Why OVDs Don't Cause IOP Rise After MIGS Canaloplasty
OVDs used during MIGS canaloplasty procedures typically do not cause sustained IOP elevation because the procedure itself creates enhanced aqueous outflow through Schlemm's canal and the trabecular meshwork, which allows for rapid clearance of the viscoelastic material from the anterior chamber.
Mechanism of OVD Clearance in Canaloplasty
Enhanced Outflow Pathway
- Canaloplasty mechanically dilates Schlemm's canal 360 degrees, which immediately improves trabecular outflow facility and creates a direct pathway for aqueous humor (and residual OVD) to exit the eye 1
- The procedure restores physiologic drainage through the conventional outflow pathway, allowing viscoelastic material to be cleared through the same route rather than accumulating in the anterior chamber 2
- Unlike traditional glaucoma surgeries that may temporarily obstruct outflow, canaloplasty specifically opens the drainage system, facilitating OVD egress 1
Surgical Technique Considerations
- Modern MIGS canaloplasty techniques (using VISCO360 or OMNI systems) involve clear corneal incisions and controlled OVD injection that is subsequently removed through the enhanced trabecular pathway 1
- The viscoelastic serves its purpose during surgery to maintain space and protect tissues, but the newly patent canal system allows for its efficient removal 2
Clinical Evidence Supporting Lack of IOP Spike
Post-Canaloplasty IOP Outcomes
- In a large retrospective study of 206 eyes, canaloplasty achieved significant IOP reduction from 21.8 to 15.6 mm Hg in eyes with baseline IOP >18 mm Hg, with no reported sustained OVD-related pressure spikes 1
- The procedure maintained IOP control at 13.9 mm Hg in eyes with baseline IOP ≤18 mm Hg, demonstrating that the enhanced outflow prevents OVD retention 1
- Long-term follow-up extending to 42 months showed sustained IOP reduction without delayed pressure elevations that would suggest retained viscoelastic 1
Contrast with Other Surgical Scenarios
When OVD Does Cause Problems
- During glaucoma drainage device implantation, viscoelastic injection can cause dramatic IOP spikes because the outflow pathway is not immediately functional 3
- In eyes without enhanced drainage (such as during routine cataract surgery in glaucoma patients), OVD retention can contribute to postoperative pressure elevation 4
The Canaloplasty Advantage
- Canaloplasty achieves IOP-lowering effects comparable to trabeculectomy but with a much lower risk profile, specifically avoiding the complications associated with bleb-dependent filtration 2
- The tissue-sparing nature of the procedure maintains anatomic integrity while creating functional drainage, unlike filtering procedures where OVD could interfere with bleb formation 1
Important Clinical Caveats
- Immediate postoperative monitoring remains essential: While sustained OVD-related IOP elevation is uncommon after canaloplasty, surgeons should still check IOP within the first 24 hours to ensure proper drainage function 1
- Complete OVD removal during surgery: Surgeons should still attempt thorough removal of viscoelastic at the conclusion of the procedure, as the enhanced outflow is meant to handle residual amounts, not large volumes 2
- Patient-specific factors matter: Eyes with severe trabecular damage or very advanced glaucoma may have less capacity to clear OVD even after canaloplasty, though this is uncommon 1
The fundamental principle is that canaloplasty creates the solution to the problem—by opening the natural drainage pathway, it provides the mechanism for OVD clearance that would otherwise cause pressure elevation in a compromised outflow system.