techniques
Changes in Ophthalmic Anesthesia Techniques
Methods evolve to keep up with ophthalmic procedures.
BY LESLIE GOLDBERG, ASSISTANT EDITOR

Over the past 25 years, cataract surgery has become less invasive with smaller incisions. The trend in ophthalmic anesthesia has also been toward less invasive techniques. A smaller percentage of cataract patients having surgery receive anesthesia delivered through needles than ever before. Patients undergoing ophthalmic surgery may be anesthetized by retrobulbar block, peribulbar injection, intracameral injection, subtenons block, topical anesthesia or general anesthesia.

Retrobulbar and Peribulbar Anesthesia

Twenty-five years ago, retrobulbar anesthesia was the most popular technique used in ophthalmology, says Scott Greenbaum, M.D., F.A.C.S., an ophthalmologist at Greenbaum Eye Associates in Forest Hills, N.Y. In the 1970s and 1980s, peribulbar blocks, in which the needles were directed away from the eye toward the other structures in the orbit, were used. "The purpose of these techniques was to numb the eye and also provide some akinesia, or stillness to the eye, so that the eye was made a non-moving target," says Dr. Greenbaum. "In addition, retrobulbar and peribulbar blocks provided some degree of amaurosis, preventing the patient from seeing the bright operating microscope light and reducing visual images."

Additionally, in the late 1970s and 1980s, the use of peribulbar anesthesia directing needles away from the retrobulbar space became more popular. "The theory behind these techniques was that you could enter the confines of the orbit — the space around the eye — and use enough anesthetic volume that it would percolate back to the retrobulbar space as well as directly block the muscles and the nerves around the eye. These worked very well," says Dr. Greenbaum. "The crucial similarity between retrobulbar and peribulbar techniques was needles. Therefore they shared all the risks inherent in the use of needles, including intraocular infections, retinal detachments, double vision after surgery and optic nerve trauma due to injection."

No More Needles

After peribulbar, surgeons assessed the needle-inherent risks and began to look for different techniques. That is how topical anesthesia came into vogue in the mid to late 1980s. "Topical anesthesia caught on like wildfire and removed most of the risks associated with needle techniques," says Dr. Greenbaum.

"In my view, this was the 'minimum daily requirement' as far as anesthesia. It doesn't provide akinesia or amaurosis," says Dr. Greenbaum. "Early instructions on use of topical anesthesia included recommendations to turn the operating microscope down to an acceptable level so that the patient was comfortable. This also meant the possibility of limiting the surgeon's view. Anesthesia required the cooperation and the intelligence of the patient to follow your instructions and to keep their eye where you needed them to," adds Dr. Greenbaum. These additional drawbacks and requirements placed limitations on the universal use of topical anesthesia, although many high-volume doctors use topical successfully. The more recent use of lidocaine further improved the efficacy of topical anesthesia — still, no akinesia or amaurosis was achieved.

The attempt to improve the effect of topical anesthesia through intracameral injection of anesthetic into the anterior chamber is more controversial. While clinical experience has demonstrated the technique to be safe, careful study has also shown it to be no more effective than topical anesthetic alone, says Dr. Greenbaum.

While this conclusion may come as a surprise to those

still touting the technique, randomized clinical studies support the abandonment of intracameral anesthesia.1,2

Subtenons Anesthesia

In the 1980s, three surgeons in the U.S. Air Force, Elizabeth Hansen, M.D., Calvin Mein, M.D. and Robert Mazzoli, M.D., attempted vitreoretinal and then cataract surgery employing a needle technique even more anteriorly — away from the muscles and the retrobulbar space — in a way that was described as subtenons anesthesia, a method that was first employed by C.S. Turnbull, M.D., in 1884 and later by Ivor John Kirby, M.D., in the 1950s, but which was otherwise forgotten.

Subtenons anesthesia is a technique that uses a needle or cannula — metal or flexible, both blunt — to infuse anesthetic, steroids, antiangiogenic drugs or any liquid through the second layer of the skins of the eye, into the subtenons space.

In the United Kingdom, subtenons anesthesia is the primary type of anesthesia used. The reason is that prior to its popularity most patients were operated on under general anesthesia. For years, U.K. anesthesiologists practiced without employing needles. When the government decided to stop funding general anesthesia, there was a great movement toward local anesthesia.

As the risks of giving needle blocks were well publicized in the United Kingdom, these anesthetists went straight to using cannulae. "Unfortunately, there are still risks with cannulae, especially long metal cannulae, because you don't know where the end is," says Dr. Greenbaum. "The end of a long metal cannula — like a long metal needle — can, and still in many cases does, rub against the optic nerve."3

There are short metal cannulae that are better. Chondra Kumar, M.D., has an ultra-short cannula that he is now beginning to teach doctors to use. In the United States, Dr. Greenbaum is using a plastic cannula, also known as an anterior subtenon's cannula, which is blunt, employs a
d-shaped opening and is 10 mm long, placing the port at the central equator of most eyes. This is where the nerves to the muscles penetrate tenons capsules. "If you have a cannula delivering anesthesia in that area, you get akinesia, you get excellent anesthesia and you get amaurosis," he says. "You do not get trauma to the muscles or to the nerve. This is not the most common technique in the United States — far from it — but it is catching on."

In 2006, for the first time, at the OAS meeting some doctors from the United States and United Kingdom observed that topical anesthesia is starting to plateau in its popularity. While it may be fast and simple, it may not always deliver the best surgical outcomes. Surgeons say they strive to ensure the best outcome for patients, not the fastest.

References

1. Boulton JE, et al. A randomized controlled trial of intracameral lidocaine during phacoemulsificaion under topical anesthesia. Ophthalmology 2000;107:68-71.

2. Pang MP, et al. Pain, photophobia, and retinal and optic nerve function after phacoemulsification under topical anesthesia. Ophthalmology 2001;108:2018-2025.

3. Kim SK, Andreoli CM, et al. Optic neuropathy secondary to sub-Tenon's anesthetic injection in cataract surgery. Arch Ophthalmol 2003;121:908-909.

4. Ophthalmic Anesthesia Society, http://www.eyeanesthesia.org (accessed Nov. 2, 2006).