Measuring oxygen transmissibility in CLS

When it comes to designing and prescribing a contact lens (CL) for patients, one question still remains: how much oxygen is enough? We thought we had solved the riddle when silicone hydrogel (SiH) CLs entered the market in 1999. The rationale behind incorporating silicone into lenses was based on increasing oxygen transmissibility. We had hopes that this new class of lenses would improve the ocular health of patients; however, what we have come to understand is that SiH lenses are not perfect for every patient.

While SiH lenses have essentially eliminated clinical signs of hypoxia such as limbal redness and vascularisation, they have been associated with lens surface issues1 and an increased risk of infiltrative events.2 Because increasing the oxygen transmissibility did not result in the dramatic decrease in all CL-related complications – in particular microbial keratitis – as we had hoped, the debate about oxygen continues. We all agree that oxygen diffusion through the lens material is important, but questions of how much oxygen is needed and how to measure it still persist.