Abstract

DO.25.04

Comparison of different centration for ablation in hyperopic LASIK

Omid Kermani, Georg Gerten, Karl Schmiedt, Uwe Oberheide

Augenklinik am Neumarkt, Köln

Objective
In hyperopic eyes eccentric fixation with a positive angle Kappa is a common finding. Here we do describe the results of a prospective study of a new laser alignment and delivery strategy that allows centration and ablation based on aberrometry measurements.
Methods
In a prospective double-blind paired eye study 32 hyperopic (-astigmatic) eyes of 16 patients were treated with LASIK.  The allows specification via numeric entry of the exact placement of the laser tapered to the position of the visual axis (VA) or the line of sight (LOS) by entering distance and axis of the shift between LOS and VA. Alignement of the excimer laser ablation zone was separated in two groups. On one eye the ablation was centered on the LOS, on the other eye on 50% of the distance between LOS and VA (offset-group). The mean distance between LOS and VA was 0.42 mm ± 0.10 mm in the LOS group and 0.40 mm ± 0.10mm in the offset group.  Pre-OP refraction was similar for both groups with 2.79 D SE (± 1.20 D SD) for LOS and 2.14 D SE (± 0.99 D SD) for the offset group.
Results
3 months post-operative the mean refraction showed no difference between the groups with 0.35 D SE (± 1.00 D SD) for LOS and 0.42 D SE (± 0.83 D SD) for offset group. Higher order aberrations (HOA) and strehl ratio of the point spread function (PSF) were analyzed. In both groups the HOA increased in total as well as for spherical aberrations, coma and trefoil. The strehl ratio, indicating the quality of the PSF, therefore decreased for both groups. The group averages for zernicke coefficients and strehl ratio showed no differences. However, intrapatient specific comparision between LOS and offset treated eyes leads to smaller changes in HOA for the offset group and less decrease in strehl ratio and therefore better PSF for the offset group.
Conclusions
Customized alignment of the ablation zone adds another tool to the surgeons armentarium. The clinical impact of shifting the center of ablation towards the visual axis is promising but needs larger patient group to verify the significance.

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