Eccentric Infrared Photorefraction: A Review of Evolution, Optical Design, Features and Applications

Photorefraction is seven-decade old technology that allows objective and non-invasive estimation of the eye’s refractive error using retro-illuminated photographs of the pupil. A special variant of this technique—eccentric infrared photorefraction—has now become the technology of choice for the screening of uncorrected refractive errors and other amblyogenic factors in the pediatric population. Eccentric infrared photorefraction is also the preferred measurement tool for scientific investigations on the physiology and pathobiology of the near-triadic reflex (accommodation, convergence and pupil miosis). Broadly, this technique uses an extended near-infrared light source that is mounted eccentric to the camera aperture to illuminate the retina. The optically double-pass reflected light generates a retro-illuminated luminance profile across the pupil, the gradient of which may be used to estimate the eye’s refractive power using standard calibration techniques. The present review summarizes the origins of photorefraction and then delves into the optical principles of eccentric infrared photorefraction, its properties, calibration techniques and associated pitfalls. The review also discusses the present and future use-cases of this technology. Overall, this review provides the basics of photorefraction for early readers of this topic and offers some practical guidelines for the moderate to advanced users of this technique.