Refractive error measurements made with the Badal optometer typically register more myopia than is actually present. In this paper we measured the influence of the image size on the end-point of a Badal optometer's refractive error measurement. The optometer was modified with a camera's zoom lens in such a way that the retinal image size could be controlled. It was found that retinal image size is a major factor in controlling the subjective endpoint. When retinal image size is diminished rather than increased as the target approaches the subject, as is the case under normal circumstances, the perceived endpoint more closely agrees with the actual refractive error.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.