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W.W. Harrison, C. Begley, H. Liu, M. Garcia, D. Warren, G. Lowther, G. Wilson, S. Kovacich; The Upper Meniscus and Tear Film Formation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):270.
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The lower tear film meniscus height (LMH) is often used to indirectly measure tear film volume. Upper meniscus height (UMH) is rarely examined. It was the purpose of this study to investigate the role of the upper meniscus in tear film formation and dry eye.
One µl of 2% fluorescein was instilled under the temporal upper lid, near the lacrimal gland, of 10 dry eye and 10 control subjects. Subjects were instructed to partially blink (PB), then keep the eye open, which was then repeated for a full blink (FB). The experiment was repeated three times and the lower and upper menisci were videotaped. Meniscus height was measured from digital videos and image analysis of tear breakup dynamics (TBUD) was used to generate maps quantifying the total area of breakup by the intensity of tear film fluorescence.
Average LMH was 0.29± 0.08mm and UMH was 0.24 ± 0.07mm for dry eye and 0.40± 0.10 mm (LMH) and 0.36 ± 0.07 mm (UMH) for controls. Both menisci were significantly decreased in dry eye compared to controls (p<0.02, t–test). S–TBUD analysis showed that significantly greater areas of breakup, and thus less stability, occurred with FB (12.7%±10.9%) compared to PB (3.7±3.9) in dry eye (p=0.19,paired t–test), whereas there was no significant difference between FB (3.4%±2.1%) and PB (4.2%±4.1%) in controls. Fresh tears moved rapidly into the lower meniscus and slowly across the upper meniscus.
Both menisci are decreased in dry eye, probably reflecting decreased aqueous. During a PB, the upper meniscus alone contributes to "fresh" tears, and is more stable among dry eye subjects than a FB. This may be due to further stretching of the already fragile tear film during a FB in dry eye.
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