Discussion
HSK is the most common infectious cause of unilateral blindness and vision impairment in the world.2 This case highlights the diagnosis and management of a patient with ISK, a type of HSK characterized by decreased corneal sensitivity and unilateral stromal opacification or neovascularization.6
ISK is caused by the herpes simplex virus (HSV), a double-stranded enveloped DNA virus that occurs worldwide with little variation, replicates in many types of cells, has rapid growth, and is cytolytic, causing necrosis of nearby cells. Transmission is via direct contact and there is a lifelong latency period in the trigeminal ganglia. Both primary and reactivation infections of HSK can affect a broad array of ocular structures, from the lids to the retina. Infectious epithelial keratitis, also known as dendritic keratitis, is the reactivation of the live virus and is the most common presentation of HSK. ISK is responsible for 20% to 48% of recurrent HSV disease and is the leading cause of vision loss. ISK is the result of an immune-mediated inflammatory response due to a retained viral antigen within the stromal tissue.7 Inflammation in the corneal stroma leads to corneal haze and eventually focal or diffuse scarring, reducing the visual potential.7 This presentation may occur days to years after the initial epithelial episode and may persist for years. Although this patient did not present with infectious epithelial keratitis, it is possible he had a previous episode not mentioned as a history was difficult to obtain, and it can be subtle or innocuous, like pink eye.
Symptoms of ISK include unilateral redness, photophobia, tearing, eye pain, and blurred vision, as described by this patient. On examination, initial manifestations of ISK include corneal haze, edema, scarring, and neovascularization.7 Again, this patient presented with edema and neovascularization. These signs may improve with prompt diagnosis and treatment. More frequent reactivated disease leads to a higher propensity of corneal scarring and irregular astigmatism, reducing the visual outcome.
The standard of care established by the Herpetic Eye Disease Study recommends that a patient with presumed ISK should be started on oral antiviral therapy and, in the absence of epithelial disease, topical steroids. Oral antivirals, such as acyclovir and valacyclovir, have good ocular penetration, a good safety profile, a low susceptibility of resistance, and are well tolerated with long-term treatment.2,8 There were no known interactions between any of the patient’s medications and valacyclovir. Oral antivirals should be used in the initial presentation and for maintenance therapy to help reduce the chance of recurrent disease. Initial treatment for ISK is 1-g valacyclovir 3 times daily. When the eye becomes quiet, that dosage can be tapered to 1 g twice daily, to 1 g once daily, and eventually to a maintenance dose of 500 mg daily. Topical steroids block the inflammatory cascade, therefore reducing the corneal inflammation and potential scarring, further reducing the risk of visual impairment.9 Initial treatment is 1 drop 3 times daily, then can be tapered at the same schedule as the oral acyclovir to help simplify adherence for the patient. After 1 drop once daily, steroids may be discontinued while the oral antiviral maintenance dosage continues. Follow-ups should be performed on a monthly to bimonthly basis to evaluate intraocular pressure, ensuring there is no steroid response.
As seen in this patient, adherence with a treatment regimen and awareness of factors, such as a complex psychosocial history that may impact this adherence, are of utmost importance.7
Conclusions
ISK presents unilaterally with decreased or absent corneal sensitivity and nonspecific symptoms. It should be at the top of the list in the differential diagnosis in any patient with unilateral corneal edema, opacification, or neovascularization, and the patient should be started on oral antiviral therapy.