CORNEAL TOPOGRAPHIC EVALUATION OF DECENTRATION IN PHOTOREFRACTIVE KERATECTOMY - TREATMENT DISPLACEMENT VS INTRAOPERATIVE DRIFT

PURPOSE: To evaluate treatment displacement and movement during treatm ent (drift) after excimer laser photorefractive keratectomy using tang ential topographic maps. METHODS: Forty-eight: eyes of 48 patients sho wing axial decentration of 0.30 mm or more at 1 month posttreatment-we re reevaluated retrospectively to determine treatment displacement of the center of the photorefractive keratectomy ablation from the center of the pupil, A drift index was calculated to determine the relative degree of movement (drift) during treatment, We subdivided patients in to four groups based on the degree of treatment displacement and drift and compared the mean axial. decentration and the mean best-corrected logMAR visual acuity among the subgroups. RESULTS: Mean treatment dis placement +/- SD from the center of the entrance pupil was 0.34 +/- 0. 21 mm, Thirty-eight eyes (79.2%) had ablations within 0.50 mm from the center oi: the entrance pupil, We observed downward displacement in 2 7 eyes (56.2%) and upward displacement in 21 eyes (43.8%), The drift i ndex showed a positive, statistically significant correlation with bes t corrected visual acuity (r = .58, P < .0001), Patients with low disp lacement and low drift had mean logMAR best-corrected visual acuity of 0.91, which was statistically significantly better than patients with high displacement and high drift (r = 0.64; P = .009). CONCLUSIONS: I n patients with gross decentration by axial topography after photorefr active keratectomy, tangential corneal topography is valuable in evalu ating and differentiating photorefractive keratectomy treatment displa cement from movement during treatment (drift), Patients with high drif t index have worse visual outcomes after photorefractive keratectomy t han those exhibiting high treatment displacement.