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Summary Table

Feature	Detail
Risk Factors	Women 40-60 years old, autoimmune disease (rheumatoid arthritis, granulomatosis with polyangiitis, systemic lupus erythematosus, relapsing polychondritis), prior herpes zoster ophthalmicus
Etiology	Immune-mediated vasculitis of the scleral vessels; infectious causes (herpes zoster, Pseudomonas) are less common
Patient Presentation	Severe, deep, boring eye pain that radiates to the forehead, brow, or jaw; worsens with eye movement; may wake the patient from sleep
Classic Physical Exam	Deep violaceous (blue-red) scleral injection that does not blanch with topical phenylephrine 2.5%; scleral edema; tenderness on palpation of the globe through closed lids
Key Diagnostic Results	Clinical diagnosis supported by slit-lamp examination; B-scan ultrasonography showing posterior scleral thickening and fluid in the sub-Tenon space (posterior scleritis); labs directed at underlying systemic disease (ESR, CRP, RF, ANCA, ANA)
Management	Oral NSAIDs (flurbiprofen, indomethacin) for non-necrotizing disease; systemic corticosteroids for moderate-to-severe cases; immunosuppressive agents (methotrexate, mycophenolate, cyclophosphamide) for necrotizing or refractory disease
Keywords	"Deep boring eye pain," "pain radiating to the jaw," "blue-violet hue," "does not blanch with phenylephrine," "associated with rheumatoid arthritis," "scleral thinning"

1. Pathophysiology

Scleritis is a granulomatous or necrotizing inflammatory process involving the full thickness of the sclera. The sclera is composed of dense, relatively avascular collagen (types I and III), which means that once inflammation takes hold, the tissue is poorly equipped to contain or resolve the damage on its own.

The underlying mechanism in most cases is an immune complex-mediated vasculitis affecting the deep episcleral and scleral vessels. Activated T-cells and macrophages infiltrate the scleral stroma, releasing pro-inflammatory cytokines (TNF-alpha, IL-1) and matrix metalloproteinases. This cascade causes fibrinoid necrosis of the vessel walls and surrounding collagen destruction. The deep vascular involvement is why the pain is so severe and why it radiates along branches of the trigeminal nerve (V1): the sclera shares sensory innervation with the periorbital structures. This also explains why the pain worsens with eye movement, because the extraocular muscle insertions tug directly on inflamed scleral tissue.

In necrotizing scleritis, the destructive process is more aggressive and leads to scleral thinning. As the sclera thins, the underlying uveal pigment shows through, producing the characteristic blue-grey or dark patch on examination. If thinning progresses, the eye is at risk for scleral perforation (globe rupture), which constitutes an ophthalmic emergency.

A key clinical teaching point: approximately 50% of patients with scleritis have an underlying systemic autoimmune condition, most commonly rheumatoid arthritis. Necrotizing scleritis in a patient with longstanding rheumatoid arthritis is strongly associated with active systemic vasculitis and carries increased mortality if the systemic disease is left untreated. This is why a new diagnosis of scleritis should always prompt a systemic workup.

2. Classification and Clinical Manifestations

Classification of Scleritis (Watson and Hayreh)

Type	Subtype	Key Features
Anterior scleritis	Diffuse	Most common form (~40%); widespread scleral inflammation and redness; least likely to cause complications
	Nodular	Firm, immobile, tender nodule(s) on the sclera; does not move with a cotton-tip applicator (unlike episcleritis)
	Necrotizing with inflammation	Most severe; intense pain; progressive scleral thinning with uveal show-through; high association with systemic vasculitis and risk of perforation
	Necrotizing without inflammation (scleromalacia perforans)	Painless scleral thinning in patients with longstanding rheumatoid arthritis; yellow-grey necrotic patches; insidious and dangerous because the lack of pain delays diagnosis
Posterior scleritis		Difficult to diagnose; presents with pain on eye movement, reduced vision, proptosis, choroidal folds, exudative retinal detachment, or disc edema; may mimic orbital tumor or posterior uveitis

Scleritis vs. Episcleritis Comparison

This is a high-yield comparison that appears repeatedly on examinations. The two conditions are often placed side-by-side in vignettes, and the distinguishing features are very testable.

Feature	Scleritis	Episcleritis
Layer involved	Full-thickness sclera (deep)	Episclera (superficial connective tissue between conjunctiva and sclera)
Pain severity	Severe, deep, boring; radiates to jaw/forehead; disrupts sleep	Mild discomfort or foreign body sensation; rarely painful
Color of injection	Deep violaceous (blue-red) hue	Bright red, "salmon pink"
Phenylephrine 2.5% test	Does NOT blanch (deep vessels unaffected by topical vasoconstrictors)	Blanches (superficial episcleral vessels constrict)
Tenderness to palpation	Globe is tender when palpated through closed lid	Non-tender
Vision threat	Yes, can cause scleral thinning, perforation, uveitis, glaucoma, or keratitis	No, self-limited and benign
Systemic disease association	Strong (~50%); rheumatoid arthritis, GPA, SLE	Weak (~30%); usually idiopathic; occasional association with mild autoimmune disease
Natural history	Chronic, progressive; requires systemic therapy	Self-limited (resolves in 2-3 weeks); may recur
Treatment	Systemic NSAIDs, corticosteroids, immunosuppressants	Artificial tears, topical NSAIDs; oral NSAIDs if needed

The phenylephrine blanching test is the single most tested discriminator. If the redness blanches with topical phenylephrine, the inflamed vessels are superficial (episcleritis). If it does not blanch, the inflammation involves the deep scleral vessels (scleritis).

3. Diagnostic Workup

Test	Purpose	Key Finding
Slit-lamp biomicroscopy	Best initial test; assess depth and pattern of inflammation	Deep scleral injection, scleral edema, nodules, or necrotic areas; distinguish from episcleritis
Phenylephrine 2.5% (topical)	Differentiate scleritis from episcleritis	Scleral vessels do NOT blanch in scleritis
B-scan ultrasonography	Most accurate test for posterior scleritis	Posterior scleral wall thickening, fluid in the sub-Tenon space ("T-sign")
Systemic labs (ESR, CRP, RF, anti-CCP, ANCA, ANA, urinalysis)	Screen for underlying autoimmune condition	Elevated inflammatory markers; positive serologies guide systemic diagnosis
CT/MRI orbits	Rule out orbital pathology in posterior scleritis	Scleral thickening, proptosis, distinguish from orbital mass or cellulitis

Scleritis is primarily a clinical diagnosis. The workup begins at the slit lamp, where the examiner identifies deep scleral vessel engorgement that is distinct from the more superficial, mobile, and bright-red episcleral injection. Instillation of phenylephrine 2.5% is the key bedside maneuver: failure to blanch confirms deep vessel involvement.

When posterior scleritis is suspected (pain on movement, decreased vision, no visible anterior inflammation), B-scan ultrasonography is the most valuable confirmatory study. The classic finding is the "T-sign", which represents thickening of the posterior scleral wall with fluid tracking into the sub-Tenon space around the optic nerve.

Because of the strong systemic disease association, every new diagnosis of scleritis warrants a laboratory evaluation for autoimmune conditions. The panel typically includes ESR, CRP, rheumatoid factor, anti-CCP antibodies, c-ANCA and p-ANCA (to evaluate for granulomatosis with polyangiitis), ANA, and a urinalysis to screen for renal involvement. This workup is not just academic: identifying an underlying systemic vasculitis changes the management and prognosis fundamentally.

4. Management and Treatment

Clinical Scenario	Treatment	Details
Mild, non-necrotizing (diffuse or nodular)	Oral NSAIDs	Flurbiprofen 100 mg TID or indomethacin 25-50 mg TID; continue for several weeks and taper based on response
Moderate or NSAID-refractory	Systemic corticosteroids	Oral prednisone 1 mg/kg/day (typically 60-80 mg), taper over 4-6 weeks; add a PPI for gastric protection
Necrotizing scleritis	Immunosuppressive therapy	Cyclophosphamide (for GPA-associated) or methotrexate/mycophenolate mofetil as steroid-sparing agents; consider biologics (rituximab) for refractory cases
Scleromalacia perforans	Treat the underlying RA aggressively	Immunosuppression; surgical scleral patch grafting if perforation is imminent
Posterior scleritis	Systemic corticosteroids +/- immunosuppressants	Similar to necrotizing; requires close ophthalmologic monitoring
Infectious scleritis	Targeted antimicrobials + surgical debridement	Culture-guided antibiotics or antivirals; avoid immunosuppression

The management of scleritis follows a stepwise escalation model. The first-line treatment for non-necrotizing anterior scleritis is oral NSAIDs. Topical drops alone are insufficient because the sclera is too thick and avascular for topical agents to penetrate meaningfully. This is a critical distinction from episcleritis, where topical therapy works well.

If oral NSAIDs fail to control symptoms within 2-3 weeks, the next step is systemic corticosteroids. Prednisone is started at 1 mg/kg/day and maintained until inflammation is controlled, then tapered gradually to avoid rebound. Patients on prolonged corticosteroids require monitoring for hyperglycemia, osteoporosis, and adrenal suppression.

Necrotizing scleritis is treated as a rheumatologic emergency. These patients typically require immunosuppressive agents from the outset, often in coordination with rheumatology. Cyclophosphamide is the traditional choice for GPA-associated necrotizing scleritis, while methotrexate or mycophenolate may be used for less aggressive autoimmune etiologies. Rituximab (anti-CD20 monoclonal antibody) has emerged as an effective option for refractory cases.

A teaching pearl: never use topical steroids as monotherapy for scleritis. They do not reach the deep scleral inflammation and may mask symptoms while disease progresses. Also, subconjunctival corticosteroid injections are contraindicated in necrotizing scleritis because they can precipitate scleral perforation in already thinned tissue.

5. Differential Diagnosis and Distractors

Differential	Why It Is Confusing	Key Discriminator
Episcleritis	Both cause a red, painful eye; both may be associated with autoimmune disease	Episcleritis blanches with phenylephrine, is mildly uncomfortable (not severely painful), has bright-red injection, and is self-limited
Acute angle-closure glaucoma	Severe eye pain, red eye, decreased vision	Mid-dilated fixed pupil, corneal edema, elevated IOP, halos around lights; no scleral inflammation
Anterior uveitis (iritis)	Eye pain, photophobia, red eye, autoimmune association	Perilimbal (ciliary) flush, cells and flare in the anterior chamber, consensual photophobia; sclera itself is not inflamed
Orbital cellulitis	Pain with eye movement, proptosis (mimics posterior scleritis)	Fever, eyelid swelling, restricted extraocular movements, history of sinusitis; CT shows orbital fat stranding
Conjunctivitis	Red eye	Discharge (purulent or watery), no pain (itching or irritation instead), no vision changes, conjunctival injection that is most prominent in the fornices
Orbital tumor	Proptosis, vision changes (mimics posterior scleritis)	Painless, slowly progressive proptosis; imaging shows a defined mass rather than diffuse scleral thickening

6. Traps and High-Yield Pearls

The most common way students miss scleritis questions is by confusing it with episcleritis. The vignette will describe a red eye with some discomfort, and the student defaults to the more benign diagnosis. The key is to look for severity markers: deep boring pain, sleep disruption, radiation to the forehead or jaw, and a violaceous hue. If the stem mentions that phenylephrine did not blanch the redness, scleritis is confirmed.

A second trap involves posterior scleritis. Because it presents with decreased vision, pain on movement, and sometimes disc edema or exudative retinal detachment, students may jump to diagnoses like optic neuritis, orbital cellulitis, or choroidal melanoma. The giveaway is the B-scan showing diffuse posterior scleral thickening with the T-sign, combined with an autoimmune history.

Third, students sometimes select topical corticosteroids as treatment. This is always wrong for scleritis. The inflammation is too deep for topical penetration, and systemic therapy is mandatory.

Finally, remember the systemic connection: a question that presents new-onset scleritis in a middle-aged woman with joint deformities is testing whether you will order a rheumatologic workup. Necrotizing scleritis in a patient with rheumatoid arthritis is an indicator of active systemic vasculitis and demands immunosuppressive therapy, not just eye-focused treatment. The core competency being tested is the ability to recognize scleritis as a systemic disease with ocular manifestation, not merely an eye problem.

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