Equine retrobulbar disease: Diagnoses and outcomes of 15 horses with exophthalmos (1988–2017)

Abstract

SummaryRetrobulbar disease, while rare in horses, can pose a clinical challenge due to the advanced diagnostic procedures necessary to determine the underlying aetiology and extent of disease. The goal of this study was to explore definitive causes of exophthalmos within a hospital population and investigate prognoses for the various aetiologies. Retrospective medical record review was used to identify 15 horses diagnosed with a definitive cause of exophthalmos. Patient signalment, disease duration, eye affected, diagnostic procedures, therapies, and histopathological diagnosis were evaluated. Geldings (12/15, or 80%) were over‐represented (P = 0.014). Mean age at presentation (14 ± 6.7 years) was not significantly different for horses with (14 ± 8.5 years) and without (15 ± 4.4 years) a diagnosis of neoplasia. Diagnosis of a neoplastic process was made in 8/15 horses (53.3%) with neuroendocrine tumour being most common. Eight of the 15 cases were classified as primary orbital disease, and seven represented extension from paranasal sinus disease. Two novel diagnoses were identified: cystic hamartoma arising from the lacrimal gland and orbital aspergillosis secondary to sinonasal disease. In total, eight of 12 horses for which follow‐up was available were euthanised due to orbital disease, two immediately following computed tomography of the skull and six due to disease progression. One horse was euthanised following a peri‐anaesthetic complication. Three horses were lost to follow‐up. Of the 12 horses for which follow‐up was available, only four (33.3%) were alive 21 months post‐diagnosis. Considering only patients for whom a definitive diagnosis was obtained, retrobulbar disease was associated with a poor prognosis for life.