The anterior sclera is the visible white portion of the eye, a protective outer layer covering over 80% of the eyeball’s surface. It extends from the edge of the cornea, the clear front part of the eye, to the optic nerve at the back. While the sclera encases a majority of the eye, only the anterior, or front, section is visible.
Anatomy and Primary Functions
The anterior sclera’s strength comes from a dense network of collagen fibers arranged in irregular, interlacing bundles, providing both durability and flexibility. This connective tissue is organized into two main layers: the episclera and the stroma. The episclera is the thin, vascularized outer layer beneath the conjunctiva, while the stroma is the thick fibrous layer that gives the sclera its toughness.
The primary function of the anterior sclera is to protect the delicate internal components of the eye from external trauma. Its rigid structure works with the eye’s internal pressure to maintain the globe’s shape, which is necessary for proper optical function. Another function is providing a firm attachment point for the six extraocular muscles responsible for controlling eye movements.
Common Inflammatory Conditions
Inflammation is the main issue affecting the anterior sclera, with two common conditions differentiated by which layer is affected. Episcleritis is an inflammation of the episclera, the thin tissue layer between the conjunctiva and the scleral stroma. It is a benign and self-limiting condition, though it can be uncomfortable.
Scleritis is a more serious condition involving inflammation of the deeper scleral stroma. This condition is rarer and can be destructive to the eye if not treated. Anterior scleritis is categorized based on its appearance. The types include diffuse scleritis, with widespread inflammation; nodular scleritis, characterized by firm, tender bumps; and necrotizing scleritis, the most severe form, which can destroy scleral tissue.
Recognizing Symptoms and Underlying Causes
The symptoms of episcleritis and scleritis differ significantly in the level of pain. Episcleritis presents with redness, often in a specific sector of the eye, and mild discomfort or a gritty sensation. Vision is usually unaffected, and the condition is often idiopathic, meaning it has no identifiable cause and is not linked to other diseases.
Scleritis is characterized by a deep, boring pain that is severe enough to interfere with sleep and may radiate to the forehead, brow, or jaw. The associated redness often has a purplish hue and can be accompanied by blurred vision, tearing, and extreme light sensitivity. Approximately half of scleritis cases are linked to a systemic autoimmune disease like rheumatoid arthritis, lupus, or granulomatosis with polyangiitis. The eye inflammation can be the first sign of such a condition.
Diagnostic Process and Treatment Options
Diagnosing an inflammatory scleral condition begins with a clinical examination by an ophthalmologist. A slit-lamp examination is used to get a magnified view of the eye’s structures and assess the depth of the inflammation. During this exam, phenylephrine eye drops help differentiate the two conditions. In episcleritis, superficial blood vessels will blanch, or whiten, while the deeper vessels in scleritis will not. If scleritis is suspected, blood tests are ordered to screen for markers of autoimmune diseases.
Treatment is tailored to the specific condition and its severity. Episcleritis often resolves on its own but may be managed with artificial tears or topical nonsteroidal anti-inflammatory drugs (NSAIDs). For non-necrotizing scleritis, the first line of treatment is oral NSAIDs. If the inflammation is severe or does not respond, systemic corticosteroids are used. Necrotizing scleritis or cases with an underlying autoimmune disease require more potent immunosuppressive medications to prevent vision-threatening complications.