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M.C. Lin, G.N. Soliman, V. Lim, C. Marmo, K.A. Polse; Channels Affect Tear Exchange Under Soft Lenses . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3689.
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Introduction: The tear exchange under a soft contact lens is directly related to the amount of lateral and traverse lens motion. [Creech et. al. Indus. Eng. Chem. Res 2001] Hydrodynamic modeling has suggested that channels placed on the back surface of a soft lens reduce fluid resistance and increase transverse lens movement. [Chauhan & Radke Optom. Vis. Sci 2001] This study measured the effect of posterior lens surface micochannels on tear exchange. Methods: Tear exchange was estimated using a fluorophotometer to measure the exponential depletion of high MW fluorescein under the lens and was expressed as the time to deplete 95% of dye (T95). 28 subjects (12 non-Asians; 16 Asians) were randomly assigned 2 pairs of identical Ocufilcon D lenses (-3.00 D, 8.6 mm BCR, 14.2 OAD, 55% H2O, 0.51 MPa) except that the experimental lens (C) had 12 channels placed radially in the mid periphery of the posterior lens surface while the other set of lenses (non-C) without channels served as the control. Subjects rated comfort from 0 to 50 (very comfortable); subjects with comfort <35 were excluded. Results: Mean comfort readings were 46 and 47 for the C and non-C lenses, respectively. Mean ± SE T95 for the C lenses were 28 ± 1.5 min, compared with 31 ± 1.8 min for the non-C lenses (p = 0.052). After stratifying data based on ethnic categories, there was a significant difference (p = 0.020) in tear mixing between the C (26 ± 1.9 min) and non-C lens group (32 ± 2.8 min) for Asians but not for the non-Asian subjects (p = 0.894). Conclusions: Overall, channels provide a modest increase in tear mixing. However, for the Asian eyes, there was a substantial improvement in tear exchange. This result might be explained by the narrow palpebral aperture and greater lid pressure of the Asian eye, which would be expected to result in more transverse movement during the blink, compared to non-Asian eyes.
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