Effects of a Schlemm canal scaffold on collector channel ostia in human anterior segments

Abstract

This study evaluates the morphologic effect of the implantation of two different sizes of the Hydrus microstent on the outer wall of Schlemm's canal (SC) and collector channel (CC) ostia. Twelve human eyes were dissected at the equator removing the iris, lens, ciliary body and vitreous. The cornea was excised with a corneal trephine exposing a direct view of the angle while leaving the trabecular meshwork (TM) intact. The Hydrus delivery system was used to deliver microstents of 8 mm and 15 mm in length into SC. Following delivery, the tissues were immediately immersed in fixative. After tissue fixation, the microstents were gently lifted out of SC through the TM leaving a small slit opening in the TM. The slit opening was widened by gently dissecting the entire TM. Control eyes underwent dissection before fixation by gently removing the TM exposing the outer wall of SC. The tissues were prepared for scanning electron microscopy (SEM). The external wall of SC was imaged using SEM and were reviewed with particular attention focused on the distribution of irregular particulate matter (IPM), the shape of the CC ostia and the health of the SC endothelium. Three eyes received the 8 mm microstent, two the 15 mm microstent and 6 eyes served as controls. Five of the controls had reported histories of glaucoma while all other eyes were normal. All eyes showed evidence of removal of the trabecular meshwork revealing the external wall of SC. CCs were regularly visible in all eyes and were not obstructed, compressed or their margins disrupted. Nuclear profiles were oriented circumferentially in SC except at regions of CC ostia where they assumed a radial configuration oriented toward the lumen of the CC. The area of microstent contact with SC external wall was examined with SEM and a comparison made between the 8 and 15 mm microstent showing a smaller area of indentation with the 8 mm microstent. The indentations were generally free of particulate debris, were smooth and were devoid of nuclear profiles. In bridged areas adjacent to areas of microstent contact, CCs were identified, appearing patent and intact like those of the control eyes. The eyes receiving 8 mm and 15 mm Hydrus microstents both maintained CC ostia patency but a smaller area of external wall contact was evident from insertion of the 8 mm microstent.

Keywords: Schlemm's canal; collector channels; drainage device; glaucoma; trabecular meshwork.