Abstract
Abstract: :
Purpose: To perform an initial evaluation of novel microsurgical tools for imaging and catheterization of Schlemm’s canal, and to determine how expansion of Schlemm’s canal with these tools affects aqueous outflow facility in perfused cadaver eyes. Methods: A prototype ultra–high resolution ultrasound system with an axial resolution of 20 microns was used to image the anterior segment and Schlemm’s canal prior to and after surgical intervention. In the control group, 5 whole human cadaver eyes were perfused at a constant pressure of 10 mm Hg through a corneal fitting while instantaneous readings of flow were provided by a variable area flow meter. In matched contralateral study eyes, a custom–designed flexible 210 micron diameter microcatheter was threaded 180 degrees into Schlemm’s canal through a scleral cutdown. Schlemm’s canal was expanded by injection of viscoelastic. The cutdown was then sealed with cyanoacrylate tissue adhesive prior to perfusion experiments. Results: Microcatheterization of Schlemm’s canal to 180 degrees was achieved without damage to intraocular structures. Real time ultrasound imaging was able to confirm viscodilation of the entire canal to between 210 and 250 degrees extent from the cutdown, with an average increase in canal major diameter from 150 to 300 microns. In some cases apparent dilation of collector channels was also observed. Whereas control eyes showed a gradual decrease in outflow facility over a 24 hour period, catheterized eyes showed an increase in outflow facility occurring approximately 6 hours after viscoelastic injection correlating with the disappearance of viscoelastic on ultrasound imaging. Mean±SD outflow facility after 24 hours of perfusion was 0.14±0.046 µl/min/mm2 in control eyes and 0.21±0.071 in catheterized eyes (p=0.04, paired T–test). Histopathological sections of catheterized eyes showed dilation of the canal with stretching and thinning of the juxtacanalicular tissue. Conclusions: In general, viscoexpansion of Schlemm’s canal increases outflow facility in cadaver eyes after washout of viscoelastic. This effect may be related to thinning of the juxtacanalicular tissue and has potential relevance to viscocanalostomy. Microsurgical access to Schlemm’s canal utilizing a flexible microcatheter and high resolution imaging may be a promising method for modifying Schlemm’s canal in vivo.
Keywords: trabecular meshwork • intraocular pressure • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)