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Editor,—Up to 92% of cases of acanthamoeba keratitis occur in contact lens users of all types.1Failure to disinfect soft contact lenses and the use of chlorine disinfection systems are major factors accounting for the increase in cases of acanthamoeba keratitis.2 It is thought that “daily disposable” contact lenses, which require no disinfection, will have a much lower risk for the development of all forms of infectious keratitis. We report a case of acanthamoeba keratitis occurring in a daily disposable contact lens wearer. We believe this is the first such reported case.
A healthy 21 year old woman, who had been wearing daily disposable contact lenses for 1 year, wore her lenses for 4 hours on 1 day and then stored the lenses in preserved saline solution overnight in a new contact lens case. She rewore the lenses for a further 3 hours the following day. She reports that this was the first time that she had done this. She then developed a painful left eye. This was initially treated as conjunctivitis by her general practitioner and local accident and emergency department. After 2 weeks her local eye unit suspected acanthamoeba keratitis and performed an epithelial scrape that “revealed amoeba species”. She was then referred to our unit for our opinion.
On examination her visual acuity was reduced to 6/18 in the left eye. There was conjunctival injection and a mild scleritis. The cornea had diffuse punctate staining with linear epithelial and perineural infiltrates (Figs 1 and 2). She had a mild anterior uveitis. Acanthamoeba was strongly suspected. Corneal epithelium was removed for microscopy, culture, and histology. Her contact lens case and solutions were also sent for culture. Acanthamoeba was cultured from both corneal epithelium and lens case, but not the lens solutions. She was treated with topical polyhexamethylene biguanide 0.02% (PHMB) and prednisolone 0.3 % as well as oral flurbiprofen (Froben, Knoll Ltd, Nottingham). Six weeks after diagnosis she was asymptomatic with a visual acuity of 6/9. The eye was quiet, though some corneal infiltrates remained.
Acanthamoebae are free living protozoa commonly found in soil and water, including bathroom tap water.3 Acanthamoeba keratitis is an uncommon but potentially devastating corneal infection. The number of cases diagnosed in the United Kingdom has steadily risen over the past 20 years owing to increased awareness of the condition and the rise in contact lens wear.4
Radford et al found that daily wear disposable contact lenses were associated with greatly increased risk of acanthamoeba keratitis compared with other lens types and wear systems.1 2 Multivariable analysis showed that this was largely attributable to a lack of disinfection, the use of non-sterile saline, and the use of chlorine based disinfection rather than alternative chemical systems. It was concluded that 80% of cases of acanthamoeba keratitis could be prevented by the adequate use of an effective disinfection system. It was felt that the “low care” philosophy of daily wear disposable lenses had become “no care” in practice.
Daily disposable contact lenses, in which the lens is discarded after 1 day’s wear only, were introduced in 1995. When used properly and discarded after a single day’s wear, they do not carry the risks of inadequate lens disinfection, contaminated lens solutions, and storage cases. A case of acanthamoeba keratitis occurring in an extended wear disposable lens wearer has been reported, illustrating that even without the risks of inadequate lens disinfection and contaminated lens cases the infection can occur.5 However, it is known that contact lens wear increases the susceptibility to keratitis independent of factors relating to disinfection and cleaning.
Our case of acanthamoeba keratitis in a daily disposable lens wearer illustrates that misuse occurs and when it does so inadequate disinfection is almost inevitable leading to greatly increased risk of acanthamoeba infection. Misuse, as in this case, may often be associated with storage in saline or water without disinfection. This has been shown by Radford et al to increase the relative risk of acanthamoeba keratitis to 55.86 (10–302) p<0.001. Our case does not, however, indicate the mechanism of infection. It is possible that the infection is unrelated to the lens misuse and could have been acquired from other unrelated sources, such as exposure to contaminated tap water while wearing lenses. However, we would recommend greater education of daily disposable lens wearers on the importance of strict adherence to wearing their lenses for 1 day only and of the risks of misuse of their lenses.
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