What is pars planitis?

Pars planitis, also referred to as intermediate uveitis is a chronic, immunological disorder that affects your eye and is a type of uveitis. The condition is characterised by inflammation to a part of your uvea, a structure comprising three components (iris, ciliary body and choroid) that surrounds your eye. Patients may experience a variety of symptoms and in extreme cases, they may experience vision loss and according to studies, there are yearly incidence rates of around 1.4-2.0 cases per 100,000 in the population. The cause is unknown but links to infectious diseases are currently being explored.^1,2,3,4

Where does pars planitis affect you?

Pars planitis is a type of uveitis, which by definition means it is a disease that occurs within your eye and causes inflammation, with the vitreous, the jelly-like substance within your eye, as the main site of infection. For pars planitis, the inflammation occurs within your uvea, which is a tissue located between your sclera, the white part of your eye, and retina, your eye’s light receptor. The infection is within the intermediate zone of your eye, between the iris at the anterior and the retina and/or choroid at the posterior.^1,3

The condition is usually bilateral, meaning it affects both eyes with over 75% of cases reported in this manner. However, there have been some reports of an asymmetrical involvement, where the less affected eye shows few signs of infection within the vitreous.⁴

Who does Pars Planitis affect?

Pars planitis is a disease that primarily affects children and adolescents, although some adult cases have been noted. The condition is most common in children between the ages of six to ten years at the time of diagnosis, and there is a mean age of 7.8.^4,5,6

The distribution of the condition between genders is less clear. In line with most research, a male predominance has been found at a male to female ratio of 5:1, while some other studies have reported a female predominance. The majority of cases within children occur in males and those that occur within adults are in females.^4,6

Further studies would be required to confirm the findings, but rates of infection have been seen to be lower in Hispanic children when compared to non-Hispanic children.

What are the symptoms?

Pars planitis does not always present with the condition, sometimes it is asymptomatic. This is particularly common in younger children and is often diagnosed during routine eye examinations. However, the more common symptoms that present are:

• Floaters - vitreal inflammatory aggregates
• Blurred vision

Less common symptoms:

• Pain
• Photophobia
• Red eye
• Retinal vasculitis
• Optic disc edema
• Anterior segment inflammation

Pars planitis is usually benign however, in more severe cases, it can lead to vision loss and blindness. This can be caused by an aggregation of floaters and complications with cataracts, cystoid macular oedema, vitreous opacities and optic disc oedema.^1,3,4

What causes Pars Planitis?

The exact cause of pars planitis currently remains unknown, but there are theories. The majority of children diagnosed have not had an underlying disease, meaning the condition is classed as idiopathic -. This is a term used to describe a condition with no known cause.^1,4

Trigger theory

The currently accepted theory is called the trigger theory. While the cause is unknown, it is widely accepted that the condition is an autoimmune disease. An autoimmune disease is a condition that causes your immune system to malfunction and produce inflammatory responses that attack itself. This is thought to be triggered by antigens. These are markers, found on bacteria and viruses that signal to your immune system that something is not supposed to be there, leading to the activation of your immune system.^1,4

One such link that is being investigated is that of HLA-DR15. This is an antigen, and patients who tested positive for this were also reported to have had systemic disorders such as multiple sclerosis, optic neuritis and narcolepsy. This link suggests a possible common background with the conditions.⁴

Diagnosis

A diagnosis of pars planitis should be performed with three key steps:

• Physical evaluation
• Patient history check
• Eye examination

There are however, some complications with a diagnosis, preventing it from being a straightforward process. There is a need to rule out an active infection or an underlying systemic disease that can mimic pars planitis, such as multiple sclerosis. The condition may also be underdiagnosed when inferior floaters are missed, in particular when an ophthalmoscopy has not been performed.^3,4

A further challenge is that there are no specific diagnostic laboratory tests which can be performed to diagnose pars planitis. In order to rule out systemic infections, tests can include:

• Serological tests
• Chest x-ray
• Purified protein derivative skin test
• Magnetic resonance imaging

When diagnosing a child, the condition needs to be differentiated from chronic anterior uveitis, a condition which can be associated with juvenile idiopathic arthritis or be idiopathic in itself. A misdiagnosis can also be achieved due to complications. These can include band keratopathy, posterior synechiae and cataracts.⁴

Treatment

The first line of treatment includes the use of oral and/or intraocular steroids to reduce inflammation. These can include triamcinolone, which is used as a steroid implant; there is a severe case of pars planitis with asymmetry and cystoid macular oedema. When the condition presents bilaterally, steroids may only be used within one eye to prevent any systemic side effects. For those who no longer require their immune system to be suppressed, immunomodulators can be used. If conventional therapy is unsuccessful, anti-tumour necrosis factor agents can be used. These should however, be used sparingly, and they are not favoured due to an increased risk of developing multiple sclerosis. As a fourth step, surgery may be performed to remove the pars plana, which will in turn, remove the inflammatory cytokines that are causing the oedema. There are risks associated with the surgery, with potential for retinal detachment and recurrence of the condition. Additional surgeries can be used such as peripheral scatter laser photocoagulation or cryotherapy, although this can be painful and again, lead to the development of retinal detachment. If a patient develops cataracts, they may need surgery for removal, which can only be performed if inflammation is controlled using corticosteroids and immunosuppressives for a minimum of three months first.^1,4

Summary

Pars planitis is an autoimmune eye disease, affecting your eye, with no known cause. It can be asymptomatic or present in a variety of ways, with extreme cases leading to vision loss. It is important to undergo regular eye check-ups and to recognise the symptoms if detected, pars planitis is treatable, but can cause lasting damage if left untouched. The current theory is that the condition is triggered by infectious diseases and systemic conditions, something that researchers are exploring. The aim is to discover the cause in the hope of adapting treatment methods to more effectively treat patients in the future.