What Is Acanthamoeba Keratitis?

Acanthamoeba keratitis (AK) is a new infectious keratopathy caused by Acanthamoeba. It was first discovered in 1973. In recent years, the number of cases has increased year by year. Due to the complicated clinical manifestations of the disease, it is difficult to diagnose and treat. It is often clinically misdiagnosed as herpes simplex keratitis or fungal keratitis.

Basic Information

English name

acanthamoeba keratitis

Visiting department

Ophthalmology

Multiple groups

Young healthy people with equal male to female ratio

Common locations

cornea

Common causes

Acanthamoeba

Common symptoms

Photophobia, tears, vision loss, severe eye pain, etc.

Causes of Acanthamoeba Keratitis

The pathogenic spontaneous living amoeba is a protozoa with a single-cell structure, which is widely present in natural environments, such as fresh water, salt water, soil, dust, dirt, spoiled plants and human and animal manure in the air. Amoeba has also been isolated from bathtubs, air filters, contact lenses for water cooling towers, and lens box care solutions. Pathogenic spontaneous life Amoeba can not only live spontaneously in nature, but can also develop and proliferate in warm-blooded hosts. Therefore, it is also called amphibious organism and belongs to facultative parasite.

Acanthamoeba was previously considered a non-pathogenic protozoan. Until 1958 it was discovered that Acanthamoeba can cause fatal infections in animals. It has been confirmed that Acanthamoeba can cause rare human granulomatous meningoencephalitis. And keratitis.

Clinical manifestations of Acanthamoeba keratitis

Acanthamoeba keratitis patients are mostly young and healthy people, with an equal ratio of men and women. Most have contact lens wear history or ocular trauma history, and most of them are affected by one eye. Individual patients can also develop symptoms in both eyes, and the onset is generally slow. . Early inflammation is mainly manifested by corneal epithelial turbidity, rough epithelium or repeated epithelial erosion, and sometimes it can appear as pseudodendritic changes. Patients often suffer from photophobia, tears, loss of vision, and severe eye pain, which often exceed the signs and form a "separation of symptoms from signs" phenomenon.

With the development of the disease, the inflammation gradually infiltrates the stroma, and the plaque, semi-annular, or annular infiltration of the pre-corneal stroma is changed. Some lesions are similar to those of disc keratitis. Some patients may have radial keratitis.

If not diagnosed and treated in time, corneal infiltration quickly develops into corneal ulcers, stromal abscesses, corneal necrosis and perforation in those with severe satellite foci and anterior chamber pus. If the corneal ulcer affects the limbus, it often leads to limbal inflammation and even scleritis.

Cataracts occur in more than 20% of severe cases, especially in cases of prolonged disease, after corneal transplantation, and in cases of chronic glucocorticoid use.

Acanthamoeba keratitis examination

1.10% potassium hydroxide (KOH) wet seal inspection

Take the corneal scraping tissue in the focus area, the culture of Acanthamoeba or the surgically removed corneal material, apply or spread it on a glass slide, and add a drop of 10% KOH solution. The double layer of the protozoan is clearly displayed under a common microscope. Wall cystic morphology. The method is simple, practical and suitable for grassroots hospitals. Hospitals with conditions can use Hemacolor staining, triple staining, Calcoflourwhite and other staining methods for examination.

2. Culture of Acanthamoeba

Place the corneal scraping tissue on the surface of 2% non-nutrient agar and drop 1 drop of live or dead E. coli broth on the surface of the inoculum, and culture in a 35 ° C incubator. Generally, a large amount can be reproduced in 3-7 days Acanthamoeba. Through an inverted microscope, the trophozoites and cysts of Acanthamoeba can be directly observed, and the state of spinous processes formed by Acanthamoeba in warm distilled water.

3. Immunofluorescence technology inspection

At least eight species of Acanthamoeba can cause human keratitis, and different species of Acanthamoeba can be used to identify species of Acanthamoeba by indirect immunofluorescence. At present, there is no such antibody in China, and if necessary, it can be sent to the US Centers for Disease Control (CDC) for identification.

4. Pathological section staining examination

The materials were taken from corneal lesion tissue drilled by ring drilling and surgically removed corneal lesion tissue, fixed, dehydrated, waxed, embedded, sectioned, and then hematoxylin-eosin (HE) or periodic acid-Schiff (PAS) staining. The above two methods of staining can clearly show the cysts of the amoeba in the cornea. Pathological examination can also verify the results of scraping or protozoa culture. According to the needs and conditions, the pathological section can be diagnosed by Giemsa, Wright, Triplet and Calcoflourwhite.

5. Direct inspection with confocal microscope

The above examination methods are all traumatic diagnostic techniques. In order to obtain tissue, it needs to be taken at the lesion site, causing certain damage to the cornea. The recently introduced confocal microscope can directly observe AK patients, and it is a non-invasive, high-contrast, high-magnification early rapid diagnosis method. Acanthamoeba can be detected in all layers of the cornea (from epithelium to endothelium). Image. Sometimes you can even find the pseudofoot extended by Acanthamoeba, or the image of irregular nerve swelling and thickening and rough edges.

Acanthamoeba keratitis diagnosis

Acanthamoeba keratitis is diagnosed mainly by clinical manifestations and laboratory tests. Corneal scrapings for Acanthamoeba protozoa culture is a commonly used test method.

Acanthamoeba keratitis treatment

(1) Drugs

1. Cationic preservatives <br /> As a first-choice medication, it shows good curative effect. At present, 0.02% chlorhexidine and 0.02% polyhexamethyl biguanide (PHMB) are commonly used, and there is no obvious toxic effect on corneal epithelium.

2. Aromatic diamidine

Currently the most commonly used treatment options. Commonly used is 0.1% propazone, 0.15% ezetimibrane. However, long-term application can produce drug toxicity on corneal tissue. In vitro tests confirmed that dimethyl sulfoxide can increase the permeability of the drug to the cysts and significantly enhance the killing effect of propazone.

3. Aminoglycoside antibiotics

The combination of paromomycin and neomycin with aromatic diamidine drugs can further improve the efficacy. Neomycin has similar effects to chlorhexidine and PHMB, can damage the outer membrane of Acanthamoeba, and promotes the entry of aromatic diamidine drugs into the insect body, but it is not effective for cysts. It should also pay attention to its toxic effect during application and avoid long-term use.

4. Imidazoles

Imidazoles can affect the stability of Acanthamoeba cell wall and play an auxiliary role in the treatment process. Medication alone is often ineffective. Drugs include clotrimazole, fluconazole, ketoconazole, itraconazole and miconazole.

5. Glucocorticoids

Whether anti-acanthamoeba treatment is applied at the same time as glucocorticoids is still controversial. In in vitro tests, glucocorticoids can inhibit the formation and decapsulation of Acanthamoeba, which is beneficial to the treatment of keratitis. However, this process has not been confirmed in animal experiments. On the contrary, the application of glucocorticoids can increase corneal infiltration and necrosis of collagen tissue in the matrix. Therefore, unless combined with scleritis or uveitis, the use of glucocorticoids should be cautious.

6. Drugs that promote ulcer repair

When the corneal ulcer enters the repair phase, it can help to apply drugs such as epidermal growth factor and fibronectin, as well as ocular surface lubricants, such as sodium hyaluronate.

(B) staged treatment

Drug treatment should use a combination of medications, and the methods of medication are different at different stages of treatment.

Intensive treatment in the acute phase

With 0.02% chlorhexidine or 0.02% PHMB combined with 0.1% propoxybenzyl isethionate, topical application is performed once an hour, day and night for 48 to 72 hours, and 0.5% neomycin eye drops can also be applied As a triple therapy.

2. Maintenance Phase

Medication is administered every 4 hours. If a toxic reaction occurs, Brolene can be discontinued to continue treatment with chlorhexidine or PHMB and neomycin. After 3 weeks, the number of medications can be gradually reduced in combination with clinical conditions.
After 2 months, 0.02% chlorhexidine can be applied alone, and the course of treatment should exceed 6 months.
If the above treatment is not effective, you can add imidazole drugs, you can use 1% clotrimazole eye, oral ketoconazole; or itraconazole.

During the treatment process, attention should be paid to the mixed bacterial, viral or fungal infection of amoeba. If the mixed infection is clinically suspected, antibacterial or antiviral treatment should be performed at the same time according to the results of microbiological examination.

(Three) surgical treatment

In the case of ineffective corneal inflammation with drug treatment, the operation should be promptly performed to remove the lesion and control the inflammation to save vision and eyeballs. If the inflammation has not affected the whole cornea, lamellar corneal transplantation is feasible; if the inflammation has affected the entire cornea with a large amount of anterior chamber pus, penetrating corneal transplantation should be performed.