Fig. 1. Probability of resolution of a 20/25 (6/7.5) target as a function of the dioptric blur of the target. The width of the curve represents the depth of focus of the eye for a given resolution probability. Pupil size was 4.6 mm. (Modified from Schwartz JT, Ogle KN: The depth of focus of the eye. Arch Ophthalmol 61:578, 1959. © 1959 American Medical Association.)