In The Mind's Eye: A Review Of The Role Of Corneal Nerve Imaging In Cognitive Impairment And Dementia

To review scientific literature concerning corneal nerve imaging and whether it has a role to play in the diagnosis and assessment of cognitive impairment and dementia.

This was a comprehensive review of the literature using the Ovid (R) databases.

A literature review was conducted using Embase 1974 to March 1 2024; Ovid Emcare 1995 to 2024 Week 08; HMIC Health Management Information Consortium 1979 to November 2023 and Ovid MEDLINE (R) ALL 1946 to March 1 2024. A Boolean search strategy was deployed incorporating 'cornea' AND 'nerve' OR 'neurone' AND 'imaging' AND 'cognitive impairment' OR 'dementia' OR 'Alzheimer's'. This yielded a total of 49 published works which were screened by abstract. Following screening, ten publications met the initial screening criteria, of which five were subsequently excluded as they were noted to be reviews rather than original research. The findings of the remaining five studies (n=5) are elucidated in this work.

Two studies used mice models of Alzheimer's Disease (AD) and demonstrated that corneal nerve density and length were reduced compared to wild type mice and may reduce prior to cognitive deficits developing. Two studies demonstrated that in human subjects with AD corneal confocal microscopy demonstrates statistically significant morphological differences in corneal dendritic cells and a trend towards a reduction of corneal nerve fibre length and density. The final study compared corneal confocal microscopy (CCM) assessment of corneal nerve fibre density compared to traditional medial temporal atrophy (MTA) assessments, finding that CCM was comparable with MTA rating for dementia and superior to MTA rating for mild cognitive impairment.

Whilst rates of dementia rise in the context of an ageing population, much of the focus has been on earlier diagnosis to help facilitate forward planning for patients and their families. In the future, earlier diagnosis will hopefully help us to intervene with disease modifying treatment earlier to reduce the morbidity of cognitive decline. Retinal imaging has been studied extensively in predicting cognitive impairment, however corneal imaging may also play an important role, particularly given the ease and comparatively tolerable process involved. More work is required in this area to confirm the diagnostic accuracy and reliability of corneal imaging in predicting future cognitive impairment, however current evidence is promising.