Importance: Individuals with autosomal dominant mutations for Alzheimer disease are valuable in determining biomarkers present prior to the onset of cognitive decline, improving the ability to diagnose Alzheimer disease as early as possible. Optical coherence tomography (OCT) has surfaced as a potential noninvasive technique capable of analyzing central nervous system tissues for biomarkers of Alzheimer disease. Objective: To evaluate whether OCT can detect early retinal alterations in carriers of the presenilin 1 (PSEN1 [OMIM 104311]) E280A mutation who are cognitively unimpaired. Design, Setting, and Participants: A cross-sectional imaging study conducted from July 13, 2015, to September 16, 2020, included 10 carriers of the PSEN1 E280A mutation who were cognitively unimpaired and 10 healthy noncarrier family members, all leveraged from a homogenous Colombian kindred. Statistical analysis was conducted from September 9, 2017, to September 16, 2020. Main Outcomes and Measures: Mixed-effects multiple linear regression was performed to compare the thickness values of the whole retina and individual retinal layers on OCT scans between mutation carriers and noncarriers. Simple linear-effects and mixed-effects multiple linear regression models were used to assess whether age was an effect modifier for PSEN1 mutation of amyloid ß levels and retinal thickness, respectively. Fundus photographs were used to compare the number of arterial and venous branch points, arterial and venous tortuosity, and fractal dimension. Results: This study included 10 carriers of the PSEN1 E280A mutation who were cognitively unimpaired (7 women [70%]; mean [SD] age, 36.3 [8.1] years) and 10 healthy noncarrier family members (7 women [70%]; mean [SD] age, 36.4 [8.2] years). Compared with noncarrier controls, PSEN1 mutation carriers who were cognitively unimpaired had a generalized decrease in thickness of the whole retina as well as individual layers detected on OCT scans, with the inner nuclear layer (outer superior quadrant, ß = -3.06; P = .007; outer inferior quadrant, ß = -2.60; P = .02), outer plexiform layer (outer superior quadrant, ß = -3.44; P = .03), and outer nuclear layer (central quadrant, ß = -8.61; P = .03; inner nasal quadrant, ß = -8.39; P = .04; inner temporal quadrant, ß = -9.39; P = .02) showing the greatest amount of statistically significant thinning. Age was a significant effect modifier for the association between PSEN1 mutation and amyloid ß levels in cortical regions (ß = 0.03; P = .001) but not for the association between PSEN1 mutation and retinal thickness. No statistical difference was detected in any of the vascular parameters studied. Conclusions and Relevance: These findings suggest that OCT can detect functional and morphologic changes in the retina of carriers of familial Alzheimer disease who are cognitively unimpaired several years before clinical onset, suggesting that OCT findings and retinal vascular parameters may be biomarkers prior to the onset of cognitive decline.