The iridocorneal angle (ICA) is the major pathway of aqueous humor outflow from the anterior chamber of the eye. Ultrasound biomicroscopy (UBM) has been utilized to characterize the morphology of this drainage pathway in numerous species. UBM may allow for early recognition of aqueous humor outflow obstructions in horses, allowing for earlier recognition of risk for glaucoma, a vision-threatening and painful disease. UBM morphology of the normal equine ICA has yet to be described.
To determine the ultrasonographic morphology of the equine ICA by UBM in standing sedated horses.
In vivo experimental study.
30 healthy adult horses underwent UBM of the ICA at 4 locations (superior, temporal, inferior, nasal) of each eye utilizing standing sedation, topical anesthesia, and auriculopalpebral perineural anesthesia. Anatomic structures were defined on ultrasound images through comparison to published histologic photomicrographs of the equine ICA.
Ultrasound imaging of the ICA at all 4 locations was easily performed in standing, sedated horses. High-resolution images of the ICA allowed for identification of the pectinate ligament, corneoscleral trabecular meshwork (TM), uveal TM, and supraciliary TM.
Pupil size was midrange in all eyes but was not strictly controlled. Lighting conditions not controlled. Various breeds included.
In vivo UBM of the equine ICA is feasible and provides high-resolution images of the structures of the aqueous humor outflow pathway.

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