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Retinitis
Retinitis is the inflammation of the retina, the thin tissue lining at the back of the eye. The retina contains photoreceptors, rod, and cone cells, which are responsible for converting light into neural signals for visual recognition. Retinitis may cause the degeneration of the photoreceptor cells, subsequently leading to vision impairment. There are different types of retinitis such as retinitis pigmentosa (RP), cytomegalovirus (CMV) retinitis, and chorioretinitis (CR). Retinitis can be caused by a variety of factors such as genetics, viral infections, and a weakened immune system. Diagnosis of retinitis involves a thorough examination by an ophthalmologist.

Types
Types of retinitis include retinitis pigmentosa, cytomegalovirus retinitis, and chorioretinitis.

Retinitis pigmentosa is an inherited disorder leading to the progressive degeneration of the photoreceptors in the retina, typically in both eyes. The inheritance of RP is considered autosomal dominant, autosomal recessive, and X-linked. RP is caused by mutations in numerous genes that encode proteins that are required by photoreceptors in the retina. These mutations can inhibit the production of proteins, produce abnormal malfunctioning proteins, or produce toxic proteins, all three situations cause damage to photoreceptors.

Cytomegalovirus retinitis is caused by cytomegalovirus, a herpes virus. Contraction of CMV does not usually cause any visible signs or symptoms of infection. Once contracted, the virus is in the body permanently and stays in a temporary inactive form. When CMV is activated, it spreads to the eye through the bloodstream and causes inflammation of the retina. CMV retinitis is more common in individuals with a weakened immune system, which can arise from the following:
 * HIV/AIDS


 * Organ transplant


 * Chemotherapy

Chorioretinitis affects the retina and the choroid, the vascular layer of the eye. Chorioretinitis is typically caused by congenital, bacterial or protozoal infections such as congenital toxoplasma or cytomegalovirus. If there is permanent damage to the choroid, this may block blood supply to the retina and will lead to vision loss.

Symptoms
Retinitis pigmentosa: Cytomegalovirus retinitis: Chorioretinitis:
 * Progressive vision loss
 * Night vision loss
 * Peripheral vision loss
 * Peripheral vision loss
 * Blurred vision
 * Cloudiness of eye
 * Blurred vision
 * Floating black spots
 * Pain or redness in the eye
 * Sensitivity to light
 * Excessive tearing of the retina

Treatment
There is no known cure for retinitis pigmentosa. However, prospective treatments such as vitamin A palmitate, docosahexaenoic acid, and Lutein supplements are being evaluated for their safety and effectiveness.

CMV retinitis is treated through strengthening the immune system with highly active antiretroviral therapy (HAART). This provides long-term management of CMV by recovering the immune function. Short-term solutions include antiviral medications such as ganciclovir, valganciclovir, or foscarnet that can be administered for a period of time as determined by a clinician. Although there are various treatment options, vision loss due to CMV retinitis cannot be regained.

Chorioretinitis can be treated by certain antimicrobials. Depending on the cause of the chorioretinitis, antivirals, antibiotics, antifungals, anthelmintics, or antituberculous drugs can be utilized to prevent further loss of vision.

Diagnosis
Diagnosis involves examinations by an ophthalmologist, an eye doctor. A visual field test, visual acuity test, and electroretinography (ERG) are used to monitor and evaluate photoreceptor function.

A visual acuity test uses the standard eye chart to measure how well a person can see at various distances. Patients with retinitis typically have worse visual acuity due to vision loss.

A visual field test is used to determine a patient’s central vision. In the test, a patient watches a dot of light move within a designated space and uses a button to indicate when they cannot see the dot anymore. A map of their vision is constructed using the results from the test. Retinitis typically results in progressive visual field loss and a visual field test can be used to locate the defects in the visual field associated with the damage to the retina.

Electroretinography uses electrical signals to measure photoreceptor function. A contact lens with electrodes attached is used to measure electrical activity in the retina. Light is flashed into the patient’s eye and the electrodes measure the electrical activity of the rod and cone cell response. A decline in electrical signal indicates photoreceptor function loss.

Laboratory testing is used to diagnose the different types of retinitis. More specifically, retinitis pigmentosa is diagnosed using genetic testing as it is an inherited disease. CMV retinitis is diagnosed with blood or urine tests which test for substances specific to CMV. For chorioretinitis, there are a variety of tests that may be applied to confirm diagnosis such as a fundus fluorescein angiography, indocyanine green angiography, ultrasonography, or optical coherence tomography.