Corneal changes induced by laser ablation: study of the visual-quality evolution by a customized eye model

Abstract

This study focuses on the changes induced in both the asphericity and homogeneity of the cornea for a group of myopic eyes undergoing LASIK surgery. Eyes were characterized by a Kooijman-based customized eye model in which changes were introduced in the form of Gaussian-distributed refractive-index variations of given correlation length for the inhomogeneities and in the form of an expression, based on the modified Munnerlyn's paraxial formula, for the post-LASIK asphericity. Visual quality was evaluated in terms of the Modulation Transfer Function and the Point-Spread Function. The results show that, on average, the evolution of visual acuity is consistent with the change in corneal asphericity, while the evolution of contrast sensitivity requires a loss in corneal homogeneity in order to be explained. By including both effects in the model, the overall model performance in predicting visual quality is improved.

SyntEyes: A Higher-Order Statistical Eye Model for Healthy Eyes

“…To study eyes that deviate from these average values, these generic models are often customized, for example, by inserting measured biometry values into a chosen eye model while keeping other unmeasured (or unmeasurable) values unaltered. [6][7][8] Alternatively, customization can also be achieved by considering the unmeasured parameters as free variables in an optimization process until, for example, the ocular wavefront of the individual eye model matches the measured values. 9,10 Although this approach leads to a data set much closer to the patient's actual biometry, one has to make sure that the inserted biometry parameters are very complete to avoid introducing systematic errors resulting from a lack of correlation between the measured data and the unaltered parameters of the original eye model.…”

Corneal Surface Asphericity, Roughness, and Transverse Contraction after Uniform Scanning Excimer Laser Ablation

“…12 Q values have been used clinically and mathematically to evaluate asphericity changes in living human corneas and mathematical models. 6,[23][24][25][26][27][28] Studies have also looked at surface roughness after excimer ablation as a cause of subepithelial haze and suggested some interaction between the laser and residual corneal tissue. 29 The residual nonablated corneal tissue is noted to have numerous histologic changes suggestive of an interaction between the excimer laser and the residual corneal stromal surface.…”