Evaluation of Retinal Thickness in Neurodegenerative Diseases using Spectral Domain Optical Coherence Tomography

Introduction: Neurodegenerative diseases are characterised by axonal lesions throughout the central nervous system, including the eye with changes in macular thickness and Retinal Nerve Fiber Layer (RNFL) on histopathologic evaluation. Optical coherence tomography facilitates retina as a surrogate measure of neurodegenerative disease activity. Aim: To evaluate macular thickness and retinal nerve fiber layer thickness in patients with neurodegenerative diseases using spectral domain optical coherence tomography (SD-OCT). Materials and Methods: An analytical observational case control study was carried out over a period of two years. Cases consisted of patients (n=20) with neurodegenerative disorders and controls were age and sex matched healthy individuals. RNFL thickness was measured using the SD OCT. The visual functions tested included the Best Corrected Visual Acuity (BCVA) and colour vision. Fundus examination was done to look for any gross retinal pathologies. All these tests were carried out for cases and controls once during the study. Statistical data analysis was performed by using Mann-Whitney U tests. SPSS for windows, version 17.0 was used to do the analysis. p-values smaller than 0.05 were considered significant. Results: The study included 13 cases of central neurodegenerative diseases and 7 cases of peripheral neurodegenerative diseases. Mean duration of disease in cases was 37.85 months with 11 cases having more than 24 months duration and 9 cases having less than 24 months duration. The mean right eye average (RNFL) thickness in cases was 87.05 μm and that of control was 87.40 μm (p=0.932). The mean left eye average retinal nerve fiber layer thickness in cases was 86.47 μm and control was 89.26 μm (p=0.419). The mean macular cube average thickness of right eye was 271.05 μm in cases and 270.85 μm in controls. The mean macular cube average thickness of left eye was 266.63 μm in cases and 269.42 μm in controls. Conclusion: Retinal segmentation techniques extend the utility of OCT to neurodegenerative disorders, enabling the in vivo objective assessment of retinal neurons in addition to axonal integrity.