What is it?
It is inflammation of the cornea caused by Acanthamoeba, a protozoan commonly found in the soil, earth and water (from the sea, our taps and swimming pools). The Acanthamoeba has two stages: trophozoites and cysts. The latter is resistent to extreme environments to guarantee its survival.
Symptoms
When this bacteria infects the cornea, the patient presents with red eye, poor vision, intolerance to light, watering eyes and above all, eye pain.
In the initial phase, the corneal epithelium, the outermost layer, gets infected and dotted lesions forming lines that represent the epithelial cells invaded by this bacteria appear. As the disease progresses, the most profound layers, such as the corneal stroma, are invaded by the Acanthamoeba and the inflammatory cells manifesting itself as corneal opacity and a loss of transparency, commonly in the shape of a ring.
One of the typical manifestations of this infection is neuritis (inflammation of the corneal nerves), which causes the intense eye pain. These symptoms and manifestations are very similar to herpes simplex keratitis which must be taken into account as treatment for it is totally different.
Causes and risk factors
Even though the Acanthamoeba is found in practically all places and environments, Acanthamoeba keratitis is not as common as you may think. The main risk factor of cornea infections is wearing contact lenses, especially soft ones.
More than 90% of patients with keratitis caused by this protozoan are contact lens-wearers. The majority do not have a good hygiene routine or have gone swimming while wearing them.
Prevention
Contact lens-wearers have to take special precaution to prevent Acanthamoeba infections. A good hygiene routine for your contact lenses, their case and your hands when handling them is fundamental.
Leaving your contact lenses in their case for a few days without using them or changing the disinfection solution is also risky as the protozoans can proliferate in these cases.
The most well-know risk factor for contact lens-wearers is wearing them while in the water, whether it be for swimming pool- or sea-based activities. For this reason, wearing contact lenses for water activities is completely forbidden.
Treatment
The earlier the treatment starts, the better the prognosis for the disease. That said, treatment for topical Acanthamoeba involving various types of eyedrops and ointments may have adverse effects on the eyes. For this reason, before treating Acanthamoeba keratitis, other causes must be ruled out and as accurate as possible a diagnosis must be made.
Unfortunately, nowadays, quickly identifying the Acanthamoeba in the cornea is not easy. Samples are taken from the patient's cornea to identify it using a special culture or a molecular biology technique called polymerase chain reaction, but these tests are available in specialist centres and the cost is high.
Cysts of this protozoan in the cornea can also be identified using a corneal tomography although the absence of cysts does not rule out their presence and the images of cysts can be confused with inflamed cells. In many cases, the diagnosis has to be made clinically as this disease cannot be objectively ruled out or diagnosed.
One of the anti-Acanthamoeba eyedrops is not available in Spain, so it must be requested from overseas with permission from the Spanish Ministry of Health, while the other is not sold and has to be specially prepared in centres with the means to do so. Other eyedrops with adjuvant effects that alleviate the eye pain must be added as part of the treatment. Due to the high resistance of the cystic state of this protozoan, treatment for Acanthamoeba keratitis must last at least 4-6 months.