Some contact lenses are to be changed daily. Others last for 2 weeks. Some last for a month. Why are they all different, and is it important to change them regularly?
Contacts sit on the eyes’ corneas. Light is able to pass through our corneas because they’re clear and don’t contain blood vessels. Consequently, oxygen, water, and other nutrients must be supplied to the cornea via the air, tears, and eyelids. When ANY contact lens is on the eye, the cornea receives dramatically lower amounts of these elements. As you can imagine, this opens the door to a lot of potential issues. Therefore it’s critical that patients and their eye doctors carefully manage the use of contact lenses.
Every type of contact lens differs in it’s physical and chemical properties. The amounts of water and oxygen that permeate through them hinge on the fit, material, prescription, and wearing schedule of the contact lens. The first three are largely concerns of one’s eye doctor. How the contacts should be worn is determined by the doctor, but the responsibility to follow said schedule is up to the patient.
I’ll illustrate by using CooperVision’s Biofinty contact lenses as an example. This lens is approved for 30 days of wear. To arrive at that number, CooperVision worked with many doctors, researchers, and the FDA to determine how long these lenses may be worn safely. Like all contacts, they permit less oxygen to reach the eye as compared to not wearing contacts at all. Experts have found that this is largely not a problem as long as the lenses are worn for 30 days or less and the patient regularly sees her optometrist. After 30 days of wear the story takes a turn for the worse. The amount of oxygen that reaches the eye is lower than professionally determined critical thresholds. This opens the floodgates for a lot of potential complications.
On the low end, wearing a contact lens for too long may cause the eyes to become slightly red. On some patients this can stay at a cosmetic level. However, frequently it’s the first warning sign of serious impending problems. With the eyes defenses reduced, bacterial and/or viral infections are much more likely to occur. It’s somewhat common for the cornea to respond to low oxygen levels by developing “subepithelial infiltrates.” These are inflammatory cells that arrive on the scene when the cornea is threatened. They interrupt a dense network of nerves in the front of the eye and are very painful. In some cases of contact lens overwear, the iris may become severely inflamed. This is a highly uncomfortable condition called iritis or anterior uveitis. The treatment for this condition is weeks of steroid drops and dilated eyes – not anyone’s idea of a good time. If left unchecked, a reduced oxygen level can even lead to ulceration of eye tissue.
The good news about all of these problems is that they are largely avoidable. By wearing your contacts lenses for the prescribed schedule, the risk of all these issues is quite low. Beyond simply wearing your contacts properly, it’s important to have them evaluated at least once a year by your optometrist. It’s his job to ensure that your eyes aren’t showing any signs of being “angry” with the lenses. It’s far better to stay on top of any complications than allowing them to run free.
Feel free to send an email if you have any questions or concerns.
Spencer Ritenour, O.D.
Do you love your contacts? Most people do, but Americans are increasingly going gaga over a new cosmetic variety known as circle contact lenses. These are special colored contact lenses that give the illusion of having large “doe eyes.” Despite their innocent appearance, this type of lens can be highly unsafe for one’s eyes. They cause a dangerously low amount of oxygen to reach the surface of the eye which can lead to painful infections, ulcers, or worse. In some cases they can even lead to a permanent reduction in vision. In fact, they are illegal in the United States, but their popularity is increasing.
It’s important to remember that all contact lenses are medical devices and must be prescribed by your eye doctor. Always be sure to follow the proper cleaning and replacement instructions and have your doctor check them annually. If you’re interested in trying contacts for the first time stop by the office, and I’d be happy to fit some on your eyes!