Abstract and Introduction
Eye movements are a source of valuable information to both clinicians and scientists as abnormalities of them frequently act as clues to the localization of a disease process. Classically, they are divided into two main types: those that hold the gaze, keeping images steady on the retina (vestibulo-ocular and optokinetic reflexes) and those that shift gaze and redirect the line of sight to a new object of interest (saccades, vergence, and smooth pursuit). Here we will review some of the major ocular motor abnormalities present in neurodegenerative disorders.
Neurodegenerative disorders are chronic conditions of the central nervous system that often lead to motor problems and dementia. With an ageing population, we are facing a rise in the incidence of these conditions. Studies have revealed that neurodegenerative conditions, including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD) have a presymptomatic phase that may be present for some years before the onset of the overt clinical syndrome. During this presymptomatic phase, considerable neuronal degeneration occurs; but the potential opportunity for preventative intervention is lost, because the diagnostic symptoms and signs have not yet appeared. Once the condition is manifest, there may still be diagnostic uncertainty, particularly in disorders such as PD, which is closely mimicked by the early stages of the so-called 'Parkinson's-plus' conditions.
Eye movement control is complex and involves many brain areas, including the brainstem, cerebellum, basal ganglia, and cerebral cortex. Abnormalities of eye movements are a source of valuable information to clinicians and scientists. Identification of an abnormality during clinical examination may allow accurate localisation of a focal lesion in the nervous system, and may give clues as to the nature of the pathology causing it. Certain eye movement abnormalities may also reflect the presence of widespread disease affecting far more than just the ocular motor system, for example, the inability to voluntarily elevate the eyes seen in progressive supranuclear palsy (PSP). Oculometry—using sophisticated measuring instruments rather than simple clinical examination—has been increasingly used as an experimental tool to gain insights into a wide range of neurological disorders.[2–5]
Eye. 2015;29(2):200-207. © 2015 Nature Publishing Group