Acanthamoeba Keratitis

What is Acanthamoeba Keratitis?

Acanthamoeba keratitis is an eye infection affecting the cornea. Contact lens users are at high risk of getting infected, though non-contact lens users are also prone to the disease.

Acanthamoeba keratitis is a serious, rare, and painful eye condition which affects the cornea of the eye, the transparent part of the eye through which the light enters. The condition is caused by a single celled amoeba, called Acanthamoeba. Prolonged infection can result in loss of vision.

Acanthamoeba are ubiquitous and can be found in air, fresh and brackish water, and soil. The acanthamoeba can also be found in heating/ventilation/air conditioners (HVAC), sewage systems, and air coolers.

Individuals who wear contact lenses are more likely to be infected with the parasite. It is more common but not limited to people who use tap water and unpreserved saline to clean their lenses.

People who swim while wearing contact lenses are also at a higher risk of developing Acanthamoeba keratitis. In addition, those who swim in brackish water, and those injured with decayed organic and vegetative matter are also at risk.

Early diagnosis of Acanthamoeba keratitis is necessary to ensure prompt treatment and therefore prevent damage to the cornea and consequent loss of vision. Treatment can last from several months to even a year.

What are the Symptoms and Signs of Acanthamoeba Keratitis?

• Severe pain in the eye
• Redness of the eye
• Watering of eyes
• Photophobia (Inability to tolerate light falling in the eyes)
• Diminished vision

Pain is particularly severe and may be out of proportion with the findings in the cornea. This is because this organism has a particular affinity for nerve tissue and so causes inflammation of the nerves in the cornea, and hence the pain.

The cornea may appear to be hazy or whitish in color.

These symptoms can persist for several months. Regardless of the appearance of the cornea, patients should consult their doctor as soon as possible to initiate treatment. Delay in treatment results in excessive damage to the corneal surface.

How do we Diagnose Acanthamoeba Keratitis?

Early diagnosis of Acanthamoeba keratitis can prevent serious damage or scarring to the cornea.

The diagnosis of acanthameba keratitis can be made from the history, symptoms, signs and investigations.

• History - a history of soft contact lens wear and /or exposure to known sources of the organism such as organic and vegetative matter or contaminated water including swimming pools.
• Symptoms - severe pain out of proportion to the findings in the cornea.
• Signs - Variable findings in the cornea, most common of which are small dendrite like figures, giving the impression of a viral infection of the cornea. In the late stages, a ring shaped infiltrate is seen in the cornea.
• Investigations:
• Scraping of the ulcer in the cornea and examination of material with KOH or special stains , which helps in immediate identification of the organism.
• Culture of the scraped material in special media. Sometimes cultures from the patient can be negative, and positive cultures may be obtained from the contact lens cases.

In vivo confocal microscopy provides a non-invasive option of diagnosing Acanthamoeba keratitis. The diagnosis has a specificity of ~90%. If good quality images are obtained, one can identify Acanthamoeba keratitis in the early stage and treatment can then be initiated.

Another useful technique that has a high specificity rate of detection is the amplification of genomic material of the amoeba using PCR (polymerase chain reaction) assays. This technique provides a high specificity rate of ~100%. However, this technique is expensive and is not being widely used across the whole world.

Most of the time, diagnosis of Acanthamoeba keratitis is delayed because of its nonspecific nature in the initial stages. A high index of suspicion combined with the above investigations can help to identify this condition in order to start early treatment. Any corneal ulcer that is not responding to the treatment being given must be viewed with suspicion and must be investigated for Acanthamoeba as a cause.

How do we Treat Acanthamoeba Keratitis?

Drugs:

The treatment of acanthamoeba keratitis is often not satisfactory because of the following reasons:

• There is no single drug that is 100 % effective against the organism
• The diagnosis is often delayed either because of a lack of suspicion initially or because if misdiagnosis as acanthamoeba keratitis often mimics other conditions in the early stages.

Treatment always consists of a combination of drugs. The usual treatment consists of:

• Polyhexamethylene biguanide (PHMB) 0.02%
• and chlorhexidine digluconate (0.02%)

Either administered singly or together, and these are often combined with propamidine (Brolene) or hexamidine.

Other drugs such as Neosporin and antifungal agents have some anti-amoebic activity and are often combined with the above drugs.

Surgical Treatment

Treatment usually required to be continued for a period of a couple of months. Often, the infection is controlled, but a scar is left behind in the cornea which has to be taken care of surgically for visual recovery.

A corneal transplantation or keratoplasty (by obtaining a donor cornea from a fresh cadaver) is carried out for restoring the vision.

Sometimes, keratoplasty may have to be carried out in the presence of active infection when drugs do not control it, and the cornea threatens to perforate.

Care of Contact Lenses

Contact lenses should be cleaned with prescribed lens solutions and stored in sterile lens solutions in clean storage cases. Contact lenses should never be worn when the eyes are in contact with water.

Users of contact lenses should take special care to avoid contamination and conditions such as Acanthamoeba keratitis. Some of the precautions below may be useful in this context.

Users of contact lenses should attend regular eye checkups, must replace contact lenses regularly, and within a given schedule.

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