Acute retinal necrosis overview

# Overview
Acute retinal necrosis is an inflammatory eye condition usually caused by reactivation of latent viruses, including Herpes simplex virus 1 & 2, Varicella-zoster virus, cytomegalovirus, and Epstein-Barr virus. Symptoms include eye pain, vision loss, floaters, flashes, excessive sensitivity to light, flu symptoms, and redness of the affected eye. The pathogenesis of acute retinal necrosis is characterized by retinal inflammation due to ocular viral infection. Particles from Herpes simplex virus 1 (HSV-1), Herpes simplex virus 2 (HSV-2), and Varicella zoster virus (VZV) infiltrate the retina through various locations of epithelial penetration, including the skin, conjunctiva, cornea, and nasal cavity. Acute retinal necrosis may be classified both by stagingacute or lateor by severity: mild or fulminant. The natural progression of ARN depends on whether the case is mild or fulminant. Mild cases of ARN present with white-yellow necrotic lesions that do not coalesce or lead to retinal detachment; the disease is self-limited. Fulminant cases of ARN will lead to progressive necrosis of retinal tissue, leading to pigmentation scarring, vitreous debris, and retinal detachment. Without treatment, ARN will usually progress to bilateral acute retinal necrosis (BARN) within weeks to a few months. With treatment, the prognosis for ARN is good if the therapy is administered early and sustained until symptoms resolve. The mainstays of medical therapy for acute retinal necrosis are regimens of empiric and pathogen-directed antimicrobial therapy. The primary risk factors for acute retinal necrosis include immunocompromised status and immunosuppression from disease and prolonged corticosteroid use.

# Historical Perspective
Acute retinal necrosis was first discovered in 1971 by Urayama A, Yamada N, Sasaki T. Acute retinal necrosis was first officially classified as bilateral acute retinal necrosis in 1978 by N.J. Young and A.C. Bird, applied to 4 cases of bilateral necrotizing retinitis that progressed to retinal detachment and phthisis despite corticosteroid and antibiotic therapy. In the 1980s, emergence of pathological and electron findings from analysis of vitrectomy and enucleation specimens led to the identification of members of the herpes virus family as the cause of acute retinal necrosis. The official diagnostic criteria for acute retinal necrosis was proposed by the American Uveitis Society in 1994.

# Classification
Acute retinal necrosis may be classified both by stagingacute or lateor by severity: mild or fulminant.

# Pathophysiology
- The pathogenesis of acute retinal necrosis is characterized by retinal inflammation due to ocular viral infection. Particles from Herpes simplex virus 1 (HSV-1), Herpes simplex virus 2 (HSV-2), and Varicella zoster virus (VZV) infiltrate the retina through various locations of epithelial penetration, including the skin, conjunctiva, cornea, and nasal cavity. Acute retinal necrosis develops from HSV-1, HSV-2, and VZV due to the viruses' ability to transmit and replicate in the central nervous system (CNS), as well as their ability to transport anterograde through the optic nerve, establish latency, reactivate, and cause retinal inflammation.
- For Caucasian populations, possessing the HLA-DQw7, HLA-Bw62, and HLA-DR4 antigens is correlated to a genetic predisposition to ARN. For Japanese populations, possessing the HLA-Aw33, HLA-B44, and HLA-DRw6 antigens is correlated to a genetic predisposition to ARN.
- Acute retinal necrosis is associated with the following ocular conditions: progressive outer retinal necrosis, uveitis, cytomegalovirus retinitis, toxoplasmic chorioretinitis, and endophthalmitis.

# Causes
Acute retinal necrosis is usually caused by reactivation of latent viruses: Herpes simplex virus 1 & 2, Varicella-zoster virus, cytomegalovirus, and Epstein-Barr virus.

# Differentiating Acute retinal necrosis other Diseases
Acute retinal necrosis must be differentiated from other diseases that cause eye pain, conjunctival infection, photophobia, and vision loss.

# Epidemiology and Demographics
- The incidence of acute retinal necrosis (ARN) is approximately 6.3 per 100,000 individuals.
- ARN developed from Herpes simplex virus 1 and Varicella-zoster virus is most common among patients older than 50 years, while the incidence of HSV-2 caused ARN is highest in children and young adults between age 9 and 22 years.
- There is no racial or gender predisposition to acute retinal necrosis.

# Risk Factors
The primary risk factors for acute retinal necrosis include immunocompromised status and immunosuppression from disease and prolonged corticosteroid use. Genetic predisposition for certain Caucasian and Japanese populations heightens the possibility of developing ARN.

# Screening
There is no established, diagnostic screening process for acute retinal necrosis.

# Natural History, Complications and Prognosis
- Symptoms of acute retinal necrosis (ARN) develop rapidly upon onset of pathogenic infection.
- The natural progression of ARN depends on whether the case is mild or fulminant.
Mild cases of ARN presents with white-yellow necrotic lesions that do not coalesce or lead to retinal detachment; the disease is self-limited.
Fulminant cases of ARN will lead to progressive necrosis of retinal tissue, leading to pigmentation scarring, vitreous debris, and retinal detachment.
- Mild cases of ARN presents with white-yellow necrotic lesions that do not coalesce or lead to retinal detachment; the disease is self-limited.
- Fulminant cases of ARN will lead to progressive necrosis of retinal tissue, leading to pigmentation scarring, vitreous debris, and retinal detachment.
- Without treatment, ARN will usually progress to bilateral acute retinal necrosis (BARN) within weeks to a few months. Complications resulting from acute retinal necrosis occur due to retinal tissue damage and subsequent infection from the causative pathogen.
- Without treatment, the prognosis for acute retinal necrosis (ARN) varies.
Mild ARN is usually self-limited and will resolve itself without treatment; risk of permanent vision loss is very low.
Fulminant ARN will usually progress to complications such as progressive outer retinal necrosis and has a worse prognosis.
- Mild ARN is usually self-limited and will resolve itself without treatment; risk of permanent vision loss is very low.
- Fulminant ARN will usually progress to complications such as progressive outer retinal necrosis and has a worse prognosis.
- With treatment, the prognosis for ARN is good if the therapy is started early and sustained until symptoms resolve.

# Diagnosis

## Diagnostic Criteria
The American Uveitis Society determined five diagnostic criteria for acute retinal necrosis in 1994.

## History and Symptoms
Patient history of prior or concurrent diseases, particularly those associated with acute retinal necrosis pathogens or sources of immunocompromised status, should be considered in the diagnosis of ARN.
Symptoms of acute retinal necrosis include:
- eye pain
- vision loss
- floaters
- flashes
- excessive sensitivity to light
- flu-like symptoms
- redness of the affected eye

## Physical Examination
Physical examination of patients with acute retinal necrosis may reveal erythema and hyperaemia of the retina, white-yellow necrotic lesions, purulent exudate, opaque vitreous, and other indications of inflammation in the eye.

## Laboratory Findings
Laboratory findings consistent with a diagnosis of acute retinal necrosis are those used to determine the presence of the viral pathogen, including PCR test results, viral cultures, immunoflourescence results, and detection of antibodies indicative of sources of ARN via the Goldmann-Witmer coefficient.

## Electrocardiogram
There are no diagnostic electrocardiogram findings associated with acute retinal necrosis.

## Chest X Ray
There are no diagnostic chest x ray findings associated with acute retinal necrosis.

## CT
CT imaging may reveal indicators of inflammation and infection by the causative pathogen for acute retinal necrosis, including hypoattenuation along the optic tractindicative of Varicella-zoster virus (VZV) infectionand hyperattenuation along the optic tract, retina, sclerae, and lateral geniculate body.

## MRI
MRI imaging may reveal lesions indicative of infection from acute retinal necrosis pathogens.

## Echocardiography or Ultrasound
There are no diagnostic echocardiography or ultrasound findings associated with acute retinal necrosis.

## Other Imaging Findings
Other imaging findings that may be helpful in the diagonsis of acute retinal necrosis include fundus autofluorescence (FAF), fluorescein angiography, and optical coherence tomography.

## Other Diagnostic Studies
There are no other diagnostic studies associated with acute retinal necrosis.

# Treatment

## Medical Therapy
The mainstays of medical therapy for acute retinal necrosis are regimens of empiric and pathogen-directed antimicrobial therapy.

## Surgery
Surgery is not the first-line treatment option for patients with acute retinal necrosis; it is indicated primarily when there is a substantial risk of complications, including retinal detachment and tissue atrophy.

## Primary Prevention
Preventing the onset of acute retinal necrosis is dependent upon preventing the causative infection from Herpes simplex virus (HSV), Varicella-zoster virus (VZV), Cytomegalovirus (CMV), and Epstein-Barr virus (EBV).

## Secondary Prevention
While recurrence of acute retinal necrosis is not completely preventable at present, the administration of topical and intravitreal antiviral therapy targeted to the specific cause of the disease can reduce the chance of recurrence.