Original articleThe Pathology of Dry Eye
Section snippets
Hormonal Regulation
Although the mechanisms of hormonal regulation of tear secretion remain poorly understood, the influence of sex hormones, and of androgens, in particular, appears to be of paramount importance. Androgens modulate the anatomy, physiology, and the immune system of the lacrimal gland in rats, rabbits, hamsters, and humans. Other hormones, such as luteinizing hormone, follicle stimulating hormone, prolactin, thyroid stimulating hormone, progesterone, and estrogens also appear to influence normal
Nervous Regulation
The cornea is very richly innervated, with 60 times more nerve endings than dental pulp, indicating the importance of nervous signals in the trophic regulation and protection of the cornea. The main and accessory lacrimal glands, mucous cells, and meibomian glands also have an abundant nerve supply. This comes mainly from the parasympathetic system (acetylcholine- and vasoactive intestinal peptide [VIP]–containing nerve terminals), but also from sympathetic nerves (neuropeptide Y and
Chronic Inflammation and Dry Eye Disease
Whatever the initial cause of dry eye disease, chronic dryness of the ocular surface results in excessive nervous stimulation aimed at triggering the mechanisms of regulation and repair. It has been hypothesized that these nervous stimuli lead to neurogenic inflammation, activation of T-cells, and the subsequent release of inflammatory cytokines into the lacrimal glands, tear film, and conjunctiva.51 Epithelial cells may independently produce interleukins 1α, 6, and 8, and tumor necrosis
Inflammation and Dry Eye in Practice
In clinical practice, dry eye disease can be assigned to two major classes: tear deficient dry eye and evaporative dry eye.13, 35 Tear deficient dry eye, the most common form, can be further classified into Sjögren's syndrome dry eye, an autoimmune disorder affecting the lacrimal and salivary glands, and non-Sjögren's syndrome dry eye, which encompasses the range of other causes of tear deficiency.
Acknowledgements
The author has no proprietary or commercial interest in any product or concept discussed in this article.
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