Introduction

Pars planitis is a chronic immunological disorder that mainly affects children and young adults. It is an idiopathic form of intermediate uveitis and is characterised by inflammation of the pars plana (narrowed area of the eye) between the iris and choroid. If you have pars planitis, you may experience blurred vision, floaters, and decreased vision. Chronic inflammation can lead to complications such as swelling of the inside of the eyes, cataracts, and even possibly retinal detachment.¹ 

Traditional therapies

Traditionally, treatment therapies have relied on corticosteroids. These are anti-inflammatory medicines which can be applied topically (on the skin), systemically (throughout the whole body, normally via the blood), or via periocular injections (injections around the eye). Although steroids often result in substantial clinical improvement,² they can also lead to adverse effects. This includes glaucoma, cataracts, and slow wound healing.³ Furthermore, if the steroid is taken as a pill, it can also lead to symptoms such as weight gain, mood changes, or bone thinning. 

Another traditional therapy for pars planitis relies on immunosuppressants. The most commonly prescribed medications include methotrexate, azathioprine, and cyclosporine. The main goal of these medications is to control inflammation.⁴ However, immunosuppressants do not work on everyone and often don’t work well on their own. Possible side effects of immunosuppressants include damage to the liver and kidneys. New biologic therapies aim to reduce the amount of side effects and therefore only target the specific parts of the immune system causing the problems.

Biologic therapies in pars planitis

TNF inhibitors

The most successful biologic therapy for pars planitis is a TNF Inhibitor called adalimumab. In the body, the immune system naturally produces a protein called tumour necrosis factor (TNF). If there is an overproduction of TNF, inflammation can occur. Adalimumab prevents the TNF from attaching to and attacking healthy cells, therefore reducing inflammation.⁵ It does this by targeting the cytokine ‘TNF-alpha’.⁶ Studies have found that adalimumab is associated with a lower risk of uveitic flare.⁷  

Adalimubab is delivered as a small injection under the skin and is typically administered every two weeks. It is also used to treat various autoimmune conditions such as Crohn's disease.⁸  

Common side effects of this medication include: 

• Headaches
• Sinus infections
• Stomach pain
• Nausea
• Muscle or bone pain
• Pain or swelling at the site of the injection

When adalimumab treatment fails or causes too many side effects, other TNF inhibitors, such as infliximab, can be used. Infliximab is given through an IV infusion every 6 to 8 weeks. It binds to TNF-alpha and blocks the inflammatory cascade, leading to reduced inflammation. 

Adverse effects of this drug include:⁹

• Headaches
• Nausea
• Abdominal pain
• Constipation
• Hypertension
• Anaemia

Interleukin inhibitors

Interleukin inhibitors are another form of biologic therapy for pars planitis. Interleukins (IL) are proteins which play an essential role in the activation and differentiation of immune cells.¹⁰ They act like messengers in the immune system, and send signals that trigger inflammation. If there is too much signalling in the eye, symptoms such as swelling or damage to the retina can occur. IL inhibitors work by neutralising a specific IL or its receptor. This disrupts the inflammatory pathway, reducing the signalling and therefore suppressing inflammation. This leads to symptom relief. 

One of the best studied IL blockers is tocilizumab. This blocker works against IL-6, which has been found to be significantly elevated in patients with uveitis.¹¹ Blocking this IL can be significantly helpful for patients with swelling in the center of their retina. This is known as cystoid macular edema. Tocilizumab has been shown to help reduce swelling, improve vision, and also prevent any relapses. 

Some possible side effects of this medication include:¹²

• Body aches
• Chills
• Dizziness
• Loss of appetite
• Back pain

Other IL inhibitors include anakinra and canakinumab. These inhibitors block IL-4. Although their results are promising, these inhibitors have only been tested in a select, small number of patients, so further trials are required.

Other targeted agents

One example of a non-IL and non-TNF inhibitor that can reduce inflammation is rituximab. This is a monoclonal antibody that targets and destroys B-cells.¹³ These cells are a type of white blood cell that make antibodies, which are then used by the immune system to fight off infections, and can also fuel inflammation. Rituximab has been used in very rare and severe cases of pars planitis where patients did not respond to other therapies. This medication can also have side effects, and it is essential to contact a medical professional if any occur. 

Some more common side effects include:¹⁴ 

• Dry mouth
• Back pain
• Ear congestion
• Headaches
• Increased thirst

Another biologic option would be abatacept, which has shown promising results in treating pars planitis, including improvements of ocular manifestations in patients.¹⁵ Abatacept is an immunomodulator that works by blocking T-cell activity. By preventing the T-cell from becoming fully active, abatacept can reduce inflammation and thus possibly protect the eye. In likeness to rituximab, this medication is only used in rare cases when all first-line treatments have been exhausted. 

Common side effects can include: 

• Headache
• Runny nose
• Nausea
• Dizziness

Challenges and future directions

Despite biologic treatments creating new possibilities for managing pars planitis, there are still many important challenges to overcome. One of the major issues is that par planitis is very rare. Reports have found that there are 1.2 to two cases per 10000 people.¹⁶ This makes it difficult for researchers to run large-scale clinical trials. Without these trials, doctors and medical health professionals have to rely on smaller reports or previous experience in treating similar eye conditions. As such, future research should focus on finding ways to better understand the mechanisms of these biologics, as well as how they should be used.

Another challenge is cost and accessibility. Biologics tend to be very expensive, and not all health systems or insurance plans cover them. The availability of these therapies is dependent on guidance from organisations like the National Institute for Health and Care Excellence (NICE). Although some biologics, such as adalimumab, are approved for use in eye conditions, access to these medications can vary across different NHS Trusts and Clinical Commissioning Groups. This can lead to delays in starting treatment and uncertainty concerning whether biologics will be funded in the long term. 

FAQs

Can pars planitis be cured?

No, pars planitis cannot be cured. It can, however, be treated through various therapies, such as TNF inhibitors, to alleviate any symptoms.

What are the standard treatments for pars planitis?

The standard treatment for pars planitis includes the use of corticosteroids and the use of immunosuppressants. Both of these medications work on an anti-inflammatory basis to try to reduce inflammation. New therapies include the use of TNF inhibitors and interleukin inhibitors.

What is pars planitis?

An immunological disorder, characterised by the inflammation of the pars plana in the eye. 

Is pars planitis hereditary?

Many ophthalmologists do not consider pars planitis to be hereditary. The cause remains unknown, although it is believed to be an autoimmune disease. 

What is the long-term outlook for patients with pars planitis?

The long-term outlook can vary between individuals. Most patients maintain good vision with timely treatment. On the other hand, some patients may have complications such as cataracts; however, the development of new biologic therapies is increasing the chances of reversing vision loss and reducing inflammation. 

Summary

Pars planitis is an extremely rare immunological disorder. It is characterised by the inflammation of the pars plana in the eye. Traditionally, treatment for this condition included the use of corticosteroids and immunosuppressants. However, recent advances in biologic therapies have led to new treatments being established. The most successful biologic therapy that has emerged is a TNF inhibitor known as adalimumab. This inhibitor reduces inflammation through targeting the TNF-alpha cytokine. If this medication does not help, other TNF inhibitors, such as infliximab, can be used. Another form of biologic therapies used to treat pars planitis include interleukin inhibitors. These inhibitors prevent the signalling that causes inflammation. This medication specifically helps symptoms such as the swelling of the eye. Despite the development of new therapies, researchers and doctors face various challenges. These include the rarity of the condition, and therefore the knowledge surrounding it, and the accessibility of the medication. Research is actively being conducted into making sure each person with the condition can have the best medications and treatment plans available to them.