Alzheimer's Disease: Biomarkers in the Visual System

Alzheimer's disease (AD) is the most common form of dementia among the aged. It is irreversible and progressive. There is indication that not memory, but visual integration processing such as contrast and motion are impacted even before memory. AD impacts vision early in the course of the disease and functional losses correlate with cognitive losses. That initial pathology of Alzheimer's disease originates in the visual association area is evidenced by studies of autopsied brains in the Framingham Heart Study. Visual losses in AD have many aspects in common with the functional losses in other neurodegenerative processes affecting the eye such as age related macular degeneration and glaucoma. Contrast sensitivity deficits in lower spatial frequencies are found in those with AD, motion perception is deficient in AD and there are visual field defects. Glaucoma impacts lower spatial frequencies in contrast sensitivity, produces visual field defects and reductions in motion perception. Age related macular degeneration impacts all frequencies in contrast sensitivity and foveal detection of motion. Imaging technology and functional visual fields currently in common use for glaucoma and macular degeneration can also identify early signs of AD. The eye exam equipment needed to identify early signs of AD is already readily available in a large percentage of optometrist's and ophthalmologist's offices. Early diagnosis of AD is important as we develop better strategies to manage and treat the disease. Yearly eye examinations for the aged are already recommended and the biomarkers of AD in the eye are easily measured.