Lithium and the retina.

Recent interest in light therapy for depression has stimulated consideration of the nature of the biological defect in affective disorder. One line of thinking suggests that manic-depressive patients are supersensitive to light and that lithium may act by altering light sensitivity and hence entrainment of biological rhythms. This paper focuses on possible mechanisms whereby lithium may influence retinal physiology and the ability to perceive light. Preliminary data were generated using the Dark Adaptation Threshold procedure with a repeated measure protocol. When depressed and unmedicated the patient was found to have significantly lowered thresholds for light detection compared to control values. This supersensitivity was alleviated following lithium treatment. Data are interpreted as suggesting that some of the therapeutic effects of lithium are localized in the retina. It is proposed that: (1) lithium primarily alters the ability of the retina to detect light and not visual acuity; (2) lithium influences sensitivity to light by modulating the functional environment of the rod photoreceptors in the retina and (3) future research should focus on the effect of lithium on the function of rod photoreceptors and the pigmented epithelial cells in patients with affective disorder.