*4.4.1 Epidemiology*

Acanthamoeba is a free-living protozoan found in soil and in freshwater that can cause keratitis primarily in contact lens (CLs) wearers [45]. The epidemiological features of Acanthamoeba keratitis may vary among different geographic regions, climate, and living environments [36].

Acanthamoeba is responsible for less than 5% of infectious keratitis [24].

### *4.4.2 Manifestations*

The classic presentation of patients with Acanthamoeba keratitis is pain out of proportion to ophthalmological finding, photophobia, and slow progressive course [36, 43, 45]. The keratitis usually presents in one eye, but in CL users, it can present with bilateral involvement [36]. The examination may reveal various findings depending on the stage of ocular involvement. Within the first month, the disease can manifest as diffuse punctate epithelial lesions, dendritic-like lesions (mimic herpes simplex epithelial keratitis), epithelial or subepithelial infiltrates, or perineural infiltrates, and ring-shaped stromal infiltrates may be presented [45, 89]. After a month, the disease is characterized by ring-shaped stromal infiltrates, anterior uveitis, endothelial plaque, and disciform keratitis

[36]. Limbitis is a common feature in both early and advance disease [36]. If not managed properly, the disease can progress and late stage findings can develop such as scleritis, iris atrophy, anterior synechiae, secondary glaucoma, mature cataract, chorioretinitis, and retinal vasculitis [89].

#### *4.4.3 Risk factors*

The majority of cases are found in contact lens wearers [43]. Infections related to contact lens are often associated with improper wear such as poor cleaning, overuse, and sleeping or swimming with them [36]. Other risk factors for Acanthamoeba keratitis are cornea trauma or exposure to contaminated fresh water, soil, or vegetation and after corneal laser refractive surgery [36, 43, 90].

#### *4.4.4 Treatment*

There are two principal issues that lead to severe visual outcomes that are misdiagnosis or late diagnosis, and lack of a fully effective therapy for highly resistant cyst stage of Acanthamoeba [36]. The current diagnostic techniques are insensitive and poor turn around time. Moreover, the better yields and rapid test such as PCR or IVCM are not widely available [62]. This keratitis should be treated as soon as possible to prevent loss of visual acuity or even blindness [36]. Thus, ophthalmologists should be familiar with varied clinical pictures of Acanthamoeba keratitis. Currently, there are n0 FDA-approved medications for Acanthamoeba keratitis [62]. Treatment for Acanthamoeba keratitis includes the following medications [62]:


Unfortunately, only the biguanides have been proven to be effective against both the cysts and trophozoite forms of Acanthamoeba [43]. The combination therapy may be of benefit [89]. The earlier the diagnosis, the better the chances of having a good visual prognosis [43]. In the early stage, epithelial debridement and 3 to 4 months of anti-amoebic therapy are enough [45]. Confocal microscopy is the most suitable tool to monitor the keratitis during the course of treatment [62]. However, after a prolonged and maximal medical treatment, recurrence can occur. Topical corticosteroids may mask clinical signs of Acanthamoeba keratitis, encystment, and an increase in number of trophozoites [89]. However, a patient with Acanthamoeba keratitis and severe inflammation may also benefit from this drug [89]. Optical keratoplasty may be considered after 3 to 6 months disease-free interval to avoid the late recurrence [62].
