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Relation between geometric corneal center adjusted centration and HOAs in conventional surface ablation

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Session Details

Session Title: Presented Poster Session: Keratorefractive Surgery Outcomes - Myopia

Session Date/Time: Sunday 06/09/2015 | 09:30-11:00

Paper Time: 09:30

Venue: Poster Village: Pod 2

First Author: : S.Lee SOUTH KOREA

Co Author(s): :    J. Lee              

Abstract Details


To analyze the accuracy of GCC(geometric corneal center)-adjusted centration method (compensation of ablation zone center from tracking system-determined pupil center) and to investigate the effects of ablation decentration on the induction of HOAs in conventional surface ablation using the VISX STAR S4 excimer laser.


Department of Ophthalmology, Yeungnam University College of Medicine, Daegu, Korea


The location of GCC-adjusted centers and their distance from the center of entrance pupils were analyzed by corneal topography (the EyeSys Corneal Analysis SystemTM equipped with pupil finding software). Risk factors for significant decentration were investigated. Three groups classified by degree of ablation decentration (Group I ≤ 0.15 mm, n=20; 0.15 < Group II ≤ 0.30 mm, n=54; Group III > 0.30 mm, n=20) were analyzed using aberrometry for 6 months. Wavefront errors were measured preoperatively and at 6 months postoperatively using a VISX WaveScan aberrometer. Statistical analysis was performed to assess the influence of ablation decentration on PRK-induced HOAs.


Mean decentration was 0.24±0.13mm (range 0.04 to 0.83 mm). Ninety-three eyes (95.9%, 93/97 eyes) were within 0.5mm of the entrance pupil center. Superior-nasal displacement of the ablation center was the most frequently occurring decentration (42 eyes, 43.3%) after ASA-PRK (p<0.05). The amount of decentration was not found to be dependent on either patient factors or surgery-related factors (p<0.05). No risk factor for significant decentration exceeding 0.3 mm was identified. Increases in PRK-induced HOAs including total HOA, coma, and spherical aberration except trefoil were significantly different among the 3 groups(ANOVA,p<0.05). Statistically significant differences were observed between groups I and III for total HOA, coma, and SA, and between groups II and III for coma(Tukey-Kramer test, p<0.05).


The compensation toward the geometric corneal center according to the pupil decentrations of individual patients was found to be highly accurate and effective at avoiding severe decentration. In addition, ablation decentration > 0.3 mm from the center of the entrance pupil was associated with greater induction of total HOA, coma, and spherical aberration after PRK, as compared with ablation decentration ≤ 0.15 mm. In addition, ablation decentration has a more significant influence on coma-inducing effects.

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