Clinical, histopathological and immunohistochemical characterization of a novel equine ocular disorder: heterochromic iridocyclitis with secondary keratitis in adult horses.
OBJECTIVE
To describe the clinical, histopathologic and immunohistochemical characteristics of an equine ocular inflammatory disease resulting in anterior uveitis and corneal endothelial inflammation associated with iris pigment dispersion and retrocorneal fibrous membrane (RFM) formation.


METHODS
Retrospective study.


METHODS
Sixteen horses with evidence of pigmented keratic precipitates (KPs), corneal edema, and/or iris depigmentation. Information collected from the medical records included signalment, clinical signs, prereferral treatment duration and response to therapy, ophthalmic examination findings, postreferral treatment, response to therapy, and outcome.


RESULTS
Twenty-one eyes from 16 horses were affected. Age ranged between 9 and 25 years (Average 16.1 years). Blepharospasm, epiphora, and/or corneal opacification were the first clinical signs noted. At the time of referral pigmented KPs, corneal edema, iridal depigmentation, and retrocorneal membranes were commonly seen. Treatment included topical and/or systemic anti-inflammatories and antibiotics with variable response. Reduction or cessation of anti-inflammatory therapy resulted in worsening of clinical signs and disease progression. Eight eyes ultimately required enucleation. Histopathology changes include iridal pigment loss and dispersion, RFM formation, and keratitis. Variable degrees of lymphoplasmacytic inflammation were dominated by T-cells within the corneal stroma, RFM, iris, and ciliary body with occasional multinucleated giant cells.


CONCLUSIONS
Heterochromic iridocyclitis with secondary keratitis (HIK) is characterized by uveal inflammation with pigment dispersion and suspected corneal endothelial dysfunction. Horses being treated for HIK require diligent and frequent follow-up examinations in combination with aggressive local immune suppression to control the disease. However, HIK may not respond to therapy and enucleation may ultimately be required to ensure the horse's comfort.
Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, 27606, USA.
Nelson I
NI
Pinto
Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, 27606, USA.|Pferdeklinik Munich-Riem, Munich, 81929, Germany.
Richard J
RJ
McMullen
Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, 27606, USA.
Keith E
KE
Linder
Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, 27606, USA.
John M
JM
Cullen
Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, 27606, USA.
Brian C
BC
Gilger
D000818:Animals; D003315:Cornea / Q000473:pathology; D005260:Female; D006734:Horse Diseases / Q000175:diagnosis / Q000473:pathology*; D006736:Horses; D015863:Iridocyclitis / Q000175:diagnosis / Q000473:pathology / Q000662:veterinary*; D007634:Keratitis / Q000175:diagnosis / Q000473:pathology / Q000662:veterinary*; D008297:Male; D014602:Uvea / Q000473:pathology
endotheliitis; iridocyclitis; keratic precipitates; keratitis; retrocorneal membrane; uveitis