**1. Introduction**

Human herpesviruses, which include HSV-1 (Herpes simplex virus type-1), HSV-2 (Herpes simplex virus type-2), HZV (Herpes zoster virus), EBV (Epstein– Barr virus), CMV (Cytomegalovirus), HHV-6 (Human herpesvirus-6), HHV-7 (Human herpesvirus-7), HHV-8/KSHV (Human herpesvirus-8, Kaposi's sarcomaassociated herpesvirus) are the causative factor of various diseases, including mononucleosis, roseola, chickenpox and many forms of ocular involvement, such as conjunctivitis, blepharitis, keratitis, uveitis and retinitis. The common features of all human herpesviruses include a double-stranded DNA genome, a 20-faceted icosahedral capsid, a surrounding proteinaceous tegument, and an external glycoproteinladen lipid envelope. All herpesviruses are able to achieve a state of the latency, where the virus remains inactive in cells and occasionally reactivates. Recurrence could be described as the most characteristic feature of corneal infections caused by HSV, subsequently leading to visual impairment and blindness. According to epidemiological data, HSV keratitis remains a leading infectious cause of blindness in the world. The estimated global incidence of HSV keratitis is roughly 1,5 million, including 40,000 new cases of each year. Additionally the recurrence rate is high. It was estimated as 9.6% at 1 year, 22.9% at 2 years, and 63.2% at 20 years after the first episode of documented HSV keratitis [1–4]. Also the worldwide seroprevalence rate is high and estimated above 50%, but recently it was reported declining in the United States [5].

In this chapter we will focus on Herpes simplex virus 1 keratitis - the detailed corneal characteristics based on slit-lamp examination, optical coherence tomography scans and confocal microscopy results. The chapter also discusses recent methods of diagnosis based on PCR testing as well as established and future methods of treatment based on the latest research results.
