posterior uveitis

DEFINITION/ANATOMY: The uvea is the vascular middle layer of the eye (iris, ciliary body, choroid). Posterior uveitis involves the choroid (choroiditis) and often the adjacent retina (chorioretinitis or retinochoroiditis), and may involve retinal vasculature (vasculitis). Classification (SUN): anterior (iritis/iridocyclitis), intermediate (vitreous/pars plana), posterior, and panuveitis.

PATHOPHYSIOLOGY: Infectious (direct pathogen invasion) or non-infectious (autoimmune/immune-mediated, or masquerade syndromes such as intraocular lymphoma). Breakdown of the blood-retinal barrier leads to inflammatory cells in the vitreous, retinal/choroidal lesions, and possible macular edema, retinal detachment, or neovascularization.

CLINICAL FEATURES: Floaters, blurred or decreased vision, scotomas, photopsias, and metamorphopsia. Usually painless, with minimal or no conjunctival injection and no photophobia (unlike anterior uveitis, which is painful, with photophobia and ciliary flush). Fundoscopy: vitritis ("headlights in the fog"), yellow-white chorioretinal lesions, retinal vascular sheathing, and hemorrhages.

KEY ETIOLOGIES: - Toxoplasma gondii: the most common infectious cause. Focal necrotizing retinochoroiditis with a "headlight in the fog" appearance (white fluffy lesion adjacent to an old pigmented scar). Treat with pyrimethamine + sulfadiazine (+ folinic acid) or TMP-SMX. - CMV retinitis: AIDS with CD4 <50. "Pizza pie" or "cottage cheese and ketchup" appearance (hemorrhage + necrosis). Treat with ganciclovir, valganciclovir, or foscarnet. - Syphilis ("great imitator"): chorioretinitis, may occur in any stage. Treat as neurosyphilis with IV penicillin G. - TB: serpiginous-like choroiditis and choroidal tubercles. - Toxocara canis: granuloma in a child, with leukocoria that can mimic retinoblastoma. - Candida (endogenous endophthalmitis): in IV drug users and those with indwelling lines. - Acute retinal necrosis: HSV/VZV. - Sarcoidosis: granulomatous, with periphlebitis ("candle wax drippings"). Look for bilateral hilar lymphadenopathy and elevated ACE. - Birdshot chorioretinopathy: HLA-A29. - Behçet disease: HLA-B51, with oral/genital ulcers and occlusive retinal vasculitis. - Vogt-Koyanagi-Harada: bilateral granulomatous panuveitis with vitiligo, poliosis, alopecia, and tinnitus or meningismus. - Sympathetic ophthalmia: granulomatous panuveitis in the uninjured eye after penetrating trauma to the other eye. - Multiple sclerosis (intermediate uveitis/pars planitis) and JIA (mostly anterior) are associated with other uveitis types.

DIAGNOSIS: Dilated fundus exam, OCT, fluorescein angiography, and targeted labs (RPR/FTA-ABS, HIV, IGRA/TB testing, Toxoplasma IgG/IgM, ACE, chest imaging, HLA typing). Aqueous or vitreous PCR if the diagnosis is unclear.

TREATMENT: Treat the underlying cause for infectious etiologies. For non-infectious disease, use corticosteroids (periocular, intravitreal, or systemic) and steroid-sparing immunosuppressants (methotrexate, mycophenolate, adalimumab). Do not give steroids alone for infectious causes without antimicrobial coverage.

COMPLICATIONS: Cystoid macular edema (the most common cause of vision loss), retinal detachment, choroidal neovascularization, optic neuropathy, glaucoma, and cataract (from chronic inflammation or steroids).

HIGH-YIELD PEARL: Painless floaters plus visual blurring in an HIV patient with CD4 <50 means CMV retinitis. A focal white retinal lesion next to a pigmented scar means Toxoplasma.