**4.3 Viral keratitis**

## *4.3.1 Epidemiology*

Herpes simplex virus (HSV) is a common cause of viral keratitis and the most common cause of unilateral infectious corneal blindness in the world [5, 9]. Varicellazoster and cytomegalovirus can also cause viral keratitis but are much less common [9]. The prevalence of viral keratitis was 0.11% in a recent population-based study [5]. The majority of corneal HSV-1 infection is not the outcome of primary ocular infection, but in response to reactivation of latent virus from the trigeminal ganglion [82]. However, recurrent corneal epithelial infection with HSV-1 can have stromal involvement known as herpes stromal keratitis (HSK), which can be necrotizing, nonnecrotizing, or a mix of both [82, 83]. One study with HSV stromal keratitis reported that disease was of the necrotizing type in 7%, nonnecrotizing in 88%, and a mix of the two in 5% [84]. In this review, we address only the herpes necrotizing stromal keratitis that may mimic infectious keratitis from other organisms.

## *4.3.2 Manifestations*

Viral keratitis differs from bacterial and fungal keratitis in that it can become recurrent and chronic [9]. In necrotizing HSV stromal keratitis, necrosis, ulceration, and dense leukocytic infiltration of the stroma are present and often associated with an overlying epithelial defect and neovascularization [18, 83, 85]. The viral keratitis diagnosis is usually based on clinical findings [43] and diagnosis by exclusion. However, in atypical cases, the investigations such as tissue culture, ELISA, and PCR may aid in the diagnostic confirmation [43].

#### *4.3.3 Risk factors*

The risk of HSV reactivation can occur after excimer laser refractive surgery such as LASIK or PRK. The exposure to ultraviolet light during corneal collagen cross-linking

**15**

*Infectious Keratitis: The Great Enemy*

previous episodes [86, 87].

*4.3.4 Treatment*

[83, 86, 88].

*4.4.1 Epidemiology*

*4.4.2 Manifestations*

**4.4 Acanthamoeba keratitis**

climate, and living environments [36].

*DOI: http://dx.doi.org/10.5772/intechopen.89798*

(CXL) can reactivate latent HSV infection [86]. Previous stromal keratitis increased the risk of stromal keratitis, and the risk was strongly related to the number of

Both immune and active viral replications are responsible for the disease pathogenesis [83]. In contrast to nonnecrotizing stromal keratitis where topical corticosteroid is the mainstay treatment, oral acyclovir is used to control the viral invasion and replication in cornea, while low-dose topical corticosteroids are given to control inflammation in necrotizing stromal keratitis [18]. Topical CsA administration can resolve stromal inflammation and neovascularization in 50 and 64% of cases, respectively [83]. Without timely and effective treatment, necrotizing HSV stromal keratitis can rapidly lead to corneal perforation [83]. Amniotic membrane transplantation onto the ocular surface promotes corneal epithelial healing and reduces stromal inflammation, angiogenesis, and scarring [83]. Various oral antiviral agents to treat active viral

replication and prevent recurrences are available as mentioned below [86]:

Data from the Herpetic Eye Disease (HEDS) study concluded that the HSV stromal keratitis patients who received 400 mg oral acyclovir twice per day for 12 months had reduced rate of recurrent HSV stromal keratitis by about 50%. The research about HSV vaccination is underway, and no vaccine is currently available

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,

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

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

1.Acyclovir: 800 mg, 3–5 times/day, 7–10 days

2.Valacyclovir: 1 g, 3 times per day, 7–10 days

3.Famciclovir: 500 mg, 2 times/day, 7–10 days

(CXL) can reactivate latent HSV infection [86]. Previous stromal keratitis increased the risk of stromal keratitis, and the risk was strongly related to the number of previous episodes [86, 87].
