ontact lens that was previously clear could indicate a more serious eye problem, and should be checked by the optometrist. Of course, it is possible that lenses can become switched between the eyes, but usually this is fairly obvious. An older lens can develop deposits and other surface problems, which can make the vision not only blurry, but also can make the lens uncomfortable to wear.Contact Lens AllergyThe fact that a contact lens is constantly touching the eye leads to the possibility of an allergy developing to the lens material, deposits on the lens, or to solutions used with the lens. The conjunctiva is a thin membrane that lines the white surface of the eye and the inside of the eyelids. Soft lenses usually extend somewhat onto the conjunctiva outside of the cornea. The inside of the eyelids is also in contact with lenses especially during blinking. The conjunctiva contains cells that can rapidly respond to allergens, leading to redness, itching, tearing or discharge, and a general inability to wear a contact lens.A common source of allergy is a preservative found in the contact lens solutions. Thimerasol was used frequently as a preservative in the past, but severe allergic problems developed. Now, benzalkonium choride and EDTA are common preservatives found in contact lens solutions. If one develops an allergy or sensitivity to these preservatives, symptoms of allergy (redness, itching, discharge) frequently develop especially when the lens is first inserted, or when rewetting drops containing these preservatives are used. Solutions marked as being for "sensitive eyes" usually contain no less preservatives than other solutions. If a lens solution allergy is suspected, switching to a preservative free lens disinfection system may help.Developing an allergy to protein deposits on lenses is common, and this may lead to a condition called "giant papillary conjunctivitis" (see below). Regular enzyme cleaning may help prevent this ...
