By using ultrasound biomicroscopy (UBM), the cross-sectional structures of the entire
iridocorneal angle (ICA) which are unable to assess with gonioscopic examination were
evaluated objectively and quantitatively in live healthy and glaucomatous dogs. The ICAs
of normotensive eyes in healthy dogs with normal open angle (NOR), a predisposition to
primary closed angle glaucoma (PCAG) (PREDIS) and suffering from unilateral PCAG (UNI), as
well as the ICAs of hypertensive eyes with acute and chronic PCAG (ACG and CRG), were
assessed. The opening of the ciliary cleft in PREDIS was smaller than that in NOR. In UNI,
the opening and area of the ciliary cleft were significantly decreased compared with those
of NOR and PREDIS. ACG had widespread structural abnormalities including marked decrease
in the ciliary cleft and scleral venous plexus, and a thinner sclera than those in
normotensive eyes, whereas the ICA collapsed in CRG with the thinnest sclera. Medical
therapy-responsive glaucomatous cases had wider ciliary cleft and scleral venous plexus
than unresponsive ones. These findings suggest that the ciliary cleft and scleral venous
plexus of the ICA are key structures contributing to not only the pathophysiology of
canine glaucoma but also the responsiveness to medical therapy in glaucomatous eyes, and
cross-sectional entire structures of the ICA should be evaluated quantitatively with UBM
when diagnosing and managing canine glaucoma.
These data suggest that the Hokkaido breed is highly susceptible to CEA because of the known CEA-associated mutation much like the Collie-related breeds.
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