Non-linear associations between retinal nerve fibre layer (RNFL) and positive and negative symptoms among men with acute and chronic schizophrenia spectrum disorder

Schizophrenia Spectrum Disorder (SSD) is a chronic psychiatric disorder with modest treatment outcomes. Changes in neuronal morphology may be associated with the symptomatology of SSD. In the present study, we compared the retinal nerve fibre layer thickness (RNFLT) of typically developed adults with that of individuals with SSD in both acute and chronic stages. Fifteen healthy adult males (mean age: 36.40 years) and 30 individuals with SSD (mean age: 37.9 years) took part in the study. Among the latter, 15 had a chronic mean SSD for 15.33 years, while 15 were in an acute psychotic phase with a mean illness duration of 12.20 years. Experts rated positive and negative symptoms of SSD. Retinal nerve fibre layer thickness (RNFLT) of all participants was measured with optical coherence tomography (OCT). Compared to healthy controls, individuals with acute SSD had the lowest macula thickness in the right eye. For nerve fiber layer atrophy, participants with acute SSD showed the largest atrophy (right eye, inferior quadrant). For retinal thickness and macular volume cube, compared to healthy controls, participants with acute SSD had the lowest thickness in the subfield of the right eye. Non-linear associations were observed between RNFL and positive and negative symptoms: e.g., for macula central and subfoveal thickness (left and right eye) and for participants with both acute and chronic SSD, exclusively positive and exclusively negative symptoms (as opposed to prevalently negative with some positive symptoms or prevalently positive with some negative symptoms) were associated with lower volumes. In participants with acute SSD, a longer disease duration was associated with thicker RNFL, while in participants with a chronic SSD a longer disease duration was associated with a thinner RNFL. The present results confirm previous findings that specific neuronal morphological abnormalities can be observed among individuals with SSD. The non-linear associations between neuronal alterations and positive and negative symptomatology suggested that higher pronounced SSD severity appears to be particularly related to morphological changes. Disease duration and RNFL thickness were linearly associated, though, in opposite directions depending on the chronic or acute state.