Chapter 7: Uveal Tract & Sclera
The normal sclera is white and opaque, so that the underlying uveal structures are not visible. Structural changes of the scleral collagen fibers and thinning of the sclera may allow the underlying uveal pigment to be seen, giving the sclera a bluish discoloration. Blue scleras also occur in several disorders that lead to disturbances in the connective tissues, such as osteogenesis imperfecta, Ehlers-Danlos syndrome, pseudoxanthoma elasticum, and Marfan's syndrome (Chapter 15). Blue scleras are sometimes noted in normal newborn infants and in patients with keratoconus or keratoglobus.
Prolonged elevation of intraocular pressure early in infancy, as may occur with congenital glaucoma, can lead to stretching and thinning of the sclera. Scleral ectasia may also occur as a congenital anomaly surrounding the disk or involving the macular area or following inflammation or injury of the sclera.
Staphyloma results from bulging of the uvea into ectatic sclera. It may be anterior, equatorial, or posterior. Anterior staphylomas are generally located over the ciliary body (ciliary staphyloma) (Figure 7-10) or between the ciliary body and the limbus (intercalary staphyloma). Equatorial staphylomas are located at the equator and posterior staphylomas posterior to the equator. Posterior staphylomas are most commonly seen near the optic nerve head. Patients with posterior staphyloma generally have poor vision and high myopia, though cases of congenital peripapillary staphyloma in patients with normal or nearly normal vision have been reported. Posterior staphyloma usually produces choroidal atrophy and may be associated with subretinal neovascularization. Staphyloma must be differentiated from extreme myopia and central coloboma of the optic nerve head.
INTRASCLERAL NERVE LOOPS OF AXENFELD
The intrascleral nerve loops are sites of branching of the long ciliary nerves. They enter the sclera close to the ciliary body, usually 3-4 mm posterior to the limbus. They are more commonly seen nasally, tend to be pigmented, and are usually accompanied by a small anterior ciliary artery.
INFLAMMATION OF THE EPISCLERA & SCLERA
Inflammation involving the episclera, the thin layer of vascularized connective tissue overlying the sclera, is referred to as episcleritis. Scleritis, in contrast, refers to primary inflammation of the sclera itself. Scleritis tends to be much more painful and is more often associated with an underlying systemic infection or autoimmune disease.
Episcleritis is a relatively common localized inflammation of the vascularized connective tissue overlying the sclera. It tends to affect young people, typically in the third or fourth decade of life; affects women three times as frequently as men; and is unilateral in about two-thirds of cases. Recurrence is the rule. The cause is not known. An associated local or systemic disorder, such as ocular rosacea, atopy, gout, infection, or collagen-vascular disease, is present in up to one-third of patients.
Symptoms of episcleritis include redness and mild irritation or discomfort. Ocular examination reveals episcleral injection, which may be nodular, sectoral, or diffuse (Figure 7-11). There is no inflammation or edema of the underlying sclera, and keratitis and uveitis are uncommon. Conjunctivitis is ruled out by the lack of palpebral conjunctival injection or discharge.
The condition is benign, and the course is generally self-limited in 1-2 weeks. In the absence of a systemic disease, associated treatment should include chilled artificial tears every 4-6 hours until the redness resolves. However, for cases associated with a local or systemic disorder, more specific therapy may be needed-eg, doxycycline, 100 mg twice daily for rosacea; antimicrobial therapy for tuberculosis, syphilis, or herpesvirus infection; or local or systemic nonsteroidal anti-inflammatory agents or cortico-steroids for collagen-vascular disease.
Scleritis is an uncommon disorder characterized by cellular infiltration, destruction of collagen, and vascular remodeling. These changes may be immunologically mediated or, less commonly, the result of infection. Local trauma can precipitate the inflammation (Table 7-7). Laboratory studies are often helpful in identifying associated systemic diseases, which occur in up to two-thirds of patients (Table 7-8).
Scleritis is bilateral in one-third of cases and affects women more commonly than men, typically in the fifth or sixth decades of life. Patients with scleritis almost always complain of pain, which is typically severe and boring in nature and tends to wake them at night. The globe is frequently tender. Visual acuity is often slightly reduced, and intraocular pressure may be mildly elevated. Concurrent keratitis or uveitis occurs in up to one-third of patients. A key clinical sign is deep violaceous discoloration of the globe due to dilation of the deep vascular plexus of the sclera and episclera, which may be nodular, sectoral, or diffuse (Figure 7-12). Use of the red-free filter of the slitlamp highlights the vascular changes. Areas of avascularity usually result from an occlusive vasculitis and portend a poor prognosis. Scleral thinning often follows bouts of inflammation. Scleral necrosis in the absence of inflammation is referred to as scleromalacia perforans, and is seen almost exclusively in patients with rheumatoid arthritis.
Posterior scleritis usually presents with pain and decreased vision with little or no redness. Mild vitritis, optic nerve head edema, serous retinal detachment, or choroidal folds may be present. Diagnosis is based on detection of thickening of the posterior sclera and choroid on ultrasonography or computed tomography (CT) scan. Localized thickening may be mistaken on ultrasonography for a choroidal tumor.
The same disease associations described above for episcleritis also occur with scleritis, though they occur more frequently and tend to be more severe. Failure to control scleral inflammation can, if severe, result in perforation. Initial treatment of scleritis is with systemic nonsteroidal anti-inflammatory agents. Either indomethacin, 75 mg daily, or ibuprofen, 600 mg daily, may be used. In most cases, there is a virtually immediate reduction in pain and subsequent resolution of inflammation. If there is no response in 1-2 weeks, or if vascular closure becomes apparent, oral prednisone, 0.5-1.5 mg/kg/d, should be started. Occasionally, severe disease necessitates intravenous pulse therapy with methylprednisolone, 1 g. Other immunosuppressive agents can also be used. Cyclophosphamide is particularly valuable if perforation is imminent. Topical therapy is not effective on its own but may be useful as an adjunct to systemic therapy, particularly when uveitis is present. Specific antimicrobial therapy should be given if an infectious cause is identified. Surgery may be required to repair scleral or corneal perforations. Scleromalacia perforans is rarely associated with perforation unless trauma or glaucoma occurs.
Hyaline degeneration is a fairly frequent finding in the scleras of persons over age 60. It is manifested by small, round, translucent gray areas that are usually about 2-3 mm in diameter and located anterior to the insertion of the rectus muscles. These lesions cause no symptoms or complications.
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