April 2018

Signalment (3134618):  Horse, 7-year-old castrated male paint horse

HISTORY:  Small non-visual eye for the past year clinically suspected chronic uveitis; other eye was normal.

HISTOPATHOLOGIC DESCRIPTION (WSC09-10, 6-4):  Eye: There are changes in all segments of the globe. There is hypertrophy of the corneal endothelium and the anterior chamber is full of proteinaceous fluid.  This iris is markedly thickened up to 2mm by many dilated, congested vessels, edema, increased amounts of fibrillar collagen (fibrosis), small amounts of fibrin and is infiltrated with large numbers of lymphocytes and plasma cells which occasionally form follicles/nodules with lesser numbers of macrophages that extend into the ciliary body.  The iris is attached to the anterior lens capsule by a fibrovascular membrane(posterior fibrovascular membrane with posterior synechia).  At the superficial/inner aspect of the ciliary body there is a 100um  thick layer of hyaline, waxy, amorphous eosinophilic material that covers the apical aspect of the inner ciliary body epithelium (amyloid like material).  Within the cytoplasm of inner non-pigmented ciliary body epithelium there are numerous linear ~ 1umX4um inclusions. There is a layer of fibrillar fibrous material extending from the surface of the ciliary body that extends to the posterior surface of the lens capsule (cyclitic membrane). The inner surface of the anterior lens capsule is covered by a thick fibrous layer (fibrous metaplasia of the lens epithelium) and lens fibers often assume a globular shape (Morgagnian globules) consistent with subcapsular cataract formation. The retina is detached and there is an eosinophilic flocculent material and few melanophages present between the retina and the mildly hypertrophic retinal pigment epithelium. Within the retina there is diffuse atrophy of the ganglion and inner nuclear layer, and the inner nuclear layer blends into the outer nuclear layer. The choroid especially at the posterior aspect is diffusely thickened, including the tapetum, with congested vessels and edema. There is pale eosinophilic fluid within the anterior chamber, posterior chamber and vitreous admixed with variable numbers of macrophages, plasma cells and small amounts of fibrin.

MORPHOLOGIC DIAGNOSIS:  Eye: Uveitis, lymphoplasmacytic, chronic, diffuse, moderate, with posterior synechia,  amyloid-like material, fibrovascular membranes, cataract formation and retinal detachment and atrophy.

ETIOLOGIC DIAGNOSIS:  Immune mediated uveitis

CONDITION:  Equine recurrent uveitis (ERU)

SYNONYMS:  Equine recurrent ophthalmitis, equine periodic ophthalmia, moon blindness, iridocyclitis







Three general causes of uveitis in horses: ocular, systemic, and immune-mediated


Immune-mediated uveitis


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