Background: Glaucoma is a complex disease, in which the optic nerve and retinal ganglion cells are injured, leading to loss of the peripheral visual field and eventually profound visual loss. Optical coherence tomography (OCT) is a high resolution noncontact imaging modality which can provide important information for detection and evaluation of glaucomatous changes. This study was designed to correlate between retinal nerve fiber layer (RNFL) thickness affection and ganglion cell complex (GCC) layer changes in cases of primary open angle glaucoma (POAG) using spectral domain (OCT). Methods: The study group with POAG was included in this observational analytic clinical trial study. All patients underwent to full ophthalmic examinations. The OCT was done to evaluate RNFL parameters in correlation with GCC parameters. Results: Thirty eight eyes of 38 patients with POAG, 22were males and 16 were females. The mean of their age was 58.18±7.89 years old. The average IOP was 23.03±7.36 mmHg. The average C/D area ratio was 0.86±0.13. The average RNFL thickness was 80.71±18.24 µ. The average GCC thickness was 80.91±16.24 µ. There was a positive statistical significant correlation of high probability between the patients’ average GCC thickness and the average RNFL thickness(P value 0.000646). Conclusions : There is strong positive correlation between the RNFL thickness and the GCC thickness in the glaucomatous patients.