Herpes zoster ophthalmicus (HZO) is a reactivation of the varicella-zoster virus involving the ophthalmic branch of the trigeminal nerve that may cause severe ocular complications, including keratouveitis, potentially resulting in permanent visual impairment. This case highlights the clinical challenge of managing active HZO-associated keratouveitis in the presence of coexisting bilateral senile cataracts, in which treatment prioritization is essential to optimize visual outcomes. A 52-year-old man presented with pain, redness, photophobia, and decreased vision in the right eye for 10 days before hospital admission. Ophthalmologic examination revealed decreased visual acuity in the right eye, with counting fingers at 0.5 m, eyelid edema, conjunctival hyperemia, discharge, conjunctival and ciliary injection, corneal haze with infiltrates, and keratic precipitates, while bilateral lens opacities consistent with senile cataracts were also identified. Dermatological examination demonstrated multiple vesicular lesions distributed along the ophthalmic branch of the trigeminal nerve with a positive Hutchinson sign. The patient was diagnosed with right-eye keratouveitis secondary to HZO accompanied by bilateral senile cataracts and was treated with oral acyclovir, topical acyclovir 3% ophthalmic ointment, topical levofloxacin, topical prednisolone acetate, and cyclopentolate. At the one-week follow-up, the patient showed reduced ocular pain, improvement in right-eye visual acuity from counting fingers at 0.5 m to counting fingers at 3 m, and resolution of ocular tenderness. However, conjunctival hyperemia, mild corneal opacity with residual scarring, and bilateral lens opacities persisted, indicating partial clinical improvement despite ongoing ocular involvement. This case emphasizes the importance of early diagnosis, prompt antiviral therapy, careful ophthalmologic monitoring, and prioritization of active ocular inflammation management before cataract intervention to minimize complications and preserve visual function.