Pars planitis is chronic intermediate uveitis for which no systemic disease or associated infection could be found. The term intermediate uveitis describes an intraocular inflammatory process with vitreous as the primary site of inflammation. Inflammation may be present in the anterior vitreous, the vitreous base overlying the peripheral retina-pars plana region. It is characterized by vitreal inflammatory aggregates (snowballs), and whitish exudates on the inferior pars plana (snowbanking). Intermediate uveitis includes posterior cyclitis, pars planitis, and hyalitis.
Pars planitis refers to the subset of intermediate uveitis, characterized by the presence of snowball or snowbank formation, without an underlying infectious or systemic disease.
Etiology of pars planitis remains unknown. 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.
In a prospective epidemiology study of 215 uveitis patients, Vadot et al. found an incidence of 1.4 per 100,000 in France and a prevalence of 5.9 per 100,000. In the United States, Gritz and Wong found an incidence of 1.5 per 100,000 and a prevalence of 4 per 100,000. The disease primarily affects children and adults through the fourth decade. Seventy percent to 90% of cases are bilateral, though most of the time one eye is more symptomatic. There is no sex or race predisposition.
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.
History and Physical
Patients with pars planitis present with minimal symptoms, for example, floaters or blurry vision. In most cases, there is the absence of photophobia and pain. Occasionally patients may present with sudden loss of vision due to retinal detachment or acute vitreous hemorrhage.
Clinical signs of anterior segment inflammation may be present, mild anterior chamber cells. A characteristic sign of pars planitis is vitreous cell infiltration, ranging from 1+ to 4+. Sometimes the cellular infiltration is so dense that it may obscure the view of the retina. Snowballs, are the yellowish, white vitreal aggregate hallmark and are found in the inferior periphery. Peripheral vasculitis may be seen in 10% to 32% of patients. This may present as venous sheathing which may lead to occlusion and occasionally retinal neovascularization. Cystoid macular edema may be present and is the usual cause of visual decline. There may be complicated cataract (posterior subcapsular cataract).
During the acute phase, white exudates are present, in the later stage, there is collagen production which results in snowbank formation. Snowbanks are mostly located inferiorly, but occasionally they may encompass the entire peripheral retina.
Diagnosis of pars planitis is based on clinical findings. The presence of more vitreous cells than anterior chamber cells, vitreous snowballs, and the presence of pars plana exudates suggest pars planitis. There may be peripheral vascular sheathing and/or cystoid macular edema/ epiretinal membrane.
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.
- Acute complications of sarcoidosis
- Inflammatory bowel disease
Although pars planitis is one of the benign forms of uveitis, severe complications secondary to chronic inflammation may occur.
An important ocular complication is epiretinal membrane formation with a reported incidence of 7% to 36%, the mean duration between onset of pars planitis and epiretinal membrane formation has been reported to be 6.5 to 7.9 years. Cataracts are reported to occur in 14% to 30% of pars planitis cases They may occur as a result of the disease or as a result of treatment with corticosteroids, and it is difficult to distinguish between the two causes. A posterior subcapsular cataract is the most commonly diagnosed cataract. Cystoid macular edema is described as the major cause of vision loss. Other complications include retinal vasculitis, retinal neovascularization, peripheral vitreous traction, and vitreous hemorrhage.
In a study, the complications of pars planitis 'included macular edema (47.7%), vitreous opacities (38.6%), papillitis (38.6%), vasculitis (36.4%), and cataract (20.5%)'.
Enhancing Healthcare Team Outcomes
The diagnosis and management of pars planitis is best done with an interprofessional team that include ophthalmology nurses and pharmacists. Clinicians should note that the diagnosis of pars planitis is based on clinical findings. The presence of more vitreous cells than anterior chamber cells, vitreous snowballs, and the presence of pars plana exudates suggest pars planitis. There may be peripheral vascular sheathing and/or cystoid macular edema/ epiretinal membrane. 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.
The treatment depends on the cause but in most cases, high dose corticosteroids and/or biological agents are used. The outcomes depend on the cause and response to treatment.