Explanation of Broca's pupillometer

Broca's pupillometer offers a simple and effective means of measuring the diameter of the pupil. However, it is often used without proper attention to the limitations of its optics. Errors of measurement may result from uncorrected refractive error, accommodation, spectacle correction, and spherical aberration (SA). A simple means of minimizing these errors is to hold the pinholes (PH's) of the pupillometer as close to the cornea as is feasible.