CORNEAL TOPOGRAPHY OF PHASE-III EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY - OPTICAL ZONE CENTRATION ANALYSIS

Purpose: To determine the amount of optical zone decentration in patie nts who have undergone excimer laser photorefractive keratectomy (PRK) and assess associations of both decentration and optical zone size wi th clinical outcomes. Methods: Optical zone centration in 185 patients after PRK was analyzed using computer-assisted videokeratography. A c omparison of decentration among the five study centers was performed. Associations of clinical outcomes with procedure decentration and opti cal zone size were assessed. Results: Decentration from the pupil cent er ranged from 0.00 to 1.44 mm (mean, 0.46 mm): 21.8% were decentered 0.25 mm or less, 42.5% > 0.25 mm and less than or equal to 0.50 mm, an d 97.1% less than or equal to 1.00 mm. In both eyes, the average decen tration from the pupil center was located inferonasally. Decentrations among the five study centers were significantly different. Decentrati on was associated with attempted refractive correction, change in kera tometric cylinder, and patient satisfaction. There was a trend toward worse postoperative uncorrected visual acuity with greater decentratio n but no association with best-corrected vision, predictability, or re fractive astigmatism. No significant relation was found between decent ration and glare/halo ranking; however, three of six patients with 1.0 0 mm or greater of decentration demonstrated a high glare/halo grade. Although optical zone size was not associated with glare or halo, subj ective patient satisfaction was greater with a 5.0-mm optical zone tha n with a 4.5-mm optical zone. Conclusions: Centration is an important surgeon-controlled variable in excimer laser PRK. Decentration of exci mer laser refractive procedures was found to be nonrandom and may be i nfluenced by preoperative pupil management. Moreover, the amount of de centration may influence clinical outcomes. Improved techniques and ce ntering procedures on nonmiotic pupils may improve future results.