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.

Multiple Sclerosis

Multiple Sclerosis is a chronic inflammatory disease characterized by central nervous system (CNS) lesions that can lead to severe physical or cognitive disability as well as neurological defects. 13 In this disorder, the immune system disrupts communication in the central nervous system by attacking myelin, a fatty substance that forms a protective layer around nerve fibres. This process damages several parts of the brain, including those involved in pathways that are responsible for vision and the optic nerve, which carries impulses between the eye and the brain 10. Visual dysfunction is one of the most common causes of disability in multiple sclerosis (MS).

By combining OCT (structural) tests with tests for low-contrast vision (functional), researchers have uncovered a correlation between a thinning retina and vision problems in multiple sclerosis. Retinal nerve fibre thinning in the eyes of patients with MS with or without prior history of acute optic neuritis (ON) have been studied. A study that involved 299 patients with MS who were tracked for 6 months to 4.5 years revealed that there is a significant association between visual loss and retinal nerve fibre layer thinning over time in both cases. RNFL thinning was also shown to correlate with MRI measure of lesion volume and normalised brain volumes. This suggests that the use of OCT may be a useful, non-invasive method for the early detection of MS and could be used to examine the progression of disease as well as testing the effectiveness of treatments.14

Using ophthalmologic evaluation for the detection of MS may lead to better and early diagnosis and treatment and potentially better outcomes for patients. It may also be used as an indicator of disease severity.

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

Schizophrenia 

Schizophrenia is a chronic and severe disorder that affects how a person thinks, feels, and behaves. People with schizophrenia may seem like they have lost touch with reality. Although schizophrenia is not as common as other neuro degenerative disorders, symptoms can be very disabling.18 While there have been genetic, physiology and neuro-imaging studies that show changes in patients with schizophrenia, there is no established objective biomarker for the diagnosis of schizophrenia in clinical settings.

The potential to use abnormalities in the retina and other structures of the eye as a biomarker to predict for schizophrenia is under research. The retina and the brain develop from the same tissue, the neuroectoderm and it is the only part of the CNS that can be seen with the naked eyes. Therefore, it can be said that the retinal changes may mirror the integrity of the brain structure and therefore serve as a marker of progressive tissue loss. The strongest evidence of this involves findings of widened retinal venules, thinning of the retinal nerve fibre layer and abnormal ERG amplitudes19 .

 

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