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T. O. Salmon, S. Yamada; Objective Evaluation of Surface Drying/Wetting in Two Daily-Disposable Contact Lenses Using Aberrometry. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5650.
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Contact lens drying is a major cause of discomfort and failure in soft lens wearers. This can be mitigated in daily-wear lenses by adding a wetting agent to the lens packaging solution. Our purpose was to compare surface drying/wetting of two daily disposable lenses, the 1day Biomedics-EV (ocufilcon D, packaged in MPC; CooperVision Japan) and the 1day Acuvue Moist (etafilcon A, packaged in PVP; Vistakon).
Using the COAS aberrometer, we measured changes in higher-order (HO) aberrations that accompanied drying of the lenses on 10 normal eyes. Subjects were fitted with each lens on a different day, and aberrometry was performed with a measurement every second for one minute, with a timed blink every 10 seconds. Measurements were taken at 20 minutes, 1, 3 and 6 hours after insertion. Basic data consisted of Zernike coefficients for each measurement (Zernike orders 3-6; 4.0-mm pupil). To quantify drying we computed the mean change in HO RMS between blinks as well as fluctuation (FI) and stability indices (SI) following the methods of Koh (Invest Ophthalmol Vis Sci 47:3318-3324, 2006).
Mean results averaged across eyes showed that HO RMS was smallest at the start of each measurement and gradually increased between blinks, presumably due to drying. Each blink caused a partial, but incomplete recovery. The effect was similar for all wearing times. On average, within each intra-blink interval, the change in HO RMS was significantly smaller for the Biomedics lens (p<0.01, Mann-Whitney U test; figure). The mean FI and SI were also significantly smaller (p=0.014 and p<0.0001 respectively; Wilcoxon signed-rank test) for the Biomedics lens.
Aberrometry provides an indirect, object method to measure subtle changes in surface drying of contact lenses on the eye. It indicates a pattern of gradual drying between blinks, with partial recovery following each blink. Our long blink intervals (10 seconds) exposed the lenses to greater drying than would be expected in most natural wearing conditions. Under these conditions the Acuvue Moist showed greater drying than the Biomedics-EV. This may have been due to differences in lens material, the wetting agents used in the packaging solutions or both.
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