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M. Rolando, A. Mastromarino, S. Barabino, G. Calabria; The Dynamic Lipid Interference Pattern (DLIP) Test in Normal and Dry Eyes . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4422.
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Purpose: The lipid layer of the tear film in normal conditions shows on its surface a number of interference fringes visible under broad band illumination. Recent studies have shown that the normal lipid layer exhibits the ability to maintain the same interference fringe pattern distribution among several blinks. The aim of this study is to evaluate the possibility of quantifying the consistency of the tear lipid interference pattern among blinks in normal subjects and in those with dysfunctional tear syndrome (DTS). Methods: Twenty normal eyes and twenty eyes with DTS were evaluated by means of the Dynamic Lipid Interference Pattern (DLIP) Test. The DLIP test measures the possibility to create a visible stable pattern of interference fringes under standardized conditions and measures the number of blinks during which the precorneal tear film lipid layer maintains such interference pattern following the pre–test blinking sequence. In particular the test includes: 1) Pre test lipid load: 5 forced blinks + 10 consecutive non–forced blinks at approximately 2 second frequency are performed in order to load lipids from palpebral reservoir into the tear film. 2) Observation under white broads band light illumination of definite reproducible intensity at the bio–microscope according to the following steps: a) Recognition and definition of a fringe pattern b) Free non forced blinking c) Recognition of the previously identified interference fringe pattern after each blink d) Blink count e) Recognition of the break–up of the interference fringe pattern. 3) The results are expressed as the number of blinks preceeding the inability to further recognise the identified interference pattern The difference between the results obtained from normal and DTS eyes were compared and the differences were statistically evaluated by means of Student t–test. Results: –In normal eyes the interference fringes assumed definite recognizable patterns which were maintained during several (average 21±12) non – forced blinks. – DTS eyes showed the inability to maintain a stable visible pattern of interference fringes for more than 2.3±1.5 successive non – forced blinks. A statistically significant (p<0.0001) difference was observed between normal eyes and those with DTS. Conclusions: Qualitative and/or quantitative changes of the tear lipid layer as well as the available amount of aqueous tear fluid can directly and indirectly be involved in the maintenance of stable interference patterns during the DLIP test. This test can be used to identify lipid layer changes associated with dry eye both for clinical and research purposes.
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