Elastofilcon A silcone rubber contact lenses induce less corneal swelling than no lens wear during sleep, and increasing the central thickness and volume of the lens does not influence its overnight performance. We sought to elucidate whether a silicone rubber lens can promote the distribution of atmospheric O2 on the cornea through a small interpalpebral opening under closed-eye conditions. Three groups of rabbit eyes comprised 12 eyes wearing Silflex (Dk 79.8 barrer) lenses, 12 with elastofilcon A (Dk 340 barrer) lenses, and 12 without lenses. All eyes were surgically closed overnight; six eyes in each group had a complete lid closure and six eyes had a partial tarsorrhaphy that left a small, central gap approximately 3 mm in length. When the lids were opened the next morning, the partially closed elastofilcon A eyes showed less corneal swelling (6.2 +/- 1.4%) than the partially closed no-lens eyes did (9.6 +/- 1.3%) (p less than 0.01), whereas the partially closed Silflex eyes were significantly more swollen (12.8 +/- 2.1%) (p = 0.01) than the other two partially closed groups were. The completely closed eyes showed no significant difference in corneal swelling among the groups. These results indicate that small lid gaps during sleep may lead to less corneal swelling when elastofilcon A lenses are used than with no lenses.