The retina in Parkinson's disease

Abstract

As a more complete picture of the clinical phenotype of Parkinson's disease emerges, non-motor symptoms have become increasingly studied. Prominent among these non-motor phenomena are mood disturbance, cognitive decline and dementia, sleep disorders, hyposmia and autonomic failure. In addition, visual symptoms are common, ranging from complaints of dry eyes and reading difficulties, through to perceptual disturbances (feelings of presence and passage) and complex visual hallucinations. Such visual symptoms are a considerable cause of morbidity in Parkinson's disease and, with respect to visual hallucinations, are an important predictor of cognitive decline as well as institutional care and mortality. Evidence exists of visual dysfunction at several levels of the visual pathway in Parkinson's disease. This includes psychophysical, electrophysiological and morphological evidence of disruption of retinal structure and function, in addition to disorders of 'higher' (cortical) visual processing. In this review, we will draw together work from animal and human studies in an attempt to provide an insight into how Parkinson's disease affects the retina and how these changes might contribute to the visual symptoms experienced by patients.

Parkinson's disease, visual hallucinations and apomorphine: A review of the available evidence

“…It is well recognized that dopamine deficiency in the occipital cortex, lateral geniculate nucleus and retina impairs lower-order visual functions, such as color discrimination and visual contrast sensitivity, as well as playing a role in higher-order visual functions, such as motion perception, visual acuity, and colour vision [41]. These deficits can be reversed with the administration of levodopa [41], suggesting a compelling link between dopamine and visual perception.…”

“…Dopamine appears to play a more specific role in retinal function with concentrations sensitive to light intensity and a circadian rhythm with lower dopamine concentrations at night and higher levels during the day [41]. Therefore, dopamine seems to be essential in mediating light-adaptive mechanisms in retinal function [42,43].…”

Combinations of Markers Provide Clues to the Underlying Neurodegenerative Disorder in REM Sleep Behavior Disorder

“…The severity of the axial www.intechopen.com motor symptoms has been shown to be more closely related to visual dysfunction than mental function. Most patients with PD showed more marked impairment along the redgreen axis than the blue-yellow axis (Oh et al, 2011), and this pattern contrasts with that typically seen in aging-predominant blue-yellow axis deficiency (Archibald et al, 2009). Color discrimination deficits also have been reported in iRBD, a potential forerunner of PD (Postuma et al, 2008).…”

Protein Misfolding and Retinal Degeneration

“…It is believed that the misfolding and accumulation of a protein, a-synuclein, plays a significant role in its pathogenesis (Schultz 2007). Although direct degenerative changes have not been reported, various alterations in vision function have been documented (Archibald et al 2009), including decline in visual acuity, contrast sensitivity, color vision, motion perception, and bioelectrical activity as measured by flash and pattern electroretinography and other types of measurements. Further studies are necessary to clarify the role of a-synuclein and better characterize the correlation between a-synuclein misfolding and accumulation in the retina and the extent of visual dysfunction observed.…”