Magnetic resonance imaging of the functional anatomy of the inferior oblique muscle in superior oblique palsy

doi:10.1016/S0161-6420(03)00331-2

Ophthalmology

Volume 110, Issue 6, June 2003, Pages 1219-1229

https://doi.org/10.1016/S0161-6420(03)00331-2 Get rights and content

Abstract

Purpose

To study size and contractility of the normal inferior oblique (IO) muscle using high-resolution magnetic resonance imaging (MRI) and to evaluate abnormalities of the superior oblique (SO) and IO muscles in chronic SO palsy.

Design

Prospective, case control study.

Participants

Thirteen patients with SO palsy and 17 orthotropic subjects.

Methods

High-resolution, surface coil MRI was used to obtain sets of contiguous, 2-mm thick coronal and sagittal images repeated in multiple gaze directions. Digital image analysis was used to measure IO and SO muscle cross-sectional areas for evaluation of size and contractility. Diagnosis of SO palsy in one bilateral and 12 unilateral cases was based on subnormal contractility and SO size less than the normal 95% confidence limit. Ipsilesional and contralesional oblique muscles were compared with controls and correlated with clinical characteristics.

Results

In all subjects, anterior movement and contractile thickening of the IO were observed in supraduction, with posterior movement and relaxational thinning in infraduction. The mean (± standard deviation) cross-sectional area of 15 normal control IO muscles was 13.4 ± 3.9 mm², with mean contractile increase from infraduction to supraduction of 5.7 ± 2.6 mm². Subjects with SO palsy had incomitant hypertropia with a wide range of overelevation and underelevation in adduction (i.e., upshoot, downshoot). SO atrophy correlated with underdepression in adduction (P < 0.0001). Contralesional SO cross-section was slightly greater than normal (P = 0.004). The IO cross-section ipsilesional and contralesional to SO palsy did not, however, differ significantly from normal and did not correlate with elevation in adduction (P > 0.2).

Conclusions

Quantitative morphometry by MRI can demonstrate IO size and contractility. Even in cases of unequivocal SO palsy associated with ipsilesional SO atrophy and deficient contractility, the degree of elevation in adduction was not correlated with IO size. This finding suggests that the associated overelevation in adduction, commonly termed “inferior oblique overaction,” actually arises from some other mechanism than IO hypertrophy or excess contractility. Revision of clinical terminology seems warranted.

Section snippets

Subjects

This study was conducted in 17 normal, orthotropic paid volunteers recruited by advertisement and 13 subjects with incomitant hypertropia. All gave written informed consent according to a protocol conforming to the Declaration of Helsinki and approved by the Human Subject Protection Committee at the University of California, Los Angeles. Normal volunteers underwent complete eye examinations verifying normal corrected vision, normal ocular versions, orthotropia in all gaze positions, and

Results

A total of 25 orbits were imaged in 17 normal subjects of mean (± standard deviation) age 44 ± 19 years (range, 21–73 years). All subjects with SO belly atrophy had been diagnosed clinically by pediatric ophthalmologists as having SO palsy before MRI. A total of 25 orbits were imaged in 13 subjects with SO palsy of mean age 34 ± 16 (range, 14–70) years. One orbit was excluded because MRI disclosed a clinically unsuspected orbital wall fracture. Subject 11 clinically was diagnosed with bilateral

Discussion

This study exploits the new technical capability of orbital MRI to clarify oblique EOM function in SO palsy. Using 2-mm image planes that are thinner than the 3-mm planes heretofore used, data in normal subjects confirmed previous reports of the capability of MRI to characterize both size and contractility of the normal SO muscle.15, 19 The current data also confirm a prior report that significant SO atrophy and reduced contractility can be demonstrated in patients with a clinical diagnosis of

Acknowledgements

Nicolasa de Salles and Frank Henriquez provided technical assistance.

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^☆

Manuscript no. 220359.

Supported by NEI grant EY-08313 to J. Demer. Joseph L. Demer received an unrestricted award from Research to Prevent Blindness (New York, NY) and is Laraine and David Gerber Professor of Ophthalmology.

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Magnetic resonance imaging of the functional anatomy of the inferior oblique muscle in superior oblique palsy☆

Abstract

Purpose

Design

Participants

Methods

Results

Conclusions

Section snippets

Subjects

Results

Discussion

Acknowledgements

Comput Biomed Res

Vision Res

J AAPOS

Am J Ophthalmol

J AAPOS

J AAPOS

Vision Res

Vision Res

The superior obliquea challenging extraocular muscle

Doc Ophthalmol

First Annual Richard G. Scobee Memorial Lecture. Diagnosis and surgical treatment of hypertropia

Am Orthop J

Classification and treatment of superior oblique palsy

Am Orthop J

Superior oblique palsydiagnosis and classification

Int Ophthalmol Clin

Superior oblique palsydiagnosis and treatment

Can J Ophthalmol

Sideways displacement and curved path of recti eye muscles

Arch Ophthalmol

Evidence for fibromuscular pulleys of the recti extraocular muscles

Invest Ophthalmol Vis Sci

Orbital connective tissues in binocular alignment and strabismus

Evidence for active control of rectus extraocular muscle pulleys

Invest Ophthalmol Vis Sci

Extraocular muscles