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S. Karim, R. Clark, E. Engel, C. Andrews, J. Demer; Magnetic Resonance Imaging (MRI) Demonstrates Optic Nerve Hypoplasia in Duane’s Retraction Syndrome (DRS) . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1622.
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Purpose: While DRS has classically been regarded as an isolated abducens motor neuron pathology, recent views suggest DRS lies in a spectrum of congenital cranial dysinnervation involving multiple nerves. We employed high resolution MRI to directly investigate sensory innervation in the optic nerve in sporadic and inherited forms of DRS. Methods: Fifteen subjects (8 males, 7 females) with DRS (4 dominantly linked to the DURS2 locus, 2 with Duane’s radial ray syndrome resulting from SALL4 mutations, and 9 sporadic cases; 8 unilateral and 7 bilateral) and 23 normal controls (12 males, 11 females) underwent T1 weighted, surface coil MRI of the orbits in the coronal plane at 2 or 3 mm thicknesses (312 – 391 micron resolution) during controlled central fixation. Optic nerve diameter was computed from digitized cross sections taken 2 – 3 mm posterior to the globe–optic nerve junction. Results: All subjects with DRS had unilateral or bilateral limitation of abduction, or of both ab– and adduction, with retraction and narrowing of the palpebral fissure on adduction. Although corrected visual acuity in DRS was nearly normal at 0.02 +/– 0.03 (SEM) logMAR, mean optic nerve diameter was 3.49 +/– 0.05 mm, significantly smaller than the mean of 3.99 +/– 0.04 mm in controls (p <0.0001). Seven of 15 subjects with DRS had optic nerve cross sections smaller than the lower 95% confidence limit of normal, with this hypoplasia occurring in both hereditary and sporadic forms. All but one of these subjects with significant optic nerve hypoplasia had bilateral nerve involvement. Three patients with bilateral ONH had only unilateral motor findings consistent with DRS. All optic nerves were ophthalmoscopically normal. Conclusions:Similar to congenital fibrosis, DRS is associated with subclinical, bilateral optic nerve hypoplasia. This finding suggests that the dysgenesis of neural structures underlying DRS is not limited to motor cranial nerves, and also includes sensory innervation. Furthermore, bilateral optic nerve hypoplasia is observed even in cases of unilateral motor involvement, perhaps indicating subclinical motor involvement on the "unaffected" side. Unilateral versus bilateral motor findings do not reliably distinguish sporadic from inherited DRS. Grant Support: EY08313 & EY13583, RPB. Commercial Relationship: None.
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