Some previous studies have used different dark adaptation periods to achieve adequate pupil dilation for photo refraction. Because efficient use of time is important in screening programs, we investigated how dark adaptation affects the quality of eye photographs.This prospective study was done on 2 groups. In the first group (40 patients), 1 horizontal flash and 1 vertical flash photograph were taken as soon as the room lights were turned off, and a second set of photographs was taken after 10 minutes of dark adaptation. In the second group (37 patients), sets of photographs were taken after 1, 5, and 15 minutes of dark adaptation. Pupillary diameters were measured by an observer who was masked to the timing of the photographs. The findings were compared using the Wilcoxon signed rank test and the Student t test for paired data.Compared with the results at 1 minute, mean pupillary diameter was significantly decreased after 10 minutes of dark adaptation, both with the horizontal (Z = -4.723; P <.001) and the vertical flash (Z = -4.668; P <.001) in the first group. In the second group, the mean pupillary diameters at 1, 5, and 15 minutes in the horizontal flash photos were 5.78 +/- 1.03 mm, 5.35 +/- 1.10 mm, and 5.04 +/- 1.05 mm, respectively, and were 5.70 +/- 0.95 mm, 5.21 +/- 1.09 mm, and 4.86 +/- 0.95 mm, respectively, in the vertical flash photos at these stages. These diameters were all significantly different (P <.001).The results indicated that dark adaptation is not a prerequisite for photoscreening, and that, in fact, it might have an adverse effect on pupillary diameter.