Retinal thickness: A window into cognitive impairment in bipolar disorder

Abstract

Introduction: Cognitive impairment (CI) in bipolar disorder (BD) significantly impacts overall functioning and quality of life. A better understanding of the neurobiological mechanisms associated with CI is needed. Studies on neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases, have revealed promising findings related to retinal thickness alterations using optical coherence tomography (OCT). Similarly, retinal differences between healthy controls and individuals with BD or schizophrenia have been described. This study explores the utility of OCT in discerning retinal changes possibly associated with CI in BD to enhance our understanding of the biological markers of BD and provide additional information to neuropsychological testing.

Material and methods: Optical coherence tomography (OCT) was employed to measure retinal thickness in the macular ganglion cell layer (GCL), inner plexiform layer (IPL), retinal nerve fiber layer (RNFL), and peripapillary RNFL (pRNFL) in 50 individuals with bipolar disorder (BD). Associations with cognitive impairments were analyzed using cross-validated Random Forest models.

Results: The analysis revealed significant associations between retinal thinning in various segments of the macular GCL, IPL, and RNFL and cognitive impairment (CI) in BD, with particular relevance to executive function deficits (AUC>0.8).

Conclusions: Thinning of the GCL, IPL, and RNFL was significantly associated with worse cognitive performance in individuals with BD. Similar patterns have been observed in schizophrenia, highlighting an innovative and promising field for research and clinical application.

Keywords: Biomarkers; Bipolar disorder; Cognition; OCT; Retina; Transdiagnosis.