Pupil centroid shift measurements during photorefractive keratectomy

Purpose: Aim: To evaluate the amount of pupil centroid shift (PCS) just before photorefractive keratectomy (PRK) and to report its correlation with preoperative refractive errors.Methods: Fifty-six patients with simple or compound myopic astigmatism who were candidates for PRK were included in this cross-sectional study. PSC was measured just before surgery using Wavelight Allegretto EX 500 excimer laser machine eye trackers. The amount of PCS in horizontal and vertical directions was recorded. The correlation of PSC with refractive error was evaluated Results: One hundred twelve eyes of 56 patients were included in the study. Mean sphere and cylinder were -4.44 ± 2.21 D and -1.14 ± 1.13 D, respectively. Mean PSC was 60.35 ± 44.93 micron in the horizontal direction and 50.52 ± 62.3 microns in the vertical direction in the right eyes. Corresponding values for the left eyes were -50.69 ± 46.4 and 37.25 ± 62.5, respectively. Generally, PSC was toward the superonasal direction in both eyes. Thirty-five eyes (31.3%) had mean vectorial PSC more than 100 microns. Mean sphere was lower in patients with PCS greater than100 microns compared to patients with PCS less than 100 microns 3.31 ± 1.96 versus -3.83 ± 2.2, respectively). Although it was not statistically significant (P= 0.21).Conclusion: Superonasal PSC is a common finding during PRK. Horizontal shift is higher than vertical shift. Two eyes showed mirror pattern in direction of PCS. No correlation between the amount of PSC and baseline refractive error was found