The Impact of Season and Light Therapy on the Cone and Rod ERG of Patients Affected With Winter Depression

Abstract

Purpose:: Seasonal affective disorder (SAD) is a syndrome characterized by the apparition of depressive symptoms in Autumn/Winter with remission in Spring/Summer. For most patients, light therapy is an effective treatment. The origin of the syndrome is unknown as well as the mechanism underlying the therapeutics of light, although retinal sensitivity anomalies have been reported by our group using the ERG. Our goal was to investigate for the first time the impact of seasons (autumn versus summer) and light therapy on ERG cone and rod functions in patients affected with seasonal affective disorder (SAD).

Methods:: This study was composed on 22 patients with SAD symptoms and 16 normal controls, sex and age matched as much as possible. Patients' cone and rod ERG luminance responses were obtained in autumn before and after 2 and 4 weeks of daily light therapy (30 min at 5000 lux SADelite lamp, Northern Light Technologies) as well as during natural remission in summer. Normal controls were evaluated once in autumn and once in summer.

Results:: Cone Vmax b-wave amplitudes were on average 17% lower in SAD patients when compared to controls (P=0.01). Rod retinal sensitivity (log K value) was 0.13 log units lower in SAD patients (P=0.01). After 4 weeks of light therapy (but not after 2), both cone (Vmax) and rod (log K) parameters were not significantly different than the controls (P>0.05). In summer, both parameters were not significantly different between patients and controls (P>0.05) and normal controls did not demonstrate any seasonal change in retina function (P>0.05).

Conclusions:: This is the first objective evidence of cone and rod function anomalies in SAD patients occurring during the depressive episode only. This represents also the first report of a biological therapeutic effect of light therapy on retinal function. Although the origin of the seasonal change in retina function in SAD patient is still unclear, we believe that a neurotransmitter imbalance (such as serotonin) could explain both the presence of the symptoms observed in these patients and the ERG findings.

Keywords: electroretinography: clinical • photoreceptors