Posterior Scleritis

1. Comprehensive Introduction & Overview

Posterior scleritis (PS) is a rare, sight-threatening, and frequently misdiagnosed inflammatory condition affecting the sclera posterior to the equator of the globe. Unlike anterior scleritis, which is easily visible on slit-lamp examination, posterior scleritis is "hidden" behind the iris and lens, often manifesting as a diagnostic challenge for general ophthalmologists and emergency physicians.

Clinically, it involves inflammation of the posterior sclera, which can extend into the adjacent uveal tissue (choroid), the retina, and the optic nerve head. Because of its proximity to these critical structures, posterior scleritis can lead to irreversible vision loss if not addressed with aggressive systemic immunosuppression. It is often associated with systemic autoimmune diseases, most notably rheumatoid arthritis (RA), granulomatosis with polyangiitis (GPA), and relapsing polychondritis.

2. Deep-Dive: Mechanisms and Pathophysiology

The Inflammatory Cascade

Posterior scleritis is primarily an immune-mediated disorder. The pathophysiology is rooted in a Type III hypersensitivity reaction or a T-cell-mediated Type IV reaction.

• Vascular Insult: The sclera is a relatively avascular tissue, but it is supplied by the episcleral capillary plexus and the deep scleral plexus. In PS, circulating immune complexes deposit in the vessel walls of the posterior sclera, triggering a complement-mediated inflammatory response.
• Tissue Destruction: The release of neutrophils and macrophages leads to the secretion of collagenases and proteases, which degrade the collagenous matrix of the sclera.
• Extension: Due to the anatomical continuity of the sclera with the choroid and the scleral canal with the optic nerve, inflammation often spreads, causing secondary choroidal effusions, exudative retinal detachments, and optic disc edema.

Etiological Associations

The condition is rarely idiopathic. A high index of suspicion for underlying systemic disease is mandatory.

3. Clinical Indications & Standard Presentation

The Diagnostic "Triad" of Symptoms

Patients typically present with symptoms that are often dismissed as simple conjunctivitis or orbital cellulitis. The classic presentation includes:
1. Ocular Pain: Often severe, deep, boring, and radiating to the brow or temple. It is typically worse at night.
2. Vision Loss: Ranging from mild blurring to light perception only, often caused by exudative retinal detachment or optic nerve involvement.
3. Redness: While anterior redness may be present, it is often absent in pure posterior scleritis.

Clinical Signs (The "Hidden" Findings)

Because the inflammation is posterior, the clinician must rely on funduscopy and specialized imaging:
* Choroidal Folds: Caused by the scleral thickening pressing against the choroid.
* Exudative Retinal Detachment: A classic hallmark where fluid accumulates beneath the retina without a visible tear.
* Disc Edema: Secondary to inflammation of the optic nerve head.
* "T-Sign" on B-Scan: The pathognomonic ultrasound finding where fluid in the Tenon’s space creates a T-shaped appearance.

4. Clinical Staging and Grading

There is no universally accepted "staging" system like cancer, but clinicians generally categorize PS based on severity and involvement:

5. Diagnostic Testing Protocols

Imaging: The Gold Standard

1. Ocular B-Scan Ultrasound: The most critical diagnostic tool. Look for:
   • T-Sign: Widening of the optic nerve shadow due to fluid in the sub-Tenon space.
   • Scleral Thickening: Typically >2.0 mm.
2. Computed Tomography (CT) / MRI: Useful to rule out orbital pseudotumor or neoplastic processes. MRI with gadolinium enhancement will show scleral thickening and enhancement.
3. Fundus Fluorescein Angiography (FFA): Often reveals "patchy choroidal filling" or diffuse hyperfluorescence in the late phase, indicating choroidal inflammation.

Laboratory Workup

To identify the systemic driver, the following panels are standard:
* CBC with differential
* ESR/CRP: To assess systemic inflammatory burden.
* ANCA (c-ANCA/p-ANCA): Essential for ruling out GPA.
* Rheumatoid Factor (RF) and Anti-CCP: For RA.
* Quantiferon-Gold / RPR: To rule out infectious etiologies.

6. Risks, Side Effects, and Contraindications

Risks of Delayed Treatment

• Scleral Melt/Perforation: Though rare in posterior cases, it can lead to globe instability.
• Permanent Vision Loss: Due to secondary glaucoma or optic nerve atrophy.
• Phthisis Bulbi: End-stage shrunken, non-functional eye.

Contraindications to Standard Treatment

• Systemic Steroid Contraindications: Uncontrolled diabetes, severe psychiatric history, or active systemic infections (e.g., untreated TB).
• NSAID Risks: Caution in patients with peptic ulcer disease or chronic kidney disease.

Treatment Hierarchy

1. First-Line: High-dose oral corticosteroids (e.g., Prednisone 1mg/kg/day).
2. Second-Line: If refractory, move to IV pulse Methylprednisolone.
3. Third-Line: Steroid-sparing agents (Methotrexate, Mycophenolate Mofetil, or Biologics like Rituximab or Infliximab).

7. Prognosis

The prognosis is guarded. While the inflammation usually responds to corticosteroids, the recurrence rate is high. Patients require long-term monitoring by a uveitis specialist. Early intervention is the single most important prognostic factor for visual recovery.

8. Frequently Asked Questions (FAQ)

Q1: Is posterior scleritis painful?
A: Yes, pain is the most consistent symptom. It is characterized as deep, boring, and severe, often waking the patient from sleep.

Q2: Can I see posterior scleritis on a standard exam?
A: Rarely. Because it is located behind the equator of the globe, it usually requires a dilated fundus exam, indirect ophthalmoscopy, and B-scan ultrasound for diagnosis.

Q3: What is the "T-Sign"?
A: It is a pathognomonic ultrasound finding where fluid accumulates in the sub-Tenon space, forming a T-shape around the optic nerve.

Q4: Is this condition contagious?
A: No. It is an autoimmune or inflammatory condition, not an infection that can be spread between people.

Q5: Will I go blind?
A: Without prompt treatment, permanent vision loss is a real risk due to retinal detachment or optic nerve damage. With early intervention, the prognosis for vision is generally good.

Q6: Why do I need blood tests for an eye condition?
A: Posterior scleritis is almost always a manifestation of a systemic disease (like RA or vasculitis). The blood tests help identify the underlying cause.

Q7: How long do I need to take steroids?
A: Treatment is typically tapered over several months. Many patients require long-term immunosuppressive therapy to prevent recurrence.

Q8: Can posterior scleritis be caused by surgery?
A: While rare, cases have been reported following ocular surgery due to the trauma triggering an inflammatory response in susceptible individuals.

Q9: What is the difference between anterior and posterior scleritis?
A: Anterior scleritis affects the visible front portion of the sclera (red eye). Posterior scleritis affects the back portion (hidden) and carries a higher risk of optic nerve and retinal damage.

Q10: Are there natural remedies for this?
A: No. Posterior scleritis is a medical emergency that requires potent, prescription-strength anti-inflammatory or immunosuppressive medications. Delaying treatment with alternative therapies can lead to permanent vision loss.

9. Conclusion

Posterior scleritis remains one of the most challenging diagnoses in ophthalmology. Its ability to masquerade as other orbital pathologies necessitates a high clinical suspicion. By combining detailed fundus examination with B-scan ultrasound and a robust systemic workup, clinicians can effectively manage this condition and preserve the patient’s visual function. Immediate referral to a uveitis or retina specialist is strongly advised upon the suspicion of this diagnosis.