Background: An anomaly in the retinal adaptation processes to the decreased light exposure in winter has been suggested as a contributing factor in winter depression. The purpose of this study was to investigate seasonal variations in rod sensitivity in normal subjects and in subjects with seasonal mood variations.
Methods: Nine normal subjects (5 men, 4 women, aged 21-28 years) and 12 subjects with subsyndromal seasonal affective disorder (S-SAD)(3 men, 9 women, aged 21-44 years) were selected based on their global seasonality score (GSS) from the Seasonal Pattern Assessment Questionnaire. Scotopic electroretinograms (ERGs) were obtained once in winter and once in summer. Retinal sensitivity, which represents a relative threshold, was obtained from the rod ERG luminance-response functions.
Results: A difference in retinal sensitivity between the two groups appeared only in the winter with lower retinal sensitivity found in the S-SAD group. A positive correlation between the GSS and the magnitude of the winter decrease in rod sensitivity was also observed.
Limitations: The S-SAD subjects studied in this research did not receive a formal psychiatric evaluation. This will be necessary in future studies to determine if the changes in retinal sensitivity are specific to seasonal affective disorders. In addition, in the present study, the differences in age and gender between the two groups limit the interpretation of the possible contribution of these two parameters to the results.
Conclusion: The seasonal changes in retinal sensitivity that parallel seasonal mood variations suggest that the ERG may represent a useful tool to investigate seasonal affective disorders.