Correlated Changes of Wavefront and Corneal Topography Aberrations Before and After Laser Refractive Treatment

Abstract

 

Purpose

 

The Advanced WaveScan Studio makes multiple measurements of the eye wavefront (WF) aberrations paired with simultaneous and co-aligned corneal topography (CT) measurements. Variations of measured WF may contribute to the errors in a laser refractive treatment planning. Analysis of the treatment results makes it necessary to compare WF and CT changes before and after the surgery. The goal is to estimate precision of the eye WF and CT measurements and to find out to what degree changes in corneal anterior surface are responsible for the changes in WF aberrations

 

Methods

 

We perform a statistical analysis of pre-operative measurement data and also paired pre-operative and 6M post-operative data from a retrospective clinical study (143 eyes). We compare aberration deviations for multiple pre-operative measurements of the same eye for synchronized WF and CT measurements data. To make a fair comparison the WF center is aligned with the corneal vertex, where the CT measurement is centered. Also the light propagation change after the treatment is taken into account.

 

Results

 

Variability of the WF and CT measurements in terms of aberrations STD, high order RMS (HORMS) and total RMS (TRMS) of multiple same eye measurements is shown in the Table 1. Post-LASIK WF and CT aberration changes are well correlated (Fig. 1), which shows that WF aberration changes are almost entirely defined by the corneal aberration changes.

 

Conclusions

 

Variations of WF aberrations up to TRMS=0.22um make a substantial contribution to the refractive treatment errors. Several pre-operative measurements followed with a careful selection and/or averaging algorithm are necessary to alleviate these errors. A fair comparison of CT and WF post-operative changes must take into account WF center deviation from CT vertex position and post-operative optical path change. A solid correlation between the CT and WF aberration changes, caused by cornea ablation, shows that changes in the anterior corneal surface have the greatest effect both on refraction and high-order aberrations. Post-LASIK changes in the interior structure of the eye do not affect post-operative aberrations.

 

 

Table 1. Variability of multiple measurements for the same eye (n=367)

 

 

Fig.1. WF vs, CT post-LASIK aberration changes

 

Keywords: 681 refractive surgery: corneal topography • 626 aberrations