Bipolar disorder (BD) is defined by the presence of mania, hypomania, mixed or depression. Individuals with bipolar disorder spend more time in depression than mania or hypomania. The depressive episodes are more disabling than other mood states and are associated with increased mortality from suicide. Only 20% of BD receive a correct diagnosis if the index episode is depressive as it lacks differentiation from unipolar depression with a latency of 5 to 10 years. For early detection, alteration in the layers of the retina could serve as a biomarker since these originate from the same embryonic layer of the brain and are interconnected through the optic nerve. The aim of the study is to estimate the prevalence of Retinal nerve fibre (RNFL) changes in patients of bipolar depression (B-I, B-II); unipolar depression (UD) vis-à-vis normal population (age and gender-matched); to delineate any relationship or causality of RNFL changes with early onset, duration of illness or severity. It will be an analytic cross-sectional study. Patients will be taken from the outdoor Department of Psychiatry, G.M.C. and Rajindra Hospital, Patiala. The socio-demographic profile and other information will be recorded. For assessment of RNFL thickness on OCT, they will be referred to the Department of Ophthalmology. Data will be analysed by the relevant tests wherever applicable at statistically significant p-value ≤ 0.05.