Ophthalmic examination in the debut and during progression of neurodegenerative diseases

Abstract

Neurodegenerative diseases (NDD) are a group of nosological forms, caused by excessive formation of protein molecules and their aggregates and leading to the death of brain cells. Classical pathophysiological mechanisms are associated with the accumulation of extracellular amyloid b -protein (A b) in Alzheimer's disease (AD) and a -synuclein protein in Parkinson's disease (PD), which are markers of neurodegenerative process. Signs of functional disorders in NDD include decreasing visual acuity, lower contrast light sensitivity with the most significant changes at the highest spatial frequencies (18 and 12 cycles per degree), and reduced color vision. These disorders correlate with the severity of cognitive impairment and duration of the disease. Changes in the indicators of psychophysical tests are accompanied by lower central retinal thickness (CRT), which is a consequence of inner layers degeneration. NDD progression is characterized by the stability of psychophysical tests, significant thinning of the peripapillary retinal nerve fiber layer (RNFL) and CRT thickening, which correlates with cognitive disfunction. A b and a -synuclein deposits in artery walls cause lumen narrowing and occlusion of blood vessels, reduced optic nerve disk perfusion density, superficial and deep capillary plexus depletion, expansion of the avascular foveolar zone. Microcirculatory disorders lead to retinal changes, which were proven to correlate negatively with the thickness of inner retinal layers and duration of the disease. An ever-growing need in the identification of specific and sensitive biomarkers at the preclinical stage of NDDs, differentiation of their causes, precise subtype classification, and assessment of progression risk is an evidence of the relevance of studying and identifying functional and structural changes in retinal neurons and axons. Non-invasive and informative methods of multimodal imaging appear to be valuable for NDD diagnosis and monitoring.