Effect of the osmolarity change in multipurpose solutions induced by an improper contact lens case cleaning procedure

Diurnal variations of tear film osmolarity on the ocular surface

The measurement of tear film osmolarity has been suggested as a gold standard in the diagnosis of dry eye. Many tear film physiological variables oscillate during the day. This review summarises current clinical knowledge regarding diurnal osmolarity variation in the tear film. A critical analysis is presented in respect of of sample size and characteristics, differences in the diurnal osmolarity variation on healthy versus altered tear film conditions or environment, and time of day and number of measurements undertaken. A comparison of 21 studies was made for studies in which one of the main objectives was to analyse the variance of tear film osmolarity at different time-points in a day on human cohorts. Tear film osmolarity appeard to be somewhat influenced by the time of day in healthy subjects and patients with ocular surface disease, or altered by environmental conditions. Both healthy and non-physiological tear film cohorts showed variations in results depending on the study: no variations during the day or statistically different values at some point in the day. These differences could be in the middle of the day or between the beginning and the end of the day, with higher values in the morning than in the afternoon, or even the opposite situation. The possibility of diurnal variations in tear film osmolarity should be considered by the clinician since the time of day when the tear film measurements are made can be critical in making the right diagnosis. Future studies in the diurnal variation field may have to use a well-established range of measurement time-points and a larger group of healthy subjects and and subjects who have a tear film altered by pathological or environmental conditions.

[Potential for use of hydroxypropyl guar in tear substitute therapy]

Of the large number of polymers used in artificial tear formulations, natural polysaccharides - hydroxypropyl guar, sodium hyaluronate, chondroitin sulfate, dextran, etc., are gaining more and more popularity. Hydroxypropyl guar stands out through its ability to form a long-lasting structured matrix adhered to the damaged ocular surface and ensuring good wettability of the latter and regeneration of epithelial cells. At that, the viscosity of hydroxypropyl guar increases with increasing tear pH (which, in turn, correlates with the severity of xerosis) and further prolongs the moisturizing effect. According to experimental studies, the in vitro protective activity of hydroxypropyl guar surpasses that of sodium hyaluronate, which is widely used. Thus, corneal epithelial cell cultures were more tolerant to drying and pericardial leaflets showed lower friction coefficient, if pretreated with hydroxypropyl guar and not hyaluronic acid. Subsequent clinical studies showed that Systane Ultra was more effective in patients with dry eye syndrome than a carboxymethylcellulose and glycerol-containing drug. It has been also proved that Systane Balance provides a greater increase in thickness of the tear film lipid layer and in overall stability of the tear film as compared to SootheXP, which has a similar lipid composition. The present review also covers potential utility of other artificial tear formulations that, besides the moisturizing effect, are able to reduce the tear film osmolarity, prevent further oxidative stress, and abate the inflammatory process.