Somani Seema, Tuan K Ashley, Chernyak Dimitri
VISX Incorporated, Santa Clara, CA 95051, USA.
J Refract Surg. 2004 Sep-Oct;20(5):S581-5. doi: 10.3928/1081-597X-20040901-32.
The optical quality of retinal images is dependent on the refracting elements of the eye including the nominally aspheric cornea and crystalline lens. This paper presents a retrospective theoretical analysis of the impact of corneal asphericity on the quality of retinal images. Clinical data are from the VISX Incorporated CustomVue IDE.
Topography, contrast sensitivity, and visual acuity data were collected from 278 myopic eyes before and after wavefront-guided laser surgery. The measured corneal surface of each eye was fitted to a conic, and a Q-value was computed for a 5.5-mm pupil. A model eye was used to simulate various amounts of optical asphericity.
Preoperatively, most corneas exhibited negative conic shape constants. Postoperatively, corneas were about equally divided between positive and negative conics. There was no statistically significant correlation between the shape of the cornea and the subjects' perceptions of image quality including contrast sensitivity and visual acuity. Simulations showed that the corneal Q-value can vary from more to less prolate depending upon the shape of the internal surface.
Following wavefront-guided laser in situ keratomileusis (LASIK), contrast sensitivity is usually good and is not dependent upon the corneal conic shape. Better visual outcomes are more likely with a customized shape than a standard best conic shape.
视网膜图像的光学质量取决于眼睛的屈光元件，包括标称非球面的角膜和晶状体。本文对角膜非球面性对视网膜图像质量的影响进行了回顾性理论分析。临床数据来自威视公司的CustomVue IDE。
收集278只近视眼睛在波前引导激光手术前后的地形图、对比敏感度和视力数据。将每只眼睛测量的角膜表面拟合为圆锥曲线，并计算5.5毫米瞳孔的Q值。使用模型眼模拟各种程度的光学非球面性。
术前，大多数角膜呈现负圆锥形状常数。术后，角膜在正圆锥和负圆锥之间大致平分。角膜形状与受试者对图像质量的感知（包括对比敏感度和视力）之间没有统计学上的显著相关性。模拟表明，角膜Q值可根据内表面形状从更扁长变为更接近球形。
在波前引导的准分子原位角膜磨镶术（LASIK）后，对比敏感度通常良好，且不依赖于角膜圆锥形状。定制形状比标准最佳圆锥形状更有可能获得更好的视觉效果。
