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E.I. Pearce, S.L. Burns, S.J. Fergus, G. Walsh; Effect of Spectacle (eyeglass) Design on Ocular Humidity Levels . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2460.
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Purpose: Increased periocular humidity has been shown to reduce symptomology in dry eye sufferers. This study investigates the role of frame design and fit on periocular humidity levels. Methods: Three frame designs were studied, a small metal frame (48mm x 25mm), a large metal frame (53mm x 38mm) and a close fitting ‘wrap-around' plastic frame (61mm x 38 mm). An SHMP-2 micro-evaporimeter was used to measure the humidity level in the space between the spectacle lens and the eye, and also on the external face of the spectacle lens for each of the three frame styles. Relative humidity and temperature was measured for 5 minutes with each frame. The order of testing the frames was randomised using a latin square. Humidity levels when wearing the spectacles were measured in 40 subjects (14 males and 26 females, mean age 27.4 ± 10.6 years) who were asymtomatic for dry eye. Data were converted from relative humidity to absolute humidity to compensate for temperature fluctuations during the course of the experiment, and from day to day. The effect of the spectacle wear on humidity was calculated by subtracting the absolute humidity outside the frame from that observed in the periocular space. Back vertex distance (BVD) was measured using an optical rule. Results: The changes in humidity for the three frames were as follows, small frame 0.96 ± 0.95 g m-3, large frame 0.93 ± 1.19 g m-3 and wrap-around frame 3.33 ± 2.95 g m-3. The data were not normally distributed (p>0.05, Kolmogorov-Smirnov) so non-parametric tests were used. Paired comparisons showed that humidity was significantly higher with the wrap-around compared to both the small and the large frame (p=0.000, Wilcoxon signed ranks test). No significant difference was found between the large and the small frame (p=0.253). A Spearmans rho test was used to test the relationship between BVD and change in humidity for the small and the large frame. Significant negative correlations were found for the small frame (rho = -0.418, p=0.024), and the large frame (rho = -0.466, p=0.011). That is, as BVD was reduced the humidity observed went up. Conclusions: Frame design does have a significant effect on periocular humidity. The biggest improvement was observed with the wrap-around frame. This indicates that these frames should be used for dry-eye patients to increase humidity and alleviate symptoms. If this is cosmetically unacceptable then frames should be fitted with the minimum BVD to bring about the maximum increase in periocular humidity. From this data it can also be predicted that using lenses of curved form or simply bowing the front of the frame may be of benefit.
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