Inverted Brown pattern may warrant inferior oblique weakening procedure

June 15, 2015

In cases of an inverted Brown pattern, a large inferior oblique weakening procedure may be the first procedure to perform-even though the inferior oblique muscle is not significantly overacting.

Take-Home Message: In cases of an inverted Brown pattern, a large inferior oblique weakening procedure may be the first procedure to perform-even though the inferior oblique muscle is not significantly overacting.

 

 

By Lynda Charters; Reviewed by David L. Guyton, MD

 

Baltimore-Although counterintuitive to many surgeons, the first procedure to use for a patient with an inverted Brown pattern-with fundus extorsion and a tight inferior oblique muscle on forced ductions-may be a large inferior oblique muscle weakening procedure.

 

David L. Guyton, MD, explained the rationale for this and shared his pearls when presented with such a patient. Dr. Guyton is the Zanvyl Krieger Professor of Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore.

 

Lancaster red-green test

The Lancaster red-green test, performed before and often after a patch test, is used to diagnose and manage cyclovertical deviations, Dr. Guyton noted.

In his version of the Lancaster red-green test, special flashlights project red and green streaks on a wall. The patient, who wears red/green goggles, controls one flashlight whereas the examiner controls the other. The patient sees the projected lights with different eyes at a distance of 1 m.

The examiner shines the first flashlight onto the wall and turns the streak until the patient reports that it is vertical. The patient is instructed to move his or her light into alignment with that of the examiner’s. The dots in the grid on the wall are separated by 15 cm, equivalent to 15 prism diopters. While the test is being performed, the patient’s nine gaze positions can be measured and quantified.

 

If the patient can fuse in any direction of gaze, it is helpful to repeat the Lancaster red-green test after patching one eye for 30 to 45 minutes. This breaks up fusional vergence adaptation, revealing the true underlying pattern of deviation, often providing more leeway to avoid overcorrection from eye muscle surgery.

“The Lancaster red-green test is invaluable for analyzing patterns of cyclovertical strabismus, but very few ophthalmologists are trained in its use,” Dr. Guyton said.

Dr. Guyton described a patient from years before with a left hyperdeviation in all gaze directions. The head tilt test indicated a left superior oblique paresis, for which he performed a right inferior rectus muscle recession with good results, with only a slight esophoria in downgaze.

However, the left superior oblique paresis pattern recurred 5 years later-i.e., overaction of the left inferior oblique muscle and underaction of the left superior oblique muscle. Dr. Guyton then performed a left inferior oblique recession with no response.

“I reasoned that a larger inferior oblique weakening procedure would work, so I performed a left inferior oblique denervation/extirpation and achieved perfect result that remained stable,” Dr. Guyton said.

The nerve of the inferior oblique muscle is isolated before cutting it with cautery. A large weakening procedure is then performed-excising a 12- to 15-mm portion of the muscle.

“This procedure seems barbaric, but it works like a charm in the right situation,” he said.

Recurrence of an apparent superior oblique paresis after contralateral inferior rectus recession may indicate a tight ipsilateral inferior oblique muscle, often requiring a large weakening procedure of the inferior oblique muscle.

 

Inverted Brown pattern

Dr. Guyton cited a study (J AAPOS. 2006;10:565-572) of the inverted Brown pattern, which he defined as a tight or inelastic inferior oblique muscle masquerading as unilateral superior oblique muscle underaction without significant ipsilateral inferior oblique muscle overaction. The characteristic pattern observed is that of a patient with limited depression especially in adduction.

 

“This can occur after surgery to treat a Brown syndrome or after orbital floor trauma, but it particularly occurs months to years after a small inferior oblique weakening procedure for superior oblique paresis,” he said. “Re-operation is how this is addressed.”

The surgery usually involves a large re-weakening procedure of the inferior oblique muscle, which, in Dr. Guyton’s experience, has provided excellent results. This presumes there is fundus extorsion and inferior oblique muscle tightness on forced ductions at the start of surgery-even though there is no significant inferior oblique muscle overaction, he noted.

In the absence of significant inferior oblique overaction, most surgeons hesitate to perform an inferior oblique muscle weakening procedure, especially in cases in which that muscle has already been weakened.

“However, this is often the very situation in which further inferior oblique muscle weakening is needed,” he said.

In this situation, some surgeons opt for a superior oblique tendon tuck, Dr. Guyton noted.

“But that is like tightening a paretic muscle against a tight direct antagonist,” he said. “Weakening of the tight inferior oblique muscle makes more sense (to me) than attempting to tuck the superior oblique muscle.”

Dr. Guyton described a patient with left inferior oblique muscle overaction who had previously had a left inferior oblique muscle recession and right inferior rectus muscle recession of 3 mm-the outcome of which was good-at least initially. But 13 years later, the patient presented with a so-called inverted Brown pattern-i.e., no inferior oblique muscle overaction and a large underaction of the superior oblique muscle.

“If turned upside down, this was just like a Brown syndrome,” he said, “with inability of the left eye to look up in adduction, intorsion of the left eye, and no significant overaction of the superior oblique muscle.”

Turned back right side up, there was an “inverted” Brown pattern with inability of the left eye to look down in adduction, extorsion of the left eye, and no significant inferior oblique overaction.

The patient was corrected with a large weakening procedure of the inferior oblique muscle (denervation/extirpation) with a good, lasting result, Dr. Guyton noted.

 

A recessed inferior oblique muscle, with an initial good result, can tighten up again-i.e., shorten-and require a denervation/extirpation to repair, according to Dr. Guyton.

Surgical experience

Over 6 years, 13 patients with superior oblique paresis presented an inverted Brown pattern, 8 of whom had undergone previous inferior oblique muscle recession with recurrent hypertropia and fundus extorsion of the higher eye.

Twelve of the 13 patients had a tight inferior oblique muscle on exaggerated forced duction testing. Three of the previously unoperated patients underwent an inferior oblique muscle recession, one of whom later underwent denervation/extirpation. Ten of the 13 underwent an inferior oblique muscle denervation/extirpation. Twelve of these 13 patients had a good result. Dr. Guyton is analyzing his 15-year experience with the inverted Brown pattern with the help of fellow and colleague, Justin Marsh, MD. ■

 

 

David L. Guyton, MD

E: dguyton@jhmi.edu

This article was based on Dr. Guyton’s presentation during Pediatric Subspecialty Day at the 2014 meeting of the American Academy of Ophthalmology. Dr. Guyton has no financial interest in any aspect of the subject matter.