Elsevier

Ophthalmology

Volume 109, Issue 4, April 2002, Pages 786-792
Ophthalmology

Effects of viscoelastic injection into Schlemm’s canal in primate and human eyes: Potential relevance to viscocanalostomy

Presented in part as posters at the Association for Research in Vision and Ophthalmology annual meeting, Ft. Lauderdale, Florida, May 2000; and the American Academy of Ophthalmology annual meeting, Dallas, Texas, October 2000.
https://doi.org/10.1016/S0161-6420(01)01006-5Get rights and content

Abstract

Objective

To study possible initial mechanisms of alterations in aqueous outflow that may result from the injection of viscoelastic into Schlemm’s canal (SC) during viscocanalostomy.

Design

Experimental animal (Macaca nemestrina) and human autopsy study.

Methods

Eyes were dissected into a limbal ring and hemisected or quartered. Uncannulated segments served as controls. In treated segments, SC was cannulated and viscoelastic injected. Segments were fixed and sectioned into continuous 500 to 1000 μm pieces, examined at the dissecting microscope, and photomicrographs were taken. Representative tissue was further prepared for scanning electron microscopy or sectioned at 1 μm.

Main outcome measures

Tissue sections were examined to determine the extent of dilation and disruption of SC and related structures. SC dimensions were measured in segments from controls, cannulated regions, and regions of viscoelastic injection beyond the cannula insertion. In the hemisected segments, the circumferential extent of SC dilation was determined, and structures within the canal were described and counted.

Results

SC was dilated with increased anteroposterior length and height in cannulated and viscoelastic-injected segments in both primate and human eyes relative to untreated controls. The walls of SC were disrupted in both regions of cannulation and of viscoelastic injection, and the collector channels were widely dilated by viscoelastic. With decreasing effectiveness, the injected viscoelastic circumferentially dilated SC as far as 14 mm and 16 mm in primate and human hemisections, respectively. Structures that bridged between the walls of SC were often disrupted.

Conclusions

Cannulation of SC and injection of viscoelastic beyond the cannula resulted in marked dilation of SC and associated collector channels. Lateral walls, inner wall endothelium, and bridging structures of SC were frequently disrupted by cannulation and sometimes by injected viscoelastic. These findings suggest that viscocanalostomy may acutely cause a direct communication between SC and the juxtacanalicular space, and so may initially enhance conventional aqueous outflow. Controlled clinical trials will be necessary to determine the long-term outcomes of this procedure.

Section snippets

Primate eyes

Postmortem eyes of Macaca nemestrina, six females and one male ages 9 to 14.5 years, were obtained immediately after the animals were killed for unrelated research. The eyes were dissected to a limbal ring encompassing SC and associated tissues. This limbal tissue was either cut into quarters or hemisected. A single suture was placed at the distal end of the tissue section, closing one end of SC. The suture was used to more closely approximate the situation in the living eye; viscoelastic entry

Primate eyes

In regions of both cannulation and viscoelastic injection, marked dilation of SC was seen (Fig 2A–C). In cannulated sections, the walls of SC were disrupted, and no structures were noted within SC (Fig 2B). In the proximal portion just beyond the cannula, where hydrostatic pressure from the viscoelastic would be expected to be the greatest, there was evidence of disruption of the endothelial lining of the anterior and posterior walls of SC (Fig 2D). In some areas there was also splitting into

Discussion

The desire to avoid trabeculectomy complications underlies the current interest in alternative surgeries for lowering intraocular pressure. Trabeculectomy, a guarded filtration surgery, is the most commonly used surgical technique for lowering intraocular pressure. Short-term complications of trabeculectomy related to anterior chamber entry such as hypotony, shallow or flat anterior chamber, choroidal detachments, and hemorrhage, can generally be avoided by tighter flap closures and modulation

Cited by (84)

  • Pharmaco-devices therapy for glaucoma

    2022, Handbook of Basic and Clinical Ocular Pharmacology and Therapeutics
  • Aqueous outflow regulation – 21st century concepts

    2021, Progress in Retinal and Eye Research
    Citation Excerpt :

    Fine structure of the walls and features within the lumen of the SC inlet valves are made manifest through transmission electron microscopy studies (Johnstone, 2004). Geometric relationships of the SC inlet valve to the TM and SC external wall and the presence of a lumen are visible in SEM images in Figs. 11 and 12, and are available in additional references (Smit and Johnstone, 2000)abs (Smit and Johnstone, 2002; Johnstone, 2004, 2016; Hariri et al., 2014; Xin et al., 2017). Tissue composition and 3D relationships become apparent with confocal fluorescence microscopy and immunohistochemistry studies (Fig. 11) (Jamil et al., 2010; Johnstone et al., 2011d; Martin et al., 2013)abs.

View all citing articles on Scopus
View full text