity and the conditions required for accurate assessment, however, have made it difficult to accurately assess.12 Contrast sensitivity measures the total visual system and should be used in conjunction with visual acuity and wavefront analysis. It provides a measure of the patients' functional visual quality and spatial distortions. Some evidence suggests that the temporary reduction in contrast sensitivity caused by LASIK improves over the first 6 months.13
The lack of interest shown by academic units in this form of surgery has resulted in almost 80% of procedures now being performed in commercial clinics. The rush to the bottom, in terms of offering reduced professional fees, inducements for surgery and the employment of an increasing number of migrating flying doctors, creates the potential for loss of clinical independence and continuity of care. The resulting environment does little to encourage patient follow-up and the collection of clinical data for prospective randomized studies. In addition, many of the opinion formers are themselves potentially compromised by a conflict of interest due to financial affiliations.
Longer-Term Follow-Up Needed
While refractive surgery — particularly LASIK — has popularized eye surgery and changed the quality of life, it has also caused visual quality problems for a minority of patients. The sustained and increasing popularity of this surgery necessitates the need for thorough and longer-term evaluation. The 10-year follow-up of radial keratotomy reinforced the importance of long-term follow-up.14 Therefore, to properly answer many of the questions relating to keratoconus, myopic regression and progression, LASIK versus LASEK, quality of vision issues and prospective multicenter studies are needed. Such studies would provide reassurance for both patients and surgeons and may reinforce the long-term safety and stability of refractive surgery.
Michael O'Keeffe, MD, practices at Mater Private Hospital in Dublin, Ireland. Professor O'Keeffe may be reached at mokeefe@materprivate.ie; +00 353 1 8858626 (telephone) or +00 353 1 8858490 (fax).
Up Front | Mar 2006
Multicenter Prospective Studies in Refractive Surgery
There are unanswered questions regarding keratoconus, myopic regression and progression.
Michael O'Keeffe, MD, and Caitriona Kirwan, MD
