Acanthamoeba keratitis is an inflammatory disease of the cornea caused by the protozoan – acanthamoeba. This type of keratitis is typical for people who use contact correction. Occurs with improper lens care. It is a long-term ongoing disease, more often with an unfavorable outcome. Patients complain of severe pain in the eye area, photophobia, decreased visual acuity. Pathology is diagnosed using the method of biomicroscopy, pachymetry, keratometry and microbiological studies. Treatment is conservative, with the help of eye drops; in severe cases, surgical intervention is necessary.
Acanthamoeba keratitis is a chronic, long-term infectious disease of the cornea caused by an amoeba of the genus Acanthamoeba, and manifested by severe eye lesions. In the works on clinical ophthalmology, it was first described in 1974. Given the great progress in the development of the contact lens industry over the past decades, many people have begun to use them as a correction method that gives excellent vision. Against this background, complications associated with improper care of the CL began to occur more often. Acanthamoeba keratitis remains the most serious of them. It is more common in men than in women. The age of occurrence of the disease ranges from 20 to 40 years. It occurs in developed countries with a frequency of 1.5-2 cases per 1 million contact lens users.
Characteristics of the pathogen
The causative agents of acanthamoeba keratitis are free-living amoebas of the genera Acanthamoeba (A. culherisom, A. castellanii, A. polyphaga and A. astronyxis) and Hartmanelta. They live in soil, standing ponds, swimming pools, sewer pipes, and tap water. Amoeba exists in the form of two forms – trophozoite (active form) and cyst (inactive). In the cystic form, it is capable of long-term viability, resistant to temperature changes, irradiation, chlorinated water in swimming pools. Under favorable conditions, the cyst is able to turn into trophozoites that produce various enzymes that help the amoeba penetrate into the tissues of the human body.
Normally, a person has a stable resistance to the introduction of amoeba cysts into the body. Infection occurs with the slightest injuries in the cornea, more often from wearing contact lenses (CL). Eye damage develops after bathing in a polluted pond or pool, when washing the CL with tap water. The pathogen is introduced into the corneal tissue, causing an inflammatory reaction and triggering subsequent changes.
Risk factors for the development of acanthamoeba keratitis also include “dry eye” syndrome (tear fluid is necessary to maintain local immunity in the eyes, with a lack of weakening to the effects of various microbial agents); diabetes mellitus (leads to less resistance of the body to infections); previously undergone eye surgery (prolonged restoration of the integrity of the protective layer of the cornea).
Depending on the changes in the cornea , there are 4 stages of acanthamoeba keratitis:
- Stage 1: Superficial epithelial keratitis. A rounded area of limited epithelial edema appears on the cornea in the central or paracentral zone.
- Stage 2: Superficial epithelial spot keratitis. The intensity of turbidity increases. Corneal infiltration is more pronounced, small protruding whitish or grayish epithelial nodules appear. Nerve trunks in the corneal stroma (radial keratoneuritis) become noticeable. There is a significant pain syndrome.
- Stage 3: Stromal ring keratitis. The devouring of the epithelial cover of the cornea by acanthamoebae is accompanied by an inflammatory reaction in the surface layers of its stroma. Corneal opacity increases and expands due to infiltration and edema of the stroma. Keratitis acquires a ring-shaped shape. There is a slight iritis.
- Stage 4: Ulcerative acanthamoeba keratitis. The destruction of the corneal stroma increases and a superficial corneal ulcer is formed more often; iritis, iridocyclitis, hypopion occur, rarely – scleritis, often – secondary glaucoma, cataract. Corneal perforation is possible.
Symptoms of acanthamoeba keratitis
Corneal infection can develop both in one eye and in both at once. The long-term chronic course of the disease is characteristic. In the initial stages of acanthamoeba keratitis, the patient complains of unpleasant sensations under the upper eyelid, a feeling of a foreign body, slight irritation of the eye, a slight decrease in visual acuity.
As the disease progresses, visual acuity continues to decrease, significant redness of the eyeball joins, periodic pain in the eye occurs. Inflammation of the cornea is accompanied by blepharospasm, lacrimation and photophobia. In the final stages of the disease, the patient is worried about constant severe pain in the area of the eyeballs, visual acuity is sharply reduced to light perception, or vision is completely absent.
Of the complications of acanthamoeba keratitis, the development of iridocyclitis, scleritis, secondary glaucoma is noted. The most formidable complication is the perforation (perforation) of the cornea, leading to the formation of a cataract and loss of visual function.
For the diagnosis of acanthamoeba keratitis, the main method is biomicroscopy of the eye, which is performed using a slit lamp. An ophthalmologist visually determines the depth of corneal damage (at the initial stages, spot epithelial erosions, epithelial edema are determined; at the advanced stages of acanthamoeba keratitis, folds of the descement shell, edema of the corneal stroma, ulceration are visualized).
When clarifying the diagnosis of acanthamoeba keratitis, additional diagnostic methods are used, such as pachymetry (measuring the thickness of the cornea), keratometry (measuring the curvature of the cornea), microbiological studies (staining or sowing scraping from the cornea on a special nutrient medium).
Treatment of acanthamoeba keratitis
The disease is quite difficult to treat. Conservative therapy consists of topical application of eye drops, the duration of treatment is at least 6 weeks. At the same time, the following groups of drugs are used: antiseptics (chlorhexidine, dioxidine), antifungal (ketoconazole, fluconazole), antibacterial (aminoglycosides, fluoroquinologists), corticosteroids. With pain syndrome, analgesics are prescribed inside. Instillations of mydriatics, as well as artificial tear preparations are used. When the condition worsens, intravenous administration of antifungal drugs is connected.
Surgical techniques are resorted to when corneal ulcers occur. Methods of therapeutic-tectonic keratoplasty with autoscleral flaps, layered surface keratoplasty using conjunctival flap, through keratoplasty are used.
Prevention of acanthamoeba keratitis is reduced to proper care of contact lenses. It is necessary to use special solutions for their storage and care, compliance with the terms of wearing, it is ideal to use one-day lenses. More thorough hand washing is required before removing or putting on the CL. It is recommended not to take a hot bath with CL, it is advisable to remove them before taking a shower or visiting the sauna. At night, you should rest your eyes, remove the CL before going to bed. Doctors recommend changing the lens case every 3 months. A visit to an ophthalmologist is a mandatory point of prevention of acanthamoeba keratitis, it must be done once every 4-5 months, regardless of the presence of complaints.
- Lorenzo-Morales J, Martin-Navarro CM, Lopez-Arencibia A, et al. Acanthamoeba keratitis: an emerging disease gathering importance worldwide? Trends Parasitol. 2013;29(4):181-187. link
- Marciano-Cabral F, Cabral G. Acanthamoeba spp. as agents of disease in humans. Clin Microbiol Rev. 2003:16(2):273-307.
- Alizadeh H, Neelam S, Hurt M, Niederkorn JY. Role of contact lens wear, bacterial flora, and mannose-induced pathogenic protease in the pathogenesis of amoebic keratitis. Infect Immun. 2005;73(2): 1061-1068.
- Alio JL, Abbouda A, Valle DD, et al. Corneal cross linking and infectious keratitis: a systematic review with a meta-analysis of reported cases. J Ophthalmic Inflamm Infect. 2013;3(1):47. link
- Garate M, Cao Z, Bateman E, Panjwani N. Cloning and characterization of a novel mannose-binding protein of Acanthamoeba. J Biol Chem. 2004;279(28):29849-56.
- Kettesy B, Modis Jr L, Berta A, Kemeny-Beke A. Keratoplasty in Contact Lens Related Acanthamoeba Keratitis. In: Keratoplasties-Surgical techniques and complications. Ed. by L. Mosca. London: IntechOpen; 2012.
- Seal DV, Pleyer U. Ocular Infection: investigation and treatment in practice. 2nd revised edition. Taylor & Francis Inc; 2007. 384 p. link