Physiological influence on ocular photometry. A review

During the development of the ocular photometer (OPM) since 1983, we have considered several physical and physiological factors that could potentially influence the measurement and its results. Attention has been given to respiratory, circulatory, and intraocular pressure provocations, and numerous publications document the influences or lack thereof. Most recently, the authors conducted a simple reproducibility study with only 1 observer and 1 subject. Measurement of the same 2 retinal sites during a 3-week period yielded no statistically significant differences, even under relatively extreme temperature conditions. Thus, changes in readings with the OPM may be considered due to variations within the eye, such as cataract. Thus, increase in lens density may be directly and correctly expressed by dual-site measurement of retinal brightness, resulting in the contrast transfer ratio.