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Study recommends imaging for diagnosis of complex strabismus
Magnetic resonance imaging or computed tomography can spot abnormalities in extraocular muscles that clinical examiniations fail to detect.
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SEATTLE — Imaging extraocular muscles for evaluation of complex strabismus was found to be a useful tool in reaching accurate clinical diagnosis, according to a study presented here.
“Imaging extraocular muscles can give insight into the causes of strabismus and challenge traditional concepts of etiology by suggesting alternative treatments,” said Joseph L. Demer, MD, PhD, here at the meeting of the American Association of Pediatric Ophthalmology and Strabismus.
Diagnostic scanning with magnetic resonance imaging (MRI) and computed X-ray tomography (CT) has now become the standard of care in many medical and surgical fields, according to Dr. Demer, a professor of ophthalmology at Jules Stein Eye Institute and professor of neurology at University of California — Los Angeles.
“Surgeons in most other specialties image their patients preoperatively. It’s time that ophthalmologists incorporate these modern imaging technologies into their surgical practices to fully benefit from the advantages they bring,” he said.
According to Dr. Demer, diagnostic imaging can detect abnormalities in varying types of strabismus when clinical evaluations fail to find a diagnosis.
“Our research shows that imaging can provide unique information that is unavailable from clinical tests alone. We believe that MRI or CT scans should be performed where indicated in the evaluation of patients with complex strabismus,” he said.
Imaging used
In a 12-year prospective study between 1990 and 2001 funded by the National Eye Institute, Dr. Demer and colleagues at UCLA evaluated 323 patients who underwent orbital imaging. In total, 62 orthotropic volunteers and 261 strabismus patients were evaluated.
“MRI was performed on 267 patients. We used high resolution protocol designed for orbital imaging of the extraocular muscles,” Dr. Demer said.
For high resolution, surface coil images with a slice thickness of 1.5 mm to 3 mm were used. All coronal images were obtained while the patient was in a central gaze position. Selected cases were supplemented with eccentric gaze positions, sagittal or axial angle images, he added.
CT scans were performed in the 56 remaining patients.
“CT scans involve radiation exposure, so these scans were only performed as part of medical therapy in patients who could benefit from radiation,” Dr. Demer noted.
All images gathered were digitally analyzed to assess the size and location of the extraocular muscles. Comparisons were made between the normal orbits of volunteers and the abnormal orbits of patients with strabismus.
In addition to scans, patients had complete ophthalmological examinations.
Clinical findings
“By comparing the normal orbits to the extraocular eye muscles of patients with strabismus, we found commonly identifiable abnormalities in the sizes or structural positioning of muscles in patients with strabismus,” Dr. Demer said.
After analyzing images, researchers found that 38 strabismus patients had absence or atrophy of the superior oblique (SO) muscle in SO palsy. There were also eight patients who had structural abnormalities of the trochlea or SO tendon, which are associated with Brown’s syndrome.
“The superior oblique muscle is attached to the upper, outer side of the eyeball and is responsible for intorsion, depression and abduction of the eye. The high resolution of the MRI showed that in SO palsy this muscle was smaller than normal muscles and did not show the normal, contractile thickening from supraduction to infraduction,” he said.
Researchers found that 15 additional cases, which were believed to be SO palsy in clinical examinations, were found to be masquerading as SO palsy.
“Based on imaging, there was no abnormality of size, structure, or contractility of the SO muscle for these cases,” Dr Demer added.
Additionally, 46 patients were found to have malpositioning (heterotopy) of a rectus pulley muscle, which is associated with incomitant strabismus. There were nine other patients who had an instability of the muscular pulleys.
“The instability of the pulleys can be best demonstrated by multipositional MRI,” he noted.
Trauma to the extraocular muscles was found in 16 patients, causing myotomy or avulsion of the rectus. Abnormalities of other extraocular muscles were also found.
“We had 10 patients with lateral rectus palsy, demonstrated as atrophy and absent contractility of the involved lateral rectus muscle,” he said.
Imaging scans found four patients with atrophy of the inferior rectus, while four other patients had atrophy of the medial rectus. In addition, four more patients demonstrated atrophy of the superior rectus.
Exams overlook
“In cases of inferior rectus palsy, CT scans showed a profound atrophied left inferior rectus muscle. The right superior oblique muscle was also atrophied, but it was missed in clinical examinations,” Dr. Demer said.
Therefore, he said, it is often necessary to perform both clinical tests and computerized scans on patients with complex strabismus to rule out all possibilities for abnormalities.
“For the most part, our study found that extraocular abnormalities correlated closely with clinical abnormal patterns of ocular motility, but added unique information. The additional information frequently guided surgical therapy more appropriately,” he added.
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For Your Information:
- Joseph L. Demer, MD, PhD, can be reached at the Jules Stein Institute, Department of Neurology, 100 Stein Plaza, UCLA, Los Angeles, CA 90095; (310) 825-5931; fax: (310) 206-7826; e-mail: jld@ucla.edu.