Describe the Herpes simplex keratitis.
Etiology: infection due to reactivated herpes simplex virus (HSV) type 1 from the trigeminal ganglion
Similar to viral conjunctivitis, but usually unilateral
± Eye pain
Foreign body sensation
Blurry vision; can lead to vision loss if untreated
Fluorescein staining: superficial corneal erosions (dendritic ulcers) that resemble the branches of a tree (geographic ulcers may be seen when dendritic ulcers widen in shape)
Direct fluorescein antibody test (HSV antigen detection) or polymerase chain reaction (PCR) test
Treatment for epithelial HSV keratitis 
Topical trifluridine solution or ganciclovir 0.15% gel
Oral antiviral (e.g., acyclovir) when topical treatment cannot be administered by the patient, prophylactic treatment after surgery, or refractory cases despite topical treatment
Corneal transplantation for patients with severe corneal scarring
Glucocorticoids should not be used in initial treatment of dendritic epithelial keratitis!
Describe the Herpes zoster keratitis.
Etiology: reactivated herpes zoster virus (involvement of the ophthalmic nerve ); see also herpes zoster ophthalmicus.
Prodrome: headache, malaise, fever
Eye irritation (foreign body sensation)
In the innervation area of the ophthalmic nerve (forehead, bridge, and tip of the nose):
Slit-lamp examination and fluorescein staining
1–2 days: punctate lesions on the corneal surface
4–6 days: pseudodendritic lesions on the corneal surface
Treatment: oral acyclovir, valacyclovir, or famciclovir