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Although no gene analysis has been done on the horse in
this case, the severity of the lesions clearly suggests that this horse was homozygous for the mutant allele. The cysts in this case were only present on the ciliary processes and no iridal hypoplasia or retinal dysplasia was seen. In Rocky Mountain horses, codominant inheritance with incomplete penetrance of the defective gene has been suggested (Ewart et al. 2000), which may explain why not all of the previously reported lesions were seen in the present case, assuming that the same inheritance pattern is present in Comtois horses as in Rocky Mountain Horses. As stated by Matthews (2013), ultrasonography is
particularly valuable for diagnosing heterozygous cyst phenotypes, which otherwise are clinically undetectable. The latter is important, as confirmation of the carrier status of animals is crucial for progressively reducing the incidence of this disease in the horse population (Matthews 2013). In the present case, post mortem MRI was performed for
teaching and academic purposes. At least theoretically, in selected cases of ophthalmic disease, the high soft tissue contrast and cross-sectional anatomic detail of MRI of (peri)ocular structures could provide the clinician with additional diagnostic and prognostic information compared to standard diagnostic tools (Holmes 2014). In human medicine, MRI is used for visualisation of the cranial and intraorbital nerves, identification of ocular and orbital tumours, assessment of blood oxygenation of the retina, studying diffusion pathways of pharmaceuticals in the eye after intravenous contrast injection and, ultimately, for providing physiological information beyond anatomy (functional MRI) (Townsend et al. 2008). However, in horses, practical issues mainly associated with limitations in coil size and with the need for general anaesthesia, preclude widespread application of this technique thus far, and, at present, equine MRI is unlikely to contribute unique information that will alter patient management. Additional magnetic resonance studies on diseased eyes and orbits are needed to determine the value of this imaging tool in equine ophthalmology (Gilger and Stoppini 2011). In conclusion, the present report documents the macroscopic, ultrasonographic and MRI findings in a histologically confirmed case of MCOA. With further development and availability of MRI technology for horses, this technique may provide additional diagnostic information in clinical cases with (peri)ocular pathology.
Authors’ declaration of interests No conflicts of interest have been declared.
Manufacturers’ addresses
1Thea Pharma, Wetteren, Belgium. 2Boehringer Ingelheim, Brussels, Belgium. 3Sterop, Brussels, Belgium.
4AstraZeneca, Brussels, Belgium. 5Ursapharm, Saarbrücken, Germany. 6Kowa Optimed Europe, Berkshire, UK. 7Mila International, Erlanger, Kentucky, USA. 8Allergan Pharmaceuticals, Westport, Ireland. 9Alcon, Vilvoorde, Belgium. 10Zambon, Bresso, Italy. 11MSD Animal Health, Brussels, Belgium. 12Hitachi Medical Corporation, Yokohama, Japan.
References
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