BACKGROUND AND PURPOSE: To investigate small vessel abnormalities in patients with cognitive impairment, we compared retinal microvascular alterations between patients with cognitive impairment related to Alzheimer's disease (ADCI) and those with subcortical vascular cognitive impairment (SVCI). METHODS: We prospectively recruited 29 amyloid-positive ADCI patients, 28 amyloid-negative SVCI patients that were confirmed by 11C-PiB-PET scan and 34 individuals with normal cognition (NC). The three groups were compared in terms of retinal vascular variables (retinal fractal dimension, vascular caliber, tortuosity and branching angle) by using a semi-automated, computer-assisted analysis of digital fundus photographs. We also investigated the relationship between retinal variables and white matter hyperintensities (WMH) on MRI. RESULTS: Compared to NC individuals, the SVCI patients had smaller total and arteriolar fractal dimensions, whereas there was no significant difference of fractal dimension between ADCI and NC. Other retinal variables did not differ among the three groups. A significant correlation existed between fractal dimension and WMH volume. CONCLUSIONS: Retinal microvascular alterations, especially retinal fractal dimension, may be useful markers that reflect cerebral microvascular changes in patients with SVCI as opposed to ADCI, who had no definite difference in retinal variables compared to the NC group.