Melanopsin and Pupil Size

Look into my eyes...

Recent discoveries of how the eyes work shed light on why we suffer from SAD, depression and sleep disorders, and knowing who might be susceptible may be as easy as looking into your eyes.

Research into circadian rhythm disorders took a giant leap forward in 2001, when Dr. George Brainard discovered a new photoreceptor in the eye, called melanopsin. It turns out that melanopsin has everything to do with body clock problems, and those people who don't have enough melanopsin cells are much more likely to have SAD, sleep problems and mood disorders.

Now researchers know that melanopsin responds to changing levels of light, and when it gets brighter in the morning for example, melanopsin becomes very active and triggers the brain's suprachiasmatic nucleus, or body clock into shifting to an active day pattern. Those of us with fewer melanopsin cells don't recognize the changing light signals, and so don't 'wake up' like we're supposed to. That is why we struggle through the day, feeling down or gloomy, and why in the summer, when it is very bright, we seem to do OK.

Melanopsin also causes our pupils to constrict and dilate, and pupils don't work as well in people with low melanopsin levels. In other words, when it is very bright outside, low melanopsin won't let the pupil constrict as much as it should. Apparently, those with a melanopsin deficiency have pupils that are visibly different than normal subjects. Scientists haven't quite determined the relationship yet, but in the future, doctors may be able to tell if you're susceptible to circadian rhythm disorders by simply looking at your pupils' reaction to changes in light.