Risk of corneal hypoxia higher with scleral lenses on normal corneas

NEW ORLEANS – While scleral lens fitting on normal corneas is becoming more commonplace, the risk:benefit ratio may be questionable, according to a presenter here at an American Academy of Optometry-sponsored press conference.

Langis Michaud, OD, MSc, FAAO ( Dipl ), FSLS, FBCLA , and colleagues evaluated oxygen under scleral gas-permeable lenses fitted with differing fluid reservoir thicknesses.

“We predicted previously that if a scleral lens is fitting with more than 200 µm to 300 µm of thickness we would introduce oxygen tension,” Michaud said at the press conference.

One eye of eight subjects was fit with a lens that achieved a 200- µm clearance (SL200) as well as a 400- µm (SL400) clearance, according to the study abstract.

Michaud said that the researchers exposed the cornea through goggles with several mixes of gases, and the oxygen level of the corneal surface was measured after 5 minutes.

He reported that fluid thickness trapped under the lens was measured at 240 ±35 µm for the SL200 and 435 ±33 µm for the SL400. He said the mean equivalent oxygen percentage beneath the SL200 was 9.0 ±2.6% and beneath the SL400 was 6.7 ±1.9%.

“If you increase the clearance under the scleral lens, you jeopardize the oxygen level,” Michaud said, and the “measured percent of oxygen is slightly higher than predicted.”

Michaud recommended limiting lens clearance.

“Higher clearance in scleral lenses is associated with chronic edematous response from the central cornea,” he said. “This raises the importance of evaluating the risk:benefit ratio before fitting patients, especially if the cornea is compromised.” – by Nancy Hemphill, ELS, FAAO

Disclosure: No products were mentioned that would require a financial disclosure.