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Retina may be the culprit in seasonal depression

Published on October 21, 2014 at 14:42 / Updated on August 19, 2019 at 19:31

For some people, the return of winter marks the beginning of a trying period. Lack of energy, fatigue and an increased need for sleep becomes an every day problem for 15 to 25% of the population. Some people are affected more deeply and suffer from what is called seasonal affective disorder (SAD). In addition to these symptoms, sufferers may experience depressive moods, increased cravings for carbs and sweets, reduced interest in activities they usually enjoy, lack of motivation, difficulty concentrating, weight gain and greater irritability.

Light therapy usually helps decrease depressive symptoms in many people with no specific explanation. The good news is that some Quebec researchers figured out how light therapy works to improve one’s mood.

According to these researchers, light therapy has a biological effect on the functioning of the retina, the thin membrane that covers the inside lining of the eye and that allows us to see. Normally, light penetrates the eye and is captured by the retina, which then transforms light energy into electric energy. The optic nerve transmits this energy to the brain where it is interpreted as images. Electrical signals produced by the retina also influence the chemical messengers in the brain called neurotransmitters, such as the mood regulating serotonin, and melatonin, which regulates daily cycles of wakening and sleep. It is at this level that light therapy proves beneficial.

The researchers measured electric activity in the retinas of subjects affected by SAD as well as those who were unaffected. They were able to demonstrate that in people suffering from SAD, there is a significant decrease in retina activity in the fall when compared with summer, while it remained normal in those unaffected by SAD. This decrease in retina activity does not affect vision. Rather, it reflects a malfunctioning of the neurotransmitters, which likely cause depressive symptoms.

The researchers took two series of measurements: before light treatment and following daily exposures of 30 minutes for a period of four weeks. At the end of the study, the mood of all participants had improved by at least 50%. More than 80% of people no longer had any symptoms of SAD. These results are excellent, even more so when taking into account the 60 to 70% level of success achieved with antidepressant treatments.

The lamps (boxes or visors) used for light treatments are different from the ones used in our houses. They emit a much more intense light that is measured in lux. Light therapy lamps generally emit 5,000 to 10,000 lux, the equivalent of at least one tenth of the luminosity of a sunny summer day and ten times that of regular office lighting. To reap the full benefits of light therapy, 30 minutes of light exposure per day, generally in the morning, should suffice. For maximum efficiency, the light must reach the retinas. You can sit approximately 50 centimetres from the lamp to read the newspaper, eat breakfast or work on the computer. The great majority of people note improvements in the first two weeks of treatment. Symptoms usually reappear if the light treatment sessions are interrupted.

Many pharmacies and orthopedics centres lease or sell light treatment lamps. It is always preferable to speak with your physician regarding your symptoms before you start a treatment. Your physician will make sure you are following the appropriate course of treatment for your condition.

Try pepping yourself up by thinking that daylight hours will already start increasing in the next few days. Each morning brings us closer to beautiful spring days, even if the weather makes us doubt we will ever get there! Spring is just around the corner!

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