Alzheimer’s disease (AD) is the most common cause of dementia globally.
The prevalence has increased dramatically with an aging population. Although
considerable progress has been made over the last few decades in understanding the
pathophysiology of AD, early and accurate diagnosis of the disorder is still a
formidable challenge, and there is currently no effective treatments available to slow
down disease progression. The fundamental issue on this disadvantage is largely due to
a lack of reliable biomarkers for neurodegeneration in the brain. However, mounting
evidence has shown that except the brain, the eye, particularly the retina, is also
affected in AD. Because of its transparent nature and ease of accessibility, the eye can
serve as a ‘window’ into the brain. Advanced imaging technologies enable observation
of changes in the retina in real time, e.g. measurement of thickness of the retinal nerve
fibre layer (RNFL) by coherence tomography (OCT), detection of changes in the optic
nerve head (ONH) by confocal scanning laser ophthalmoscopy (cSLO), and monitoring
of retinal neuronal apoptosis by DARC (Detection of Apoptosing Retinal Cells). In
addition to the ocular structural changes in AD patients, similar pathological
mechanisms identified in the brain have also been established in the retina, including
increased amyloid-ß (Aß) deposition and tau pathology. Furthermore, AD-related
changes in the retina have also been observed in eye diseases, including glaucoma and
age-related macular degeneration (AMD), and targeting of Aß has been demonstrated
to be neuroprotective for those eye diseases. This review focuses on the recent
advances in ocular changes, particularly retinal neurodegeneration in AD, discusses
pathological similarities between AD and eye diseases, and highlights the potential of
retinal imaging in identification of promising biomarkers for early AD.
Keywords: Aß, Alzheimer’s disease, AMD, DARC, Glaucoma, Retinal imaging,
Retinal neurodegeneration, Tau.
