Abstract
Although visual processing impairments are common in schizophrenia, it is not clear to what extent these originate in the eye vs. the brain. This review highlights potential contributions, from the retina and other structures of the eye, to visual processing impairments in schizophrenia and high-risk states. A second goal is to evaluate the status of retinal abnormalities as biomarkers for schizophrenia. The review was motivated by known retinal changes in other disorders (e.g., Parkinson’s disease, multiple sclerosis), and their relationships to perceptual and cognitive impairments, and disease progression therein. The evidence reviewed suggests two major conclusions. One is that there are multiple structural and functional disturbances of the eye in schizophrenia, all of which could be factors in the visual disturbances of patients. These include retinal venule widening, retinal nerve fiber layer thinning, dopaminergic abnormalities, abnormal ouput of retinal cells as measured by electroretinography (ERG), maculopathies and retinopathies, cataracts, poor acuity, and strabismus. Some of these are likely to be illness-related, whereas others may be due to medication or comorbid conditions. The second conclusion is that certain retinal findings can serve as biomarkers of neural pathology, and disease progression, in schizophrenia. The strongest evidence for this to date involves findings of widened retinal venules, thinning of the retinal nerve fiber layer, and abnormal ERG amplitudes. These data suggest that a greater understanding of the contribution of retinal and other ocular pathology to the visual and cognitive disturbances of schizophrenia is warranted, and that retinal changes have untapped clinical utility.
Keywords
Schizophrenia; Vision; Perception; Retina; Macula; OCT, ERG
Visual processing impairments are well established in schizophrenia, including abnormalities in contrast sensitivity (Kelemen et al., 2013 and Kiss et al., 2010); various excitatory and inhibitory functions (Kaplan and Lubow, 2011, Keri et al., 2005a and Robol et al., 2013) including those involved in masking (Green et al., 2011) and surround suppression (Tibber et al., 2013); and form and motion processing (Chen, 2011, Green et al., 2011, Javitt, 2009 and Silverstein and Keane, 2011). There has been little work on color processing to date (Shuwairi et al., 2002), but clinical reports indicate frequent descriptions of increased intensity, or alterations in color perception (Chapman, 1966 and Vollmer-Larsen et al., 2007). One study reported a 62% incidence of visual distortions in schizophrenia, with brightness, contrast, and motion increases being the most commonly reported (Phillipson and Harris, 1985). Visual distortions also had the highest predictive validity, among all basic symptoms, for conversion to a psychotic disorder (Klosterkotter et al., 2001), and visual distortions in help-seeking adolescents are associated with suicidal ideation, even after controlling for age, gender, depression, thought disorder, paranoia, and auditory distortions (Grano et al., 2015). Finally, visual impairments contribute substantially to poorer real-world functioning in people with schizophrenia (Green et al., 2012 and Rassovsky et al., 2011).