Time of day variations were studied both in the dark focus of accommodation and in steady-state accommodation. All subjects (n = 16) were measured in the morning and again 12 hr later. The mean nighttime dark focus was 0.5 diopters (D) greater than the morning value. Overaccommodation to far targets (0 D) and underaccommodation to near targets (3-20 D) occurred for both 4.2 and 8.4 cycle/deg square-wave gratings. A shift in steady-state accommodation was found with the nighttime values being somewhat greater (0.25 D) than the morning values.
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