The primary goals of this study are to use optical coherence tomography (OCT) angiography (blood vessel mapping) to:

1. Detect retinal blood vessel and blood flow changes in participants with dementia.
2. Detect amyloid protein deposits in the retinas of participants with dementia.

Inclusion Criteria for dementia subjects:

• Physician-confirmed diagnosis of probable Alzheimer's disease
• Mild dementia, as defined by score of 20 or greater on the Mini-Mental State Exam, or score of 15 or greater on the Montreal Cognitive Assessment, or Clinical Dementia Rating Scale score of 1.
• Age older than 55 years.
• Able to comply with study procedures
• Corrected visual acuity at least 20/400 in either eye.
• Has a legally authorized representative who can sign study consent form and accompany the participant to the OCT study visit.

Inclusion Criteria for dementia-free controls:

• Age older than 55 years
• Able to comply with study procedures
• Able to maintain stable fixation for OCT imaging
• Corrected visual acuity of at least 20/40 in either eye
• Dementia-free, as defined by score of 24 or greater on the Mini-Mental Status Exam, or a score of 18 or greater on the Montreal Cognitive Assessment, or Clinical Dementia Rating of <1.0.

Exclusion Criteria for both dementia and dementia-free subjects:

• Non-Alzheimer's disease related primary neurologic disease affecting the central nervous system (i.e. multiple sclerosis, Parkinson's disease)
• Evidence on ophthalmological exam within the last year of other ocular diseases or pathology that would confound the assessment of dementia (e.g. glaucoma, diabetic or hypertensive retinal disease, amblyopia, etc.)
• Media opacity such as cataract, corneal scar, or vitreous opacity that could interfere with retinal imaging.
• Previous intraocular surgery except for uncomplicated cataract extraction with posterior chamber intraocular lens implantation
• Inability to maintain stable fixation for OCT imaging or provide informed consent
• Spherical equivalent refractive error greater than +3 or -7 diopters, or astigmatism magnitude of greater than 2 diopters.
• Diabetes for more than 10 years or hemoglobin A1C level of > 10 within the 180 days prior to OCT scanning.
• Uncontrolled hypertension. : SBP > 170 or DBP > 100
• Arrhythmia: irregular pulse, or heart rate not between 50 and 110 beats per minute
• Pregnancy or breast feeding.

Dementia subjects will be recruited from the Layton Aging & Alzheimer's Disease Clinic at Oregon Health & Science University. Dementia-free subjects will be recruited from those currently being followed in the Layton Aging & Alzheimer's Disease Center longitudinal aging study with MRI and amyloid PET imaging.