Evaluation of retinal layer thickness in patients with bipolar disorder, their relatives, and healthy controls using optical coherence tomography.

Background: Bipolar disorder (BD) is a chronic psychiatric condition characterised by mood episodes and associated structural changes in the central nervous system. Optical coherence tomography (OCT) offers a non-invasive method to assess retinal layer thickness, potentially serving as an endophenotypic biomarker for neurodegeneration. This study aimed to compare retinal thickness among BD patients, their first-degree relatives, and healthy controls to identify structural markers and assess their alignment with existing literature.

Methods: Thirty-six BD patients, 30 first-degree relatives, and 38 healthy controls were recruited from Van Yüzüncü Yıl University. Comprehensive ophthalmologic examinations and retinal layer thickness measurements using Spectralis OCT were performed. Retinal layers were analysed at 1 mm, 3 mm, and 6 mm concentric circles per the ETDRS protocol. Peripapillary retinal nerve fibre layer (RNFL) thickness was evaluated across seven regions. Due to significant age differences among groups (p = 0.002), an ANCOVA analysis was used to control for the age effect.

Results: Retinal analysis revealed a significant increase in the inferonasal (NI) nerve fibre layer thickness in BD patients and their first-degree relatives compared to healthy controls (p = 0.008). Optic nerve head analyses showed non-significant thinning in the temporal (T), inferotemporal (TI), and superotemporal (TS) nerve fibre layer thicknesses in BD patients and their relatives compared to healthy controls. The thicknesses of the macular retinal layers did not differ significantly among the groups (p > 0.05).

Conclusions: The observed increase in NI optic nerve fibre layer thickness in BD patients and their first-degree relatives contrasts with the expected thinning reported in previous literature on neurodegeneration in psychiatric disorders. This finding underscores the complexity of structural changes in BD and raises the possibility of alternative pathophysiological mechanisms or methodological considerations influencing retinal measurements. Further research is needed to elucidate these phenomena and their implications for understanding BD.