Visual impairment and dementia: Potential new risk factors considered

A recent study suggests a link between vision loss in older people and dementia. What is the evidence behind this controversial topic?

Retinal nerve fibre layer (RNFL) thickness and Alzheimer's disease

The human eye offers the possibility of an early diagnosis for neurodegenerative diseases via various biomarkers. It is therefore not surprising that in recent years more scientific studies have been published that point to a neurodegenerative connection between dementia and the visual system.1,2 Nevertheless, there is still a long way to go before ophthalmological biomarkers for neurodegenerative diseases can be used in clinical practice, as there are still discrepancies in this field.

Changes in the thickness of the RNFL may indicate an early onset of Alzheimer's disease.1 The use of optical coherence tomography (OCT) could therefore be an early diagnostic tool and has already been proposed as a potential biomarker for Alzheimer's disease. However, scientific opinion is still divided on this issue, as there are controversial results depending on the study.4

Optical coherence tomography angiography in neurodegenerative diseases

In addition to measuring retinal nerve fibre layer thickness, optical coherence tomography angiography (OCT-A), a non-invasive imaging method, can also provide evidence of microvascular damage in neurodegenerative diseases. The microcirculation of the retina and the brain are similar in many aspects. In addition to Alzheimer's disease, a research group from Italy also looked at microvascular findings of the eyes in Parkinson's disease and multiple sclerosis, as part of a literature review.

According to this research, there are numerous indications of a connection between neurodegenerative diseases of the eye, such as glaucoma, and diseases of the central nervous system, such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. All of the diseases mentioned are characterised by an impairment of retinal microvessels.3

Secondary analysis of NHATS provides new ophthalmic risk factor for dementia

The recently published secondary analysis of the National Health and Aging Trends Study (NHATS) investigated a potential association between dementia and vision loss in people over 71 years of age. The NHATS secondary analysis included a total of 3,817 people. NHATS tablet-based tests were used to assess distance and near visual acuity and contrast sensitivity (CS) with habitual correction. Cognitive impairment in dementia was assessed using the AD8 Dementia Screening Interview Score.

Visual impairment greater than 0.30 logMAR for distance and near acuity could be associated with higher dementia prevalence. In addition to neurodegenerative changes, a lack of sensory input to the brain in low vision could also play a role in this observation. Since many visual impairments are preventable, the goal here would be to optimise the vision of these patients.2

12 risk factors for dementia

Vision loss is not yet one of the 12 risk factors that can be controlled to significantly reduce the likelihood of dementia (up to 40% of dementia cases do). This could change in the near future thanks to this study data. The 12 risk factors for dementia include:

  1. Liu D. et al. (2015). Thinner changes of the retinal nerve fiber layer in patients with mild cognitive impairment and Alzheimer's disease. BMC Neurol. 2015 Feb 21;15:14. 
  2. Killeen OJ. et al. (2023). Objectively Measured Visual Impairment and Dementia Prevalence in Older Adults in the US. JAMA Ophthalmol. 2023 Jul 13:e232854. 
  3. Pellegrini M. et al. (2020). Optical Coherence Tomography Angiography in Neurodegenerative Disorders. J Clin Med. 2020 Jun 2;9(6):1706. 
  4. Killeen OJ. et al. (2023). Objectively Measured Visual Impairment and Dementia Prevalence in Older Adults in the US. JAMA Ophthalmol. 2023 Jul 13:e232854. 
  5. Sánchez D. et al. (2018). Usefulness of peripapillary nerve fiber layer thickness assessed by optical coherence tomography as a biomarker for Alzheimer's disease. Sci Rep. 2018 Nov 5;8(1):16345.