The effective corneal refractive surface as a function of a point in visual space: a three‐dimensional analysis

Abstract

This comprehensive optical model of object space and the anterior segment of the eye allows clinicians to better understand the effects of corneal light transmission on vision.

Effective corneal patch of an astigmatic heterocentric eye

“…One can think of the effective corneal patch as a magnified version of the pupil as Freedman and Brown 1 have already pointed out. However in the presence of astigmatism the magnification is generalized: it may be thought of in terms of familiar magnification, possibly different in different meridians, and possibly combined with rotation as illustrated in and .…”

“…This is the basis of a definition of optical axis for eyes proposed elsewhere 19 . (Eyes are usually described as not having true optical axes 1,20–24 15 which, by the traditional definitions, also do not strictly exist for heterocentric astigmatic eyes.…”

“…The rest transmits light which enters the pupil. It is what Freedman and Brown 1 call the effective corneal refractive surface, and its shape, size and position on the cornea depend on the position of the object of regard. Optical imperfections and opacities in this patch of cornea have the potential to compromise vision; those outside it do not, at least not directly.…”

“…Using conventional geometrical optics Freedman and Brown 1,3 obtain solutions for the effective corneal patch for a point source anywhere in visual space. However their analysis treats only an eye with a single spherical surface as cornea and a circular pupil with cornea and pupil both centred on a common axis.…”

“…Of course there is a cost. Although the approach is much more general than that of Freedman and Brown, 1 and it generates explicit formulae, linear optics implies that accuracy is compromised for large angles away from the line of sight. Nevertheless, linear optics proves to be remarkably powerful although it cannot compete with geometrical optics for objects that subtend extreme angles from the line of sight.…”