Corneal Sensitivity and Tear Function in Neurodegenerative Diseases

Abstract

Neurodegenerative diseases may be associated with reduced corneal sensitivity and abnormal tear function.

Association Between Meibomian Gland Testing and Ocular Surface Sensitivity

“…In addition, the sensations experienced at the ocular surface are difficult to quantify in each subject because sensation perception can be affected by several factors including medications, systemic conditions, and the environment. 17,19,[42][43][44][45] Even the various receptors discussed previously (mechanoreceptors, polymodal receptors, and cold receptors) have been shown to affect each other. 46,47 These factors may need to be considered together to fully understand the association between the tear-producing glands and the ocular surface sensations.…”

“…16 These findings have been supported by studies that have shown that subjects with neurodegenerative conditions or diabetes have reduced sensitivity and compromised dry eye tests such as tear breakup time and Schirmer test when compared with control subjects. [17][18][19] In addition, a group of subjects with rheumatoid arthritis had reduced corneal sensitivity and Schirmer strip results and worse symptoms based on the ocular surface disease index questionnaire (OSDI) compared with control subjects. 19 Another study, which classified subjects based on symptoms and Schirmer strip results, found a statistically significant difference between corneal and bulbar conjunctival mechanical thresholds in subjects with dry eye compared with normal subjects.…”

Evaluation of corneal parameters in patients with Parkinson’s disease

“…Kwon et al reported reduced lacrimation by Schirmer test in patients with PD [25]. Recently, Ö rnek et al evaluated corneal sensitivity and tear function tests including Schirmer test and TBUT in neurodegenerative diseases and found decreased corneal sensitivity in PD patients compared to controls and the researchers found that TBUT levels in PD groups were significantly lower than in Friedreich's ataxia and epilepsy groups and Schirmer test scores in PD groups were significantly shorter than in multiple sclerosis, Friedreich's ataxia and epilepsy groups [26]. All abnormalities in tear film production cause more common ocular complaints of dry eyes, namely higher OSDI index, in patients with PD [3].…”

“…However, the osmolarity of the tear film increase in dry eye and the hypertonic tear film which affects corneal hydration leads to a reduction in corneal thickness [28]. Furthermore, reduced corneal sensitivity has been demonstrated in patients with PD [21,26]. Reddy et al investigated the BR and corneal sensitivity in patients with PD and found that BR was positively correlated with corneal sensitivity.…”

“…The researchers reported that reduced BR might be caused by reduced corneal sensitivity [21]. Ö rnek et al suggested that impairment of blinking, damage to neurological mechanisms of tear secretion, inflammation, and decreased corneal sensitivity might aggravate the symptoms of dry eye in PD [26]. Using ultrasonic pachymetry, Dayanır et al demonstrated that central corneal thickness might reduce during 1 minute of drying.…”