Optical models of the human eye

Abstract

Optical models of the human eye have been used in visual science for purposes such as providing a framework for explaining optical phenomena in vision, for predicting how refraction and aberrations are affected by change in ocular biometry and as computational tools for exploring the limitations imposed on vision by the optical system of the eye. We address the issue of what is understood by optical model eyes, discussing the ‘encyclopaedia’ and ‘toy train’ approaches to modelling. An extensive list of purposes of models is provided. We discuss many of the theoretical types of optical models (also schematic eyes) of varying anatomical accuracy, including single, three and four refracting surface variants. We cover the models with lens structure in the form of nested shells and gradient index. Many optical eye models give accurate predictions only for small angles and small fields of view. If aberrations and image quality are important to consider, such ‘paraxial’ model eyes must be replaced by ‘finite model’ eyes incorporating features such as aspheric surfaces, tilts and decentrations, wavelength‐dependent media and curved retinas. Many optical model eyes are population averages and must become adaptable to account for age, gender, ethnicity, refractive error and accommodation. They can also be customised for the individual when extensive ocular biometry and optical performance data are available. We consider which optical model should be used for a particular purpose, adhering to the principle that the best model is the simplest fit for the task. We provide a glimpse into the future of optical models of the human eye. This review is interwoven with historical developments, highlighting the important people who have contributed so richly to our understanding of visual optics.

Key words:

• finite models
• optical models
• paraxial models
• schematic eyes
• visual optics

Acknowledgements

One of the greatest joys of a research career in academia is being inspired by and collaborating with, other researchers. While acknowledging the help of many people in his career, the first author would like to single out a few individuals. First, he is grateful for the research culture developed by Barry Cole and Barry Collin, while he was a student in the Department of Optometry at The University of Melbourne, and he thanks Ken Bowman and Leo Carney for replicating this culture at the School of Optometry at the Queensland University of Technology. A physicist called George Smith took a lecturing position in the department in Melbourne and was trying to learn about vision at the same time that Atchison was trying to learn about optics. This started a fruitful collaboration that was to last for 30 years. This paper is based in part on a paper written by George Smith 20 years ago.1995 The first author also thanks the second author for many stimulating discussions over the last 30 years and finally thanks his mentor and colleague Neil Charman, who taught him that research can be a lot of fun.