Purpose: Melanopsin-containing retinal ganglion cells (mRGCs) play a central role in regulating the circadian rhythm and are expected to be affected by seasons. We investigated the seasonal change in mRGCs by recording their electrophysiological responses.
Subjects and methods: Subjects were 6 healthy subjects and 6 eyes (mean age 21.8 years). An electroretinogram (ERG) was recorded by providing a light stimulus for eliciting mRGC responses using a 4-primary-color stimulator. The peak wavelengths (nm) of the stimulus were 633,593,508, and 468 nm. After light adaptation, stimulation of the mRGC was given in additional 40% intensity and 250-msec duration, with an average of five responses. Measurements were taken twice a day, in the morning and at noon, and in two seasons, spring and autumn. Circadian rhythm and light environment were controlled from a few days before recording until the end of the study.
Results: Two negative waves were recorded after stimulation and N1 and N2 from baseline were used to refer to these waves. Morning (M) /afternoon (A) amplitudes (mean±SD [μV]) were N1: spring (S) 56.3±14.5/35.9±16.4, autumn (A) 19.7±13.9/21.6±20.9, N2: S 39.9±19.8/29.4±10.0, A 24.0±7.6/32.1±18.6, implicit time (mean±SD [ms]) N1: S 161.7±24.9/161.1±17.1, A 147.3±33.5/152.3±38.6, N2: S 400.8±56.6/382.8±62.9, A 406.4±45.4/414.9±78.3. In terms of diurnal changes, decreases from M to A in amplitude were observed except for N2 A, which significantly decreased from M to A only for N1 S (p=0.046, paired t-test). There were no significant differences in implicit time in each component and season. In terms of seasonal change, the difference between M and A (M-A) for N1 amplitude was statistically significant (p=0.021, paired t-test) between two seasons. There were no significant differences in N2 amplitude and N1 and N2 implicit time between seasons.
Conclusion: The function of mRGCs may change according to seasons.
Nippon Ganka Gakkai Zasshi (J Jpn Ophthalmol Soc) 127: 449-455,2023.