Many people suffer from dryness and redness in the eyes while wearing contact lenses. They think, incorrectly, that lenses "with high water content" are the solution to these problems. Water content is the percentage of water absorbed by the lens in its entire volume. According to USFDA's (United States Food and Drug Administration) classification, high water content means an object contains more than 50% water, low water content means it has less than 50% water. The higher the water content, the more water the lenses need under normal circumstances, and lenses will have to absorb more tears in order to maintain their shape and water content.
Contact lenses made with hydrogel transport oxygen mainly by water; therefore, high water content lenses have higher oxygen transmissibility. High water content lenses are softer and more comfortable to wear, so the irritation in the eyes is rather lessened. However, when the water contained in the lens vaporizes, the lens will have to absorb more tears from our eyes like a sponge in order to make up its water content, subsequently making our eyes dry.