Objectives Neuroimaging studies in patients with bipolar disorder have suggested that a neuropathological process may be effective in this disease. Neurodegenerative changes in the retina can be followed by optical coherence tomography, a non-invasive imaging method that allows in vivo visualization of the retinal layers. The aim of this study was to investigate the possible differences in optical coherence tomography parameters during euthymic, manic, and depressive episodes in patients diagnosed with bipolar disorder. Methods A total of 150 patients with bipolar disorder were included in the study, divided into three groups (50 patients in a euthymic state, 50 patients in a manic state, and 50 patients in a depressive state) and compared with 50 healthy controls. Ganglion cell complex thickness was measured with automated macular segmentation software of spectral-domain optical coherence tomography. Results Ganglion cell complex thicknesses were thicker in all quadrants in patient groups than the control group but the differences were significant in perifoveal superior and perifoveal inferior quadrants (p < 0.001, p < 0.001). There were no differences in ganglion cell complex thickness among the patient groups (p > 0.05). Conclusion The evaluation of ganglion cell complex thickness by spectral-domain optical coherence tomography may give a clue for monitoring neurodegenerative changes in patients with bipolar disorder.