A New Hypothesis on Tear Film Stability

Abstract

Classically, the stability of the lacrimal film is due to the surfacting of the epithelial surface by the mucus produced by the goblet cells. However, there are many objections to this hypothesis. Deducing from electron microscopy of the epithelial cells, which shows vesicles in the superficial layer and glycocalix threads on the microvilli and other clinical facts, we think that the surfacting agent is not mucus but glycocalix. The disappearance of goblet cells during sicca syndrome is not the cause but the result of the dryness. Epithelial cell integrity is essential for the stability of the tear film and therapeutics must aim at regenerating these cells rather than only replacing the lacrimal film by tear substitute.

Eye Discomfort and Air Pollution

“…Our data showed that tear film components and stability, presence of inflammatory cells and degree of dryness can change one by one. This suggests that DES may also be produced by the impairment of only one component of the eye surface; this is consistent with the hypothesis that the ocular surface is a functional unit represented by the cornea and conjunctival epithelia, the tear film and the glycocaliceal junction between the two [25]. Whenever one of these components changes its functional, physical or chemical characteristics, the equilibri-Versura/Profazio/Cellini/Torreggiani/ Caramazza um with the others can also change and ocular discomfort is the final result.…”

Long term course of tear gland function in patients with keratoconjunctivitis sicca and Sjogren's syndrome

“…Also, a decrease in tear fluid lysozyme concentration has been shown 24. In view of the findings of a significant overall improvement of tear gland function in the present study we favour avoiding the term ‘age related KCS’.…”

Prevalence of ocular symptoms and signs with preserved and preservative free glaucoma medication

“…43 An improvement in symptoms after withdrawal of the preservative was also observed in the management of dry eye syndrome, 44-46 a pathology frequently found in glaucomatous patients. 47 The toxic effect of preservatives is very rapid in vitro: 0.007% benzalkonium chloride induces the lysis of 50% of cultured epithelial cells in less than 2 minutes. 48 The damage to the ocular surface observed during the treatment with preserved antiglaucoma eye drops probably reflects an imbalance between mucosal regeneration and daily low grade cytotoxicity of the preservative.…”