Purpose: This study was conducted to measure the corneal thickness changes associated with wearing 30-day tisilfocon A (Dk = 163) and 6-day etafilcon A (Dk = 28) contact lenses. The probable cause of the outcomes is discussed.
Methods: Thirty subjects were fitted with Menicon Z rigid gas-permeable (RGP) contact lenses and a control group (n = 30) was fitted with ACUVUE hydrogel lenses, at two study sites. After a 2-week period of daily wear, subjects began prolonged wear. Measurements were performed at the dispensing visit, and then at the 2-week daily wear, the 1-week, 6-month, and 12-month extended- and continuous-wear visits.
Results: Repeated measures analysis of covariance was performed on mean corneal thickness. There was a significant increase in corneal thickness in the hydrogel lens extended-wear group compared to the RGP group (P = 0.03). The mean corneal thickness in the ACUVUE group was 2.58% higher at the 2-week daily wear visit, 2.38% higher at the 1-week extended-wear visit, 2.96% higher at the 6-month, and 2.97% higher at the 1-year visit compared to the RGP continuous-wear patients.
Discussion: Patients wearing high-Dk RGP contact lenses for continuous wear may have thinner corneas (within the normal thickness range) probably because of minimal hypoxia-induced corneal stromal swelling; RGP-induced reversible corneal epithelial compression; deceased epithelial sloughing; or long-term contact lens-induced keratocyte apoptosis. Patients wearing hydrogel contact lenses for extended wear may have thicker corneas because of hypoxia-induced corneal stromal swelling. Additional evidence of corneal hypoxic stress is seen in the higher prevalence of striae and epithelial microcysts in the hydrogel group and greater variability of corneal thickness measurements in the soft contact lens group in our results.