The pH-induced Change in Oxygen Transmissibility of Clear and Circle Soft Contact Lenses

Purpose: This study aimed to analyze the change in oxygen transmissibility of soft contact lenses made of the same material based on pigmentation and material characteristics. Methods: Oxygen permeability in central and peripheral areas of clear and circle lenses made of nelfilcon A, hilafilcon B, and etafilcon A was measured by the polarographic method after incubation in phosphate buffer solutions with pHs of 6.6, 7.4, and 7.8, respectively, for 24 hours. Oxygen transmissibility was calculated after measuring the thickness of the central and peripheral areas of the soft lenses. Results: The oxygen transmissibility of the clear central area without pigmentation showed an increasing tendency with increasing pH, except in the nelfilcon A circle lens. On the other hand, the oxygen transmissibility of the peripheral area, which differs in pigmentation, showed an increasing tendency with increasing pH, except in the nelfilcon A clear lens. In addition, the degree of change in the oxygen transmissibility of the soft lenses made of the same material was greater in the central area of the clear lenses than in the circle lenses. For the peripheral area, the degree of change was tended to be greater in the circle lenses than in the clear lenses. Conclusions: From these results, it was revealed that the changes in oxygen transmissibility of soft lenses induced by pH changes depended on the pigmentation and the lens location. The change in oxygen transmissibility of circle lenses appeared to be primarily affected by oxygen permeability or lens thickness. Therefore, pH changes can result in changes of comfort and vision correction or the occurrence of complications in clinical trials, depending on the materials and pigmentation of soft lenses.