Scleritis and uveitis are distinct, potentially sight-threatening inflammatory eye conditions that can present with similar symptoms, making diagnosis challenging. Differentiating them requires identifying the precise anatomical location of the inflammation and recognizing key differences in manifestation. Understanding these distinctions is fundamental because the underlying causes and required medical management protocols vary significantly. Both conditions require prompt, specialized care to preserve vision and address any associated systemic illness.
Anatomical Location and Definitions
Scleritis is defined as inflammation affecting the sclera, the tough, opaque white outer coating of the eyeball. This dense layer is primarily composed of collagen and provides structural integrity to the eye. Scleritis is classified as anterior (affecting the visible front of the eye) or posterior (affecting the back of the eye).
Uveitis, in contrast, involves the uveal tract, which is the middle, vascular layer of the eye. The uvea is a pigmented layer situated beneath the sclera and is composed of the iris, the ciliary body, and the choroid. Inflammation is classified based on the component involved, such as anterior uveitis affecting the iris and ciliary body, or posterior uveitis involving the choroid and retina.
Distinct Symptom Presentation
The pain associated with scleritis is a hallmark symptom, typically described as severe, deep, and boring. This intense pain frequently radiates to the jaw, temple, or brow, often waking the patient from sleep, and usually does not respond well to over-the-counter pain relievers. The ocular redness has a characteristic deep, violaceous or bluish-purple hue, caused by inflammation of the deep scleral vessels.
Uveitis symptoms focus more on visual disturbances and light sensitivity. Anterior uveitis, the most common type, causes photophobia, blurred vision, and sometimes a characteristic redness known as ciliary flush concentrated around the edge of the iris. Posterior uveitis, affecting the back of the eye, often presents with a sudden onset of floaters or reduced vision rather than pain. Additionally, a scleritic eye is often intensely tender to the touch, while a uveitic eye typically is not.
Associated Systemic Conditions
Scleritis has a strong association with underlying autoimmune and connective tissue diseases, with up to 50% of non-infectious cases linked to a systemic disorder. Associated diseases often include Rheumatoid Arthritis, Systemic Lupus Erythematosus (Lupus), and Granulomatosis with Polyangiitis. Scleritis can sometimes be the first manifestation of a severe, life-threatening systemic vasculitis.
Uveitis also has strong systemic associations, but the profile of linked diseases differs significantly. Anterior uveitis has a particularly high association with the HLA-B27 gene, a genetic marker linked to Spondyloarthropathies. These conditions include Ankylosing Spondylitis, Reactive Arthritis, and Psoriatic Arthritis.
Differential Treatment Strategies
The anatomical depth of scleritis dictates contrasting treatment protocols. Because scleritis involves the deep collagen of the eye wall, topical anti-inflammatory eye drops are generally ineffective. Treatment for non-infectious scleritis usually requires high-dose systemic Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) or systemic immunosuppressive therapy. Medications such as methotrexate, azathioprine, or cyclophosphamide may be necessary to control the destructive inflammation and manage the underlying systemic disease.
Anterior uveitis is often effectively managed with localized treatment methods. The standard initial therapy involves topical corticosteroids to suppress inflammation in the front of the eye. Cycloplegic eye drops are also used to paralyze the ciliary muscle and iris, which relieves pain and prevents complications. Systemic immunosuppression is typically reserved for severe, recurrent, or posterior uveitis that does not respond to local therapy.