Though goniotomy was first performed in the 1930s, it has only been since the introduction of minimally invasive glaucoma surgeries (MIGS) that the procedure has achieved the safety profile and efficiency necessary to make it a preferred treatment for primary open-angle glaucoma (POAG) as well as congenital glaucoma.1
This is primarily due to advances in the surgical instrumentation used to incise/excise the trabecular meshwork (TM) and open Schlemm’s canal. The SION (Sight Sciences) is one such device.
In this video, Nathan Radcliffe, MD, demonstrates the procedure and shares his experience with SION, which can be performed as a standalone goniotomy or in conjunction with cataract surgery.
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Key features of the SION
The SION features several design characteristics that might aid in maneuverability and allow the surgeon to achieve smooth movement throughout the goniotomy, including its signature bladeless design with a rounded toe configured to gently puncture the TM.2
The tip of the instrument contains both a lower foot and upper foot, with the heel of the lower foot acting as a guide with the support of the scleral wall (technically resting against to act as an anchor) to move along Schlemm’s canal while the upper foot assists in directing the TM into the trap and collection window.
The trap contains the accumulated tissue, and the collection window allows for visualization of this material. Of note, the lower foot contains a textured surface, which can provide an extra edge to grasp the TM during the procedure.
Figure 1 highlights the above-mentioned features of the SION.
Figure 1: Courtesy of Sight Sciences.
The SION in action
Dr. Radcliffe tends to opt for goniotomy for certain individuals, such as POAG patients with narrower angles, crowded anatomy, and those with a higher level of hyperopia.
In the first case, Dr. Radcliffe demonstrates how easily the SION can address the angle, engage the trabecular meshwork, and glide along the canal of Schlemm. Dr. Radcliffe notes that because the instrument is designed to slip into the canal, you do not have to worry about the “angle of the attack.”
However, if you do feel resistance, he advised to check your instrument positioning to ensure you have neutral placement on the wound. He also points out that, during a goniotomy, blood from the limbal incision “sets the timer” on the case due to visibility factors.
SION surgical pearls
Dr. Radcliffe offered several surgical pearls during his SION demonstration to increase the ease and effectiveness of the procedure.
- Aim for wound neutrality. Keep the instrument centered across the wound while getting as much of the angle as possible, resulting in a central incision across 90 degrees of nasal angle.
- If it seems there is excess bleeding, remember that with MIGS, there is significant magnification.
- If a strip has not been fully excised, it is advised to rub the irrigation and aspiration instruments together to achieve amputation.
- Spend ample time in the eye performing irrigation and aspiration to remove excess viscoelastic, as retained viscoelastic can result in higher pressure on Day 1 post-op.
- Hydrate the wounds while irrigating to prevent reflux bleeding.
- Though a strip of TM may remain, it is preferable to completely remove the strip to reduce the risk of complications. Another method beyond what has been mentioned above (see #3), go back through the initial incision with the tip to facilitate total excision.
Figure 2 demonstrates the clean removal of a TM strip.
Figure 2: Courtesy of Nathan Radcliffe, MD.
Closing thoughts
MIGS, in general, including enhanced goniotomy, are now the go-to for many surgeons looking to reduce intraocular pressure (IOP) in individuals who have difficulty with medication compliance or suffer adverse ocular surface effects from topical glaucoma medications.
In Dr. Radcliffe’s professional medical opinion, improved MIGS devices such as the SION can make these procedures safer, quicker, and more reliable, leading to potentially enhanced surgical and clinical outcomes.
Disclaimer: The SION Surgical Instrument is a manually operated device used in ophthalmic surgical procedures to excise trabecular meshwork. The SION Surgical Instrument is a sterile, single-use device. The medical opinions and views expressed in this article are those of Nathan Radcliffe, MD.
