Introduction: I investigate the potential bidirectional association between visual impairment and psychosis. I consider the implications for the detection, understanding, prevention and treatment of each condition.//

Methods: I conducted a systematic review and meta-analysis to collate existing evidence regarding an association between these conditions. Next, I investigated whether worse visual acuity at ages 7-11 is associated with psychotic symptoms at ages 17-24 using the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. I investigated whether genetic evidence supports a causal association between visual impairment and schizophrenia. These analyses were based on two-sample Mendelian Randomisation (MR) using data from the UK Biobank and Psychiatric Genomics Consortium, and genome-wide association studies of myopia and refractive error. I used the UK Biobank cohort of adults aged 40-69 to test whether poorer visual acuity and size of retinal structures were associated with psychotic experiences 8 years later, and whether cases with visual impairment were more likely to have a Schizophrenia-Spectrum Disorder (SSD) diagnosis than controls without.//

Results: Existing cross-sectional studies consistently showed an association between visual impairment and psychosis, whereas findings from longitudinal studies were mixed. In ALSPAC, poorer visual acuity at age 11 was associated with psychotic experiences in young people. In the Mendelian Randomisation study, I found no evidence that poorer visual acuity was a causal risk factor for schizophrenia, though there was evidence for the converse. In Biobank participants, poorer visual acuity was associated with psychotic experiences 8 years later, though thinner retinal structures were not. People with visual impairment were more likely to have been diagnosed with SSD.//

Conclusions:
I found evidence that psychotic illnesses contribute causally to visual impairment, but not the converse. Future research to understand the mechanisms by which psychotic illnesses could be causal risk factors for visual impairment will aid prevention.