In order to see the difference in oxygen permeability and corneal edema caused by the proportion of contact lens material, a lens of PHEMA in group 1, a daily wearable lens of silicone hydrogel in group 2, and a disposable lens of silicone hydrogel with different portion, were used for 8 hours, and the thickness of cornea were measured respectively. And the physical feature of the 3 lenses was examined by the method in the ISO 18369-4:2006 regulation.
The corneal edema was identified with the scheimpflug camera by measuring the thickness of core cornea. The pre-measurement was implemented between 6 and 9 p.m. one day before wearing the lens. Following the measurement, the double blind disposed lens was randomly selected and provided for the users to wear next day. Wearing lens was allowed to wear at least 2 hour lapse after sleeping to exclude the effects of corneal edema while sleeping, and the use of glasses was recommended until it is worn. The post-measurement was conducted during the 8 hours of its wearing.
The oxygen permeability of the lens was measured; 8.02×10?9(cm×mlO2)/(sec×ml×mmHg), 6.27×10?9(cm×mlO2)/(sec×ml×mmHg), and 81.38×10?9(cm×mlO2)/(sec×ml×mmHg) in group 1, group 2, and group 3, respectively. After measurement, the edema was observed in the core of cornea in each group; 23.61±10.71㎛ in group 1, 18.25±8.64㎛ in group 2, 2.36±6.15㎛ in group 3, respectively. The analysis using Wilcoxon signed rank test showed that the statistically significant difference edema was gained in group 1 and group 2 but it wasn’t occurred in group 3 in the thickness of the edema when it was compared with that of pre-measurement (p=0.075). Additionally, in the ANOVA analysis of the difference observed in its thickness after wearing 3 lenses, the likelihood of statistically significance was lower than 0.001. And the edema was individually compared one another among 3 groups in the order of group 1 and group 2, group 1 and group 3, group 2 and group 3. While the size of edema was similar due to the use of the lenses between group1 and group 2, the edema created after using the lenses in group 2 and group 3 was quite different.
By the proportion of its materials, the permeability of oxygen was different in the silicone hydrogel lens. And the degree of the corneal edema created by the lens after its 8-hour recommended use was also not similar. Therefore, it is suggested that the special care in deciding the recommended use hour in accordance with the portion of material is needed even in wearing the silicone hydrogel lens.