Biomedics XC are not only designed to be extremely comfortable (XC), but also prevent complications which can threaten ocular health. Determining whether a patient is a good candidate for contact lens wear requires a series of tests including a tear breakup timing test.
Sodium fluorescein dye is added to the eye and the corneal tear film is viewed through a slit lamp while the patient avoids blinking. The amount of time it takes tiny dry spots to develop on the tear film will determine whether a person possesses both the quantity and quality of tears to wear contacts.
The longer this process takes, the more stable the corneal tear film. Any time over 10 seconds is thought to be normal, 5 to 10 seconds is marginal, and less than 5 seconds would indicate someone prone to symptoms of dry eye syndrome. An individual may produce the quantity of tears required, but not the quality.
Tears possess lipids and other nutrients to assist in maintaining the healthy balance of the corneal tear film. If the composition of tears is lacking they will either not adhere to the corneal tear film surface or evaporate too quickly resulting in dry eye complications. Biomedics XC are designed to address these problems and prevent the complications associated with dry eye syndrome.
Biomedics XC lenses are comprised of two hydrogel polymers having hydrophilic (water-loving) properties. The base substrate, omafilcon A, is a hydrogel polymer composed of 60% water. A coating of phosphorylcholine molecules are coated to the omafilcon A substrate. Phosphoryl-choline is a polarized charged molecule attracting other molecules, specifically water, to prevent dry eye complications associated with an unstable corneal tear film.
This polymer is used in other medical applications such as heart stents since it has a very low rejection rate and high level of biocompatibility. Maintaining the corneal tear film is important for overall ocular health. If dry eye symptoms are allowed to persist, the cornea will become more prone to allergies, infections and compromised visual acuity. Biomedics XC are designed to combat all of these problems in addition to adding extended comfort, hence the “XC” designation, during the wearing process.
These lenses provide the patient with comfort due to the highly slick phosphorylcholine polymer coating, but in addition they are providing benefits not typically considered by the wearer. Due to the consistency of the lens surface, long protein strands are not allowed to gain a foothold on the surface of the lens. Quite simply, this prevents the buildup of protein molecules known to create defects in the cornea’s surface and in extreme cases warp the cornea to the point of inducing irregular astigmatism.
Due to their high level of biocompatibility, they also prevent a condition known as corneal neovascularization — an autoimmune response initiated by the eye when the cornea is deprived of proper oxygenation and nutrients. This ingrowth of new blood vessels may hinder visual acuity by blocking the visual axis.