Lipid deposition on contact lenses in symptomatic and asymptomatic contact lens wearers

Cholesterol is an essential component for neuronal physiology not only during development stage but also in the adult life. Cholesterol metabolism in brain is independent from that in peripheral tissues due to blood-brain barrier. The content of cholesterol in brain must be accurately maintained in order to keep brain function well. Defects in brain cholesterol metabolism has been shown to be implicated in neurodegenerative diseases, such as Alzheimer’s disease (AD), Huntington’s disease (HD), Parkinson’s disease (PD), and some cognitive deficits typical of the old age. The brain contains large amount of cholesterol, but the cholesterol metabolism and its complex homeostasis regulation are currently poorly understood. This review will seek to integrate current knowledge about the brain cholesterol metabolism with molecular mechanisms.

To examine tear film, contact lens, medical, and patient-related factors associated with self-reported contact lens-related dry eye. Four hundred fifteen contact lens wearers were recruited and enrolled in this phase of a larger cross-sectional study. A variety of tear film (e.g., interferometry, osmolality, phenol red thread, meibography, fluorescein, and lissamine green staining), contact lens (i.e., water content, refractive index, material), and patient-related (e.g., gender, sociodemographic, education, income, and medical health) factors were examined in relation to dry eye status. Univariate and multivariate logistic regression models were used to examine the relation between these tear film, contact lens, and patient-related factors associated with dry eye status. Of the 415 enrolled, the data from 360 were used in the analyses. The average age was 31.1 +/- 11.5 years, 245 (68%) participants were female, and 55.3% were classified as having-contact lens-related dry eye via self-report. Overall, 327 (90.8%) were hydrogel lens wearers and 33 (9.2%) were gas-permeable lens wearers. Several factors were shown to be related to dry eye status in multivariate modeling, including female gender (P = 0.007), lenses with higher nominal water content (P = 0.002), rapid prelens tear film thinning time (P = 0.008), frequent usage of over-the-counter pain medication (P = 0.02), limbal injection (P = 0.03), and increased tear film osmolality (P = 0.05). Contact lens-related dry eye may be explained mechanistically by increased tear film thinning times (evaporation or dewetting) resulting in increased tear film osmolality. Other contributing factors include the use of high-water-content lenses, which have traditionally been reported to be associated with less patient comfort than lower-water-content lenses, potentially due to spoilation and deposition. As found in other studies of dry eye, women are more likely to report contact lens-related dry eye than are men.

Human meibomian gland secretions (MGS, or meibum) are formed from a complex mixture of lipids of different classes such as wax esters, cholesteryl esters, (O-acyl)-ω-hydroxy fatty acids (OAHFA) and their esters, acylglycerols, diacylated diols, free fatty acids, cholesterol, and a smaller amount of other polar and nonpolar lipids, whose chemical nature and the very presence in MGS have been a matter of intense debates. The purpose of this review is to discuss recent results that were obtained using different experimental techniques, estimate limitations of their usability, and discuss their biochemical, biophysical, and physiological implications. To create a lipid map of MGS and tears, the results obtained in the author's laboratory were integrated with available information on chemical composition of MGS and tears. The most informative approaches that are available today to researchers, such as HPLC-MS, GC-MS, and proton NMR, are discussed in details. A map of the meibomian lipidome (as it is seen in reverse phase liquid chromatography/mass spectrometry experiments) is presented. Directions of future efforts in the area are outlined.