Alzheimer’s disease is the most common cause of dementia in the Western world. Its prevalence in Americans aged 65 years or older is estimated to be around 6.5 million. It is a progressive neurodegenerative disorder, which is characterized by gradual shrinking and death of neuronal cells. Patients typically develop a continuous decline in their cognitive ability and social skills. This can significantly interfere with the activities of daily living. Increasing age and positive family history are associated with an enhanced risk of developing Alzheimer’s dementia.
Alzheimer’s disease is thought to develop due to the abnormal accumulation of proteins in and around brain cells. One of these proteins is known as amyloid, which can collect between brain cells to form plaques. These plaques hinder the functioning of these neurons and eventually lead to neuronal death.
Amyloid deposits in the retina
Interestingly, amyloid deposits have also been found to occur in the retina of patients with Alzheimer’s disease. The retina is the posterior-most part of the eye. Photoreceptors in the retina receive light signals and transfer them to the retinal ganglion cell layer. Nerve fibers from this layer then carry these signals to the brain via the optic nerve. Since the retina is connected to the brain, researchers believe that it may provide a glimpse of the pathological processes taking place in the brain.
In a study published in 2021, researchers performed retinal scans on patients with Alzheimer’s disease and found small spots in the retina, consistent with amyloid deposits. These spots correlated with the brain scans of patients with higher levels of brain amyloid.
Retinal thinning and Alzheimer’s disease
Non-invasive retinal imaging modalities, including optical coherence tomography (OCT) and OCT angiography (OCT-A), have also shown that the thinning of retinal layers may be associated with early stages of cognitive decline and the risk of developing Alzheimer’s disease. This is because cell loss, resulting in retinal thinning, is a hallmark of neurodegenerative disorders.
These research findings suggest that non-invasive retinal imaging may be a useful tool in the screening and detection of Alzheimer’s disease at an early stage. This is significant because Alzheimer’s disease is a life-limiting illness, and early identification and treatment may help mitigate symptomatic cognitive decline seen in the advanced stages of this disease.