Pars planitis

Other Names: Intermediate uveitis; Peripheral retinal inflammation; Vitritis

Pars planitis is a disease of the eye that is characterized by inflammation of the narrowed area (pars plana) between the colored part of the eye (iris) and the choroid. This may lead to blurred vision; dark, floating spots in the vision; and progressive vision loss. As the condition advances, cataracts, retinal detachment, or macular edema (fluid within the retina) may develop. Pars planitis most often affects young men and is generally not associated with any other disease or symptoms (idiopathic); however, it can be associated with other autoimmune conditions such as multiple sclerosis and sarcoidosis.

Cause

The exact underlying cause of pars planitis is unknown. Scientists suspect that it is an autoimmune condition in which the body's immune system mistakenly attacks healthy tissues (certain parts of the eyes, in this case). This is further supported by the fact that pars planitis is sometimes associated with other autoimmune conditions such as multiple sclerosis and sarcoidosis. Although most cases occur sporadically in people with no family history of the condition, pars planitis can rarely affect more than one family member. In these cases, there may be a genetic component; however, a disease-causing gene and specific inheritance pattern have not been identified. The most widely accepted hypothesis is that pars planitis represents an autoimmune disorder of the eye. Exposure to an antigen initiates it. The nature of the antigen is not yet known, and this antigen exposure leads to activation of the immune system. The immunogenetic association has been suggested by studies citing association of HLA-B51, HLA-DR2, HLA-DR15, and HLA-DRB1*0802 haplotypes with pars planitis.

Pathophysiology

The pathogenesis of pars planitis is not completely understood. Pars plana exudates are composed of a loose fibrovascular layer containing occasional fibrocyte-like cells and scattered mononuclear cells.

T cells are the predominant cells present in the vitreous; their percentage varies from 11% to 95%. CD4+ T cells account for 5% to 75% of all the T cells. CD4+ T cells that express CD69, an activation marker, are found in aqueous humor and the blood of the patients with pars planitis. The role of CD8+T cells and B cells in the pathogenesis of pars planitis is not clear. Levels of IL-6 are elevated when compared to other cytokines: IL-1, TNF-alpha, and IL-2. After T cells, macrophages are the second most common cells present.

Symptoms

Pars planitis is characterized by inflammation of the narrowed area (pars plana) between the colored part of the eye (iris) and the choroid. This may lead to blurred vision; dark, floating spots in the vision; and progressive vision loss.Approximately 80% of cases are bilateral (affecting both eyes), although one eye is typically more affected than the other. As the condition advances, cataracts, retinal detachment, or macular edema (fluid within the retina) may develop.

Diagnosis

Pars planitis is typically diagnosed based on a specialized eye examination. During the exam, the ophthalmologist will typically see clusters of white blood cells trapped within the eyeball that are called snowballs (or "inflammatory exudate"). If these clusters are located on the pars plana, they are known as snowbanks. Snowbanks are considered a "hallmark" sign of pars planitis. It is often recommended that people over age 25 with pars planitis have an MRI of their brain and spine to rule out multiple sclerosis.

Clinical evaluation includes the measurement of visual acuity, intraocular pressure, and slit lamp examination. All patient with pars planitis should be evaluated with a thorough peripheral retinal examination with scleral depression.

Chest x-ray or CECT (contrast-enhanced computed tomography) scan of the chest may be done to evaluate for the presence of sarcoidosis and tuberculosis. Serum angiotensin-converting enzyme (ACE) level may be checked. This may be elevated in patients with sarcoidosis. Other investigations may include complete blood count, erythrocyte sedimentation rate (ESR), venereal disease research laboratory (VDRL) or rapid plasma reagin test, Mantoux, and serology for human immunodeficiency virus (HIV).

In cases with extensive vitritis, infective causes including toxoplasmosis, acute retinal necrosis, and endophthalmitis must be ruled out before starting steroid therapy.

In very elderly patients with vitritis/vitreous haze and no cystoid macular edema, primary intraocular lymphoma should be ruled out.

Fluorescein angiography will show the extent of vasculitis and show areas of retinal nonperfusion and neovascularization. Optical coherence tomography will show the presence of macular edema, epiretinal membrane, and vitreoretinal traction.

In occasional cases with severe vitreal infiltration, when posterior uveitis, retinitis, endophthalmitis, or tumors are difficult to exclude, a diagnostic vitrectomy may be performed.

Treatment

The first approach to treating pars planitis is corticosteroid eye drops or injections near the eye to control inflammation. Non-steroidal anti-inflammatory drugs (NSAIDs, including aspirin) or steroid medications (such as prednisone) can be taken by mouth. If these strategies are not successful, other medications may be given to reduce the body's immune response (medications called immunosuppressants, such as methotrexate).

If medications are not effective, surgery may be considered. Cryotherapy has been performed in affected people to remove eye tissue that has inflammation. Although this surgery has been shown to be effective in restoring clarity of vision, there are concerns that it may cause damage to other parts of the eye. Another surgery, known as vitrectomy, can be done to remove cloudy fluid (vitreous humor) from the eye.

The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition.

• Adalimumab (Brand name: Humira)adalimumab (Humira) received expanded approval for the treatment of non-infectious intermediate, posterior, and panuveitis to include pediatric patients 2 years of age and older. It was approved for use in adults with non-infectious intermediate, posterior, and panuveitis in June 2016.