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EVOLUTION OF SOFT CONTACT LENS MATERIALS
Currently there are two main categories of soft contact lens materials available in the market namely hydrogels and silicone hydrogels. This article provides a summary of the pros and cons of these materials and suggests a new type of material that could be a new direction for material development moving forward. Hydrogel lenses are biocompatible, hydrophilic, comfortable to wear, and have excellent optical properties. However, the oxygen transmissibility (Dk/t) of hydrogel lenses is limited by its water content and the lens thickness. A higher percentage of water will provide greater oxygen transmissibility but high water content materials are also more prone to dehydration. Silicone hydrogels (Si-hys) were first introduced in 1999. Silicone was added to hydrogel to increase the oxygen permeability and eye care professionals had hoped that this material can resolve most of the issues related to contact lens wear. Si-hys have offered multiple times increase in Dk/t over hydrogels, but they have not reduced the incidence of microbial keratitis nor contact lens drop-out rate. In addition, si-hys are not perfect for every patient, they are generally stiffer (with higher modulus) and are more likely to induce ocular complications due to its mechanical properties. Si-hy lenses are also associated with lens surface issues and an increased risk of infiltrative events. The addition of silicone does not seem to be without problems. Si-hy is an important step, but not a big leap and definitely not the only choice for our patients. A new material called Hypergel was developed using the concept of bio-inspiration. Scientists have learnt from the eye and applied three bio-inspired features to make the material works like the eye. Firstly, hypergel has 78% of water content and that matches the water content of the cornea. Secondly, it meets the oxygen level the open eye needs to maintain healthy white eyes. Thirdly, it mimics the lipid layer of the tear film to prevent dehydration. Without the addition of silicone, this material can meet the oxygen need of the open eye and can resist dehydration.
