Oculo-Visual Dysfunction in Parkinson's Disease

Abstract

This review describes the oculo-visual problems likely to be encountered in Parkinson's disease (PD) with special reference to three questions: (1) are there visual symptoms characteristic of the prodromal phase of PD, (2) is PD dementia associated with specific visual changes, and (3) can visual symptoms help in the differential diagnosis of the parkinsonian syndromes, viz. PD, progressive supranuclear palsy (PSP), dementia with Lewy bodies (DLB), multiple system atrophy (MSA), and corticobasal degeneration (CBD)? Oculo-visual dysfunction in PD can involve visual acuity, dynamic contrast sensitivity, colour discrimination, pupil reactivity, eye movement, motion perception, and visual processing speeds. In addition, disturbance of visuo-spatial orientation, facial recognition problems, and chronic visual hallucinations may be present. Prodromal features of PD may include autonomic system dysfunction potentially affecting pupil reactivity, abnormal colour vision, abnormal stereopsis associated with postural instability, defects in smooth pursuit eye movements, and deficits in visuo-motor adaptation, especially when accompanied by idiopathic rapid eye movement (REM) sleep behaviour disorder. PD dementia is associated with the exacerbation of many oculo-visual problems but those involving eye movements, visuo-spatial function, and visual hallucinations are most characteristic. Useful diagnostic features in differentiating the parkinsonian symptoms are the presence of visual hallucinations, visuo-spatial problems, and variation in saccadic eye movement dysfunction.

Keywords: PD dementia; Parkinsonian syndromes; Parkinson’s disease (PD); differential diagnosis; oculo-visual dysfunction; prodromal phase.

Fig.1

Retinal image of a normal control subject using optical coherence tomography (OCT) showing the various functional layers: Fo = Location of fovea, NFL = Nerve fibre layer, GCL = Ganglion cell layer, IPL = Inner plexiform layer, INL = Inner nuclear layer, OPL = Outer plexiform layer, ONL = Outer nuclear layer, RPE = Retinal pigment epithelium, PR = Photoreceptor layer, N = Nasal direction, T = Temporal direction. A specific thinning of INL in the parafoveal region has been recorded in Parkinson’s disease (PD). (Image courtesy Dr R Heitmar, Aston University)