Invited Review Schematic eyes: history, description and applications

Abstract

A schematic eye is a mathematical or physical model that represents the basic optical features of the real eye. By its nature, it is a simplified version and there is a range of schematic eyes that have been developed which offer different levels of simplicity or complexity, from the simplest reduced version that consists of a single refracting surface to the complex model with four aspheric surfaces and a gradient index lens.

Schematic eyes have many applications, particular as teaching aids in optics, optometry, ophthalmology, psychology (vision and visual perception) and visual ergonomics. Besides showing the basic optical structure of the eye, the dimensions and other ocular parameters allow one to trace rays through the eye and determine the position, size and orientation of images and assess the aberrations and hence quality of the retinal image. However, there are many other applications which will be discussed in this article.

This article will begin with the historical development of our knowledge of the structure and function of the eye from the first recorded writings of the ancient Greeks. It will then examine the range of schematic eyes currently available, describe their properties and applications and finish with a brief discussion of the probable direction of further developments. (Clin Exp Optom 1995; 78: 5: 176–189)

Key words:

• schematic eye
• Gullstrand
• Helmholtz
• paraxial models

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Erratum