Anterior chamber to frontal sinus shunt for the diversion of aqueous humor: a pilot study in four normal dogs

Abstract

Silicone tubing was used to divert aqueous humor from the anterior chamber of the right eye to the rostral compartment of the right frontal sinus in four clinically normal mixed-breed dogs. Biomicroscopic examination, and pneumoapplanation tonometry and tonography, completed for up to 18 weeks postoperatively, confirmed gonioimplant function in all four cases. The dogs were euthanized at 6, 8, 16 and 18 weeks postoperatively. Gonioimplant patency was further confirmed by postmortem examination of the globes, implants and frontal sinuses. Gross and light microscopic examinations revealed iridal attachments to the implant (n = 4), mild anterior uveitis (n = 3), anterior subcapsular cataracts (n = 4), and focal corneal (n = 3) and scleral (n = 3) scarring in the operated globes. Light microscopic examination of frontal sinus specimens revealed mild lymphocytic proliferation and fibrosis immediately adjacent to the implant entrance site. There were no bacteria detected on aerobic or anaerobic cultures of the frontal sinuses or light microscopic examination of the globes or frontal sinuses. Results indicate that the frontal sinus shunting of aqueous humor is a safe and effective means of extraorbital aqueous diversion with potential applicability in the management of glaucoma.

Surgical Treatment of Canine Glaucoma

“…However, the increased size of the tube may be detrimental to its pliability, with potential increased corneal contact and secondary endothelial decompensation. 18,19 …”

“…18,19 The aim of this type of shunting procedure is to prevent bleb fibrosis and implant failure by diverting the AH to an epithelium-lined, air-filled space, such as the frontal sinus.…”

“…18 Reported complications of the Cullen shunt relate to the thick and more rigid intracameral tube, including corneal decompensation from endothelium contact; anterior uveitis with fibrin formation; and tube displacement from the anterior chamber. 18,19,39 Despite the risks of possible retrograde bacterial contamination from the dorsal sinus, only one case of endophthalmitis has been reported. 40 …”

“…20 Inadequate placement of the tube may result in corneal endothelial damage and edema caused by its excessive length, its obstruction by the base of the iris when trimmed too short, or its displacement secondary to failure of the securing sutures. 18,19,47 Transient anterior uveitis is expected after implantation of the silicon tube in the anterior chamber, and it can lead to tube occlusion by intracameral fibrin. 7,9,12 Intracameral injections of TPA (25-37.5 mg) are usually effective in dissolving the fibrin within or surrounding the gonioimplant tube.…”

Cullen frontal sinus valved glaucoma shunt: preliminary findings in dogs with primary glaucoma

“…Presently, the most common site used for the extraocular diversion of aqueous humor using glaucoma drainage devices is the subconjunctival space 8–10,12,14,18 . In attempts to prevent fibrosis and early implant failure, studies have focussed on (1) diverting aqueous humor from the anterior chamber to sites other than subconjunctivally; 11,14,19,20 (2) the biocompatibility of the material forming the implant, 1,14,21 and (3) using antimetabolites such as mitomycin‐C and 5‐fluorouracil to suppress fibrosis 22–25 …”