Can the retinal ganglion cell layer (GCL) volume be a new marker to detect neurodegeneration in bipolar disorder?

The aim of this study was to compare the ganglion cell layer (GCL) volume and retinal nerve fiber layer (RNFL) thickness in bipolar patients and controls using optic coherence tomography to demonstrate neurodegeneration in bipolar disorder.

This study involved 43 euthymic bipolar I patients who were being followed by the Psychiatry Department of Adiyaman University Medical School and 43 healthy volunteers as controls. Optic coherence tomography (OCT) measurements were performed for both groups. The RNFL thickness and GCL volumes were measured and recorded automatically by a spectral OCT device.

No differences in sociodemographics were detected between groups, except for unemployment status, which was significantly higher in the patient group. The RNFL thickness was lower in patients compared with controls at all measured regions, and this decrease was statistically significant for the global RNFL measurement. The GCL volume was also significantly lower in the patient group. There was a significant negative correlation between the disease parameters, such as the disease duration, YMRS score, CGI score, and number of hospitalizations, and GCL volume.

These findings suggest that neurodegeneration occurs during the course of bipolar disorder. This degeneration may be demonstrated by decreased GCL at early stages, and as the disease progresses, involvement of other retinal layers, such as the RNFL and IPL, may be observed.