| Purpose:
|
| 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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