Correlations in a change in aqueous tear evaporation with a change in relative humidity and the impact.

PURPOSE: To establish scientific relationship between relative humidity (RH) and aqueous tear evaporation to elucidate possible significance of this relationship in normals and aqueous tear deficiency patients. DESIGN: Prospective experimental laboratory study. METHODS: Ocular surface evaporation was determined using evaporometry and calculated for two ranges of RH, 25% to 35%, and 35% to 45% in a randomized clinical patient population. RESULTS: Average evaporative rate in the higher humidity range was between 0.029 +/- 0.009 through 0.043 +/- 0.016 microl/cm2/min. At lower humidity, range was between 0.044 +/- 0.013 through 0.058 +/- 0.018 microl/cm2/min. Differences in the corresponding evaporative rates were statistically significant (between P < .003 through P < .043) for each analysis. CONCLUSIONS: A decrease of 10% RH resulted in an average difference of between 28.33% to 59.42% increase in evaporation. The increase in evaporation at lower humidity has significant clinical implications for patients with aqueous deficient dry eyes, and possibly those undergoing laser-assisted in situ keratomileusis (LASIK).

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.

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.

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.

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.

Eyelid disorders: the meibomian gland, blepharitis, and contact lenses.

PURPOSE: To present our results to date on the evaluation of the pathophysiology of chronic blepharitis and its relationship to the tear lipid layer, and to propose a structure to that layer. METHODS: Compilation of work to date. RESULTS: A classification system of chronic blepharitis has been developed that has use in diagnosis, planning therapy, and assessment of mechanisms. Abnormalities in meibum have been identified that provide insight into disease mechanisms and have led to the development of a proposed structure to the tear lipid layer. A defect in polar lipids explaining the frequently associated evaporative dry eye has been identified. Mechanisms accounting for the therapeutic benefit of minocycline have been elucidated. CONCLUSION: Chronic blepharitis has associated meibum abnormalities that explain defects in the tear lipid layer that may result in a frankly unstable tear film and that explain the frequently associated evaporative dry eye.

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.

Presumed hyposecretory/hyperevaporative KCS: tear characteristics.

PURPOSE: To characterize patients with ocular surface drying and a diagnosis of keratoconjunctivitis sicca (KCS). METHODS: Patients with a prior diagnosis of KCS and symptoms of dryness or foreign-body sensation who also had vital staining of the interpalpebral fissure ocular surface in the absence of lid and ocular surface inflammation were entered into the study along with normal controls. Patients were segregated into those with "classic" KCS, who did not have concomitant meibomian gland dysfunction (MGD), and those with KCS and MGD. The latter had slit-lamp evidence of difficult-to-express or turbid meibomian secretions upon expression. Patients and normal controls were evaluated for tear volume, flow, and turnover using fluorophotometry; meibomian gland dropout by meibography; evaporation by evaporometry; and tear production by the Schirmer 1 test. RESULTS: All patients with KCS had decreased tear volume, flow, and Schirmer 1 values as well as increased meibomian gland dropout. None of the patient groups were found to have increased tear evaporation compared with normals or other disease subgroups. No correlation between degree of meibomian gland dropout and evaporation was found. The degree of total vital staining or presence of corneal staining correlated with a more severe aqueous deficiency. CONCLUSIONS: Patients with ocular surface drying in the absence of inflammation have decreased tear volume, flow, and Schirmer 1 values as well as increased meibomian gland dropout. The role of meibomian gland dropout or slit-lamp MGD in disease is unclear and in our study specifically did not correlate with increased tear evaporation.