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A 22-year-old lady presented with squint of left eye (OS) since four months. She also complained of decrease in vision and instability while walking since the past one year. She had no complaints of diplopia. Best corrected visual acuity was OD 0.5; OS 0.05.
Ocular motility is shown in Figure 1. End-gaze Nystagmus was observed. While anterior segment exam was unremarkable, fundus evaluation showed temporal pallor of the optic discs (OS > OD). Cup-disc ratio was 0.2 with normal macula in both eyes.
MRI brain was obtained [Figure 2] which showed multiple demyelinating lesions.
Internuclear ophthalmoplegia (INO) is a gaze abnormality affecting the horizontal saccades. There is impaired adduction of the affected eye with abduction nystagmus of the contralateral eye. INO is named by the side of the adduction deficit. Convergence is often preserved (Cogan′s Posterior INO). When convergence is affected it is known as Cogan′s Anterior INO. Pathophysiology involves lesion in the Medial Longitudinal Fasciculus (MLF). MLF coordinates and synchronizes eye movements by connecting pontine paramedian formation (PPRF)-Abducens nucleus complex of one side with the oculomotor nucleus of the other side. Bilateral presentation is rare, but when seen in young patients, is pathognomonic of multiple sclerosis. In older patients with unilateral presentation, vascular etiology is often the underlying cause. Multiple sclerosis is a demyelination disease of the CNS with neurological, ophthalmological and psychiatric manifestations; 80% cases have ocular manifestations - optic neuritis, optic atrophy, INO being the most common. MRI scan shows demyelinating periventricular plaques. Treatment is with steroids, immunosuppressives and interferons. Treatment of INO basically involves the treatment of the etiology. In patients with large angle exotropia and bilateral adduction deficit, when diplopia is incapacitating, large bilateral LR recessions and MR resections have been tried and found successful.