Bipolar patients taking lithium have increased dark adaptation threshold compared with controls.

Recent epidemiological studies of mania suggest that admissions correlate with length of day and sunlight. As well, seasonal affective disorder--a depression occurring in winter, is reported to respond to light therapy and it has been proposed that supersensitivity to light is a trait-marker of manic-depressive illness. Dark adaptation threshold (D.A.T.)--a measure of night vision--was assessed in 19 euthymic manic-depressive patients stabilized on lithium, and in 19 drug-free healthy controls. The D.A.T. was significantly raised in the patients taking lithium. It is concluded that lithium induces subsensitivity to light.