Реферат: Contact Lens Complications Essay Research Paper IntroductionThe
Contact Lens Complications Essay, Research Paper
The last 20 years has seen a tremendous increase in the use of contact lenses. Despite the recent trend towards fashionable eyewear and the advances in refractive surgeries, there are still approximately 1 million Australians who are currently wearing contact lenses. This is partly because of the variety of lens materials, replacement schedules, specialty designs, and convenient contact lens care systems available today.
While there are many benefits of contact lenses, both cosmetic and therapeutic, contact lens wear is not without risk of complications. Ocular complications of contact lenses include iatrogenic (inappropriate fit, prescription or wearing schedule), patient non-compliance or misuse, as well as inherent problems with the patients tear film, lids, lashes, or meibomian glands. Contact lenses are implicated in the pathophysiology of many anterior segment disorders. Most commonly, these complications are due to hypoxia (oxygen deprivation to the cornea), mechanical stress, infection, or immunological factors. Soft contact lenses, also known as hydrogels, worn as extended wear (that is, up to a 7 consecutive day wearing schedule including overnight wear) have a significantly higher incidence (10-15 times the rate for daily wear hydrogels) of ocular complications. This is because corneal hypoxia is greatly exacerbated by overnight contact lens wear.
A recent study found that in any given year, over 7% of all contact lens wearers experience an ocular complaint that is serious or bothersome enough to warrant a visit to their optometrist. The list of potential problems is long, and while many of the complaints are relatively minor, a few are potentially sight-threatening (see Table).
Table: Possible complications of Contact Lens Wear
Potentially Sight ThreateningUsually Not Sight ThreateningUlcerative bacterial keratitisCorneal edemaFungal and protozoal keratitisGiant papillary conjunctivitisSuperior limbic keratoconjunctivitis3-9 O’clock stainingCorneal vascularizationCorneal abrasionCorneal distortionSolution hypersensitivityEpithelial microcystsEndothelial polymegathismContact Lens Acute Red Eye (CLARE) Contact Lens Related Problems
Lens comfort problems
There are many reasons why a contact lens may be uncomfortable to wear, including underlying eye disease and other contact lens complications discussed on this page. In cases where the eyes are healthy and the contact lenses are new, there is always the possibility that a lens is defective. Generally, if a lens of a given brand and curvature has been worn successfully in the past without problem, a new and uncomfortable lens makes one strongly suspicious of an abnormally curved lens, or a lens with a scratch or other defect. Since most manufacturers offer a warranty for defective lenses, it may be reasonable to return the lens for replacement or refund. In cases of new gas permeable or hard lenses, sometimes the lens can be smoothed or polished to improve the comfort.
If a new lens of a different brand than has been worn before is uncomfortable, the problem may be with the fit (tightness) of the lens, the thickness of the lens, and the edge design of the lens. Some soft contact lenses have a very high oxygen permeability (extended wear type lenses), and these may be more comfortable for some people. However, these lenses also demand more ocular lubrication to keep them hydrated and moist, so eyes which are somewhat dry may not be comfortable with this type of lens. If a lens is too tight, the cornea may become starved for oxygen, leading to discomfort (see Tight Lens Syndrome below). On the other hand, a lens that is too loose may irritate the eye due to excessive movement with blinking. Finally, certain characteristics of lenses (thickness and edge design) may be simply uncomfortable for some people. It may take a follow-up examination by the optometrist to distinguish between these problems.
An old lens that becomes uncomfortable may be developing deposits on the lens, scratches or nicks in the lens, or problems with the tears lubricating the surface of the lens. People are different with how long a given lens will remain comfortable, and good care of lenses will usually extend the life of a lens. Having to replace lenses frequently due to rapid protein deposit formation or other problems is a good reason to consider disposable lenses.
As mentioned above, the development of an underlying eye disorder not related to the contact lenses can make their use uncomfortable. Some conditions include eye allergy, dry eye, blepharitis, conjunctivitis, eyelid problems, iritis, phlyctenulosis, and pterygium. Pregnancy or hormonal changes are known to cause difficulty in contact lens use in women. Finally, other contact lens complications discussed below can cause discomfort with lens use.
Wearing Time Problems
People can develop problems with being unable to wear a lens as long as they would like. Sometimes this problem is simply related to external problems such as a high pollen count or being in an environment with poor air quality or low humidity. In cases where it becomes increasingly difficult to wear an older lens as long as previously, the lens may be developing protein deposits or other defects. Hard or gas-permeable lenses can often be polished, and will be comfortable to wear again, while soft lenses usually have to be replaced.
Some people are unable to wear any type of lens for the entire day, but can only wear the lens for a limited period of time. In cases where the eyes are somewhat dry, the use of rewetting drops (preferably preservative-free) can extend the time that the lenses can be used. Some people need to remove the lenses at some point during the day, such as lunchtime, and can then subsequently wear them longer during the afternoon. If one is having a problem with the wearing time of lenses, it is usually a good idea to have an eye examination to rule out any other potential problem such as infection or allergy. A lens case with solution should be carried if the lenses need to be removed during the day, since wearing a lens longer than it is comfortable can lead to disaster. One should never put a contact lens in tap water, or in solutions not designed for lens storage or disinfection. It is also unwise for a contact lens wearer to use solutions other than those recommended by their optometrist.
Contact lenses are better at correcting certain types of vision problems than others can correct. Simple nearsightedness or farsightedness is usually easily corrected using contact lenses, but astigmatism can be more challenging to correct, especially with soft lenses. Contact lenses have varying success in correcting the need for reading glasses, with bifocal contact lenses rarely being successfully prescribed.
Toric soft lenses have an astigmatism correction built into the lens, but rotation of the lens can lead to a shifting of the astigmatism correction, and temporarily blurred vision. For people with severe or irregular astigmatism, rigid gas-permeable lenses (RGPs) or hard lenses may offer better visual results. Irregular astigmatism is a situation where the cornea is distorted due to a scar or underlying disorder. Sometimes rigid contact lenses are the ONLY way to correct the vision in these cases, as even glasses will not help (as in keratoconus).
Many people who use contact lenses may experience halos around lights at night, and sometimes ghost images. This probably is a normal phenomenon in most people, and occurs when the pupil is larger (or more dilated) than the optical area of a soft lens, or of the lens itself in cases of rigid lenses. However, seeing a rainbow around lights indicates swelling of the cornea (corneal oedema), and indicates that the lenses have been in too long and should be removed.
Blurred vision in one eye or the other with a contact 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 Allergy
The 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 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.
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.