The aim of this study was to investigate retinal nerve fiber layer (RNFL) thickness in patients with Alzheimer disease (AD) without visual impairment using spectral domain optical coherence tomography (SD-OCT) and to compare the results with healthy controls. A total of 80 subjects, including 40 patients with early untreated AD (mean age, 69.3±4.9 years) and 40 healthy controls (mean age, 68.9±5.1 years) were enrolled. Both eyes of patients with AD and controls were imaged using SD-OCT. The average RNFL thickness was significantly less in the AD patients than in controls (65±6.2 μm vs 75±3.8 μm; P= 0.001). There was selective thinning of the RNFL in the superior quadrant, the mean superior quadrant RNFL thickness being 76±6.7 μm in AD patients and 105±4.8 μm in controls (P= 0.001). In our study, the thickness of RNFL in patient with AD was lower than that of controls. This suggests that SD-OCT has the potential to be used in the early diagnosis of AD as well as in the study of therapeutic agents. Further studies are needed to validate this technology as a viable ocular biomarker over time in AD.