Abstract
Background Duane retraction syndrome (DRS) is a congenital cranial dysinnervation disorder (CCDD)
of ocular movements, characterized by deficits in horizontal duction associated with
narrowing of palpebral fissure, retraction of eye globe on attempted adduction and
occasionally accompanied by upshoot or downshoot of the eye globe. It is caused by
congenital absence of sixth cranial nerve, which results in fibrotic changes in the
extraocular muscles leading to an abnormal ocular motility--a concept known as CCDD.
Depending on whether only abduction/adduction or both are affected, DRS has been classified
into three types designated as type-I, type-II and type-III. The torsional movements
of the affected eye in DRS have not been reported to be deficient hitherto, which
could be due to difficulties in the routine bedside evaluation of such movements.
Case Presentation An unusual case of a patient of left unilateral type-III DRS is reported, who presented
with a short history of vertigo on getting up from supine to sitting position and
on assuming right lateral recumbent position. The diagnostic right Dix-Hallpike test
(DHT) revealed upbeating torsional geotropic positioning nystagmus in the normal right
eye and upbeating positioning nystagmus without torsional component in the abnormal
left eye and this clinical finding was video recorded.
Conclusion The observed lack of incyclotorsion of the left eye, affected with DRS-III during
right Dix-Hallpike positioning, is primarily due to the absence of initial slow-phase
excyclotorsional component. If the slow phase of VOR does not occur, then the fast-phase
VOR, which is a refixation saccade, will be lacking too. An anastomosis, either in
the lateral wall of the cavernous sinus or within the orbit, between the trochlear
nerve and fibers of the oculomotor nerve can lead to simultaneous co-contraction of
the inferior and superior oblique muscles. This is the most probable explanation for
such finding of asymmetrical absence of torsional component in the left eye affected
by DRS-III, during right Dix -Hallpike positioning. Thus, the recording of eye movements
(voluntary and involuntary) opened a window into the brain to conceptualize neural
and mechanical factors influencing the human eye movements.
Keywords
cranial dysinnervation disorder - Dix–Hallpike test - incylotorsional - excyclotorsional
- positioning nystagmus - geotropic
