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T.N. Truong, A.D. Graham, J. Kwan, J. Esposito, C. Hsiao, M.C. Lin; Do Soft Lens Fitting Characteristics Predict Post–lens Tear Mixing? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2386.
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Creech and Radke’s dispersive mixing model suggests that vertical and in–and–out lens movement can affect post–lens tear mixing of a soft contact lens. Of which, in–and–out lens movement has more substantial effect on tear mixing compared with vertical movement. In this present study, we examined the relationship between vertical lens movement, along with other soft lens–fitting characteristics, and post–lens tear mixing.
21 subjects were fitted with polymacon lenses of 38% H2O, 9.0 mm OZD, 14.0 mm OAD and 8.7 mm BCR with two different lens designs – spherical and channels on the posterior surface. Lens fitting characteristics (e.g., lens centration, tightness, and movement) were assessed by slit lamp with a graticule. Tear mixing, expressed as the time to deplete 95% of high molecular weight fluorescent dye from the post–lens tear film (T95), was measured with a scanning fluorometer over a 30 minute period while the subject blink rate was maintained at 15 blinks per minute.
The mean + SD of lens fit variables and correlation (r) with T95.
The Pearson correlation ranges from –1 to +1, with 1 reflecting a perfect positive linear relationship. Our observed correlations ranged from –0.154 to +0.282, showing that lens fitting characteristics are only weakly correlated to T95.
There were no significant correlations between lens fitting characteristics and post–lens tear mixing. It is possible that soft lens tear mixing can only be significantly enhanced by different lens designs (e.g., channels or fenestration). Standard clinical manipulation of lens fitting characteristics has a minimum effect on the efficiency of tear mixing of a soft lens without significantly compromising lens wearing comfort.
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