Anatomy of Inferior Oblique - The Private Eye Clinic

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12/14/2007Anatomical Variations – Kraft 2Neuro(fibro)vascular bundle of IO Bottom-line:– About 10% of normals and IOOA have doublebellied IO– If pt has fundus excyclotorsion – look hard for 2bellies, but if no fundus exc doesn’t rule out 2bellies.– No pathognomonic signs that can predict 2bellies. David Stager, Texas,JAAPOS, 1997 Cadaveric eyes andsurgical specimens To investigate why IOanterior transpositionoften converts to IO toan “anti-elevator”Neuro(fibro)vascular bundle of IONeuro(fibro)vascular bundle of IO This study showed that the NFVB has a linear (notcircuitous) course in the orbit. It is 27mm long and extends from the orbital apex tothe midportion of IO just temporal to the lateralborder of IR. The terminal 8mm of the nerve lies encased withinsurrounding fibrous tissue bands that attachposteriorly to IR muscle capsule and anteriorly to IOmuscle caspule. These fibrous bands may represent a posteriormodification of Lockwood’s ligament into a checkligament that binds the 2 muscles. This study also shows that the NFVB:– Has anatomical and physiological properties likea ligament (it is stiff).– Functions as an ancillary origin for IOImaging of IOResults Joseph Demer, Ophthalmology, 2003 Aim: To study the size and contractility of thenormal IO using high-res MRI and toevaluate abnormalities of SO and IO musclesin chronic SO palsy. Subjects: 13 pts with SO palsy, 17orthotropic pts Methods: 2mm sagittal and coronal imagesrepeated in multiple gaze directions. MRI confirmed ipsilateral decrease in SOsize and contractility in pts with chronic SOpalsy. In all subjects, anterior movement andcontractile thickening of IO was observed insupraduction, with posterior movement andrelaxational thinning in infraduction.4
12/14/2007Results But, in pts with chronic unilateral SO palsy,the IO cross-sectional area did not differ fromeither eye, nor from normal subjects. So despite these pts having IO “overaction”,their IO on MRI is not hypertrophied, norexhibits supranormal contractractility. “Overaction in adduction” due to a normal IOfaced with a weak antagonist SO?5
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Anatomy of Inferior Oblique - The Private Eye Clinic

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