Scleral edema describes swelling that affects the sclera, the dense, white outer layer of the eyeball. This condition occurs when fluid accumulates within the layers of the scleral wall, usually signaling a deeper inflammatory process. Since the sclera provides the eye’s structural integrity, this swelling often indicates a serious internal inflammatory response.
Understanding the Sclera and Edema
The sclera is the opaque, fibrous protective layer that constitutes the “white” of the eye, extending from the cornea to the optic nerve sheath. It is composed primarily of tough collagen fibers and is relatively avascular, meaning it has few blood vessels. Microscopically, the sclera consists of the episclera, the scleral stroma, and the lamina fusca, which blends into the underlying choroid.
Edema refers to the accumulation of excess fluid in the interstitial spaces between cells and tissues. Scleral edema means this fluid buildup occurs within the dense layers of the scleral wall, often driven by inflammation that increases the permeability of nearby blood vessels. This condition is distinct from chemosis, which is the common, gelatinous swelling of the conjunctiva, the thin membrane covering the sclera. Scleral edema involves the structural tissue itself, making it a deeper process than superficial chemosis.
Factors Leading to Scleral Edema
The primary cause of scleral edema is scleritis, a severe inflammation of the sclera that leads to fluid accumulation. Scleritis is frequently associated with systemic autoimmune disorders, with up to 50% of cases having an underlying condition. These conditions include rheumatoid arthritis, systemic lupus erythematosus, or granulomatosis with polyangiitis. The inflammation is essentially a localized autoimmune attack on the scleral collagen, which triggers the swelling.
The edema can also result from infectious causes, though these are less common, accounting for 5% to 10% of all scleritis cases. Bacteria such as Pseudomonas aeruginosa are the most frequently identified pathogens in infectious scleritis. Fungal organisms, including Aspergillus flavus, are also known to cause this condition, particularly in certain geographical areas.
A history of ocular surgery or trauma is another factor that can disrupt the integrity of the scleral tissue. Procedures like pterygium excision or glaucoma filtration surgery can create entry points for pathogens or trigger a localized inflammatory response. In post-surgical cases, the swelling is often a delayed complication occurring months or years after the initial procedure. Edema localized to the episclera, known as episcleritis, is a milder, self-limiting inflammation that does not involve the deeper sclera.
Identifying the Signs and Diagnostic Methods
Scleral edema is characterized by a deep, severe pain that can radiate to the jaw or temple and often wakes the patient at night. The white of the eye develops localized or diffuse redness, appearing as a deep, bluish-red or violaceous hue due to the inflammation of deeper vessels. The swelling may appear as a raised, tender, immovable nodule (nodular scleritis), or as a more generalized, diffuse thickening.
A physical examination using a slit lamp is the initial diagnostic step, allowing the doctor to observe deep vascular congestion. A key test involves applying a topical vasoconstrictor like phenylephrine; if the redness is superficial (episcleritis), the vessels will blanch, but in true scleral edema, the deep scleral vessels will not blanch. To confirm the diagnosis and assess severity, imaging techniques are used to visualize the deeper tissue.
Anterior Segment Optical Coherence Tomography (AS-OCT) is employed to objectively measure increased scleral thickness and distinguish it from episcleritis. AS-OCT images reveal hyporeflective areas within the sclera, which represent the fluid accumulation or edema. For posterior involvement, B-scan ultrasonography is used to detect thickening of the back of the eye and the characteristic “T sign,” indicating fluid accumulation around the optic nerve.
Managing and Resolving the Edema
Management of scleral edema focuses on treating the underlying inflammatory or infectious cause, as topical treatments are rarely sufficient. For mild to moderate, non-infectious cases, the initial approach involves high-dose oral nonsteroidal anti-inflammatory drugs (NSAIDs), such as indomethacin or naproxen. If the inflammation does not respond to a two-week trial of NSAIDs, or if the case is severe, treatment is escalated to systemic corticosteroids.
The standard second-line treatment involves oral prednisone. This high dose is maintained until the inflammation resolves, after which the dosage is slowly tapered to avoid a flare-up. For patients with severe or necrotizing scleritis, or those who cannot tolerate the long-term side effects of steroids, immunosuppressive agents are introduced.
Immunomodulatory therapy (IMT) aims to control the systemic inflammatory process and reduce the need for chronic high-dose steroid use. Agents such as methotrexate, azathioprine, and mycophenolate mofetil are commonly prescribed to manage the underlying autoimmune disease. In refractory cases, or those associated with severe vasculitis, biologic agents like infliximab or adalimumab may be utilized. If the edema is caused by an infection, treatment shifts immediately to appropriate broad-spectrum antibiotics, antifungals, or antivirals, often combined with surgical debridement of the infected tissue.