Your Optometrist may have new guidelines for contact lens solutions in the future. The Food and Drug Administration has decided to review the testing procedures for contact lens solutions against the organism acanthamoeba. Acanthamoeba is a type of microorganism called a protozoa that thrives in moist environments and can be found almost everywhere, although it has a much higher incidence in regions with humid, warmer climates like the states in the South Eastern part of the country. Areas with low humidity like Colorado have a lower overall incidence. It is very common in most soil in addition to fresh water. Most forms of acanthamoeba do not effect the eye but one can with serious consequences. It is not unknown to find acanthamoeba when culturing contact lens cases of patients that are currently show no signs of infection.
The eye has it’s own immune system including substances secreted in the tear film that can keep most infections from gaining a foothold. Contact lens wearers who over wear their lenses and use their solutions inappropriately are more susceptible to any type of eye infection. Over wear disrupts the tissue on the front of the eye, the corneal epithelium. This disruption allows organisms like acanthamoeba to enter into the eye tissue and multiply. The Centers for Disease Control and Prevention (CDC) confirmed 138 cases of Acanthamoeba infection of the corneal tissue (keratitis) in 35 different states during 1997. This type of infection has shown an increasing trend in recent years after slowing in the past when homemade saline solutions were discontinued.
The increasing incidence may be related to the tendency to decrease or eliminate chlorination in drinking water although there are also many more people choosing contact lenses for their vision correction, and multipurpose solutions that are ineffective against acanthamoeba have become the contact lens care systems of choice. More contact lens wearers also mean more patients leaving their contact lenses on while enjoying a soak in a Jacuzzi. Chlorination of hot tubs is often inadequate; especially considering how frequently people overload the suggested capacity for occupants. Acanthamoeba exists in two forms and the cyst forms are very resistant to treatment. Unlike the active form the cysts can survive under extreme conditions of chemicals and large temperature ranges. Eye Doctors find acanthamoeba keratitis infections are difficult to treat and even with the care of the best corneal specialists they may still result in blindness and require corneal transplants.
Acanthamoeba infections are almost unknown in the United States in patients who replace their lenses daily or don’t wear contact lenses. Hydrogen Peroxide contact lens cleaning systems kill the cyst form when used as directed. Chlorhexidine and heat systems will also kill the cyst form. Chlorhexidine is an older preservative fairly toxic to the corneal eye tissue and had a high incidence of allergic reactions when it was commonly used in contact lens solutions in past years. Heat disinfection bakes deposits on the lenses and was frequently skipped when it was the most common form of contact lens disinfection. All of these older cleaning systems have lower compliance rates and I believe 100% compliance with less effective solutions is better than 95% compliance with solutions having lower kill rates, especially considering the most common bacteria that cause keratitis are usually eliminated by multipurpose no rub solutions when they are used as directed. Using no rub solutions and adding back in a rubbing step on most days is a compromise that is probably the best system we have today. However, none of the multipurpose solutions have the capacity to effectively destroy acanthamoeba cysts. Hopefully the FDA review will help fill this gap in the future. In the interim the following guidelines like the FDA suggestions should help prevent most acanthamoeba eye infections.
(1) See your eye care professional immediately if you experience symptoms of eye infection such as redness, pain, excessive tearing, increased light sensitivity, blurry vision, and/or sensation of something in the eye.
(2) Wear and replace your lenses according to the schedule prescribed by Optometrist.
(3) Remove your lenses before any activity involving water, including showering, using a hot tub, or swimming.
(4) Wash your hands with soap and water for about 20 seconds, and dry them before handling your lenses.
(5) Clean your lenses according to the manufacturer’s guidelines and instructions from your eye doctor.
(6) Use fresh cleaning or disinfecting solution each time your lenses are cleaned and stored.
(7) Never use saline solution and rewetting drops to disinfect your lenses. Neither solution is an effective or approved disinfectant.
(8) Ask Your Eye Doctor about using a rubbing step with adequate rinsing even with no rub solutions. Rubbing the lenses removes surface deposits and has been shown to improve the disinfecting efficacy.
(9) Store your lenses in the proper storage case.
(10) Rinse your storage case with sterile multipurpose contact lens solution (never use tap water-it is a primary source of acanthamoeba) and leave the storage case open to dry after each use.
(11) Replace storage cases at least once every 1-2 months-you can usually find a case packaged with solution at no added cost.