Role of meibum and tear phospholipids in the evaporative water loss associated with dry eye.

It is generally believed that the tear film lipid surface film inhibits the rate of evaporation (Revap) of the underlying tear aqueous. It is also generally believed that changes in the composition of the tear film lipid layer is responsible for an increase in Revap in patients with dry eye. Both of these ideas have never been proven. The purpose of the current studies was to test these ideas. Revap was measured in vitro gravimetrically. Lipid spreading was measured using Raman spectroscopy and microscopy. The influence of the following surface films on the Revap of the sub phase of physiologically buffered saline (PBS) was measured: 1-hydroxyl hydrocarbons, meibum from normal donors and donors with dry eye with and without added phospholipids and phospholipids. The Revap for longer chain 1-hydroxyl hydrocarbons was significantly higher compared with shorter chain 1-hydroxyl hydrocarbons. However, the differences were minor, \u3c 1%. The Revap of tears and PBS were not different. None of the combinations of lipids mentioned above altered Revap more than 1%. A 50% reduction in Revap would be expected if lipid films inhibited Revap. Although surface lipids did not attenuate Revap, phospholipids appeared to facilitate the spreading of meibum. All of the lipid systems studied completely covered the aqueous surface. Meibum from patients with dry eye on the surface aggregated into clusters, but when the same meibum samples were applied to a layer of phospholipids, clustering decreased (66 ± 16 %) significantly. In conclusion, it is unlikely that 1-hydroxyl hydrocarbons can be used to inhibit the Revap of reservoirs. Our data do not support the idea that meibum with or without phospholipids inhibit the Revap of the tears. Perhaps stiff ordered lipids cause the surface lipids to aggregate into ‘islands’ that inhibit the spreading of the tear film which may contribute to tear film instability associated with dry eye symptoms

Camel Milk and the Prevention of Glucose Cataract, an Organ Culture Study

Purpose: To test if camel milk affects glucose-induced opacity in organ cultured rat and human lenses.Methods: Whole human and rat lenses were cultured in various media containing either 55 mM glucose, camel milk, or a combination of both glucose and milk. Some lenses were cultured in a media containing neither moiety to establish a control. Absorbance spectra of human and rat lenses were measured daily using a visible/ultraviolet light spectrometer. Lens opacities were graded by a blinded grader from photographs taken daily. Aldose reductase activity, catalase activity, glutathione and receptor for advanced glycation end products levels were assayed.Results: The optical density and light scattering intensity of human lenses cultured with glucose were higher after two to four days in organ culture compared with lenses cultured without glucose. Camel milk in the culture media attenuated the glucose-induced increase in optical density, light scattering intensity and opacity grade after two to four days for both human and rat lenses. Aldose reductase activity, catalase activity and glutathione levels were restored but the receptor for advanced glycation end products was similar in rat lenses cultured with glucose compared with those cultured with glucose and camel milk. There were no differences between the assayed moieties in human lenses cultured with glucose or glucose plus milk. Since camel milk restored rat lens glutathione levels, it is possible that camel milk may protect the lens from oxidation and significantly reduce the glucose-induced increase in light scattering of human lenses. Structurally and physiologically, rat lenses are distinct from human lenses, therefore, the rat lens data was highly variable when compared with the human lens data, highlighting the importance of using human lenses in future studies.Conclusions: Camel milk present in the organ culture medium inhibited the glucose-induced opacity in human lenses and restored the amount of glutathione to the same levels of lenses not cultured in glucose. The positive results of the current study leads to future studies to determine the moieties in camel milk that are responsible for cataract inhibition and in vivo studies involving camel milk

Human Meibum Age, Lipid–Lipid Interactions and Lipid Saturation in Meibum from Infants

Tear stability decreases with increasing age and the same signs of instability are exacerbated with dry eye. Meibum lipid compositional changes with age provide insights into the biomolecules responsible for tear film instability. Meibum was collected from 69 normal donors ranging in age from 0.6 to 68 years of age. Infrared spectroscopy was used to measure meibum lipid phase transition parameters. Nuclear magnetic resonance spectroscopy was used to measure lipid saturation. Increasing human meibum lipid hydrocarbon chain unsaturation with age was related to a decrease in hydrocarbon chain order, cooperativity, and in the phase transition temperature. The change in these parameters was most dramatic between 1 and 20 years of age. Meibum was catalytically saturated to determine the effect of saturation on meibum lipid phase transition parameters. Hydrocarbon chain saturation was directly related to lipid order, phase transition temperature, cooperativity, changes in enthalpy and entropy, and could account for the changes in the lipid phase transition parameters observed with age. Unsaturation could contribute to decreased tear film stability with age

Human Meibum Age, Lipid–Lipid Interactions and Lipid Saturation in Meibum from Infants

Tear stability decreases with increasing age and the same signs of instability are exacerbated with dry eye. Meibum lipid compositional changes with age provide insights into the biomolecules responsible for tear film instability. Meibum was collected from 69 normal donors ranging in age from 0.6 to 68 years of age. Infrared spectroscopy was used to measure meibum lipid phase transition parameters. Nuclear magnetic resonance spectroscopy was used to measure lipid saturation. Increasing human meibum lipid hydrocarbon chain unsaturation with age was related to a decrease in hydrocarbon chain order, cooperativity, and in the phase transition temperature. The change in these parameters was most dramatic between 1 and 20 years of age. Meibum was catalytically saturated to determine the effect of saturation on meibum lipid phase transition parameters. Hydrocarbon chain saturation was directly related to lipid order, phase transition temperature, cooperativity, changes in enthalpy and entropy, and could account for the changes in the lipid phase transition parameters observed with age. Unsaturation could contribute to decreased tear film stability with age