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Strabismus after cataract surgery a growing concern
Sub-Tenon’s infusion is recommended as an alternative to retrobulbar or peribulbar anesthesia.
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BALTIMORE — Over the past two decades, strabismologists have noticed an increase in the number of patients with strabismus after cataract surgery that seems to be caused by the anesthetic used in the procedure.
“The concept of anesthetic myotoxicity causing strabismus was first published in 1985,” said David L. Guyton, MD, a professor of ophthalmology at the Wilmer Eye Institute here. A surgeon in California reported at that time on four of his cataract patients.
“He injected 0.75% bupivacaine into each of the rectus muscles, believing he could use less retrobulbar anesthetic that way,” Dr. Guyton said. All four of these patients developed strabismus.
The surgeon consulted with a muscle physiologist. “The two of them discovered that anesthesia causes severe myotoxicity and loss of muscle fibers in the animal studies that had been done in the past,” Dr. Guyton said. The physiologist then experimentally injected monkey and human extraocular muscles. Those humans were scheduled for enucleation for other reasons shortly thereafter.
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The researchers noted widespread degeneration of the muscle fibers when they injected into the muscles. This occurred not when they bathed the muscles in anesthetic, but only when they injected into the muscles. The fibers regenerated in the young monkeys, but in the elderly humans there was minimal regeneration by 1 week, usually with fibroblastic scar tissue developing.
Sequence of events
Dr. Guyton speculated on the sequence of events that lead to postoperative strabismus.
“Intramuscular injection of the anesthetic, followed by degeneration of the muscle fibers locally, renders a temporary paresis with double vision from the paresis upon patch removal the next day. As the segmental fibrosis begins — not contracture but fibrosis — the initial double vision disappears,” he said.
This is followed by recurrence in the reverse direction. “The double vision worsens over about 2 to 3 months,” he said.
A few patients have been photographically documented with this sequence of events. One patient seen at the Bascom Palmer Eye Institute in Miami had undergone cataract surgery in the left eye with 14 cc of peribulbar anesthesia, a mixture of Xylocaine (lidocaine HCl, AstraZeneca) and Marcaine (bupivicaine HCl, Abbott). (Note: The cataract surgery with this unusually large volume of anesthetic had been performed elsewhere.)
Two weeks later the patient had a significant paresis of the superior rectus muscle and double vision. The patient was lost to follow-up, but returned 6 months later. “The left eye no longer had a superior rectus paresis, but there was significant left hypertropia,” Dr. Guyton said. The patient was corrected by a vertical rectus recess-resect on the left eye.
“Fortunately, surgical correction is usually successful in these patients. I favor a single large resection on an adjustable suture; however, others have used recess-resect procedures on adjustable sutures,” he said. Either procedure often achieves good results.
Prevalence
How often are patients afflicted with strabismus after cataract surgery?
“Dr. Howard Gimbel’s anesthetist in Canada estimates it occurs in about 1 in 500 cases,” Dr. Guyton said. Dr. Guyton, who has mostly an adult strabismus practice, estimates about 5% of his cases are caused by the same mechanism. “It may happen more frequently in the absence of hyaluronidase in the anesthetic mixture.”
Over a period of 4 years, Dr. Guyton has tabulated 30 patients he considers having developed strabismus after cataract surgery in a similar fashion.
“By far, most of the muscles involved were the inferior rectus muscles. We had four superior rectus muscles, three inferior oblique, two superior oblique, two lateral rectus and two medial rectus.” he said. Two other patients had multiple muscles involved.
By inserting a 1.5 inch, 25-gauge needle over the inferior temporal orbital rim of these patients, the needle penetrates quite far back into the orbit. In fact, a study at Bascom Palmer Eye Institute using cadavers showed that “with the globe in place, and with this route of injection, you can inject any of the extraocular muscles.”
Recommended precaution
“So what do we do with our tried-and-true method of retrobulbar or peribulbar anesthesia?” Dr. Guyton asked. As an alternative, he recommends a sub-Tenon’s infusion with a blunt cannula for local anesthesia when performing anterior segment and posterior segment surgery.
“For our own local anesthesia, we apply some antiseptic solution in the surgical quadrant. We make a small snip incision with scissors, use a blunt cannula and inject 1.5 cc to 2 cc of anesthetic agent. We’ve had very good results,” he said.
Using this technique “eliminates the risk of retrobulbar hemorrhage and should eliminate the risk of anesthesia-induced postoperative strabismus,” Dr. Guyton said.
For Your Information:
- David L. Guyton, MD, can be reached at Wilmer 233, Johns Hopkins Hospital, 600 N. Wolfe St., Baltimore, MD 21287-9028; (410) 955-8314; fax (410) 955-0809; e-mail: dguyton@jhmi.edu.