AIM: To provide an insight to the common pathophysiology of both most frequent and neurodegenerative diseases by comparing thickness parameters of macula and retinal nerve fiber layer (RNFL) by using spectral-domain optical coherence tomography (SD-OCT) in patients with early stage of Parkinson’s disease (PD), and early stage of primary open angle glaucoma (POAG). METHODS: A retrospective review was conducted of 48 patients with an early stage of POAG, 34 patients with an early stage of PD and 37 age- and gender-matched healthy eyes as a control group. The RNFL and macular thicknesses in the nine macular quadrants according to the ETDRS were measured with an SD-OCT and Mean Deviation (MD) values by a visual field analyzer. POAG patients were selected only MD smaller than -6 dB. Patients with MD values below -6 dB were considered as early-stage glaucoma. PD severity was assessed using Hoehn and Yahr (H&Y) and Unified Parkinson’s Disease Rating Scale (UPDRS). The PD group selected only H&Y Stage I-III patients. RESULTS: Statistically significant difference was determined between all groups RNFL measurements except temporal RNFL (P<0.05). Statistically significant difference was determined between all groups including fovea, mean macula thickness and macula outer quadrant thickness evaluations (P<0.05). There was not any significant difference between thickness evaluation of macula inner quadrant for POAG and PD groups (P>0.05). A weak negative correlation was determined between duration of disease and UPDRS score together with macula and RNFL thickness parameters in PD group. CONCLUSION: Similar thinning was detected by using SD-OCT for thickness parameters of macula and RNFL in early stage of POAG and early stage of PD group. However this thinning was more significant in early stage of POAG group. It can be declared that neurodegeneration on the macula which is caused by glaucoma is more destructive than PD. Thinning on foveal region is remarkable for PD patients.