Scleritis is an inflammatory condition that affects the sclera, while episcleritis is an inflammatory condition that affects the episclera. Because the episclera is the outermost layer of the sclera, episcleritis is a more superficial condition. While the etiology of episcleritis is usually idiopathic, scleritis often occurs in individuals with underlying systemic disease (e.g., rheumatoid arthritis, systemic lupus erythematosus). Both conditions can also be caused by infections or reactions to medications. They are diagnosed based on the patient history and physical examination. A search for underlying systemic illness is especially important when scleritis is diagnosed, but it is also warranted in suspected episcleritis if there are other signs of systemic disease present (e.g., arthritis, rash). Systemic treatment with corticosteroids is generally required in necrotizing scleritis, scleritis that does not resolve with NSAIDs, and scleritis affecting the posterior portion of the sclera. In refractory cases, immunosuppressive drugs may be required. Episcleritis typically regresses after 1–2 weeks, and treatment is not necessary in most cases.
Anatomy of the eye
- Definition: inflammation of the episclera
- Epidemiology 
- Most commonly idiopathic
- Associated with underlying systemic disease in a minority of cases (most commonly rheumatoid arthritis)
- Less common causes
- Bacterial/viral infection
- Drug reaction (e.g., bisphosphonates)
- Clinical features
Subtypes and variants
- Simple/diffuse episcleritis: most common subtype
- Nodular/focal episcleritis: prolonged inflammation, usually occurring in patients with underlying systemic disease
- Diagnosed based on patient history and physical examination
- Vasoconstricting eye drops (phenylephrine) may allow episcleritis to be differentiated from scleritis. 
- Further diagnostics are required if systemic disease is suspected.
- Symptomatic treatment (e.g., cold compresses, eye lubrication)
- In persistent or severe cases: NSAIDs and/or topical steroids
- Treatment of any underlying conditions
- In most cases, spontaneous regression occurs after 1–2 weeks.
- Recurrent bouts of the disease may occur every 1–3 months.
- Rarely progresses to reduced visual acuity
Although episcleritis is usually self-limiting, it manifests similarly to other, less innocuous conditions of the eye (e.g., scleritis, keratitis) that do require treatment. These conditions should be ruled out prior to diagnosing episcleritis (see “Differential diagnoses” below).
- Definition: transmural inflammation of the sclera
- Epidemiology 
- In up to 60% of patients, scleritis is associated with an underlying systemic disorder or infection (most commonly rheumatoid arthritis, but also SLE, granulomatosis with polyangiitis, polymyositis, and gout).
- May also be idiopathic
Subtypes and variants
- Non-necrotizing (nodular or diffuse)
- With inflammation (severe pain and eye redness)
- Without inflammation (painless) → scleromalacia perforans
- Posterior scleritis
- Anterior scleritis
Clinical features 
- Subacute onset of symptoms
- Severe deep, aching, and boring eye pain that is exacerbated by eye movement; and palpation; may radiate to the rest of the face
- Eye redness
- Photophobia and/or loss of vision
- Fixed scleral nodules (esp. in anterior nodular scleritis)
- Scleral thinning (esp. in scleromalacia perforans): may appear as violet or blue discoloration of the eye
- Diagnosis based on history and physical examination
- Ultrasound: to detect signs of posterior scleritis
- Orbital CT/MRI: to differentiate between orbital lesions, e.g., tumors, and posterior scleritis 
- Workup for potential systemic disease (e.g., RF, ANA, ANCA, and HLA typing)
- NSAIDs: first-line therapy in mild to moderate cases
- Systemic glucocorticoids: in posterior or necrotizing scleritis; patients unresponsive to NSAIDs
- Systemic immunosuppressive therapy (e.g., azathioprine, methotrexate): in patients unresponsive to steroids
- Scleral transplantation: in patients with impending perforation
- Treatment of any underlying systemic conditions
- Prognosis: Recurrent bouts of disease often occur if scleritis is not treated → cataracts, corneal changes, glaucoma, and even permanent loss of vision 
In a patient with focal eye pain with tenderness to palpation of the eye, with or without violet discoloration of the sclera, an ophthalmologic consult is warranted!
In order to diagnose scleritis, a workup should be done to evaluate for underlying systemic disease!
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Other diagnoses to consider
- Herpes keratitis
The differential diagnoses listed here are not exhaustive.