Method for assessing the impact of residual roughness after corneal ablation in perception and vision

Abstract

PurposeDespite theoretical models for achieving laser‐based ablation smoothness (Invest Ophthalmol Vis Sci. 2017;58:2021–2037), methods do not yet exist for assessing the impact of the residual roughness after corneal ablation, in perception and vision. As solution, we propose a method to convert wavefront aberrations with associated roughness, to a visual point spread function (PSF), to calculate the polychromatic retinal image.MethodsUsing SCILAB (Scilab Enterprises, Versailles, France) patient‐specific Zernike expansion coefficients and Pupil diameter were used to calculate the wavefront including chromatic compensation for the Red, Green and Blue channels (Optom Vis Sci 2003;80:6–14). Random noise was added to the calculated wavefront to simulate roughness in the cornea after laser ablation, within user‐defined limits. PSF of the eye was calculated for Red, Green and Blue channels and the retinal image was determined, as weighted combination of different color channels. Several corneal roughness conditions were compared in terms of the calculated perceived image quality based on metrics like Michelson Contrast, Weber Contrast and Modulation Transfer Function.ResultsFor a constant roughness term, reducing the pupil size resulted in sharpening the PSF and perceived retinal image. The impact of varying roughness in ablation could be quantified through the calculated image quality metrics, deteriorating dramatically with increasing roughness.ConclusionsThe proposed model can be used for quantifying the impact of residual roughness in corneal ablation processes at relatively low cost. This method can help compare different refractive laser platforms in terms of their associated roughness in ablation, indirectly improving the quality of results after Laser vision correction surgery.