Optical effects of ocular surgery including anterior segment surgery

Ocular surgery may alter the refraction and the corneal power of an eye. Ho wever, refraction and corneal power are not fundamental optical properties of the eye as such. Refraction is a fundamental property of a lens in front of the eye and an indirect or derived property of the eye, while corneal p ower is a fundamental property of only part of the eye. Nor are they the on ly clinically relevant paraxial optical effects of surgery. There are also effects on size, shape, and orientation of retinal images, for example, whi ch are not simply related to refraction and corneal power. Quantitative ana lyses of the effects of surgery on the eye that account only for refraction and corneal power are necessarily incomplete. This paper offers an approac h to the analysis of the optical effects of surgery that is complete Within the limitations of paraxial optics. The key is the concept of the ray tran sference, which contains the 4 fundamental optical properties of an optical system. The surgery is represented by a hypothetical optical system, the a nterior surgery-equivalent system, in front of the preoperative eye. The tr ansference of this system, the anterior surgical transference, is a complet e paraxial quantification of the optics of the surgery and is what needs to be studied in analyses of surgery. In this approach, ocular surgery in gen eral is optical equivalent to a thick system placed in front of the preoper ative eye. A simple model is developed for the case of anterior segment sur gery in particular. In terms of the model, anterior segment surgery is show n to be equivalent to placing a thick bitoric lens in front of the preopera tive eye. In particular cases, the surgery may be equivalent to an anterior thin lens. Astigmatism is an aspect of optical effects in general. It is n ot directly amenable to quantitative analysis in isolation; quantitative an alyses of astigmatism should be done in terms of the concept of antistigmat ism. In thin systems, astigmatism manifests only in power. However, in thic k systems such as the eye, astigmatism can manifest in 4 fundamentally diff erent ways. Among them are some phenomena currently described as irregular astigmatism. The foundation is laid for the complete analysis of paraxial a stigmatism in general and in ocular surgery in particular.