Abstract
Purpose: :
Assessment of refractive stability is key to excluding eyes with keratoconus or nuclear sclerosis from refractive surgery. A large corporate laser center database was analyzed to determine clinically significant factors in change in prescription, as well as predictive value of past refractive change.
Methods: :
Using a database with 2.5-million spectacle and contact lens patient visits, 252,899 non-LVC patients (489,982 eyes) with ≥ 2 sequential visits over a 6.5-year period were analyzed. Manifest sphere and/or cylinder must have been captured for inclusion, with initial and most recent visits separated ≥ 3 years. Total and annualized changes in refraction were stratified by age, gender, and initial refractive error. A subset of 15,864 patients (29,213 eyes)with 4 consecutive examinations separated by 12 months (+/- 1 month) was also analyzed. Using a predictive model, the value of past refractive stability in predicting future stability was analyzed using the current standard of ≤ 0.5 D of yearly change in either sphere or cylinder.
Results: :
Mean overall myopia was -2.43 D; mean hyperopia +2.08 D; and mean cylinder -0.87 D. Over a mean interval of 4 years, 70.9% of sphere refractions and 91.2% of cylinder refractions were stable (</= 0.50 D change). On an annualized basis, 95.0% of sphere refractions and 99.6% of cylinder refractions were stable. An age-related myopic shift was seen through late teens, with a smaller percentage progressing through age 30. There was a hyperopic shift in adulthood to age 65, then a myopic shift >65. Most (94%) of the patients deemed unstable at a baseline exam subsequently would have been deemed stable; 10% of patients deemed stable would subsequently become unstable. For the subset analysis of eyes with multiple examinations, the majority (94%) of eyes that changed by more than 0.50D in either sphere or cylinder between the 1st and 2nd exam had subsequent exams (either 2nd to 3rd or 3rd to 4th) where both the sphere and cylinder changed by 0.50D or less. Similarly, a minority (10%) of eyes that changed by <=0.50D in both sphere and cylinder between exam 1 and 2 had a change of either sphere or cylinder of >0.50D change between either the 2nd to 3rd or 3rd to 4th examinations. Young (<17 yrs) and old (>70 yrs) patients were the most likely to have a consistent and consecutive change in either sphere or cylinder >0.50D between each of the 4 examinations.
Conclusions: :
Between the ages of 30-60, refractive error, especially cylinder, is very stable. However, the current community standard for determining refractive stability is not supported by these data, as past refractive change does not appear to be predictive of future change in patients between 18 and 70 years old.
Keywords: refractive surgery: LASIK