Background: High myopia is defined as refractive error above -6.0 D and axial length above 26 mm. High myopia and its complications are considered to be one of the most significant causes of blindness and visual impairment in young people. Objective: To evaluate the effect of the degree of myopia on the peripapillary retinal nerve fiber layer (RNFL) thickness by spectral-domain optical coherence tomography (OCT). Patients and Methods: The study had been carried out in Embaba Ophthalmic Hospital during the period of June 2018 to February 2019. The study included 60 eyes, divided equally into 3 groups: Group A: Mild myopia (spherical equivalent between −0.5 and −3.0 D). Group B: Moderate myopia (spherical equivalent between −3.1 and −5.99 D). Group C: High myopia (spherical equivalent more than −6.0 D). Results: This study showed that RNFL thickness was lower in the high and moderate myopic eyes compared with low myopic eyes in all quadrants except in temporal quadrant. A highly significant positive correlation was evident between spherical equivalent and RNFL thickness in each quadrant. A highly significant negative correlation between axial length and RNFL thickness was found in each quadrant. Conclusion: High myopia should be considered in the interpretation of OCT data because of thinning of RNFL thickness and normative database corrected for refractive error and axial length should be incorporated. It is difficult for OCT to discriminate between high myopes with and without glaucoma. Therefore, clinical signs of glaucomatous nerve fiber damage are very important.