Corneal Shape and Visual Performance After Keratorefractive Surgery.

摘要

Keratorefractive surgery includes any corneal surgery designed to modify the refractive state of the eye. Changes in corneal shape have been associated with changes in the aberration structure of the eye, specifically an increase in spherical aberration. The purpose of this study was to evaluate visual performance after refractive surgery, how the cornea changes in terms of clarity and shape, and how these changes relate to visual performance. The procedures evaluated in this study included photorefractive keratectomy (PRK), astigmatic PRK (PARK), laser in-situ keratomileusis (LASIK), and intrastromal corneal ring segments (ICRS). Corneal shape changes were analyzed using the point spread function of the anterior cornea, standard topographic indices and newly developed indices based on the refractive power distribution of the corneal surface. Performance on the high contrast visual acuity (HCVA) test and contrast sensitivity on the Small Letter Contrast Test (SLCT) both decreased after refractive surgery. The impact of refractive surgery on SLCT performance was more significant than for HCVA performance, potentially because the SLCT has a sampling advantage over HCVA. Corneal factors that correlated with the amount of performance decrement included transient corneal haze after surface excimer procedures, the range of powers of the central cornea, and changes in the optical quality of the cornea. The amount of correction, size of the pupil, and type of procedure were additional factors contributing to the quality of vision. The best results are obtained when the refractive correction was well centered, the corneal surface had a uniform and minimal power distribution, no subepithelial haze was present and the pupil was small.