Colour vision impairments in bipolar disorder: A systematic review.

Visual impairments are common in patients with bipolar disorder (BD), and the neuropathophysiology may suggest a potential influence on colour vision. This systematic review aimed to assess existing data of colour vision impairment, including chromatic discrimination and colour blindness in patients with BD. Comprehensive literature search compliant with PRISMA 2020 was conducted in Medline, Embase, and Google Scholar from inception to February 28th, 2023. Our inclusion criteria were: (1) patients with a diagnosis of bipolar I or II disorder based on DSM, ICD, or clinical diagnosis, and (2) study investigating colour vision (i.e., including colour blindness and discrimination), with (3) no restrictions on the condition of the comparator group. Study quality appraisal was performed using the NIH Study Quality Assessment Tool. Five studies from Brazil, Netherlands, and USA, with 338 patients were included. Three cross-sectional studies assessed chromatic discrimination and two case-series assessed colour blindness in patients with BD. The three cross-sectional studies support reduced chromatic discrimination during mild to moderate mania in BD when compared to healthy comparators. The latter two articles presented low evidence of an X-linked inheritance of BD. Our review indicates evidence of reduced chromatic discrimination in mild to moderate mania. However, further research is needed to validate these findings and to extend to other mood states in BD given current limitations. Future studies can benefit from further multi-institutional data, larger sample sizes, appropriate blinding, the use of biomarkers, and statistical adjustment to confounders to fully elucidate the role of chromatic discrimination in BD.