Acute retinal necrosis has been described as a clinical entity for nearly 30 years. Acute retinal necrosis is a potentially visually devastating necrotizing vaso-occlusive retinitis affecting both healthy and immunocompromised patients. Acute retinal necrosis is caused by the herpes group of viruses, mainly varicella zoster, herpes simplex types 1 and 2, and, rarely, cytomegalovirus. Recently, polymerase chain reaction techniques have enabled detection of very small amounts of viral DNA from intra-ocular fluid samples. This can help in both the diagnosis of atypical cases of retinitis and uveitis and directing treatment in cases of acute retinal necrosis.