PURPOSE. To examine the hypothesis that the corneal overnight swelling resp
onse (ONSR) is a predictor of ocular complications in contact lens extended
wear (EW).
METHODS. The Berkeley Contact Lens Extended Wear Study (CLEWS) was a random
ized, concurrently controlled clinical trial in which more than 200 subject
s in EW with rigid gas-permeable (RGP) lenses were observed for 1 year. Aft
er adapting to EW, subjects were randomized to either medium or high oxygen
-permeable (Dk) RGP lenses and underwent clinical assessments. keratometry,
and corneal pachometry at 3-month intervals.
RESULTS. The ONSR was directly related to lens Dk (P = 0.01) and exhibited
substantial variability across subjects. The probability of remaining free
of complications over time was not significantly lower for subjects with a
mild ONSR compared with those with greater edema (P = 0.84). The risk of de
velopment of keratopathy was not significantly related to the ONSR (relativ
e risk = 1.00).
CONCLUSIONS. The corneal ONSR is not a good predictor of ocular complicatio
ns in I year of RGP EW. Lenses that cause little or no corneal edema are no
t necessarily safer for overnight wear.