| Purpose:
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| High Dk silicone hydrogel lenses that meet the Holden/Mertz criteria for the oxygen requirements of the cornea to avoid overnight edema were studied. The long-term results of two markers of hypoxic stress, microcysts and limbal hyperemia, were monitored in prospective continuous wear clinical trials for up to 3 years. Results for conventional low Dk lenses worn on a 6N extended wear schedule are presented for comparative purposes. |
| Method: |
| 38 patients were fitted with high Dk silicone hydrogel lenses (30N EW basis with monthly replacement) and monitored for a minimum of 2 years. In addition, 83 patients were monitored for 12 months whilst wearing conventional low Dk disposable lenses on a 6N EW and weekly replacement schedule. The patients were monitored every 3 months. The numbers of microcysts and level of limbal hyperemia (graded 0-4 scale) were recorded at each visit. A repeated measures ANOVA was used to test for changes with time and a multiple comparisons Bonferroni test was conducted to examine differences between specific visits. Differences between the groups were assessed using Fishers Exact test. |
| Results: |
| The results across time with the high Dk group indicated that there were no significants increases observed for either microcysts or limbal hyperemia. In contrast, there was a significant increase in time for both microcysts (p<0.05) and limbal hyperemia (p<0.01) for the low Dk group. Significantly higher numbers of microcysts (p<0.05) and levels of limbal hyperemia (p<0.01) observed with low Dk DSCL group compared with the high Dk group across the 12 months. |
| Conclusions: |
| The oxygen transmissibility provided by the high Dk silicone hydrogel lenses alleviates the hypoxic stress normally associated with extended wear of contact lenses. No long-term effects are evident in terms of hypoxic stress in the 3 year follow up period of this study.
This research was supported in part by the Australian Federal Government through the Cooperative Research Centres Program, Ciba Vision, and Bausch and Lomb. |
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