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Pars planitis is a form of uveitis, one of a diverse group of potentially blinding but treatable inflammatory eye disorders affecting the middle layer of the eye know as the uvea or uveal tract. The uvea, responsible for the eye's blood supply, is made up of three structures: the iris, the ciliary body, and the choriod. The pars plana is part of the ciliary body.
Pars planitis is one form of intermediate uveitis, and some physicians may use this term, "intermediate uveitis", to describe the condition rather than pars planitis.
Pars planitis is inflammation of the pars plana, a part of the ciliary body. The ciliary body is the structure behind the iris responsible for making aqueous humor, the fluid in the eye that nourishes the lens and cornea. The ciliary body is divisible into two parts: the pars plana and the pars plicata.
Pars planitis can occur in one or both eyes. In some instances, this disorder occurs as a complication of systemic illness. In other cases, the cause cannot be determined. In either instance, pars planitis is a treatable condition and may require the use of systemic immunosuppression medication and/or surgery to halt its progression. Untreated, 20% of patients with pars planitis will have significant vision loss, and some will become blind. Once vision loss from pars planitis has occurred it can not be reversed, so early treatment of the disorder, before there is vision loss, is very important. The need for aggressive treatment of pars planitis has, generally, been underappreciated by the medical community but is now well documented in the medical literature. Chronic steroid use no longer represents the standard of care for this disorder. Patients with pars planitis are urged to seek care from a uveitis specialist or ocular immunologist.
Once the pars plana develops inflammation, white blood cells and other by-products of that inflammation, ("inflammatory exudates"), are spilled into the middle chamber of the eye, called the vitreous chamber, where the patient can observe "dots" or "streaks" or other "stuff" in their visual field.
The first observable sign of pars planitis is the accumulation of inflammatory exudates in the vitreous. The medical terms for this is "vitritis". The accumulation may be small or extensive and is typically relegated to the inferior retina by gravity. That is, over time, gravity causes the inflammatory material to settle on the retina.
There also may be the presence of cataract, especially posterior subcapsular, and cystoid macular edema. In extreme cases, there may be retinal vasculitis and neovascularization. In some instances, this disorder occurs as a complication of systemic illness. In other cases, the cause cannot be determined. MS has been reported to develop in 7.4% of patients with pars planitis. And, there are many health conditions associated with the broader category of uveitis.
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