Blood Vessel Growth

Abnormal growth of blood vessels in the cornea, especially at the edges of the cornea (corneal neovascularization) is often due to corneal hypoxia (lack of oxygen). It is a common sign associated with over wear of soft contact lenses. The cornea, which normally has no blood vessels, derives its oxygen primarily from air and minimally from the bloodstream. Contact lenses reduce the cornea’s ability to derive oxygen. The cornea responds to chronic oxygen deprivation (which can occur during extensive contact lens wear) by growing new, abnormal blood vessels. Sometimes by changing the type of contact lens material or your wearing schedule the new blood vessel growth can be reversed. In some cases you may simply need to stop wearing your lenses completely. Excessive neovascularization can lead to corneal breakdown, tissue loss, and ultimately infection.

Contact lenses are designed to allow an adequate amount of oxygen through the lens. This only works if they are worn properly and evaluated on a regular basis. Many patients try to extend the life of their lenses by wearing a monthly disposable lens for five to six weeks instead of four. Another example would be sleeping in a lens prescribed for daily wear. This cuts the life of the lens in half. At the end of the life of the lens, oxygen does not permeate the lens. This initiates the body to respond to oxygen deprivation by growing new blood vessels into the cornea. This process progresses however does not cause pain or discomfort until basically, it’s too late. At this stage rapid changes can occur over night or over a matter of days. Corneal edema occurs, the superficial tissue sloughs off and bacteria on your lids and contact lens invade the cornea. Ulcers can form and permanent vision loss may occur. In some cases lenses must be discontinued permanently or for several weeks to months to give the cornea time to return to normal. In many cases permanent scarring can lead to vision loss and the inability to wear contact lenses. Patients who wear their contacts like they are advised seldom have these problems. Those who don’t, on the other hand frequently do.

Contact lens technology has significantly improved over the last two decades and impressively in the last 3-4 years. The improvements have been geared toward higher oxygen permeability to allow for improved corneal health, less complications, and improved comfort. The materials being used to accomplish these improvements are called silicone hydrogels. Silicone hydrogels provide a great deal more oxygen vs. previous contact lens materials. Some silicone hydrogels are designed to be worn for 30 days without removal while others are two or four week disposables worn on a daily basis. Silicone hydrogels are now available in both spherical correction and for astigmatism.

Corneal Infections

The development of a corneal ulcer (an infection of the cornea) as mentioned above can be a complication of contact lens wear. A corneal infection is a localized corneal excavation due to hypoxia and then subsequent epithelial disruption. Although there is a higher incidence of corneal infections associated with soft contact lens wear vs. rigid gas permeable lens wear, all lenses have some risk. A corneal ulcer starts when a bacteria infects an area of breakdown in the corneal surface. Normally, a corneal abrasion, even if tiny, is uncomfortable. However, a contact lens can act as a bandage on the eye and mask symptoms such as pain or foreign body sensation. Some contact lens wearers, especially those who abuse their wearing schedules, develop a lack of sensitivity of the cornea. Therefore, they don’t recognize that there is a problem until it is too late.

Eventually the corneal infection reaches a threshold resulting in acute pain that is felt in conjunction with a foreign body sensation, and the eye typically becomes red and light sensitive. Vision loss is not uncommon. Even with successful treatment, a corneal ulcer may still leave a scar that may affect vision or the ability to resume successful contact lens wear.

If you are interested in learning more about silicone hydrogels or anything with respect to contact lenses please contact one of our offices in Stillwater @ 405-372-1715 or Pawnee @918-762-2573. We also invite you to visit the contact lens section on our website @www.cockrelleyecare.com.