Comparison of Oxygen Flux in Hydrogel and Silicone Hydrogel Contact Lenses
Cohan, Jonathan; Cho, Eun Ae; Connors, Megan
The prevalence of contact lens use has been continuously growing for their convenience and for cosmetic reasons. Although contact lenses do offer many advantages over glasses, the major concern for many contact lens users is dryness that results from a lack of oxygen that goes through the contact lens to meet the demand of eye tissue. A new type of contact lens, made out of silicone hydrogel, has been introduced in the market which has garnered much attention from many contact users. The silicone hydrogel is different from the traditional hydrogel contact lens since oxygen is permeable through silicone, which was not possible through hydrogels. The hydrogel contact lenses must have high water content for oxygen delivery, silicone hydrogel contacts depends on their high oxygen diffusivity while having low water content. Night and day contact lenses are made out of silicone hydrogel whereas traditional ones for day use are often made out of hydrogel. A model was developed to validate the advantage of wearing silicone hydrogel contact lenses in both day and night conditions. By analyzing the center area of the eye around the pupil as a thin slab, the performance of these two types of contact lenses were compared by computing average oxygen concentrations in the stroma, which is the largest layer of cornea. Using COMSOL Multiphysics, the simplified geometry that included the layers of contact lens, tear, endothelium, and stroma was used as our model to find the oxygen concentration after eight hours of use either with eyes open or closed. The thickness of 80/mu m was used for both hydrogel and silicone hydrogel, the average oxygen concentration was found to be 9.100219x10-8mol/cm3 and 4.198608x10-8 mol/cm3 respectively for day setting with eyes open for eight hours and 3.536442x10-8 mol/cm3 and 2.119774x10-8 mol/cm3 respectively for night setting with eyes closed. Variations of other parameters in modeling also showed the same trend that silicone hydrogel contact lenses ended up with less oxygen in the cornea than hydrogel. Thus, the modeling showed how the silicone hydrogel did not offer any increase in oxygen delivery in both day and night settings.
Silicone Hydrogel Contact Lenses; Oxygen Permeability