Introduction

Pars planitis is an eye disorder characterised by inflammation occurring in the pars plana, a narrow region situated between the iris (the coloured part of the eye) and the choroid. The choroid is a layer of tissue in the eye, specifically between the retina and the sclera (the white outer layer of the eye). 
This inflammation can result in a range of visual disturbances, including blurred vision, the perception of dark, floating spots in the visual field, and a gradual loss of vision. As the condition progresses, it may lead to complications such as cataracts, retinal detachment, or macular edema (accumulation of fluid within the retina that is also common with people diagnosed with diabetes).

Who does pars planitis affect?

Pars planitis primarily affects young people who are assigned male at birth  and is typically categorised as occurring without a known underlying cause or accompanying symptoms. Nevertheless, it can be associated with other autoimmune disorders, such as multiple sclerosis (MS)and sarcoidosis. Treatment for pars planitis generally involves the use of corticosteroid medications, immunosuppressive drugs, and in some cases, surgical interventions.²

What are the symptoms?

The typical initial symptoms include the presence of floaters and a noticeable blurriness in vision. Additionally, peripheral retinal vasculitis, optic disc edema, and inflammation in the anterior segment of the eye are commonly observed manifestations. These manifestations would all be indicators of potential pars planitis to the trained physician.
Although pars planitis is generally considered a relatively mild form of uveitis in many cases, it has the potential to lead to severe vision impairment due to complications that may arise, including cataractsand optic disc edema. Notably, cystoid macular edema stands out as the primary contributor to visual morbidity in this condition.Uveitis is a medical term that refers to inflammation of the uvea, which is the middle layer of the eye. The uvea consists of the iris (the coloured part of the eye), the ciliary body, and the choroid.²

What is uveitis

Uveitis is an inflammatory condition within the eye, posing a significant threat to vision. It affects both the uveal tract  and many neighbouring structures in the eye. Due to its recurrent intraocular inflammation, uveitis can lead to temporary or permanent vision impairment and ocular complications that may not respond well to treatment. Uveitis can manifest as a co-occurring condition with autoimmune disorders, infections, or as an adverse effect of medications and toxins. In some cases, it occurs as a purely unexplained ocular inflammation.

The prevalence of uveitis is relatively low, estimated at 38 cases per 100,000 individuals, and is  more common among younger individuals, with the average age of onset being less than 40 years old. Uveitis ranks as the fourth leading cause of blindness in the working-age population in developed countries, although its broader economic and social impact remains unassessed.

The recognition of uveitis remains a challenge, often leading to delayed referrals to specialists and in diagnosis which increases the risk of irreversible damage to various eye structures. To address this issue and improve patient referrals, we conducted a systematic review to investigate the distribution of uveitis subtypes and their systemic associations.¹

Pars planitis explained

Detailed definition and description

Pars planitis is a form of chronic intermediate uveitis, primarily observed in children and adolescents. "Intermediate uveitis" encompasses inflammation affecting the anterior vitreous, ciliary body, and peripheral retina, and this inflammation may or may not be linked to infections or systemic diseases.²

Key clinical features and symptoms

The most frequently reported symptomsof pars planitis are floaters and blurred vision. Other, less common symptoms include pain, photophobia, and red eye. In severe cases, significant visual loss can occur due to the clumping of floaters in the vitreous or the development of macular edema.

It's worth noting that pars planitis can sometimes be asymptomatic and may be incidentally detected during routine eye examinations, particularly in young children. In some cases, young children may present with strabismus due to the development of amblyopia or complications leading to leukocoria.

Although pars planitis is generally considered a mild form of uveitis in most instances, the clinical severity can vary widely. This is because symptoms are often minimal and the diagnosis of pars planitis is frequently delayed, which can result in complications and permanent vision loss in young children.

Distinctive characteristics setting it apart from other uveitis types

Common diagnostic findings in pars planitis typically include diffuse vitreous cells, haze, snowballs, and snowbanks. Vitreous snowballs, which are yellow-white inflammatory clumps, are typically observed in the mid-vitreous and the lower peripheral vitreous region. Snowbanks, on the other hand, are exudates (located on the pars plana, often found in the lower part of the eye. These distinctive diagnostic findings aid in the identification and characterisation of pars planitis.²

Diagnosis and Clinical Evaluation

Diagnosing idiopathic pars planitis relies on clinical observations. It may go undetected, particularly if lower vitreous "snowballs" or "snowbanks" are overlooked, especially when thorough eye examinations involving ophthalmoscopy are not conducted. There is not a specific laboratory test for diagnosis. However, it's crucial to rule out systemic associations and primarily infectious causes of intermediate uveitis. Systemic assessments include serological tests, chest X-rays, purified protein derivative skin tests, and brain magnetic resonance imaging. Given the significant link between the condition and MS, neuro-imaging is particularly important for adult patients, in whom systemic associations are more common.

In children, it's essential to distinguish pars planitis from chronic anterior uveitis, which can have an unknown cause or associated with juvenile idiopathic arthritis (JIA). Both conditions follow a chronic and asymptomatic course, resulting in similar complications. Distinguishing features include pronounced anterior segment inflammation and related complications like band keratopathy, and cataracts in pediatric pars planitis. These factors may lead to a misdiagnosis of chronic anterior uveitis. The primary indicators for diagnosing JIA-associated uveitis are inflammation predominantly affecting the anterior segment of the eye and the presence of chronic arthritis.

Sarcoidosis should also be considered in the differential diagnosis of childhood pars planitis. Typically, it manifests as chronic granulomatous anterior uveitis and has  distinctive features. These features will be visible through ophthalmoscopy, as part of the eye examination from the trained physician. In young children with sarcoidosis, pulmonary involvement is less common. They may instead present with polyarthritis, skin nodules, and uveitis. Comparing serum angiotensin-converting enzyme (ACE) levels to age-matched controls is essential, as ACE levels are typically higher in children.^{2, 3}

Treatment and management

Treatment strategies for pars planitis depend on the severity of infiltration in the pars plana, the extent of vasculitis, and the presence of coexisting macular edema.

Regional corticosteroid injections:

Initially, corticosteroid injections were administered regionally or around the eye. If this was not  effective, oral prednisolone was given. Cryotherapy or laser photocoagulation of the peripheral retina was the second step. If the previous options failed, Pars Plana Vitrectomy (PPV) was considered.

 If all the above options were ineffective, steroid-sparing agents with immunosuppressive properties were considered.

However, in current practice, uveitis specialists mainly use periocular (subtenon)/intraocular and/or oral steroids for pars planitis. If both eyes are affected, one eye may be treated before the other to avoid systemic side effects. Patients are informed about the potential risk of glaucoma and cataracts associated with these interventions.

For bilateral cases that are unresponsive to periocular or intraocular steroids and severe pars planitis, oral prednisolone is initiated at a dose of 1-1.5mg/kg/day. Also, intravenous pulse methylprednisolone (1g) is an option for rapid action.

Immunomodulatory therapy is the second step for patients requiring longer immunosuppression. Commonly used steroid-sparing immunomodulatory agents include methotrexate, mycophenolate mofetil (MMF), azathioprine, and cyclosporine.

If conventional immunomodulatory therapy is ineffective, anti-tumour necrosis factor (TNF) agents are used as the third step. Adalimumab, a TNF inhibitor, is approved for treating noninfectious uveitis, but its use in pars planitis necessitates careful consideration of the risk-benefit ratio, especially concerning potential demyelination risks. Interferon has also shown success in treating pars planitis, although it carries adverse effects like depression and suicidal tendencies.³

Prognosis and outlook

The prognosis of patients with intermediate uveitis can be influenced by various factors:

• Visual acuity at the time of presentation: this will be tested by the trained physician at the clinical examination. 
• Chronicity and severity: Intermediate uveitis can have varying levels of chronicity, classified as mild, moderate, or severe. Each level has unpredictable responses to treatment, though the severe form is often more challenging to treat. Permanent remission rates are generally low, and the disease tends to be chronically active or follow a course of intermittent exacerbation punctuated by periods of quiescence.⁴
• Pediatric patients: Pediatric patients with intermediate uveitis often face an unfavourable prognosis due to late presentation and challenges in using immunosuppressive agents for treatment. Long-term follow-up studies in pediatric patients show varying outcomes, with a proportion experiencing legal blindness over several years, especially if diagnosed at a younger age. Understanding these prognosis-related factors helps in managing patients effectively, optimising treatment plans, and providing appropriate counselling regarding the potential course of the disease and vision outcomes.⁴

Summary

Pars planitis is characterised by chronic intermediate uveitis, and notably, it's not associated with any systemic disease or infection. Patients affected by pars planitis typically exhibit minimal symptoms, although they may complain of floaters or blurry vision. Photophobia or pain is generally absent in most cases. However, there are instances where patients may experience sudden vision loss, often attributed to retinal detachment or acute vitreous haemorrhage. An interdisciplinary approach ensures a well-rounded and comprehensive management plan for affected individuals.³