Soft contact lens wear does not affect corneal biomechanical properties

A study found no alteration in corneal hysteresis and corneal resistance factor from long-term contact lens wear.

FORT LAUDERDALE, Fla., U.S.A. — Use of soft contact lenses for up to 32 years did not have a significant impact on corneal hysteresis and corneal resistance factor, a study found.

“Long-term soft contact lens wear seems not to alter the corneal biomechanical properties,” Anja Kissner, MD, and colleagues said in a poster at the Association for Research in Vision and Ophthalmology meeting.

Dr. Kissner and colleagues conducted a prospective clinical trial of 34 eyes of 17 subjects who wore soft contact lenses daily. The key result from the study, Dr. Kissner said in a subsequent telephone interview with Ocular Surgery News, was that contact lens wear does not cause or enhance corneal ectasia.

“The most important conclusion was that soft contact lens wear seems to have no effect on corneal biomechanical properties. Keratoconus patients often need contact lenses for a better visual acuity. They often need rigid contact lenses. We only investigated the effect of soft contact lenses, but due to the limited gas permeability, the alteration caused by soft contact lenses is presumed to be more severe compared to rigid contact lenses,” Dr. Kissner said. “For that reason, we suppose that wearing rigid contact lenses would also not affect the cornea biomechanical properties in case of keratoconus and would not enhance or increase the ectatic disease.”

While previous studies found that contact lenses have a physical impact on corneal thickness, the results indicate that corneal biomechanical properties were not affected, Dr. Kissner said.

“[Contact lenses] alter the corneal thickness due to edema and swelling of the cornea, but the corneal biomechanical properties, such as corneal hysteresis and the corneal resistance factor, would not be affected,” she said.

Study methods

Eyes in the study were divided into two groups: intermediate contact lens wear and long-term wear. In group 1, 20 eyes had 2 to 5 years of contact lens use; in group 2, 14 eyes had 6 to 32 years of contact lens use. The mean time of contact lens wear was 3.14 years in group 1 and 13.6 years in group 2.

In addition, a control group of 34 eyes of 17 subjects with no history of contact lens use was included.

The study examined corneal hysteresis and corneal resistance factor by Ocular Response Analyzer (Reichert). Central corneal thickness was measured by ultrasound pachymetry. A formula was used to define results, accounting for how Ocular Response Analyzer measurements are dependent on IOP and central corneal thickness, corneal hysteresis and corneal resistance factor, the researchers said.

Results

Dr. Kissner and colleagues found no statistically significant differences between the two contact lens wear groups and the control group for all measurements and results.

According to the formula used for corneal hysteresis, combined results from contact lens patients in both groups measured 10.53 ± 1.35 mm Hg, while the control subjects measured 10.60 ± 1.19 mm Hg, which was not a significant difference. There was also no significant difference in the formula used for corneal resistance factor, with all contact lens patients measuring 11.32 ± 1.75 mm Hg and the control subjects measuring 11.53 ± 1.55 mm Hg.

Central corneal thickness measurements were also not significantly different between all patients and the controls, the study found. – by Erin L. Boyle

• Anja Kissner, MD, can be reached at the Department of Ophthalmology, University of Dresden, Fetscherstr. 74, Dresden, Germany-01307; +49 351 458 3381; e-mail: anja.kissner@uniklinikum-dresden.de.

Dr. Kissner and colleagues conducted a prospective clinical trial to determine if long-term contact lens wear had any adverse effect on corneal biomechanical properties. Specifically, they measured corneal hysteresis and corneal resistance factor with the Ocular Response Analyzer and central corneal thickness.

Corneal hysteresis is an indicator of the viscoelastic or mechanical properties of the cornea. The premise is that corneas that have low corneal hysteresis may be “weak corneas” and are susceptible to corneal diseases or complications. For example, patients with keratoconus and Fuchs’ dystrophy have low corneal hysteresis. Low corneal hysteresis is also found in eyes with glaucoma and in normal-tension glaucoma. In addition, patients who develop ectasia after LASIK are believed to have low corneal hysteresis. The findings from this study would indicate that wearing contact lenses, even for long periods of time, does not affect the biomechanical properties of the cornea. The concept of corneal hysteresis and its relationship to cornea disease is new, and studies investigating this relationship are ongoing.

– Peter C. Donshik, MD
OSN U.S. Edition Contact Lenses Board Member