Exploring the relationship between the density of the iris color and bipolar disorder: a case-control study, Egypt

The eyes serve as a portal to the brain and are highly connected neurologically, making them the only externally visible part of the brain. Moreover, the correlation between the physical attributes of the eye and psychiatric disorders has been increasingly established in recent years. Therefore, this study examined the association between iris color density and bipolar I disorder (BD).

In a case-control study, 48 subjects diagnosed with BD are compared to an equal number of healthy controls. A semi-structured interview questionnaire is designed to collect sociodemographic, psychiatric, medical history, and clinical data from all participants. The Group with BD is diagnosed based on clinical assessment by the Consultant/specialist by using a semi-structured clinical interview for DSM 5 Clinician Version (SCID-5-CV) to diagnose BD's current episode and to exclude the other comorbid mental disorders. Additionally, the group with BD is further assessed by The Young Mania Rating Scale (YMRS) and Hamilton Depression Rating Scale (HDRS) to evaluate the severity of manic and depressive symptoms. The iris color of participants in both groups was evaluated using a standardized photographic system for iris imaging.

It showed a statistically significant increase in the percentage of the colored iris in the patients' group compared with the control group, and the presence of a colored iris significantly increases the risk of BD by 2.36 folds. There is no statistically significant difference between iris color and either hospitalization, suicide, Electroconvulsive Therapy (ECT), family history, medical history, duration, or frequency of episodes.

Our findings revealed a strong association between iris color and bipolar disorder (BD) but no significant association between iris color and clinical factors such as hospitalization, suicide, electroconvulsive therapy (ECT), family history, medical history, or the duration and frequency of episodes. These results suggest that iris color may serve as a trait marker rather than a state marker in BD, potentially offering a simple and non-invasive indicator of bipolarity.