Decreased retinal sensitivity in depressive disorder: a controlled study

OBJECTIVE: To compare pupil responses in depressed patients with a seasonal pattern, depressed patients without a seasonal pattern and healthy controls as a function of daylight hours on the testing day.

METHOD: Patients suffering from a major depressive episode were included in wintertime. The pupil light reflex was measured at inclusion and in the following summer using a binocular pupillometer. A protocol of low (1 lux) and high (400 lux) intensity red and blue lights was used to assess rod, cone and melanopsin-containing intrinsic photosensitive retinal ganglion cell input to the pupil reflex.

RESULTS: The mean group pupil responses associated with a melanopsin-mediated sustained pupil response at 400 lux blue light were significantly reduced in the depressed subjects (N = 39) as compared to the healthy controls (N = 24) (P = 0.023). Across all groups, a reduction in number of daylight hours was significantly associated with a reduction in sustained pupil response (P = 0.007). All groups showed an equal effect of daylight hours on the melanopsin-mediated sustained pupil response.

CONCLUSION: The melanopsin-mediated sustained pupil contraction to offset of high-intensity blue light is reduced in depressed patients. These results further emphasize the interaction of light exposure with depression.