Comparison of retinal nerve fiber layer thickness and macular thickness in schizophrenia patients and their healthy siblings and its effect on cognitive functions

Objectives: A large number of studies showed various structural changes, early visual deficits, and cognitive deficits both in schizophrenia patients and their healthy siblings over the past years. Optical coherence tomography (OCT) is a relatively new, non-invasive imaging method used to obtain high-resolution cross-sectional images of the retina. A growing body of evidence reports thinning of retinal layers in patients with schizophrenia which is considered as a proxy for CNS alterations. Numerous studies conducted in recent years report that retinal layers, which are considered an indirect indicator of the central nervous system, are thinning in patients with schizophrenia, but its relationship with cognitive functions has not yet been investigated sufficiently. It was aimed to investigate its relationship with cognitive functions and to show whether retinal layer changes can be observed in healthy siblings in parallel with those seen in patients as a potential endophenotype candidate. Method: 28 patients with schizophrenia in remission who met the inclusion and exclusion criteria and who were diagnosed with schizophrenia according to DSM-5 diagnostic criteria followed in the outpatient clinic of the Psychotic Disorders Unit of Celal Bayar University Hospital Psychiatry Department. 28 healthy siblings who were not diagnosed with organic disease and 28 healthy controls were included in the study. Stroop test, Wisconsin Card Sorting Test, Trail Making Test, Eyes Test, Percentage Discrimination of Emotions Test, Implication test were applied to the volunteers and OCT scans were performed. Statistical analyzes were performed using SPSS Statistics 22.0 program. Results: As a result of the analysis made; It was observed that the cognitive capacity of the control group was significantly better than the patients, and the cognitive capacity of the healthy sibling group was among the schizophrenia patients and the healthy control group. There was no difference in thicknesses of MK, MV, RNFL in the comparisons between groups. However, there was a statistically significant increase in cup volume measurements in both eyes in the patient group compared to the controls group. Although the GHT-IPT complex in the left eye mean thickness decreased in the patient group compared to the control group, a similar difference was found between the healthy sibling group and control groups. However, a weak correlation was found between the retinal layers in the patient group and the healthy sibling group with both neurocognitive and social cognition tests. Also, it was determined as a result of regression analysis that retinal layers do not predict social cognition. Conclusion: Our findings suggest that GHT-IPT thinning may be promising as a useful endophenotype for genetic and early diagnosis studies, and because of the possibility of being affected by confounding factors such as antipsychotic drugs and metabolic variables, there is not enough evidence yet for the use of cup volume measurements in diagnosis and follow-up. Therefore, structural retinal changes in schizophrenia patients are more important than prognosis of cognitive symptoms or functionality; It should continue to be investigated that it can have an important place in identifying high risk groups. Evaluation of this area may contribute to elucidating the neurodevelopmental hypothesis of schizophrenia.