Retinitis is a condition characterized by an inflammatory process that affects the retina of the eye. It may be a genetic defect, termed as retinitis pigmentosa or a result of bacterial or viral infection. Retinitis pigmentosa involves progressive degeneration of the retina and is a wide category that includes a multitude of such diseases and infectious retinitis is most commonly caused by a cytomegalovirus (CMV) infection.
Retinitis pigmentosa (RP)
The condition includes a multitude of syndromes leading to retinal degeneration and starts to manifest with nyctalopia and peripheral vision impairment that develops gradually   . Central vision may also be affected, but its onset is usually delayed. Retinitis pigmentosa initially starts to manifest at some point between the age of 10 to 30 years old, although nyctalopia and peripheral vision abnormality may first be experienced during childhood or infancy. Regarding the signs of RP, pigmentation abnormalities tend to appear as granules or localized aggregates, as retinal pigmentation is unevenly distributed. Various other ophthalmologic pathologies may accompany RP, including myopia, keratoconus, glaucoma (open-angle), cataract and vitreous irregularities.
Retinitis caused by a CMV infection presents as a viral necrotizing retinitis and is primarily diagnosed in patients who are immunodeficient due to various causes, including AIDS syndrome, chemotherapy, organ transplantation or leukemia    . The precise distribution of the retinal lesions stipulates the type and extent of the symptom initially reported by the patients; thus, damage to the peripheral retinal regions may be asymptomatic and lesions located more centrally tend to lead to a reduced visual acuity. Retinitis caused by CMV develops gradually over time and ultimately causes blindness, if left untreated .
Patients suspected to be suffering from retinitis pigmentosa are first evaluated via slit-lamp biomicroscopy. A comprehensive ophthalmological assessment is required as well, including a visual acuity and visual field evaluation, a pupillary response test and a color defectiveness determination test.
The examination that plays the most pivotal role in the diagnosis of RP is the electroretinogram (ERG), which requires specialized ophthalmologists to be carried out. The ERG method has been developed over the recent years and is a valuable tool that can help to establish a definitive RP diagnosis  . It enables the physicians to accurately measure and map the response of the retina to light stimulus and evaluate the functionality of rods and cones. Additional tests that may be required include an ocular ultrasound, optical computer tomography (OCT) and fluorescein angiography.
Retinitis caused by a CMV infection can be diagnosed via a variety of diagnostic methods. As far as serology is concerned, it can detect both immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies in the serum. An infection that has been recently contracted is expected to yield results including a 4-fold augmentation of IgG antibodies and a significant increase of IgM antibodies. Of note, patients with a concurrent Epstein-Barr virus (EBV) or human herpesvirus 6 infection can also exhibit the aforementioned increase in IgG and IgM antibodies.
Furthermore, the polymerase chain reaction test (PCR) can also be used to detect a CMV infection that has caused retinitis. It can yield positive results earlier than serology, especially in cases of patients with viremia, following transplantation. A shell vial assay can produce positive culture results in 24 to 48 hours, thus allowing for prompt treatment initiation. A chest radiograph and a chest computerized tomography scan (CT) can both help to detect lesions in the lungs that are compatible with a CMV infection. Lastly, a biopsy can also be used to identify an ocular CMV infection.