Contrast Sensitivity after Wavefront-optimized (WFO) and Wavefront-guided (WFG) Photorefractive Keratectomy (PRK) and its Effect on Military Target Identification

Abstract

Purpose: To determine the effect of contrast sensitivity after WFO and WFG PRK in the ability to identify armored vehicles of military interest.

Methods: This is a prospective study of 27 myopic participants randomized to undergo either WFO (n=13) or WFG PRK (n=14). Corrected distance high and low contrast visual acuities were determined preoperatively and at 1, 3, and 6 months (M) postoperatively. Military task performance was evaluated preoperatively (corrected visual acuity) as well as 6 weeks and 6M postoperatively (uncorrected visual acuity). Participants were asked to identify combat vehicles in varying contrasts using software. Change in probability of identification (PID) for each observer preoperatively and 6M postoperatively was assessed. Repeated measures analysis of variance and the Fisher exact test were performed to compare contrast sensitivity and military task, respectively, between the treatment groups. A p-value of <0.05 was considered statistically significant.

Results: WFO PRK seemed to outperform WFG PRK in SuperVision high contrast, SuperVision low contrast, Night Vision, and 25% low contrast acuity tests (p≤0.01) but not in 5% low contrast acuity (p=0.14). There was no significant difference between the treatment groups in their ability to identify military vehicles (p=0.59) at 6M postoperatively. Eight of 10 WFO PRK participants performed equivalent to or better than preoperative PID, while two participants performed more than one standard deviation (1σ) below preoperative PID. Ten of 11 WFG PRK participants performed equivalent to or better than preoperative PID, while one participant performed more than 1σ below preoperative PID.

Conclusions: Performance in high and low contrast acuity tests appeared to be better after WFO PRK than after WFG PRK. However, performance of participants in the WFO and WFG PRK groups were statistically comparable in their ability to identify vehicles of military interest presented in varying contrasts.

Keywords: 679 refractive surgery: comparative studies • 686 refractive surgery: PRK • 478 contrast sensitivity