Giant Papillary Conjunctivitis
Approximately 1-3% of contact lens wearers develop GCP, consisting of conjunctival infection, mucous discharge, itching, tear film debris, coated lenses, blurred vision, excess lens movement, and blurred vision. These symptoms may remain minimal or progress to complete lens intolerance. The linings of the upper eyelids are most affected.

GPC begins with the formation of deposits on the surface of the lens. The constant trauma of the blinking lid rubbing on the surface of the lens exposes the deposits to the conjunctival lymphatic system. The antigens associated with the deposits incite an immune response in the conjunctiva. This condition is most commonly associated with failure to replace soft contact lenses as scheduled.

The symptoms increase with increased numbers of deposits, increased size of the contact lens, and increased wearing time, especially overnight wear. Treatment of GPC consists of using medications, for a short duration, that suppress the immune response. It is important to reduce the amount of contact between the deposits and the conjunctiva. Frequent cleaning, frequent replacement, reducing wearing time, and using lenses that resist deposit formation are effective treatments.

Hypoxia, Lack of Oxygen
Oxygen needed by the cornea diffuses from the tears on the corneal surface. Contact lenses create a barrier that reduces the amount of available oxygen. Contact lens wear (especially with a closed lid during sleep) can cause acute hypoxia. If mild, hypoxia produces epithelial edema and temporary blurred vision. If severe, it can cause epithelial cell death.

Contact lens users who over-wear their lenses or fail to replace their lenses may also have chronic or long term hypoxia. Epithelial microcysts produce a mild decrease in vision. It takes several weeks for the microcysts to disappear after dicontinu7ation of the contact lenses. Also, swelling of the cornea may cause temporary or even permanent changes of prescription, usually increased nearsightedness.

With more severe chronic corneal hypoxia there may be neovascularization. Neovascularization is new blood vessel growth. If less than 2 mm it is not visually significant and generally is well tolerated but is a sign of hypoxia and may be a harbinger of more significant problems. Deep stromal neovascularization can occur with significant abuse of contact lenses. Chronic hypoxia can cause decreased corneal sensitivity. That may be the reason why some patients experience decreased comfort with more oxygen-permeable contact lenses.

Chronic hypoxia also leads to thinning of the epithelium, decreased epithelial shedding, increased cell size, and increased binding of bacteria to the corneal surface. The thinner epithelium poses less of a barrier to bacterial penetration. The reduced shedding of epithelial cells allows the attached bacteria to remain on the eye for longer periods of time. The increased binding of bacteria enables greater numbers of bacteria to attach to the epithelial surface. Thus, over-wear of contact lenses greatly increases the risk of eye infections.