Optometry & Vision Science

Skip Navigation LinksHome > November 2010 - Volume 87 - Issue 11 > Why Preoperative Acuity Predicts Postoperative Acuity in Wav...
Optometry & Vision Science:
doi: 10.1097/OPX.0b013e3181f6fb49
Original Article

Why Preoperative Acuity Predicts Postoperative Acuity in Wavefront-Guided LASIK

Aaron, Michelle T.*; Applegate, Raymond A.*; Porter, Jason†; Thibos, Larry N.‡; Schallhorn, Steve C.§; Brunstetter, Tyson J.*; Tanzer, David J.§

Collapse Box


Purpose. To critically evaluate the following clinical wisdom regarding custom (wavefront-guided) laser in situ keratomileusis (LASIK) that subjects with better-than-average best-corrected visual acuity (BCVA) before surgery have a greater risk of losing BCVA postoperatively than do subjects with worse-than-average BCVA before surgery.

Methods. High contrast BCVA was measured once before and 3 months after custom LASIK in one eye of 79 subjects. Preoperative spherical equivalent refractive error ranged between −1.00 and −10.38 D. The sample was divided into one of two subsamples: eyes that had better-than-average preoperative BCVA (<−0.11 logMAR) and eyes that had average or worse-than-average preoperative BCVA (≥−0.11 logMAR). Controls were implemented for retinal magnification and for the statistical phenomenon of regression to the mean of the preoperative acuity measurement.

Results. On average, for the entire sample, moving the correction from the spectacle plane to the corneal plane increased letter acuity 4.7% (1 letter, 0.02 logMAR). For each subsample, the percentage regression to the mean was 57.24%. After correcting for magnification effects and regression to the mean, eyes with better-than-average preoperative acuity had a small but significant gain in acuity (∼1 letter, p = 0.040) that was nearly identical to the gain for eyes with worse-than-average preoperative acuity (∼1.5 letters, p = 0.002).

Conclusions. Custom LASIK produced a statistically significant gain in visual acuity after correction for magnification effects. Dividing the sample into two subsamples based on preoperative acuity confirmed the common clinical observation that eyes with better-than-average acuity tend to remain the same or lose acuity, whereas eyes with worse-than-average acuity tend to gain acuity. However, when only one acuity measurement is taken at a single time point and the sample is subsampled nonrandomly, this clinical observation is due to a statistical artifact (regression to the mean) and is not attributable to the surgery.

© 2010 American Academy of Optometry


Article Tools


Article Level Metrics

Search for Similar Articles
You may search for similar articles that contain these same keywords or you may modify the keyword list to augment your search.