The cornea is the thin, clear watch glass like tissue on the front of the eye. It vaults over the iris, the colored tissue inside your eye. The cornea has very high needs for oxygen. Since it has no blood vessels supplying it, oxygen diffuses in from the air through the tear film and is supplied at the edge by blood vessels that normally end at its margin. Contact lenses act as a barrier to the flow of oxygen.
While normal contact lens wear supplies enough oxygen to keep this tissue healthy, there are a few exceptions. Lenses that become coated with tear proteins and oils do not allow adequate air to pass through. All lenses become significantly coated within several months, often sooner. Regular lens replacement is vital for long-term contact lens success. Sleeping in lenses adds the eyelid as another barrier to air flow in conjunction with the contact lens. In the majority of contact lens materials this is inadequate for normal corneal health.
The cornea normally swells 3-4% overnight just from your eyelid blocking air transmission. With the exception of the silicone hydrogel contact lenses, most lenses will increase this swelling to 7-8%. At 7-8% swelling the tissue is metabolically unable to compensate in a large number of patients. The new generation of super permeable contact lenses supply enough oxygen permeability that the increase in swelling compared to not wearing a contact lens in insignificant. The response of the cornea to inadequate oxygen is to allow the growth of new blood vessels into the tissue starting from the margins progressing inward. This is an effort to have another supply of oxygen to keep the cornea alive. Neovascularization (new vessel growth) is the name applied to this phenomenon whether it occurs in the cornea or anyplace else in the body. Neovascularization occurs inside the eye on the retina as a complication of long-term diabetes.
A small amount of neovascularization in the cornea is tolerable as long as the problem is addressed, and it is not observed to be progressing. A large amount can allow more rapid infections of the cornea and in some cases cause permanent clouding of the tissue and loss of sight. A number of treatment options are available today. You can discontinue overnight wear if you have been sleeping in your lenses. This may be enough to stop progression but not always. Sometimes changing to a daily disposable soft contact lens will halt progression. With the advent of super permeable soft contact lens materials this option is now a second tier choice in our office. Switch to a super permeable material if it is available for your prescription- these materials are made by blending the traditional soft hydrogel material with silicone. Because silicone is hydrophobic (water hating) it does not wet well. Contact Lens manufacturers have developed different types of plasma treatments for soft contact lenses and altered the polymer structures to overcome this problem. The result is a new generation of soft contact lenses that wet even better that the previous generation and most have much higher resistance to deposits.
The oxygen transmission will typically be increased by 400% to 600% compared to the contact lenses you have worn in the past. All soft contact lenses develop deposits and with time this coating becomes significant enough to reduce the oxygen permeability below safe levels for corneal metabolism. Changing lenses on the schedule you Eye Doctor recommends is vital, even in the new generation of soft contact lenses if you want to avoid progression of neovascularization. I have not seen a single case of soft contact lens induced corneal neovascularization progress with silicone hydrogel lenses that have been replaced as directed. This is a remarkable phenomenon and leap in contact lens material technology. See your Optometrist to monitor for any changes of the neovascularization with regular eye exam visits. Rigid gas permeable lenses now come in super oxygen permeable materials also.
If you can comfortably wear a rigid gas permeable lens, a well fitting design may prevent progression. Optometrists now have the option of plasma treatment of rigid gas permeable contact lenses, which markedly helps comfort. With the advent of the silicone hydrogel super permeable soft contact lenses there is no reason for neovascularization to be an issue for future eye patients. Ask your Eye Doctor about these contact lens materials. There are a growing number of vision correction options including the Bausch & Lomb Purevision soft contact lenses that now come in eye prescriptions that correct for astigmatism (toric) and Presbyopia (bifocal). Update to today’s contact lens technology to let your cornea breathe better and breathe a sigh of relief for your future eye health