Ability to read, understand and sign informed consent.
Ability to understand and follow study instructions
Ability and willingness to take study medication
Age >/= 18 years
For females of reproductive age, willingness to use highly effective contraception
Herpes Zoster Ophthalmicus (HZO) diagnosed in one eye based on standardized criteria:
History of characteristic vesicular rash in V1 and V2 dermatome distribution
Medical record documentation of an episode of active dendriform epithelial keratitis, stromal keratitis, endothelial keratitis, and/or iritis due to Herpes Zoster Ophthalmicus within the preceding year. The episode may be due to Herpes Zoster Ophthalmicus of recent onset (within 6 months) or chronic Herpes Zoster Ophthalmicus (over 6 months); may be new, worsening or recurrent disease after a period of inactivity; and may occur after medication was reduced.