Visual symptoms in Parkinson's disease

Abstract

Parkinson's disease (PD) is a common disorder of middle-aged and elderly people in which degeneration of the extrapyramidal motor system causes significant movement problems. In some patients, however, there are additional disturbances in sensory systems including loss of the sense of smell and auditory and/or visual problems. This paper is a general overview of the visual problems likely to be encountered in PD. Changes in vision in PD may result from alterations in visual acuity, contrast sensitivity, colour discrimination, pupil reactivity, eye movements, motion perception, visual field sensitivity, and visual processing speeds. Slower visual processing speeds can also lead to a decline in visual perception especially for rapidly changing visual stimuli. In addition, there may be disturbances of visuospatial orientation, facial recognition problems, and chronic visual hallucinations. Some of the treatments used in PD may also have adverse ocular reactions. The pattern electroretinogram (PERG) is useful in evaluating retinal dopamine mechanisms and in monitoring dopamine therapies in PD. If visual problems are present, they can have an important effect on the quality of life of the patient, which can be improved by accurate diagnosis and where possible, correction of such defects.

Figure 1

The layers of the retina (PE: pigment epithelium, PR: visual receptors, ONL: outer nuclear layer, OPL: outer plexiform layer, INL: internal nuclear layer, IPL: internal plexiform layer, GC: ganglion cell layer, and SO: Stratum opticum). Dopamine neurons (TOH+: Tyrosine hydroxylase positive neurons, Type 1 cells and Type 2 amacrine cells) are primarily concentrated in the INL and dopamine positive neurites (Type 1 in stratum 1 and type 2 ramify above stratum 1) in the IPL. Type 1 cells may synapse onto GABA interpelexiform cells (IPCs). Some dopamine activities may also be observed in the ganglion cell layer.

Figure 2

Cells from the cerebral cortex showing the presence of Lewy bodies (α-synuclein immunohistochemistry, haematoxylin stain, bar = 25 μm).

Figure 3

The dopamine projections of the central nervous system (OB: Olfactory bulb, SFC: superior frontal cortex, CG: Cingulate gyrus, ST: Striatum, HY: Hypothalamus, VT: Ventral tegmentum, SN: Substantia nigra).