HISTOLOGICAL-FINDINGS IN CORNEAL STROMAL ABSCESSES OF 11 HORSES - CORRELATION WITH CULTURES AND CYTOLOGY

Histopathology was compared to culture results and cytology from horse s with corneal stromal abscess at the Auburn University and the Ohio S tate University Veterinary Teaching Hospitals. Significant bacteria we re not isolated in culture or seen on histopathology in any of the hor ses. Although most bacteria infecting equine corneas can be isolated w ith blood and MacConkey's agars, failure to detect bacterial growth ma y not rule out infection because anaerobic or intracellular bacteria w ould not be isolated. The inability to visualise bacterial organisms o n histological sections did not rule out their presence in the tissue, because there is often destruction of bacteria by neutrophils, macrop hages and antibiotic therapy greatly reducing their numbers. Fungal ke ratitis was diagnosed by histopathology in 4 of 11 eyes (36%) and kera titis with no aetiological agent in 7 of 11 eyes (64%). Nine of 11 hor ses (82%) had a prominent neutrophilic stromal infiltrate and 2 (18%) had a predominately pyogranulomatous reaction. Two of the 4 lesions th at showed histological evidence of fungal infection were positive for identifiable fungi on culture and cytology. Fungal cultures of the oth er 2 cases with histological evidence of mycotic keratitis were negati ve or grew unidentifiable fungi which were considered pathogenic becau se, on histopathological sections, fungal hyphae were found deep in th e corneal stroma surrounded by an inflammatory reaction. In 3 of 6 cas es where fungi were recovered on culture, they were considered contami nants based on lack of evidence of organisms in histopathological sect ions. Histopathology and the use of special stains were important in t he interpretation of culture and cytology results.