Ultrasonographic examination of ocular lesions in farmed halibut

This paper describes the use of ultrasound to document ocular abnormalities occurring in farmed halibut. A cystic condition of the posterior segment of farmed halibut with a number of ocular sequelae has been reported previously. Further research to elucidate the aetiology and pathogenesis of this condition requires in vivo determination of ocular health over and above that provided by ophthalmoscopy alone. Ocular ultrasonography would appear to be an optimal technique for evaluating the presence of gas- or fluid-filled cysts in the posterior segment and retrobulbar space. The aim of this study was to evaluate this technique for investigation of the piscine eye and specifically to define the role of ultrasonography to detect gas bubble formation in the choroid of farmed halibut, a factor considered central to ocular pathology in many of these fish. In particular the study sought to assess the minimum size of halibut in which intraocular cystic lesions could be identified by ultrasonography and the minimum size of lesion identified by ocular ultrasonography. A second objective was to correlate ultrasonographic findings with lesions found at post mortem ocular examination. A number of halibut of varying sizes, with and without clinically apparent ocular lesions, were subjected to examination under anaesthesia. A proportion of these fish were subsequently sacrificed to allow post mortem ocular evaluation with the aim of correlating ultrasonographic findings with intraocular pathological defects.