What is Acanthamoeba Keratitis and How is it Treated?

by Feb 1, 2022

This is the third part of our series regarding corneal transplants and why one might be needed.

Our previous articles in the seriesWhat Is Fuch’s Endothelial Dystrophy and Is Keratoconus a Serious Conditionhave discussed the two most common causes for corneal transplantation. Both of which are conditions where, for whatever reason, the cornea becomes disfigured or nonfunctioning without outside influence (i.e. intrinsic conditions).

Today we are going to change direction a bit and focus on infectious diseases (i.e. extrinsic conditions) which may result in the need for corneal transplantation.

Over the next several weeks we’ll be discussing infectious agents such as Acanthamoeba Keratitis, Trachoma, Herpes Virus, and severe corneal ulcers before rounding out the series with a post about what corneal transplants entail and the different types available.

When it comes to corneal infections, most will not require a corneal transplant, however, there are cases in which extensive scarring, inflammation, and thinning of the cornea result in the need for a corneal transplant.

Today’s infectious agent discussion will be focused on the “eye-eating parasite” the Acanthamoeba.


What is Acanthamoeba Keratitis?

Acanthamoeba is a microscopic, single-celled organism that lives primarily in fresh water and soil. These organisms are very common and live all across the globe in various climates.

While acanthamoebas are commonly found, eye infections secondary to acanthamoeba are rather rare, which is a good thing because these little creatures can wreak havoc in the eyes.

In order to infect an eye, an acanthamoeba must have an entrance into the eye. Acanthamoebas typically do not cross through an intact cornea.

The most common entry points for acanthamoebas to enter the eye is through small, unnoticeable scratches on the cornea.

In fact, acanthamoeba infections are most common in contact lens wearers who are more prone to accidently scraping or scratching the cornea during lens insertion or removal.

Now, if an individual has a scrape or scratch on the cornea and he or she goes swimming, hot tubbing, gardening, etc. (essentially exposing themselves to soil or freshwater), he/she runs the risk of an acanthamoeba entering the eye through the scratch or scape, resulting in an acanthamoeba eye infection—acanthamoeba keratitis.

Once entering the eye, an acanthamoeba survives off of consuming basement membranes and other cells found within the eye. Yes, you read that correctly, acanthamoebas literally eat away at the cornea.

It only takes 1-2 weeks for an acanthamoeba keratitis infection to really take off resulting in the symptoms of extreme pain, light sensitivity, blurry vision, eye redness, and/or foreign body sensation (the feeling like something is in the eye).

Treatment for acanthamoeba keratitis is very aggressive, and the earlier treatment is initiated the better the prognosis.


Treatments for Acanthamoeba Keratitis

Early treatment for acanthamoeba keratitis includes instilling a plethora of eye drops such as Polyhexamethylene Biguanide (PHMD), antifungals, antibacterials, antivirals, cycloplegics, and occasionally steroids.

Some of these drops may need to be instilled as frequently as once an hour (even throughout the night!).

The goal of all these drops is to kill the acanthamoeba before too much damage is done. As the acanthamoeba munches away on the cornea, it of course causes structural damage resulting in thinning of the cornea, inflammation, and scarring.

What makes acanthamoeba keratitis even more frustrating is that the organisms multiply and switch back in forth between “active” and “inactive” stages.

In the active stages the acanthamoebas eat away at the cornea. In the inactive stages the acanthamoebas go dormant, walling themselves off into little protected cyst-like pockets that are impenetrable by medications.

This means the acanthamoebas can only be killed when in the active state, making treatment a long, frustrating process.

Once the acanthamoebas are all killed off, the patient’s pain should be reduced. However, depending on the extent of the damage caused by the infection, the cornea may be left in disarray and heavily scarred.

Not every case of acanthamoeba keratitis will need a corneal transplant—it really all depends on the amount of scarring, corneal thinning, or presence of ulceration post-infection.

As we know, the cornea needs to be transparent to allow for the passage of light and image formation.

Scar tissue is dense and does not transmit light. Instead, it obstructs vision, reflects light causing increased glare and light sensitivity, and overall decreases a person’s visual acuity.


When is a Corneal Transplant Needed?

Scar tissue is the main reason a corneal transplant will be considered in acanthamoeba keratitis cases. In most situations, doctors will want to wait for active infection to clear and the inflammation of the eye to decrease as this will better the chances of a successful transplant.

In other cases, it may not be possible to wait this long as acanthamoeba keratitis can result in painful corneal ulcers, speeding up the process in which a person receives a corneal transplant.

Regardless of the timeline, the two most common types of corneal transplants for acanthamoeba keratitis treatment are deep anterior lamellar keratoplasty (DALK) and full thickness penetrating keratoplasty (PK).

We’ll discuss these transplants in further detail in a couple weeks. In the meantime, stay tuned for more infectious corneal diseases! Next up we’ll chat about the leading cause of preventable blindness worldwide—Trachoma.


Dr. Nathan Abraham and the staff of the Abraham Eye Center specializes in cataract surgery, LASIK, PRK, and various corneal surgeries.  Call our ophthalmologist in Valencia, CA today at 661-977-7377 or schedule an appointment online if you are interested in learning more about acanthamoeba keratitis treatments.  Our eye doctor provides only the highest quality eye care and surgical services amongst eye doctors in the Valencia California area.

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