Ultrasound biomicroscopic findings of the iridocorneal angle in live healthy and glaucomatous dogs

Abstract

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.

Ultrasound Biomicroscopy Studies to Evaluate Ciliary Cleft Parameters in Healthy Eyes of American Cocker Spaniels

“…2). C. CCW measurement: CCW was measured from the superior surface of the root of the iris to the inner surface of the sclera on a perpendicular line (Hasegawa and Kawata, 2015) (Fig. 3).…”

“…Gonioscopy is a classical method for evaluation of the ICA width and anatomy and the degree of pectinate ligament dysplasia (Kato et al, 2006) However, gonioscopic examination has limitations (Renwick, 2014). First, it cannot be used to quantify abnormal structures in the ciliary cleft region (Hasegawa and Kawata, 2015). Second, gonioscopic analysis of the angle is not always accurate, and ICA may occasionally appear narrow or closed if the iris root is close to the corneosclera (Gibson et al, 1998).…”

“…UBM may be used to produce information regarding pathogenesis and prognosis and can be performed on opaque or edematous corneas (Gibson et al, 1998;Martin, 2018). UBM thus compensates for the limitations of gonioscopy (Gibson et al, 1998;Hasegawa and Kawata, 2015) and is expected to be clinically useful for the elucidation of unknown pathophysiologies, selection of accurate treatment approaches, and improvement of prognosis in patients with ocular diseases (Hasegawa and Kawata, 2015;Yan et al, 2018).…”

The future of canine glaucoma therapy

“…It is beyond the scope of this article to list pros and cons for all of these methods, but continual assessment of their usefulness is needed since they are constantly evolving. Technological advances have been most dramatic in high‐resolution imaging, such as OCT and HRUS/UBM (Figures and ), and functional testing such as chromatic pupillary light reflex and advanced electroretinography . As prices for many of these technologies decrease, and they become more user‐friendly, their application will be more realistic for the veterinary practice.…”

“…Technological advances have been most dramatic in high-resolution imaging, such as OCT and HRUS/UBM (Figures 2 and 3), and functional testing such as chromatic pupillary light reflex and advanced electroretinography. [15][16][17][18][19][20] As prices for many of these technologies decrease, and they become more userfriendly, their application will be more realistic for the veterinary practice. To go even further, improvements of monitoring by dog owners will likely become possible in the not too distant future thanks to smartphone applications, user-friendly home tonometry, and continuous IOP monitoring with telemetric F I G U R E 1 Cross-sectional anatomy (A) and aqueous humor drainage routes (B) in the canine eye.…”