non-Sjögren sicca – MUC16) are two known examples of mucin abnormalities that negatively affect tear film. Sjögren's syndrome – MUC5A) and decreased glycosylation of cell surface-associated mucin (e.g. 6ĭecreased gel-forming mucin gene expression (e.g. Combined with efficient tear clearance, lymphatics, inherent immunologic proteins, and secondary immune responses, mucins help the ocular surface to maintain optimal health.
Secreted mucins have been described as having critical ‘cleaning’ capabilities, addressing unwanted debris, allergens, and microbes. 3 The various ocular surface mucins are described in Table 4.1. Additionally, shed cell surface-associated mucins contribute to tear fluid. The gel-forming mucins appear to work together with cell surface-associated mucins to maximally protect the epithelium and limit desiccation. Cell surface-associated mucins (also called ‘membrane-associated’) form the glycocalyx. The secreted mucins are either soluble (located closer to the tear film lipid layer) or gel-forming (located closer to the conjunctival apical cells). Mucins can be categorized as secreted or cell surface-associated. Their O-glycans have hydrophilic properties to help keep the tear film in contact with the epithelia. Recent assays have helped clarify the mucins' role in: (1) clearance of allergens, pathogens, and debris, (2) lubrication, (3) antimicrobial activity. Mucins are large heavily glycosylated proteins, exhibiting extensive tandem amino acid repeats, and multifunctional utility. Mucins are well-studied products of mucus membranes that are critical for conjunctival health. In addition to the supportive role of accessory lacrimal glands (Krause and Wolfring), arguably the conjunctiva's greatest contribution to the tear film is the production of hydrophilic mucins. Jessica Ciralsky, in Ocular Surface Disease: Cornea, Conjunctiva and Tear Film, 2013 Tear Film
In most cases, significant increases from normal tear film evaporation are seen in patients with aqueous deficient dry eye (ADDE), evaporative dry eye (EDE), and meibomian gland dysfunction (MGD). However, a pattern to the observations reported in the literature does exist, making evaporation rate a useful measurement in the differential diagnosis of dry eye. The use of different techniques for measurement of tear film evaporation makes comparison of evaporation rates in different studies difficult because the absolute values recorded are technique-dependent. Reprinted from The Ocular Surface ( with permission. This technique involves the measurement of the vapor pressure gradient from recordings of relative humidity and temperature at two points a known distance above the ocular surface. Tear film evaporation rate measured by a modified ServoMed EP-3 Evaporimeter (Kinna, Sweden). Phospholipid liposomal spray achieved a significantly greater reduction in lid-parallel conjunctival folds and lid margin inflammation and improvement in TBUT compared with hyaluronate eye drops or triglyceride gel.įigure 2. 61,62 Patients received hyaluronate eye drops, triglyceride gel or a phospholipid liposome eye spray, each for a minimum of 6 weeks.
56 A lipid-containing liposomal spray has been studied in patients who have evaporative dry eye, as defined by low TBUT and inflammatory lid margin changes. In recent years, newer formulations have been better accepted. Historically, lipid-containing lubricant eye drops have not been used widely because of the induced blurring of vision after their use. Supplementation of tear film lipids has been attempted by the use of lipid-containing eye drops and sprays, emulsion-type eye drops and ointments. Nathan Efron AC BScOptom PhD (Melbourne) DSc (Manchester) FAAO (Dip CCLRT) FCCLSA FACO, in Contact Lens Complications (Fourth Edition), 2019 Topical lipid supplements
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