Contact Lenses and the Cornea

Soft contact lenses sit on the front surface of your eye called the cornea. More specifically soft contact lenses sit on the thin tear film that coats the cornea. Contact lenses can correct your vision very similarly to how glasses correct your vision. Contact lenses can be a great alternative to glasses but like everything, contact lenses need to be used and cared for properly or they can potentially cause harm. When you look at your eyes in the mirror you can see your eye color. Each person’s eye color is slightly different. Your eye color is dependent on the amount of melanin in your iris. The clear tissue that covers your pupil and iris is called the cornea. The cornea is where you will find your tear film and where you place your contact lens when wearing them. Our cornea is avascular by design. Avascular (no vessels) means no blood vessels. This is how our cornea is able to allow light to pass through it and enter our eyes uninterrupted. You can imagine if the cornea was filled with blood vessels how difficult it would be to see through all of those vessels.  Like all the tissue in our body, the cornea needs oxygen to run aerobically. Typically oxygen is transported through your body via the blood vessels. So the next question you may be asking yourself is, “If there are no blood vessels bringing oxygen to the cornea, but the cornea needs oxygen to run, where does the oxygen come from?” The answer to this is the oxygen comes from the atmosphere, it diffuses into the tear film and then into the cornea.  Now you can probably imagine having a contact lens sitting over your cornea would create a barrier that blocks the oxygen from diffusing into the tears, and to a certain extent, you are correct. Although this is true, contact lenses are specifically created to allow oxygen to diffuse through them. Each contact lens brand, type, the modality has different abilities to allow oxygen to diffuse. Some are very good, some are not so good. It’s your doctor’s job to select the lens that is the most appropriate for your specific needs. If patients wear their contact lenses longer than recommended or sleep in their contact lenses, the cornea will become slightly hypoxic (oxygen deficient). If this happens on a long-term basis, the vessels we see over the whites of our eyes will start to grow radially towards the cornea searching for oxygen. Eventually, these vessels will pierce the cornea and grow into it. This is not good and can lead to many problems, as minor as impeded vision, to the most severe being the need for a corneal transplant. Good contact lens habits are a must, and balancing your glasses and contacts to allow your cornea to get fresh unimpeded oxygen is significant for a long healthy corneal life.