Abstract
The human tear film is a multi-layered and chemically complex structure, which performs numerous functions relating to the health of the corneal surface. One of the core functions of the tear film is to protect the eye against invasion by pathogens. Thus its middle layer, the ‘core aqueous stratum’, harbours a myriad of immunologicaland antimicrobial proteins. In this review we discuss the most abundant of these proteins (immunoglobulins, toll-like receptors, cytokines, lactoferrin, lysozyme, lipocalins, surfactant protein-Aand -D and defensins). In order to illustrate how the levels of immunological/antimicrobial proteins in tears change in response to eye disease, we review literature in which levels of these proteins have been measured in tears of patients with dry eye disease (DED) and keratoconus (KC). Finally, we report results of a preliminary study to measure the concentration of secretory immunoglobulin A (sIgA) in the tears of DED and KC patients. The study showed a significant decrease of sIgA levels in DED compared to control. Further analysis must be done to determine whether or not DED and KC may be associated with differential expression of immune proteins. (S Afr Optom 2012 71(3) 123-132)
Highlights
The surface of the human eye is covered by a tear film (TF), known as the precorneal tear film (PTF)[1] or commonly known as tear fluid[2]
This three-layered structure has an outer lipid layer produced by the meibomian glands within the tarsal plate of the upper and lower eyelids; the core aqueous stratum which consists of various proteins, electrolytes and water produced by the lacrimal glands and accessory lacrimal glands and lastly the inner mucous or mucin layer covering the corneal and conjunctival epithelium[3, 4]
We found that levels of secretory immunoglobulin A (sIgA) in patients with dry eye disease (DED)
Summary
The surface of the human eye is covered by a tear film (TF), known as the precorneal tear film (PTF)[1] or commonly known as tear fluid[2]. Tear fluid is a complex liquid produced by various glands associated with the human eye These gland secretions are transported by means of ducts that open on the ocular surface[2]. The PTF has been thought to consist of three discrete layers. This three-layered structure (first presented by Wolff3) has an outer lipid layer produced by the meibomian glands within the tarsal plate of the upper and lower eyelids; the core aqueous stratum which consists of various proteins, electrolytes and water produced by the lacrimal glands and accessory lacrimal glands and lastly the inner mucous or mucin layer covering the corneal and conjunctival epithelium[3, 4]. The corneal and conjunctival epithelia synthesize a mucin-like glycoprotein (MUC1) at the apical surface of the epithelium to constitute the glycocalyx[5], see Figure 1
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