Occasionally, the condition is bilateral with medial rectus palsy and
adduction deficit in each eye and nystagmus upon abduction in both eyes (bilateral
internuclear ophthalmoplegia, or BINO) While there appears to be medial recti palsy, most
patients will be able to converge (posterior INO or BINO). In some cases, the patient will
not be able to converge (anterior INO or BINO).
For example, for a patient to gaze to the left, the left supranuclear control center of horizontal eye movements [paramedian pontine reticular formation (PPRF)] must signal the left CN VI nucleus to turn the left eye outwards. At the same time, the PPRF must signal the right CN III nucleus, via the right MLF, to simultaneously turn the right eye inwards. A lesion of the right MLF would not allow the neural impulse to reach the right medial rectus. In this case, the left eye would abduct, but the right eye would not adduct. Further, the left eye would go into an abducting nystagmus.
Most lesions of the MLF are located in the pons, or caudal mesencephalon. Thus, patients with INO or BINO will be able to converge (posterior INO/BINO). However, if the lesion affects the MLF within the mesencephalon and involves the CN III nucleus, then the patient will not be able to converge (anterior INO/BINO).
Possible causes of INO/BINO:
Typically, multiple sclerosis causes a bilateral presentation, whereas
ischemic vascular infarction causes a unilateral episode. Also, myasthenia gravis can
produce a pseudo-INO/BINO with a motility pattern identical to true INO/BINO.
Other reports in this section
Eyelids & Eyelashes | Conjunctiva & Sclera | Cornea
Uvea | Vitreous & Retina | Optic Nerve & Brain | Oculosystemic Disease
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