Ophthalmology – Intermediate Uveitis and Pars Planitis

Basics

Description

Intermediate uveitis (IU) is an inflammatory disorder in which the predominant inflammation involves the vitreous, pars plana, ciliary body, and peripheral retina. The anterior chamber may also be involved, but vitreous inflammation is usually the dominant feature.

Pars planitis is a subset of intermediate uveitis in which there is no identifiable infectious or systemic inflammatory cause. It is classically associated with inflammatory aggregates in the vitreous called snowballs and exudative plaques over the pars plana called snowbanks.

IU is often bilateral, although the severity can differ considerably between the two eyes.

Epidemiology

Intermediate uveitis accounts for approximately 15% of uveitis cases.

There is no strong sex predilection.

Disease is bilateral in roughly 70–90% of patients, although involvement may be asymmetric.

Pars planitis represents a large proportion of idiopathic intermediate uveitis.

It has traditionally been described as having two age peaks:

• Childhood and adolescence, approximately 5–15 years
• Young adulthood, approximately 20–40 years

Risk Factors

No specific environmental risk factor has been clearly established for idiopathic pars planitis.

Genetics

Associations have been reported with:

• HLA-DR15
• HLA-DR51

These associations support an immune-mediated mechanism but are not diagnostic.

Pathophysiology

The pathogenesis is not completely understood.

The disease is thought to represent an immune-mediated inflammatory response against ocular antigens.

Inflammation frequently centers around the peripheral retinal veins, producing retinal periphlebitis.

Persistent inflammatory cells in the vitreous can organize into snowballs, while chronic inflammation over the pars plana may produce fibroinflammatory exudates known as snowbanks.

Longstanding inflammation may ultimately lead to structural complications such as macular edema, epiretinal membrane, cataract, retinal neovascularization, and retinal detachment.

Commonly Associated Conditions

Intermediate uveitis can be associated with systemic or infectious disease.

Important associations include:

• Multiple sclerosis
• Sarcoidosis
• Syphilis
• Tuberculosis
• Lyme disease
• Toxocariasis
• Bartonella infection
• HTLV-related disease in selected populations

By definition, pars planitis has no identified systemic or infectious cause.

Diagnosis

History

The most common symptoms are:

• Floaters
• Blurred or decreased vision

Patients often have a relatively white and quiet eye, despite substantial vitreous inflammation.

Some patients experience:

• Photophobia
• Mild redness
• Mild ocular discomfort

Redness and anterior segment inflammation are more commonly prominent in children.

Physical Examination

A complete uveitis examination should include careful evaluation of the anterior chamber, vitreous, peripheral retina, macula, and optic nerve.

Typical findings include:

Anterior Vitreous Cells

Inflammatory cells within the vitreous are the defining clinical feature.

The amount of vitreous haze should also be assessed because it correlates with inflammatory activity.

Snowballs

Snowballs are rounded whitish aggregates of inflammatory cells suspended within the inferior vitreous.

They are commonly located near the inferior peripheral retina.

Although characteristic, they are not absolutely specific for pars planitis.

Snowbanks

Snowbanks are broad, gray-white inflammatory exudates involving the pars plana, most often inferiorly.

They represent fibroglial and inflammatory tissue.

Snowbank formation generally indicates more substantial or chronic disease and is associated with a higher risk of complications such as peripheral retinal neovascularization.

Retinal Periphlebitis

Peripheral retinal venous inflammation may appear as:

• Vascular sheathing
• Tortuosity
• Leakage on fluorescein angiography
• Peripheral nonperfusion in more severe cases

The retinal veins are the most commonly involved vessels.

Pediatric Considerations

Children may have more pronounced anterior chamber inflammation than adults.

Because young children may not report floaters or blurred vision reliably, disease can remain undetected until complications develop.

Children are particularly vulnerable to:

• Amblyopia
• Cataract
• Band keratopathy
• Glaucoma

Therefore, careful long-term monitoring is essential.

Diagnostic Tests and Interpretation

Laboratory Evaluation

The laboratory workup should be guided by clinical findings and systemic symptoms.

Commonly considered tests include:

• CBC with differential
• ESR and/or CRP
• Syphilis serology
• Tuberculosis screening
• ACE or other testing when sarcoidosis is suspected
• Lyme serology when epidemiologically appropriate
• Bartonella testing when clinically indicated

Testing should be tailored rather than indiscriminately broad.

Chest Imaging

A chest radiograph may be obtained when sarcoidosis or tuberculosis is suspected.

If suspicion for sarcoidosis remains high despite a normal radiograph, chest CT may provide greater sensitivity.

Fluorescein Angiography

Fluorescein angiography is particularly useful for detecting:

• Cystoid macular edema
• Retinal periphlebitis
• Peripheral vascular leakage
• Areas of capillary nonperfusion
• Retinal neovascularization
• Optic disc leakage

Peripheral angiographic abnormalities may be more extensive than suggested by ophthalmoscopy alone.

Optical Coherence Tomography

OCT is now central to monitoring intermediate uveitis.

It is especially useful for identifying and following:

• Cystoid macular edema
• Epiretinal membrane
• Vitreomacular traction
• Macular structural damage

Because CME is a major cause of visual loss, serial OCT is often more useful than visual acuity alone.

Ultrasound Biomicroscopy

UBM may help visualize:

• Pars plana exudates
• Anterior vitreous abnormalities
• Ciliary body changes

It can be particularly useful when the pupil is small or direct visualization of the pars plana is difficult.

Diagnostic Vitrectomy

Diagnostic pars plana vitrectomy may be considered when there is concern for:

• Intraocular lymphoma
• Chronic endophthalmitis
• Unusual infectious uveitis
• Atypical or treatment-resistant inflammation

Vitreous samples can undergo cytology, flow cytometry, culture, and molecular testing according to the suspected diagnosis.

Pathological Findings

Histopathology may show lymphocytic inflammation around retinal veins.

Snowbank tissue is composed of a mixture of:

• Fibroglial tissue
• Inflammatory cells
• Extracellular material

The pathological findings are generally nonspecific and must be interpreted in clinical context.

Differential Diagnosis

Important differential diagnoses include:

• Primary vitreoretinal lymphoma
• Chronic endophthalmitis
• Sarcoid uveitis
• Infectious uveitis
• Fuchs uveitis syndrome
• Vogt–Koyanagi–Harada disease
• Retinal vasculitis of other causes
• Toxocariasis

In an older patient with new vitreous inflammation, vitreoretinal lymphoma must be considered carefully.

Treatment

Treatment depends on:

• Cause
• Severity
• Visual symptoms
• Presence of macular edema
• Degree of vitreous haze
• Structural complications

If an infectious cause is identified, the infection must be treated specifically, and immunosuppression should be used cautiously.

Corticosteroids

For noninfectious disease causing visual symptoms or complications, corticosteroids remain an important first-line therapy.

Periocular Corticosteroids

Posterior sub-Tenon corticosteroid injections may be used for:

• Unilateral or asymmetric disease
• Macular edema
• Moderate inflammation

They provide high local concentrations while reducing systemic exposure.

Potential complications include:

• Elevated IOP
• Cataract
• Globe perforation
• Ptosis
• Local tissue atrophy

Oral Corticosteroids

Systemic corticosteroids may be used when:

• Disease is bilateral and severe
• Local therapy is inadequate
• There is extensive retinal vasculitis
• Sight-threatening complications are present

Long-term systemic steroid dependence should generally prompt consideration of steroid-sparing immunomodulatory therapy.

Intravitreal Corticosteroids

Intravitreal corticosteroid therapy may be considered in refractory cases, particularly when cystoid macular edema is prominent.

Potential complications include:

• Cataract
• Ocular hypertension
• Glaucoma
• Endophthalmitis

Long-acting steroid implants may also be considered in selected chronic noninfectious cases.

Immunomodulatory Therapy

Steroid-sparing therapy is appropriate when inflammation is:

• Chronic
• Recurrent
• Steroid-dependent
• Resistant to corticosteroids
• Producing unacceptable steroid-related adverse effects

Agents may include:

• Methotrexate
• Mycophenolate mofetil
• Azathioprine
• Cyclosporine
• Tacrolimus

Biologic therapy may be used in selected refractory cases under specialist supervision.

Laser and Cryotherapy

Peripheral laser photocoagulation or cryotherapy was historically used to treat:

• Snowbank-associated neovascularization
• Peripheral ischemic retina
• Persistent inflammatory exudates

Today, these treatments are used selectively, especially when neovascularization or ischemia is present.

They are not routine therapy for every case of pars planitis.

Pars Plana Vitrectomy

Pars plana vitrectomy may be useful for:

• Persistent dense vitreous opacities
• Chronic vitreous inflammation
• Epiretinal membrane
• Vitreomacular traction
• Retinal detachment
• Persistent CME in selected cases
• Diagnostic uncertainty

Vitrectomy can reduce the inflammatory load and improve media clarity.

Cystoid Macular Edema

CME is the most important cause of visual impairment in intermediate uveitis.

Treatment may involve:

• Periocular corticosteroids
• Intravitreal corticosteroids
• Systemic corticosteroids
• Immunomodulatory therapy
• Vitrectomy in selected refractory cases

OCT should be used to document response.

Cataract

Cataract may result from:

• Chronic inflammation
• Corticosteroid therapy

Cataract surgery should ideally be performed when inflammation has been well controlled for a sustained period.

Perioperative corticosteroid or other anti-inflammatory therapy is commonly used to minimize postoperative recurrence.

Glaucoma

Both open-angle and angle-closure glaucoma may occur.

Mechanisms include:

• Chronic inflammation
• Peripheral anterior synechiae
• Steroid response
• Pupillary block

IOP should be monitored carefully throughout treatment.

Follow-Up

Patients require long-term ophthalmic follow-up because intermediate uveitis often follows a chronic relapsing-remitting course.

Monitoring should include:

• Visual acuity
• Anterior chamber activity
• Vitreous cells and haze
• Peripheral retinal examination
• OCT for CME
• IOP
• Cataract progression
• Retinal neovascularization

Referral

Depending on the suspected cause, referral may be appropriate to:

• Rheumatology
• Neurology
• Infectious disease
• Pulmonology
• Retina or uveitis specialists

Patients with neurologic symptoms or findings suggestive of demyelinating disease may require evaluation for multiple sclerosis.

Prognosis

Intermediate uveitis often has a prolonged course, lasting many years, with periods of exacerbation and remission.

A minority of patients experience spontaneous resolution.

Visual prognosis depends primarily on:

• Severity of inflammation
• Development of CME
• Retinal ischemia
• Cataract
• Glaucoma
• Retinal detachment

Pars planitis generally has a favorable long-term visual prognosis when inflammation and complications are appropriately controlled.

The presence of extensive snowbanking or chronic CME is associated with a less favorable outcome.

Complications

Important complications include:

• Cystoid macular edema
• Cataract
• Secondary glaucoma
• Band keratopathy
• Epiretinal membrane
• Peripheral retinal neovascularization
• Vitreous hemorrhage
• Retinal detachment
• Chronic vitreous opacification
• Permanent visual impairment

The most important practical point is that intermediate uveitis describes the anatomic location of inflammation, whereas pars planitis specifically refers to idiopathic intermediate uveitis without an identifiable infectious or systemic cause.