Beyond the Branches: A Closer Look at Ocular Herpes, Part 2
BY WILLIAM TOWNSEND, OD
My last column discussed an overview of ocular herpetic disease and focused on epithelial herpes simplex keratitis (HSK). This month I'll focus on differentiating and treating stromal herpes.
Defining Stromal Herpes
Stromal herpes presents with a corneal infiltrate and reduced corneal sensitivity. It often follows episodes of epithelial HSK. Uveitis usually accompanies stromal HSK, but it rarely may occur independently. You'll note anterior chamber inflammatory cells, trabeculitis and elevated IOP. Differential diagnosis includes herpes zoster, syphilitic keratitis, Acanthamoeba and fungal or bacterial keratitis. Old corneal scars appear well-defined, whereas active disease typically shows hazy margins and anterior chamber activity.
Stromal HSK usually recurs; one-fifth of all patients who contract ocular herpes eventually have stromal disease. Males are twice as likely to experience recurrences, usually in autumn and winter. Stromal herpes likely results from active viral infection of the stroma and/or the immune response to viral material within the stroma. Stromal opacification results from an inflammatory response mediated primarily by CD4 lymphocytes. Recurrent stromal herpes may cause progressive scarring, neovascularization and stromal necrosis.
Treating Stromal Herpes
Treat the inflammatory response with prednisolone acetate (Pred Forte, Allergan) frequently enough to control inflammation (usually t.i.d or q.i.d.). Steroids reduce damage from the immune response, but patients who have recurrent disease tend to become dependent on them. Cycloplegia improves comfort and reduces posterior synechia formation.
Because steroids can exacerbate active herpes infection, prescribe topical trifluridine (Viroptic, King Pharmaceuticals) concurrently at the same dosing schedule as the steroid. Once you've controlled inflammation, slowly taper the steroid and antiviral. Reduce the dosing frequency as the clinical appearance of the keratitis/uveitis improves. To prevent rebound disease, keep the patient on a once-daily dosing of the combination for three months or longer.
Oral Medications for HSK
Valacyclovir (Valtrex, GlaxoSmithKline) is preferable to acyclovir because of reduced dosing frequency (b.i.d. vs. five times daily). Oral antivirals are secreted in tears, so consider them as an alternative treatment for individuals who can't or won't take drops. The Herpetic Eye Disease Study (HEDS) demonstrated that oral acyclovir is ineffective for treating active stromal disease or uveitis that's concurrently treated with steroids and topical trifluridine. The HEDS study also showed that oral antivirals reduce recurrences of epithelial and stromal disease by about 40 percent.
Secondary glaucoma and trabeculitis can accompany herpetic stromal disease, so include a medication (a topical beta blocker or a carbonic anhydrase inhibitor) that reduces aqueous production. Avoid topical prostaglandin analogs because they may actually promote the recurrence and severity of herpetic eye disease.
Educate Your HSK Patients
Kaufman et al (1996) demonstrated that once a strain of HS infects the trigeminal ganglion, further infection by another strain isn't possible. If a patient acquires a strain that doesn't cause recurrent or stromal disease, then this protects him from acquiring "bad" strains. If a patient acquires a strain that recurs and/or causes stromal disease, then he may have a problem for life. We must educate patients who have "bad" HS strains that recurrences are possible and that time is of the essence if they experience symptoms.
Dr. Townsend is in private practice in Canyon, Texas, and is an adjunct professor at UHCO. E-mail him at firstname.lastname@example.org.