Colour vision defects in schizophrenia spectrum disorders: A systematic review

This systematic review synthesized the existing literature to summarize colour vision disturbances experienced by patients with schizophrenia. A comprehensive literature search compliant with PRISMA-2020 was conducted in Medline and Embase from inception to February 28, 2023. Studies were included if they: (1) included people diagnosed with schizophrenia, (2) investigated colour vision, (3) had a comparator with or without schizophrenia. Study quality appraisal was performed using the NIH Study Quality Assessment Tool. Seven studies of fair quality with 695 patients were included, of whom, 46.5% (n = 323) patients were diagnosed with a schizophrenia-spectrum disorder. Compared to healthy controls, patients with schizophrenia either made more mistakes in discriminating between colours, or were delayed in recognizing colours. One study found that Positive and Negative Syndrome Scale for Schizophrenia (PANSS) scores correlated weakly with error scores related to colour vision impairments. The most common shortcomings were lack of sample size justification (k = 7, 100%), and lack of blinding (k = 7, 100%). Our review indicates early evidence of colour vision deficits among patients with schizophrenia, and an unclear relationship between severity of schizophrenia with colour vision deficits. Possible mechanisms may include alterations in retinal dopamine transmission or schizophrenia-related cognitive deficits interacting with colour vision outcomes. Future studies may benefit from large registry analyses of patients with various schizophrenia spectrum disorders, analyzing ocular parameters (e.g., OCT), collecting data on cognitive impairment, and pursuing multivariate analyses to elucidate mechanisms for schizophrenia-related colour vision changes.