The way in which the retina processes visual information from the optic nerve is measured with something called an electroretinogram. This method of assessing visual processing provides information related to any retinal gain contrast abnormalities. Visual impairments are common in some psychological and neurological conditions. Research has shown that people with depression have decreased retinal gain contrast that improves with remission.
Likewise, individuals with Parkinson’s disease have also been shown to have reduced contrast gain and other visual impairments. These conditions also present other similarities, including hormonal imbalances. Specifically, dopamine levels and activity are altered in both Parkinson’s and depression, and are directly linked to retinal contrast gain impairment. But until now, this physiological marker had not been examined in other psychological conditions.
Therefore, Emanuel Bubl of the Department of Psychiatry and Psychotherapy at the Albert-Ludwigs University of Freiburg in Germany conducted a study designed to see if the same visual impairments existed in individuals with attention deficit hyperactivity (ADHD). Bubl chose ADHD because dopamine dysfunction is common in this condition. For the study, Bubl recorded visual electroretinograms from 20 participants with ADHD and 20 without.
He found that although dopamine dysfunction was common with the ADHD participants, contrast gain deficits did not exist. In fact, they had the same retinal contrast gain levels as the controls. This finding suggests that retinal contrast gain is not a specific predictor of marker of ADHD, despite the fact that dopamine regulation is impaired. Bubl also looked at the ratings of ADHD and severity of symptoms and found no association between severity and retinal contrast gain.
“Therefore,” he said, “with this study, we found some specificity of retinal contrast gain as a marker of major depression, at least in comparison to ADHD in adulthood.” These findings are significant and can help provide further ways to identify individuals at risk for depression and those not.
Additionally, retinal contrast gain appears to return to normal when depression is in remission, but not with antidepressant treatment alone. Understanding why is a topic for future research. Bubl also hopes that this study will prompt future work looking at visual impairments in other psychological conditions such as bipolar and schizophrenia, as they too can be affected by altered dopamine and hormonal levels.
Bubl, E., Dörr, M., Philipsen, A., Ebert, D., Bach, M., et al. (2013). Retinal Contrast Transfer Functions in Adults with and without ADHD. PLoS ONE 8(5): e61728. doi:10.1371/journal.pone.0061728
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