.. bility 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 complication, but often lenses with deposits need to be replaced. Rarely, one can develop an allergy to lens material itself, and trying a different brand, or switching to a rigid type of lens may help. A more unusual but common allergy problem is phlyctenulosis, the development of an allergy to bacteria present on the edge of the eyelid. These bacteria produce toxins that become trapped in the tears, especially beneath a contact lens.
Lens deposits Protein deposits can frequently form on both soft and rigid types of lenses. With soft lenses, the regular use of enzyme cleaners as well as proper disinfection and daily cleaning of lenses can help prevent the protein deposition. Rigid lenses may develop deposits especially during seasons with high pollen counts, and polishing the lenses usually will buff off any deposits. When a lens develops deposits, the eye can become irritated, itchy, and red. Wearing time may be decreased, and the vision may be somewhat blurred. Complications such as giant papillary conjunctivitis (GPC) may occur, which can limit the use of contact lenses for an extended period of time.
Once unremoveable deposits form on a soft lens, the lens usually has to be replaced. Rapid development of deposits on lenses is a valid reason to consider disposable lenses. Some contact lenses on the market are designed to be resistant to deposit formation. Contact Lens Wear Complications Ulcerative Bacterial Keratitis (UBK) The development of a corneal ulcer (an infection of the cornea) unfortunately is a common complication of contact lens use. Both Rigid Gas Permeable (RGP) and soft hydrogel lenses are associated with significant problems though hydrogel lens wearers are more prone to infection than are wearers of RGPs.
This is partly because the soft lens provides a good surface for bacterial attachment. Additionally, RGPs are more easily cleaned and are less prone to bacterial adherence than soft lenses. Disposable contact lenses worn extended wear were found to have a much higher risk of corneal ulcer than any other type of lens, for reasons that are not fully understood. A corneal ulcer starts when a bacteria (or rarely a fungus or parasite) infects an area of breakdown in the corneal surface. The surface may break down, forming a small corneal abrasion, due to routine lens use.
Overwear of lenses, improper cleaning of lenses, extended wear use of lenses, and overly tight lenses may increase the risk of developing this surface breakdown. Normally, a corneal abrasion, even if tiny, is uncomfortable. However, a contact lens can act as a bandage on the eye masking symptoms, and some contact users develop a lack of sensitivity of the cornea. Once an infection begins, most people experience severe symptoms. The eye typically becomes red and painful. There may be tearing or discharge and sensitivity to light.
The vision may be variably blurred. There are other disorders that can cause these symptoms, but the risk of corneal ulcer in contact lens users is such that the most important thing to do initially is to remove the contact lens. An appointment should be arranged immediately with an ophthalmologist to determine if an infection is present. A corneal ulcer needs to be treated intensively with antibiotic eyedrops, and often a culture of the infected cornea, or of the lens or lens case is performed. Frequent follow-up appointments will help the ophthalmologist determine if the infection is being adequately treated with the antibiotics.
Usually a week or two of antibiotic eyedrops is needed, and contact lenses cannot be worn during this time. Ulcerative Bacterial Keratitis is among the most severe complications of contact lens wear. Approximately two-thirds of all cases are contact lens related. A successfully treated corneal ulcer may still leave a scar that could affect the vision. It is important to avoid situations which can lead to corneal ulcer, such as overwear of lenses, poor disinfection techniques, swimming with contact lenses in, and ignoring symptoms of pain or redness.
Disposable Contact Lens Use Disposable contact lenses can be a useful option for some contact lens users, and there seems to be a trend toward increased use of this type of lens. Even disposable lenses that are discarded on a daily basis are available, although most people use the type of lens that is discarded after 2 weeks. Some reasons and situations for which disposable lenses may be useful include: Rapid deposit formation on lenses, with or without the development of giant papillary conjunctivitis. Having to replace contact lenses frequently, whether it be because of lens deterioration, damage, or the losing of lenses. Sensitivity to solutions used to clean or disinfect lenses. Difficulty in finding another type of lens that is equally comfortable for an individual.Some problems associated with disposable lenses include: A higher risk of infection (corneal ulcer), whether or not the lenses are used extended wear. A higher cost than most lenses.
At wholesale cost, the 8 six-pack boxes needed to replace a lens every two weeks costs about $150 a year. One may be able to buy 4 sets of daily wear lenses at this cost. A tendency to abuse the use of the lenses, such as wearing a lens for more than two weeks, an absence of lens disinfection, and wearing the lenses in situations not usually recommended, such as swimming. (These factors may lead to the increased risk of infection). Poorer vision with disposable lenses.
These lenses are very thin, and correct very little astigmatism. If an eye has borderline astigmatism, a more substantial lens may correct the vision better. Problems using the lens with dry eye. Disposable lenses require more eye fluid to keep them hydrated.There are definite situations where disposable lenses are appropriate, and some situations where they should be avoided. Exercising caution with the use of any contact lens helps to prevent complications. Extended Wear Contact Lens Use Many people are able to wear lenses continuously for many days with no apparent problem or complication. However, sleeping in contact lenses, while convenient, substantially increases the risk for infection and other complications.
The oxygen supply to the cornea drops overnight while wearing a contact lens. This can lead to swelling of the cornea (giving blurred vision or the visualization of rainbows around lights), breakdown of the corneal surface, and ultimately infection of the cornea (ulcer). This risk is high enough that many eyecare providers discourage against the use of contact lenses on an extended wear basis. If the lenses are used this way, extreme caution should be taken, and the lenses should be removed with any sign of trouble (eye redness, pain, blurred vision, sensitivity to light, etc). In fact, it may be reasonable to consider refractive surgery as an alternative to extended wear contact lens use.