Foveal vision is impaired in Parkinson's disease.

PURPOSE: The article aims to review foveal involvement in Parkinson's disease. SCOPE: Clinical observations as well as electrophysiological and anatomical studies in animal models provide evidence that Parkinson's disease (PD) affects vision. The retina is the most distal locus of visual dysfunction in PD as shown by electroretinographic (ERG) and optical coherence tomographic (OCT) studies. Thinning of the retinal nerve fibre layer (RNFL) and the fovea has been reported in PD. This review summarises retinal physiology and foveal visual dysfunction in PD and quantification of retinal thinning as reported in different studies and using different instruments. At this point due to methodological diversity and relatively low number of subjects studied, a meta-analysis is not yet possible. Results obtained on one equipment are not yet transferable to another. The author also briefly alludes to some links of visual processing deficits beyond visual detection, such as visual discrimination, visual categorisation and visuospatial orientation in PD.
CONCLUSIONS: There are some promising results suggesting the potential applicability of ST-Oct as a biomarker in PD. Furthermore, these data raise some interesting neurobiological questions. However, there are identifiable pitfalls before OCT quantification may be used as a biomarker in PD. Analysis standardisation is needed on a larger than existing healthy and patient population. Furthermore, longitudinal studies are needed. The exact relationship between retinal foveal deficits and visuo-cognitive impairment in PD remains a challenging research question.