To the Editor.—
Seasonal affective disorder (SAD)1 is a recurrent form of depression associatedwith the length of daylight or photoperiod. It can be effectively treated by exposure to bright light.2 This novel therapy developed from circadian models of seasonal behavior in mammals and, by analogy, has thus been hypothesized to be a circadian intervention. One study suggests that, indeed, the response to light is mediated by the eye,3 but none of the proposed mechanisms has received unequivocal empirical support, whether it is that the therapeutic effect is mediated by a phase shift induced by a light pulse, by an augmentation of circadian amplitude, or an increase in number of photons absorbed.We suggest that SAD could be tied to a deficiency in retinal photoreceptor renewal mechanisms. Since retinal response to light is the first step in circadian rhythm regulation, understanding it is therefore crucial in considerations of
Remé C, Terman M, Wirz-Justice A. Are Deficient Retinal Photoreceptor Renewal Mechanisms Involved in the Pathogenesis of Winter Depression? Arch Gen Psychiatry. 1990;47(9):878–879. doi:10.1001/archpsyc.1990.01810210086016
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