Ocular Surface Features in Patients with Parkinson Disease on and off Treatment: A Narrative Review

Abstract

Parkinson disease (PD) is a progressive, neurodegenerative disease of the central nervous system. Visual disturbance is one of the most frequent nonmotor abnormalities referred to by patients suffering from PD at early stages. Furthermore, ocular surface alterations including mainly dry eye and blink reduction represent another common finding in patients with PD. Tears of PD patients show specific alterations related to protein composition, and in vivo confocal microscopy has demonstrated profound changes in different corneal layers in this setting. These changes can be attributed not only to the disease itself, but also to the medications used for its management. In particular, signs of corneal toxicity, both at epithelial and endothelial level, are well described in the literature in PD patients receiving amantadine. Management of PD patients from the ophthalmologist's side requires knowledge of the common, but often underdiagnosed, ocular surface alterations as well as of the signs of drug toxicity. Furthermore, ocular surface biomarkers can be useful for the early diagnosis of PD as well as for monitoring the degree of neural degeneration over time.

Keywords: Parkinson’s disease; amantadine; cornea; dry eye; ocular surface; tears.

Figure 1

In vivo confocal microscopy findings showing highly reflective round shaped epithelial deposits induced by amantadine in a patient of 73 years who used the drug for 5 months for the treatment of Parkinson disease (A–C).

Figure 2

In vivo confocal microscopy of the cornea in a patient of 69 years who used amantadine for 2 years to treat Parkinson disease. The scans show decreased density and increased pleomorphism and polymegathism of corneal endothelial cells; furthermore, highly reflective deposits are present at this level (A–C).