Eligibility Details:  
        PARTICIPANT INCLUSION CRITERIA
        To be eligible for study participation, an individual must meet all of the following
        criteria:
          1. Ability to understand, and willingness and ability to read and sign, the informed
             consent form.
          2. Ability to understand and follow instructions and study procedures.
          3. Willingness to comply with all study procedures and be available for the duration of
             the study.
          4. Ability to take oral medication, and are willing to adhere to study medication
             regimen.
          5. Age 18 years or older.
          6. Diagnosed with HZO in one eye based on both of these criteria:
               1. History of characteristic unilateral, usually vesicular, rash in the dermatomal
                  distribution of cranial nerve V1.
               2. Medical record documentation of an episode of active dendriform epithelial
                  keratitis, stromal keratitis, endothelial keratitis, and/or iritis due to HZO
                  within the preceding year. This episode of active anterior segment ocular disease
                  may be due to HZO of recent onset (within the preceding 6 months); or chronic HZO
                  (with onset six or more months ago); may be new, worsening, or recurrent disease
                  after a period of inactivity; and may occur after medication was reduced.
             i. Study participants with chronic HZO must be on a stable treatment regimen and off
             antivirals for at least 30 days before enrollment. Study participants with chronic HZO
             who do not meet this criterion may be rescreened, if they are able to meet this
             criterion within 3 months after the study visit. (This is not a requirement for study
             participants with recent onset HZO, who may be enrolled at any time, preferably after
             completing recommended acute antiviral treatment, if prescribed, is completed).
          7. For females with reproductive potential, willingness to use highly effective
             contraception (e.g., hormonal contraception, barrier contraception, intrauterine
             device, or abstinence).
        PARTICIPANT EXCLUSION CRITERIA
        An individual who meets any of the following criteria will be excluded from participation
        in this study:
          1. History of immunocompromised status as defined by current CDC contraindications for
             the vaccine against zoster (44).
               1. Study participants who are diagnosed with leukemia, lymphomas or other malignant
                  neoplasms affecting bone marrow or lymphatic system, unless leukemia in remission
                  and off chemotherapy for at least 3 months.
               2. Study participants who are diagnosed with Acquired Immune Deficiency Syndrome
                  (AIDS) or presents with other clinical manifestations of Human Immunodeficiency
                  virus (HIV) including CD4 count of ≤ 200 cells/ml.
               3. Study participants on immunosuppressive therapy including:
             i. High-dose corticosteroids (greater than equivalent of prednisone 20 mg/day within 1
             month) ii. Chemotherapy, other than low dose used for treatment of immune-mediated
             diseases within 3 months iii. Study participants receiving recombinant human immune
             mediators and immune modulators, especially antitumor necrosis agents, within 1 month
             prior to enrollment d. Study participants with unspecified cellular immunodeficiency.
             e. Study participants with history of hematopoietic stem cell transplantation.
          2. Medical history of a systemic disease and thought likely to meet one of the exclusion
             criteria listed in exclusion criterion #1 during the 18-month study period.
          3. Renal insufficiency:
               1. Requires dialysis or has history of renal transplant or
               2. eGFR less than 45, determined within 30 days preceding enrollment.
          4. Allergy or adverse reaction to valacyclovir or acyclovir.
          5. History of vaccination against zoster within one month prior to enrollment. Study
             participants who meet this exclusion criterion may be rescreened. If the study
             participant receives the Herpes Zoster Subunit vaccine (Recombinant Zoster Vaccine
             (RZV), Shingrix), rescreening should take place one month after the second required
             dose of the vaccine.
          6. Keratorefractive surgery, other than limbal relaxing incisions or astigmatic
             keratotomies at the time of cataract surgery, within 5 years of enrollment, or
             keratoplasty of the involved eye with zoster.
          7. On systemic antivirals with activity against herpes within the past 30 days, including
             acyclovir, valacyclovir, or famciclovir, for any reason except for treatment of acute
             HZO, including investigational drug trial.
          8. History of another condition that may require treatment with one of these three
             antivirals listed above in exclusion criterion #7, during the course of the study;
             study participants who require chronic suppressive antiviral treatment with these
             medications will be excluded.
          9. Sexually active women who are pregnant, nursing, or in their reproductive years who do
             not agree to use contraception during the 1-year treatment period.
         10. Incarceration
         11. Any condition or circumstance that in the opinion of the study investigator, would
             place the study participant in increased risk or affect his/her full compliance or
             completion of the study.
         12. Participation in a clinical study testing a drug, biologic, device or other
             intervention within the last 30 days from enrollment visit. Study participants who
             meet this criterion may be rescreened.