Evaluation of the pinhole pupillometer

Abstract

Evaluation of pupil diameter is used in many clinical and research fields to aid diagnosis of neurological disorders and to monitor pharmacological effects upon the eye. Methods used to determine pupillary diameter have evolved from simple scale measurements to much more complex systems, supposedly improving accuracy and repeatability. However, many techniques are restricted to the consulting room or research laboratory due to the size of the equipment, its cost, or the expertise required. We have evaluated a portable pupillometer originally developed by Broca, capable of precise measurements on fixed, dilated pupils, that has the potential to be used by unsupervised patients. Luminance levels will still need to be controlled because, although luminance does not influence the mechanics of the pupillometer itself, it significantly affects the natural pupil. The pinhole size should ideally be 1.1 mm in diameter, since smaller pinholes underestimate and larger holes overestimate pupil size. The pupillometer also exhibited reasonable accuracy in fixed pupils dilated with tropicamide. Pupil measurements were overestimated by 0.5% using the 1.1 mm pinholes (insignificant if the pupil can be measured to the nearest 0.25 mm) and both intra- and inter-visit repeatabilities were relatively good. The results from this study therefore indicate that the pinhole pupillometer may be of use in pupil research, since it facilitates more frequent pupillary measurements over much longer time intervals than are currently achievable.