Activities that may lead to addiction cause an increase in dopamine in the reward systems of the brain. Dopamine is also released in response to light in the retina. Chronic use of drugs such as cocaine may cause a depletion of dopamine. 9 patients and 11 controls were included in a study to assess dopamine levels in the retinas and, indirectly, levels in the reward systems of cocaine users during withdrawal. Electrooculogram readings were done to measure the potential differences during light and dark adaptation in subjects. The normal 5 mv increase in potential from the cornea to Bruchs membrane, the innermost layer of the choroid, reaches a trough during the dark and a peak during light. Results obtained from troughs partially from peaks in linear regression analyses revealed a trend of decreased light responses in the patient group compared to controls which did not reach statistical significance.

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