Describe sympathetic ophthalmitis with its prevention and treatment.

Definition and Pathogenesis

• Sympathetic ophthalmitis (sympathetic ophthalmia) is a bilateral, diffuse, granulomatous panuveitis occurring after a penetrating injury or intraocular surgery to one eye.
• The injured eye is called the exciting eye and the fellow eye the sympathising eye.
• Mechanism — a type IV (delayed) hypersensitivity reaction to sequestered uveal and retinal antigens which are normally hidden behind the blood-ocular barrier and to which the immune system is therefore not tolerant. Penetrating injury exposes these antigens to the lymphatics of the conjunctiva and orbit, sensitising the host, whose immune response then attacks both eyes. There is an association with HLA-A11 and HLA-DR4
• The essential precondition is a penetrating wound with uveal incarceration; it does not follow a closed (blunt) injury, however severe
• Incidence is very low — of the order of 0.2 to 0.5% after penetrating injury and far less after surgery; but the consequence is bilateral blindness, which is why it dominates the management of the injured eye
• Latent period — minimum 2 weeks; 65% occur within 2 months and 90% within 1 year; but cases have been reported decades later, so no patient is ever entirely beyond risk

Clinical Features and Pathology

• In the exciting (injured) eye — the injury fails to settle, with persistent low-grade inflammation, ciliary tenderness and photophobia. Increasing irritability of an injured eye after the initial recovery is the warning sign
• In the sympathising (fellow) eye — the earliest symptoms are photophobia, lacrimation and a loss OF accommodation (difficulty with near work), from involvement of the ciliary body — which appears before any obvious inflammation and should be asked about specifically. Then blurring and floaters
• Signs — a granulomatous anterior uveitis with mutton-fat keratic precipitates and iris nodules; vitritis; and, in the posterior segment, DALEN-FUCHS nodules — small, discrete, yellowish-white subretinal lesions composed of epithelioid cells and lymphocytes lying between the retinal pigment epithelium and BRUCH membrane. Also papillitis, exudative retinal detachment and, in the healed stage, a "sunset glow" fundus
• Histopathology — a diffuse granulomatous infiltration of the whole uvea by lymphocytes, epithelioid cells and giant cells, characteristically sparing the choriocapillaris and the retina — a distinguishing feature