Comparison of two fast quantitative methods for evaluating the Stiles-Crawford function

Stiles-Crawford (SCE) functions are determined using an increment threshold procedure. The customary technique requires considerable time to obtain a full SCE function and in many situations, both clinical and experimental, it is imperative that the SCE function be evaluated at many retinal loci in as short a time as possible. We have been using two different variants of the standard method, one requiring a very limited number of threshold settings at five fixed entry points in the entrance pupil (5-point method) and in the other, thresholds are determined at only three preselected entry points (3-point method). The time required to obtain a complete SCE function is the order of 5 to 8 min using either method. Comparison and statistical evaluation of the techniques are presented.