Determination of oxygen tension on rabbit corneas under contact lenses

Purpose: To determine oxygen tension (PO 2 ) on rabbit corneas beneath rigid gas permeable (RGP), hydrogel, and silicone elastomer lenses under open- and closed-eye conditions and to demonstrate the relationship between PO 2 and overnight corneal swelling response in the rabbit model. Methods: An improved PO 2 monitoring system (PO-2080) with a platinum-micro-wire-electrode was used to measure PO 2 . An ultrasonic pachymeter (DGH-2000) was used to measure corneal thickness after overnight wear. Results: The relationship between PO 2 and oxygen transmissibility (Dk/ L) of the contact lens was linear for Dk/L between 0 and 70 × 10 -9 (cm/ sec)(mLO 2 /mL × mmHg). For Dk/L greater than 70 × 10 -9 , PO 2 gradually reached a plateau at 120 mmHg for open-eye conditions and 20 mmHg for closed-eye conditions. PO 2 was inversely related to the overnight corneal swelling, ranging from 5.1% swelling at PO 2 113.5/17.5 mmHg (openlclosed-eye) for a hyper Dk/L lens (125 × 10 -9 ) to 15.1% swelling at PO 2 10.4/5.1 mmHg for a low Dk/L lens (11.5 × 10 -9 ). Conclusions: Polarographic determination of PO 2 provides reliable information about the amount of oxygen available to the cornea under a lens for both open-eye and closed-eye conditions. The data demonstrate that it is not possible to achieve normal oxygen levels with contact lens wear, even when hyper Dk/L lenses are worn.