Testing the range of movement to the right and to the left indicates a bilateral adduction deficit, typical of bilateral internuclear ophthalmoplegia. The range of vertical eye movements is not impaired. Testing of horizontal saccades (40 seconds) shows a clear reduction of the velocity and the amplitude of the adduction saccade on both sides, another typical finding of a bilateral INO. Vertical saccades not impaired (1 minute).
When looking to the right, a clear impairment of the adduction of the left eye can be seen. The best test to examine this is the examination of saccades (55 seconds), which also shows a slowing of the adduction saccade of the left eye. Typical of a left-sided INO. Vertical saccades (1 minute 10 seconds) are not impaired.
When looking to the left (15 seconds), a clear impairment of the adduction of the right eye can be identified, which is the pathognomonic sign of an INO on the right side. The dissociated nystagmus to the left is also seen (30 seconds). Examination of the horizontal saccades also indicates an impairment of the adduction of the right eye (35 seconds onwards).