Abstract
Retinal nerve fibre layer (RNFL) thickness and macular volume (MV) can be measured in vivo using optical coherence tomography (OCT) providing a “window into the brain”. RNFL and MV are promising biomarkers in neurological diseases. This study explores the potential of RNFL and MV to detect axonal abnormalities in vivo in schizophrenia and their correlations with clinical features. OCT was performed in 49 patients (38 schizophrenia, 11 schizoaffective disorder) and 40 healthy controls matched for age and gender. Group comparisons were made between whole retina and quadrant RNFL thickness and MV using multi-level analyses. In patients, associations were sought between RNFL and MV with symptom severity (positive/negative). Patients and controls had similar whole retina RNFL thickness (p=0.86) and MV (p=0.64), but RNFL in the right nasal quadrant of the schizoaffective group was thinner than in the schizophrenia group (p=0.02). In patients, positive symptom severity was associated with smaller MV (right β=−0.54, p=0.02; left β=−0.49, p=0.04). Normal MV and RNFL thickness suggests unmyelinated axons in patients with schizophrenia/schizoaffective disorder remain unaffected. Longitudinal studies using higher resolution OCT will clarify whether progressive RNFL and MV changes occur and whether they can be used as state or trait markers in schizophrenia.
Highlights
Schizophrenia lacks a clearly defined or diagnostic neuropathological signature
Patients recruited to this study were selected from a larger cohort and had a firmly established diagnosis of schizophrenia or schizoaffective disorder using the DIP-DM Diagnostic Interview for Psychosis (Jablensky, 2000), which includes items from the Operational Criteria Checklist for Psychosis (OPCRIT) (McGuffin et al, 1991) and the WHO Schedules for Clinical Assessment in Neuropsychiatry (SCAN) (Wing et al, 1990)
This study did not detect any differences in whole retina Retinal nerve fibre layer (RNFL) thickness or macular volume (MV) between patients with schizophrenia or schizoaffective disorder and healthy controls
Summary
Schizophrenia lacks a clearly defined or diagnostic neuropathological signature. The best validated neuropathological abnormalities include possible reductions of neuronal density in the thalamus, but not in the cerebral cortex or hippocampus, in these structures pyramidal neurons may have smaller bodies with reduced dendritic arborisation and spines (Harrison and Weinberger, 2005). Reductions in the number of some interneurons and in the number and function of oligodendrocytes, relevant to myelination and neuronal and synaptic integrity, complete the picture (Harrison and Weinberger, 2005). In keeping with these findings, neuroimaging studies have reported grey matter volume deficits in those with chronic schizophrenia (Ellison-Wright and Bullmore, 2009), those in their first episode of psychosis (Bangalore et al, 2009), in a prodromal phase of illness (Pantelis et al, 2003), or at high genetic risk of schizophrenia (Witthaus et al, 2009). Compromised white matter integrity rather than volume loss has been reported in first episode (Price et al, 2007) and chronic schizophrenia (Kanaan et al, 2009)
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