Sankhajyoti Saha, M.Optometry, Specialty Fellowship in Low Vision

Assistant Professor , NSHM Knowledge Campus, Kolkata

Alzheimer’s disease (AD), the most common form of dementia- is a progressive neurologic disorder that causes the brain to shrink (atrophy), resulting multiple cognitive deficits (such as decline in thinking, aphasia, and the inability to initiatebehavioural and social skills). ^{(1, 2)}Scientists believe that certain proteins (beta-amyloid) begin to develop and become toxic to the brain, even before the onset of the disease.⁽³⁾

The prevalence of AD emerges to be increasing with 36 million people globally, with as many as 3 in every 4 patients remain undiagnosed. It is expected that without proper treatment and effective awareness, by 2050 around 160 million people will suffer from disease globally. ⁽⁴⁾

At present no single clinical diagnostic trial is available for detecting AD. Validation of AD is multi-diagnostic approach and is only possible when the condition has progressed up to an irreversible neurological mutilation.

Interrelation between AD &Eyesight:

Researchers believe vision and smell may be key biomarker to early detection of AD even before symptoms occur, as AD affects the parts of their brain that handle visual information.Eyes are the extension of the brain because of their nerve fibres.

Through an extensive literature assessment, several visual problems have been reported including reduced visual acuity, colour vision deficiency, restricted visual field, fixation troubles, defective smooth and saccadic eye movements, experiencing of visual hallucinations,REM Sleep, changes in contrast sensitivity and disturbances of complex visual functions such as reading, visual-spatial function. Additionally, few pathological alterations have been reported affecting the visual pathway and visual cortex. ^{(5, 6)}

As an indicator of the onset of Alzheimer’s, morphological changes in patients with pre-clinical AD to healthy individuals showed significant narrowing of the retinal neuron (RFNL, ONL & IPL) that comes out of the brain.⁽⁷⁾

Figure 1: Normal Optical Coherence Tomography, which can be used to detect any morphological changes in patient with preclinical AD

A recent study showed that people who have macular degeneration, glaucoma or diabetic retinopathy are more likely to be diagnosed with Alzheimer’s disease than people without these conditions. All of them are degenerative meaning they get worse over time.⁽⁸⁾

The takeaway

It is a misconception that a person with AD will not be able to manage a sight test. There are certain practices which can help such as allowing more time, assessing qualitative visual performance, adapting the test, and allowing the peer group to guide. A careful clinical approach is required to separate the sign of vision loss (like cataract, macular degeneration, and normal ageing of the eye) from those of AD, as very often one condition may mask another.

As an Eye Care Provider, along with optimizing visual performance, the treatment regimen also demands communication with other health care providers, mainly with the patient’s primary care physician to confirm the diagnosis.

As of now, prevention in the form of encouraging people with a positive lifestyle is the only foothold. To understand “the eye-brain connection” more research is entailed, with some promising outcomes already available.

References:

1. Alzheimer’s disease – Symptoms and causes. (2020, December 29). Mayo Clinic. Retrieved from https://www.mayoclinic.org/diseases-conditions/alzheimers-disease/symptoms-causes/syc-20350447 (Last accessed: February 23, 2021, 11:40 IST)
2. Merriam-Webster. (n.d.). Alzheimer’s disease. In Merriam-Webster.com dictionary. Retrieved from https://www.merriam-webster.com/dictionary/Alzheimer%27s%20disease(Last accessed: February 20, 2021, 16:00 IST)
3. Alzheimer’s &Eye Sight: Is There a Connection? (n.d.). Kadrmas Eye Care New England. Retrieved from http://www.kadrmaseyecare.com/eye-health–care-blog/alzheimers-eye-sight-is-there-a-connection-alzheimers-brain-awareness-month (Last accessed: February 19, 2021, 20:20 IST)
4. Alzheimer’s Statistics. (2021, January 7). Alzheimers.Net. Retrieved from https://www.alzheimers.net/resources/alzheimers-statistics. (Last accessed: February 23, 2021, 22:00 IST)
5. Armstrong, R. A. (2009).A lzheimer’s Disease and the Eye. Journal of Optometry, 2(3), 103-111. https://doi.org/10.3921/joptom.2009.103
6. Osa A, Bowen T & Whitson J. (2020). Charles Bonnet Syndrome in a Patient with Parkinson’s Disease and Bilateral Posterior Capsule Opacification. International Medical Case Reports Journal, Volume 13, 7-10.https://doi.org/10.2147/IMCRJ.S218687
7. Santos, C. Y., Johnson, L. N., Sinoff, S. E., Festa, E. K., Heindel, W. C. & P. J. (2018). Change in retinal structural anatomy duringnthe preclinical stage of Alzheimer’s disease. Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, 10(1), 196-209. https://doi.org/10.1016/j.dadm.2018.01.003
8. Common Eye Conditions Increase Chance of Alzheimer’s Disease Diagnosis. (2018, October 23). American Academy of Ophthalmology. Retrieved from https://www.aao.org/eye-health/news/common-conditions-increase-chance-of-alzheimers (Last accessed: February 21, 2021, 20:20 IST)