Neuro-retinal Conditions

Screening for Neuro-retinal Conditions

Studies have highlighted that changes in the structural and functional features of the eyes are linked with neurodegenerative disease including Alzheimer’s disease, Multiple Sclerosis, Parkinson’s disease and Schizophrenia.  This suggests that eye examinations may be useful for the early detection and diagnosis of these conditions ^9,10.

Alzheimer’s Disease

Alzheimer’s disease is the most common form of dementia and it is characterized by destroyed and damaged connections between neural cells, due to abnormal accumulations of β-amyloid protein in the form of amyloid plaques and neurofibrillary tangles. It is difficult to diagnose and to treat ¹⁰. Ocular degeneration in Alzheimer’s disease (AD) is thought to arise as the retinal nerve fibre layer thins. Many researchers are looking at the eye as a promising new tool that may be useful for the early detection of AD.

Researchers used optical coherence tomographic angiography (OCTA), to look at retinal microvascular alterations in patients, with high levels of amyloid-beta but who do not yet exhibit the symptoms of Alzheimer’s disease compared patients without Alzheimer’s disease.

Results revealed that the foveal avascular zone of the retina, was about one-third larger, on average, in people with elevated amyloid-β. Also, the mean inner foveal thickness was decreased in people with elevated amyloid-β ^{10, 11.}

This shows that cognitively healthy individuals with preclinical Alzheimer’s disease have retinal microvascular abnormalities in addition to architectural alterations and that these changes occur at earlier stages of Alzheimer’s disease than has previously been demonstrated. OCTA analysis of the foveal avascular zone may offer a non-invasive, cost-efficient, and rapid screen to identify preclinical Alzheimer disease. This highlights the potential benefit of screening the ageing eye.

A large prospective cohort’s data; Adult Changes in Thought (ACT) was designed which included 3877 participants who were followed for over 31,142 person-years. In this study, participants were screened biennially with the Cognitive Abilities Screening Instrument, which is used in screening for dementia, monitoring disease progression, and providing profiles of cognitive impairment. Results showed that glaucoma, AMD, and diabetes-related retinopathy (DR) are associated with increased risk of AD ¹².

Participants with AMD have a 20% higher risk of AD and there is 44% higher AD risk in patients with DR in comparison with those without AMD. AD risk in participants with recent and established AMD were 20% and 50% respectively. Participants with recent and established DR were at a higher AD risk by 67% and 50% compared with those living without the condition.

This suggests that retinal degeneration may be a risk factor for AD, therefore, it may be worthwhile checking patients with AMD and DR for possible dementia. It may also allow for early detection of AD and developing better treatments.

Parkinson’s disease (PD)

Parkinson’s Disease is a multifactorial neurodegenerative disease that involves the progressive impairment of voluntary motor control due to the gradual loss of brain cells that produce dopamine, a substance that helps control movement¹⁵.

Symptoms of PD typically manifests only when more than 70% of dopaminergic cells are lost. Definitive diagnosis of PD can only be made histologically post-mortem.¹⁶ Finding ways for earlier diagnosis is important.

Ahn et al. recently identified a link between the thinning of the retina and the loss of the brain cells that produce dopamine. They found that the greater the retina thinning, the greater the severity of the disease. This suggests that a simple eye scan may be useful in detecting Parkinson’s disease early as well as following its progression.¹⁷