New infusion system improves delivery of sub-Tenon’s anesthesia

Specially designed scissors and cannula help deliver effective anesthesia and akinesia with a minimum amount of bleeding and tissue ballooning.

Thomas John

Ophthalmic anesthesia has evolved greatly over time from retrobulbar anesthesia, to peribulbar anesthesia, to sub-Tenon’s and topical anesthesia. For an occasional patient who is not a suitable candidate for any of these modalities, general anesthesia can often be considered as an option.

Retrobulbar anesthesia, although very effective, is associated with pain, and the use of a long sharp needle carries with it an occasional risk of potential complications, including retrobulbar hemorrhage, intraocular needle penetration and potential loss of the eye. Thus, the need for safety was of paramount interest to the ophthalmic surgeon, and this gave birth to blunt-tipped needles and other needles specially designed for retrobulbar anesthesia.

Over time, ophthalmic surgeons moved away from the retrobulbar space to safer peribulbar and sub-Tenon’s regions for administration of anesthesia, especially for cataract surgery. Anatomically, Tenon’s capsule is a thin layer of connective tissue that envelopes the globe to fuse with the conjunctiva anteriorly at the level of the limbus and extends posteriorly in all directions around the globe to finally fuse with the dura of the optic nerve. Thus, the sub-Tenon’s space is a potential space between the Tenon’s capsule and the sclera. Local anesthetic administration into this space results in analgesia and akinesia by diffusing posteriorly into the retro-orbital space to block the sensory and motor nerves.

When comparing these different types of ophthalmic anesthesia, sub-Tenon’s block seems to be better than retrobulbar block and topical anesthesia in patient satisfaction. When comparing sub-Tenon’s block to topical anesthesia, more significant anesthesia and analgesia was achieved with sub-Tenon’s block, leading to more favorable surgical conditions and enhanced patient and surgeon satisfaction. Thus, many ophthalmic surgeons prefer sub-Tenon’s block over other types of ophthalmic anesthesia.

In this column, Dr. Korenfeld describes the use of the Katalyst sub-Tenon’s infusion system for ophthalmic anesthesia.

Thomas John, MD
OSN Surgical Maneuvers Editor

by Michael S. Korenfeld, MD

Michael S. Korenfeld

Sub-Tenon’s anesthesia offers advantages to both anterior and posterior segment surgeons that other common methods of anesthesia do not. They include no blind passage of anything sharp behind the globe, direct visualization of the delivery of the injected local anesthesia, and achievement of both anesthesia and akinesia.

Sub-Tenon’s anesthesia

I have developed an improved infusion system (Katalyst Surgical) to deliver sub-Tenon’s anesthesia for intraocular surgery. In the traditional method, there are several tissue planes that must be opened in order to effectively deliver sub-Tenon’s anesthesia. Most surgeons open these tissues in the inferior-oblique quadrant.

The conjunctiva is intrinsically transparent, except for the vasculature, which runs within the conjunctival plane, with an occasional bridging vessel that crosses into Tenon’s fascia. A small hole can usually be cut through the avascular conjunctiva without producing much bleeding. Blunt dissection can then enlarge the opening. Cutting a conjunctival vessel always makes it bleed, while blunt dissection only occasionally makes it bleed, therefore making blunt dissection preferable.

Tenon’s fascia is below the conjunctiva. It is typically avascular, thicker than the conjunctiva, and only has vessels that bridge through it from the episcleral layer below. Tenon’s can be lifted and cut with the sharp inner aspect of the blades of specially designed scissors, or it can be grasped and elevated with conjunctival forceps and then bluntly dissected with the outside surface of the scissors blade, near the somewhat fused junction of Tenon’s with the episclera. The relatively adherent Tenon’s-episcleral junction serves as countertraction to the elevation of Tenon’s with the forceps, and blunt dissection can be effective in penetrating Tenon’s at that location. Once a small hole is created in Tenon’s, then blunt dissection is again preferred over cutting.

The tissue plane has now been accessed for the infusion. Surgical manipulation in this plane causes most of the bleeding that concerns the surgeon. Most of the vessels in the episclera and sclera run in a plane that is horizontally oriented, with occasional bridging vessels that cross into Tenon’s. Any blunt dissection that is done through any of these tissue planes is therefore best done with the scissors opening vertically because the surgeon is much less likely to damage a blood vessel. All that is needed is to convert a “potential space” into a dissected tunnel under Tenon’s that extends approximately to the equator.

The conjunctiva is elevated, and the scissors are inverted to incise an avascular region.

Scissors are up-righted, and blunt dissection of the tunnel is started through Tenon’s fascia. Images: Korenfeld MS

Scissors are progressively advanced down the tunnel, allowing the bottom curve of the scissors to follow the globe’s curve.

Scissors are fully advanced down the tunnel.

Infusion cannula is fed down the tunnel while countertraction is applied to the cut edges of the conjunctiva and Tenon’s fascia.

Infusion cannula is advanced fully, the tunnel wall is collapsed down onto the cannula with forceps, and the infusion starts.

Creating a surgical tunnel

The Katalyst sub-Tenon’s infusion scissors are designed to optimize this anatomy. The scissors open vertically, have a low profile to create an appropriate surgical “tunnel,” have blunt tips that will not cut tissue as the closed scissors are advanced under Tenon’s, and are curved to match the curve of the globe, so blunt dissection can be accomplished without creating undesirable stretching of tissues. In use, once an opening in Tenon’s is established, the closed scissors are placed through the hole and advanced approximately 0.5 cm along the curve of the globe. The scissors are then opened and withdrawn along the same path. The scissors are again closed and advanced further with each passage, withdrawing the scissors while opening them vertically. With each pass, it is desirable to re-grasp the Tenon’s fascia while the scissors are open, which greatly improves the visibility of where to grasp the cut edge of Tenon’s, so that Tenon’s can be kept on sufficient traction to prevent it from bunching up as the closed scissors are advanced along the episcleral surface.

Once a suitable tunnel is created, the syringe with the specially designed sub-Tenon’s infusion cannula is obtained. While maintaining countertraction on the edge of Tenon’s, the cannula is fed down the “tunnel.” If the dissection is good, and the Tenon’s is kept under moderate traction, the advancement of the cannula can be visually tracked around the curve of the globe. The cannula is configured to emulate the curvature of the sclera, and the unique shape of the cannula allows the surgeon to track along the curve of the globe without the concern of abrading the corneal surface with the proximal cannula, which is common with a conventional sub-Tenon’s infusion cannula.

Once the cannula has been advanced to approximately the equator, the conjunctival forceps collapse the tunnel around the cannula to increase resistance to the reflux of the infused injectate. Another trick is to start the infusion at the equator with a purposeful but not violent infusion. As the injectate leaves the cannula, it hydrodissects the potential space that has not been prepared by the scissors. As the local is injected, the surgeon can bounce back and forth a little, which, along with the hydrodissection activity, will allow the cannula to be placed even farther around the globe, further reducing the risk of the tissues ballooning. Generally, the farther back the infusion starts, the less ballooning that will occur. A violent hydrodissection will be more prone to overstretch bridging vessels, so a careful visualized “tunnel” dissection with the scissors is generally preferable to aggressive hydrodissection.

With some practice, a little luck and the Katalyst sub-Tenon’s infusion system, safe and effective anesthesia and akinesia can be reliably achieved with a minimum amount of bleeding and tissue ballooning.

• Michael S. Korenfeld, MD, can be reached at Comprehensive Eye Care, 901 E. 3rd St., Washington, MO 63090-3010; 636-390-3999; email: michaelkorenfeld@hotmail.com.
• Edited by Thomas John, MD, a clinical associate professor at Loyola University at Chicago. He is in private practice in Oak Brook, Tinley Park and Oak Lawn, Ill. and can be reached at 708-429-2223; fax: 708-429-2226; email: tjcornea@gmail.com.
• Disclosure: Dr. Korenfeld is a paid consultant for Katalyst Surgical. Dr. John has no relevant financial disclosures.