Ward E. Shine

Meibomian Gland Function and the Tear Lipid Layer

The meibomian glands of the lid produce a lipid material whose synthesis is dependent on neuronal, hormonal, and vascular factors. This lipid material is fluid, spreads easily, is a surfactant as well as an aqueous barrier and must remain functional after a blink. To satisfy these requirements, the meibomian lipids have a specific composition. Even after delivery it may be modified by lipases produced by ocular bacteria, and modifications in the lipid components can lead to unique disease states. For example, bacteria may degrade lipids, producing an unstable tear film and irritating free fatty acids; and hormonal imbalances may alter lipid profiles to destabilize the tear film and produce evaporative dry eye.

Polar lipids in human meibomian gland secretions.

Purpose. To determine the polar lipid composition of human meibomian gland secretions and their relationship to the preocular tear film. Methods. Meibomian secretions were collected from normals and patients with chronic blepharitis. These lipids (meibum) were first separated by thin layer chromatography. Polar lipids were then separated utilizing high-pressure liquid chromatography with ultraviolet detection. Individual peaks were identified by comparison with standards. Collected sample peaks were subjected to differential transmethylation with sodium methoxide-methanol and the resulting fatty acid methyl esters were analyzed by gas chromatography-mass spectroscopy. Results. Three phospholipids were identified as phosphatidylcholine, phosphatidylethanolamine and sphingomyelin; other unidentified phospholipids were also present. Also present in secretions were the sphingolipids ceramides and cerebrosides. Fatty acids present were 12-18 carbon chain length. All fatty acids were normal (not branched) saturated fatty acids except in sphingolipids, where hydroxy fatty acids were also present. Unsaturated normal fatty acids were present only in meibum from patients with meibomianitis. Conclusions. The composition of the polar lipids in meibomian gland secretions is more complex than previously thought. On the other hand, the type and carbon chain length of the polar lipid fatty acids appears strictly controlled. The relationship of these findings to the preocular tear film should be considered in terms of overall functionality. The polar lipid layer most likely is only one to three molecules thick and serves as a surfactant between aqueous tears and the thicker nonpolar lipid layer.

The lipid layer of tears: dependent on meibomian gland function

There is growing laboratory and clinical evidence implicating the meibomian glands of the eyelid as playing a critical role in the pathogenesis of various ocular surface disorders such as chronic blepharitis and dry eye. Meibomian glands produce a lipid material whose synthesis is dependent on factors such as stem cells, neurological stimulants and hormones. This lipid material is fluid, spreads easily, is a surfactant as well as an aqueous barrier, and must remain functional after a blink. Before delivery it can be modified by factors such as hormone abnormalities and even after delivery it may be modified by lipases produced by ocular bacteria.

Minocycline effect on meibomian gland lipids in meibomianitis patients.

The objective of this research was to determine the effect of oral minocycline on the meibomian gland nonpolar and free fatty acid lipids of chronic blepharitis patients. Patients--seborrheic blepharitis (SBBL), acne rosacea (AR) without ocular involvement, and acne rosacea with meibomianitis (AR-MKC). Minocycline treatment--50mg orally for 2 weeks followed by 100mg to the end of 3 months; this was followed by 3 more months with no treatment. Meibomian gland secretions (meibum) were collected before treatment, at the end of the 3 months on treatment, and 3 months after stopping treatment. Lipids were separated and analyzed for wax and sterol esters, triglycerides, diglycerides, free cholesterol and free fatty acids. Data were analyzed statistically by ANOVA. Minocycline treatment resulted in decreased diglycerides and free fatty acids in the group AR-MKC, which continued into the second 3 months (off treatment) and was significant. Cholesterol decreased, but triglycerides initially decreased with treatment and then increased when treatment in the group was discontinued (second 3 months); these results, however, were not significant. Thus, minocycline has its greatest effect on lipid types, which result from degradation (lipase) reactions, suggesting a lipase inhibition effect and/or direct effect on ocular flora. This minocycline effect continues even after treatment is discontinued, suggesting a more lasting effect on ocular microflora. Minocycline may be most effective when the treatment period is longer than 3 months. These results give insight into disease mechanisms associated with chronic blepharitis.

Changing concepts in the diagnosis and management of blepharitis.

Purpose. Chronic blepharitis is one of the most common conditions seen in the ophthalmologists office; but, it is difficult to treat effectively. Nevertheless, much progress has been made over the last quarter century, not only in diagnosis but also in treatment of blepharitis. Methods. Perhaps the most important progress has been made as the result of extensive and detailed clinical evaluations of patients, sometimes over extended periods of time with diverse patient populations. Results. The availability of sophisticated instrumentation and laboratory techniques, as well as an array of antibiotics, has enhanced the whole picture for effective blepharitis treatment. Conclusion. Although much progress has been made, it is important to build on the present understanding. Most important is the continued development of targeted treatment protocols that address specific signs, as is now possible with microbial abnormalities. Progress in the understanding and treatment of relevant inflammatory processes will benefit from continuing biomedical discoveries.

Meibomian gland triglyceride fatty acid differences in chronic blepharitis patients.

In this study, we analyzed the triglyceride fraction of human meibomian gland secretions to determine whether specific fatty acids were significantly associated with specific chronic blepharitis disease groups. Triglycerides, isolated from the lipid component of human meibomian secretions by thin-layer chromatography, were transmethylated with sodium methoxide/methanol. Samples from individuals were then analyzed by gas chromatographymass spectroscopy (GC-MS). Significant fatty acid differences were determined by nonparametric analyses, utilizing Kruskal-Wallis analysis of between group differences and Student-Newman-Keuls multiple comparisons. The analyses showed that the triglyceride samples contained the expected normal, iso, and anteiso fatty acids; disease group differences (from normals) in some of these fatty acid types were significant only without a Bonferroni adjustment. The triglycerides also contained previously unreported polyunsaturated fatty acids as well as two four-member families of fatty acids that had mass spectra and retention times consistent with dimethylated carbon chains. Additionally, some members of the meibomian keratoconjunctivitis (MKC) group contained an unusual pattern of normal 20-carbon fatty acids, including a higher level of saturated and lower levels of unsaturated fatty acids. An important exception was the presence of a monounsaturated fatty acid whose GC retention time and mass spectrum were consistent with the uncommon cis- 10-20:1 isomer. This pattern was associated with the presence of patient posterior hordeola. Thus, the association of triglyceride fatty acid composition with chronic blepharitis disease signs could be much more important than previously thought. Furthermore, this is the first example of the association of specific fatty acids with a specific chronic blepharitis disease sign.

The lipid layer: the outer surface of the ocular surface tear film.

The outer layer of the tear film—the lipid layer—has numerous functions. It is a composite monolayer composed of a polar phase with surfactant properties and a nonpolar phase. In order to achieve an effective lipid layer, the nonpolar phase, which retards water vapor transmission, is dependent on a properly structured polar phase. Additionally, this composite lipid layer must maintain its integrity during a blink. The phases of the lipid layer depend on both lipid type as well as fatty acid and alcohol composition for functionality. Surprisingly, the importance of the composition of the aqueous layer of the tear film in proper structuring of the lipid layer has not been recognized. Finally, lipid layer abnormalities and their relationship to ocular disease are beginning to be clarified.

Association of meibum oleic acid with meibomian seborrhea

Purpose. We sought to determine whether patient meibum fatty acid unsaturation is associated with meibomian gland secretion consistency. Methods. Meibomian gland secretions were dissolved in chloroform and separated into lipid classes by thin-layer chromatography. Fatty acids in individual lipid classes were characterized by gas chromatography after transmethylation. Results. Meibum from patients with meibomian seborrhea was higher, and meibum from patients with meibomian keratoconjunctivitis (meibomianitis) was lower in the monounsaturated fatty acid, oleic acid, than that of other disease groups and normal subjects. Conclusion. Our results strongly suggest that the melting characteristics of meibum, influenced primarily by the amount of oleic acid in wax and sterol esters and free fatty acids, greatly influence the consistency of meibomian gland secretions.

Effects of minocycline on the ocular flora of patients with acne rosacea or seborrheic blepharitis.

Purpose. To assess the effect of minocycline on the ocular flora in patients with acne rosacea or blepharitis. Methods. A total of ten patients were enrolled in this prospective study, with six patients diagnosed with acne rosacea with concomitant meibomianitis, two patients with acne rosacea without concomitant ocular involvement, and two patients with seborrheic blepharitis. The eyelids and conjunctiva of both eyes were cultured before the initiation of systemic minocycline therapy, after 3 months of active therapy, and 3 months after the discontinuation of therapy. Isolated bacteria were identified and quantified, and antibiotic susceptibility was determined. Results. The colony-forming units (CFU) isolated from the eyelids significantly decreased after a 3-month treatment with minocycline (P = 0.0013). The CFU significantly increased to approach that of the baseline with the discontinuation of minocycline (P = 0.0275). The most common isolated bacteria, including coagulase-negative Staphylococcus (CNS), Staphylococcus aureus (S. aureus), and Propionibacterium acne (P. acne), except for corynebacterium, had a significant decrease in bacterial count with minocycline therapy compared with baseline (P < 0.05). There was a trend in the decrease of bacterial CFU isolated from the conjunctiva with minocycline therapy, although this was not statistically significant (P = 0.1955). Four of the ten patients carried tetracycline-resistant CNS strains, but none of the S. aureus or P. acne isolated at baseline was resistant to tetracycline. All six patients with acne rosacea and concomitant meibomianitis had marked clinical improvement. Conclusion. Minocycline effectively decreased eyelid bacterial flora in patients with acne rosacea or blepharitis. One of the mechanisms of newer generation tetracycline analogues may be a decrease or elimination of bacterial flora from the eyelids.

Meibomianitis: polar lipid abnormalities.

Purpose: To determine abnormal meibomian gland secretion polar lipids from meibomianitis patients and to determine the significance of these lipid differences. Methods: Meibomian gland secretions were collected from controls and patients with chronic blepharitis. These meibomian gland lipids (meibum) were first separated by thin-layer chromatography. Polar lipids were then separated utilizing high-pressure liquid chromatography with ultraviolet detection. Individual peaks were identified by comparison to standards and retention time. Results: A polar lipid with an HPLC retention time longer than either phosphatidylcholine or sphingomyelin and shorter than phosphatidylethanolamine was significantly greater in the meibomianitis group (P < 0.05) compared with other chronic blepharitis groups and normals. This polar lipid’s retention time was similar to that of dimethylphosphatidylcholine or possibly lysophosphatidylcholine. Additionally, meibomianitis polar lipids’ normal fatty acids were highly unsaturated and differed from those of other groups, none of which were unsaturated. Conclusion: Many of the most significant differences in meibomianitis meibum composition occur in the polar lipids rather than the nonpolar lipids. Further investigations will determine the true significance of these findings.