Temporal stability of the dark focus of accommodation.

The temporal stability of the dark focus of accommodation (the refractive power of the eye in total darkness) was examined using a laser optometer. It was found that dark focus does not vary greatly in most subjects over a period of 2--3 weeks. Intrasubject ranges varied from 0.08--2.92 over that period, with a mean range of 1.07 D. Theoretical and practical implications of these findings are discussed.