Eric S. Pearlstein
Episcleritis is a relatively benign, self-limiting condition affecting the outer coat of the eye. There are few if any serious sequelae, and it therefore demands little in terms of evaluation and treatment. Clinically, the condition is categorized as either simple or nodular. Nodular episcleritis has a well-demarcated, elevated area of inflamed episcleral tissue. The simple form demonstrates vascular congestion of the episclera but without a discrete nodule.
Episcleritis should not be thought of as simply a mild version of scleritis. These two diseases should instead be regarded as distinct clinical entities, since the implications of the usually harmless episcleritis differ significantly from the more ominous scleritis.
The episclera is comparable to a synovial membrane, allowing smooth movements of the globe as would the synovial tissue in a ball-and-socket joint. The rheumatologic analogy goes further when one considers the higher incidence of scleral and episcleral inflammatory conditions associated with rheumatologic conditions.
The episclera is a fibroelastic structure consisting of collagen bundles, fibroblasts, melanocytes, proteoglycans, and glycoproteins., It has two layers: an outer parietal layer and a deep visceral layer. These two layers are loosely fused by fine connecting fibers. The outer parietal layer, which is the more superficial, is vascularized by the superficial episcleral capillary plexus. This capillary plexus with its uniquely straight and radially oriented vessels helps distinguish this layer from the deep visceral layer (Fig. 103.1). The outer parietal layer fuses with the muscle sheaths. As it approaches the limbus, the outer parietal layer also fuses with conjunctiva and the deep visceral layer of episclera.