EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY (PRK) FOR MYOPIA - PRESENT STATUS - AEROSPACE CONSIDERATIONS

Excimer laser photorefractive keratectomy (PRK) to reduce myopia has been studied the past 3 yrs at multicenters authorized by the FDA. The excimer laser ablates the central cornea to a new calculated power. A review of the cases reported in the literature reveals the following information: Corneal scarring may be reflected in the loss of best-corrected vision. Regression of the refractive effect is a complication. Predictability was the percentage of eyes obtaining 20/40 or better vision; this varied from 62.5-91%. Conversely, 9.0-37.5% were 20/50 or worse. Low to moderate myopes had better visual success. Accuracy was the refractive correction within +/- 1.00 D (spherical equivalent); this varied between 64.7-93%. The higher percentages were with low to moderate degrees of myopia. Loss of best corrected vision was due to scarring and haze, and occurred more frequently with high myopia and deeper ablations. Patient satisfaction after 2 yrs was reported as 82.6-90%; 17.4% were not satisfied. Advantages: a) PRK effectively and safety corrected myopia and myopic astigmatism; b) there was no diurnal variation of refraction or vision; c) vision remained fairly stable with some regression up to 24 mo and; d) accuracy of correction to +/- 1.00 D was fair. Disadvantages: a) post-operative scarring and haze was present after 6 mo to 2 yrs of follow-up in some cases. Scarring was less with low myopia and worse with high myopia; 6) regression of correction and blur; and c) poor night vision, halos, and glare sensitivity occurred after pupil dilation. Aerospace considerations: PRK appeared to be effective, sate, and satisfactory, with sufficient predictability and accuracy tor a high percentage of the selected patients of the studies. Aviators require more critical visual criteria for air safety and long-term stability of vision. The goal of retractive surgery on normal sighted eyes of pilots is that the uncorrected vision attained must be at least as good or better than the pre-surgical best-corrected vision. The predictability, accuracy, and complications reported to the present time appeared to pose adverse and unacceptable risks for air transport pilots.