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It may seem to some readers that the retina is far removed from what is important about schizophrenia. However, the retina is part of the central nervous system (CNS), and published reports continue to indicate that schizophrenia is associated with thinning of retinal layers (using optical coherence tomography; OCT), reduced retinal cell responses (using electroretinography; ERG), and, in some cases, widened retinal venules as measured with fundus photography.1,2 These data may both contribute to a better understanding of the multiple forms of subjective and laboratory-based visual processing changes observed in people with schizophrenia,3 and serve as a window into brain function in the syndrome. Kazakos and Karageorgiou4 have provided a valuable contribution to this growing field by providing an up-to-date meta-analysis of this literature, and the first meta-analysis based on individual participant data.

One of the main conclusions from the paper is that, despite nearly every published study indicating significant between-group differences on multiple variables, the ability of retinal indices to discriminate schizophrenia and control groups was generally fair to poor, with only OCT indices related to macula volume and thickness performing better. Such analyses are critical for evaluating cumulative progress in this growing field of research. However, considering the heterogeneity within the diagnostic category of schizophrenia and the substantial overlap typically observed between patient and control groups (e.g., 45%, 50%, and 65% for biological, psychophysiological, and cognitive markers, respectively5), mapping onto psychiatrist- or structured interview-generated diagnoses may not be the most important outcome to assess in this field (or for the cognitive neuroscience of schizophrenia in general). (Even with a [typically not achieved] between-groups effect size of d = .80 (large), there will be 52.6% overlap between group scores when values in both groups are normally distributed.) Instead, a more productive approach may be to determine the concurrent and predictive implications of abnormal retinal findings in subgroups within the category of schizophrenia and/or psychotic disorders. Related to this, one interesting feature of OCT findings in other neuropsychiatric conditions (e.g., multiple sclerosis, Parkinson’s disease) and in normal aging is that retinal thinning significantly predicts features such as cognitive impairment, cognitive decline, brain volume loss, and overall disease progression.6–9 Therefore, the primary clinical utility of techniques such as OCT may be in rapid and reliable screening for overall CNS difficulties and their progression over time. This could help identify people who could benefit from more intensive evaluations (e.g., MRI, neuropsychological assessment) to clarify level of CNS impairment and plan for rehabilitative interventions.

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