Clinical, histopathological and immunohistochemical characterization of a novel equine ocular disorder: heterochromic iridocyclitis with secondary keratitis in adult horses

Abstract

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.

Evaluation of equine corneal disease using spectral domain optical coherence tomography (SD‐OCT)

“…The use of SD‐OCT for measurement of equine corneal thickness has also been described; but to date, only a single study exists of the use of this imaging modality in horses with corneal disease . This single study used SD‐OCT imaging to describe the corneal lesions of horses with heterochromic iridocyclitis including the characteristic pigmented keratic precipitates, detached Descemet's membrane, and retrocorneal membrane …”

“…Corneal imaging with SD‐OCT was selected for this subset of horses to gain a better understanding of the underlying cause, the extent, and depth of the corneal lesion and, in some cases (ie, neoplasia), to determine whether corneal tissue had been invaded. For corneal imaging, SD‐OCT was used as previously described . Briefly, horses were tranquilized with detomidine HCL (0.01‐0.04 mg/kg body weight, IV) and palpebral nerve blocks were performed (1 mL lidocaine HCL).…”

“…Advanced imaging of the equine cornea may assist the clinician to determine the cause, depth, and extent of corneal disease . Modalities such as high‐frequency ultrasound, in vivo confocal imaging, and spectral domain optical coherence tomography (SD‐OCT) provide high‐resolution imaging and show great promise for imaging of the equine cornea . Optical coherence tomography obtains high‐resolution cross‐sectional images of tissue architecture in vivo by interferometry, which correlates the light backscattered from the tissue and the light that has travelled a known distance (reference arm length) to measure the magnitude and echo time delay of backscattered light .…”

“…In horses, the use of SD‐OCT was first reported in 2014 where the technique and feasibility of SD‐OCT use in the standing horse were described along with the normal anatomy of the equine cornea, retina, and optic nerve of the normal horse . The use of SD‐OCT for measurement of equine corneal thickness has also been described; but to date, only a single study exists of the use of this imaging modality in horses with corneal disease . This single study used SD‐OCT imaging to describe the corneal lesions of horses with heterochromic iridocyclitis including the characteristic pigmented keratic precipitates, detached Descemet's membrane, and retrocorneal membrane …”

Highlights of recent clinically relevant papers

“…This retrospective study by Nelson Pinto and colleagues in the USA and Germany describes the clinical, histopathological and immunohistochemical characteristics of a novel equine ocular disorder: heterochromic iridocyclitis with secondary keratitis in adult horses .…”