Unconventional aqueous humor outflow of microspheres perfused into the equine eye

Abstract

SUMMARY Normal drainage of aqueous humor from the anterior chamber of the equine eye occurred through conventional and unconventional routes. To determine the degree of uveoscleral outflow in the pony, 1- and 3-μm (diam) microspheres were perfused through the anterior chamber for 60 and 90 minutes. Two eyes were treated with pilocarpine before perfusion of spheres to observe any effect on outflow. Presence of spheres was detected by scanning electron microscopy and verified by light microcoopy. By 60 minutes of the perfusion 1- and 3-μm spheres thoroughly infiltrated the anterior uveal trabecular meshwork. The 3-μm spheres were notably excluded from the corneoscleral trabecular meshwork, whereas the 1-μm spheres packed into the corneoscleral trabecular meshwork and mixed with the angular aqueous plexus and intrascleral plexus vessels. After 90 minutes, 1- and 3-μm spheres penetrated the prominent supraciliary space and mixed with the suprachoroidea of the midchoroid. The 1-μm spheres infiltrated tissues more extensively than did the 3-μm spheres, packing into the anterior meshwork and supraciliary space and also moving as far posterior as the suprachoroidea of the peripapillary retina. Spheres also entered the iris, mostly at the root. Several 3-μm spheres moved into the interstitial spaces around axon bundles and vessels in the iris. The 1-μm spheres packed into these spaces in the iris root and were observed in the lumens of iris vessels. Single 1-μm spheres were observed in the lumens of choroidal vessels posteriorly. The present study supported evidence for uveoscleral and uveovortex flow in the horse and indicated that it may be more extensive than that in other species investigated (ie, the dog).