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F.A. Proudlock, I. Gottlob, S.J. Farooq; Internuclear Opthalmoplegia and Reading . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2922.
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Background: Internuclear ophthalmoplegia (INO) is a condition resulting from lesions to the medial longitudinal fasciculus and is characterised by an adduction deficit on the side of the lesion and a dissociated nystagmus on abduction of the contralateral eye. On clinical presentation we have observed that patients often report that reading is easier if one eye is closed. We have investigated reading in INO patients under monocular and binocular viewing conditions. Methods:Eye movements (250Hz) were recorded from 13 patients with INO (mean age = 45.7, SD = 10.4) whilst reading a card of simple text (28.6° wide x 23.3° vertical) with either right eye open, left eye open or both eyes open (order randomised). The adduction deficit was quantified by plotting adduction velocities against abduction velocities from either eye to saccadic targets at –20°, –10°, 0, 10°, 20°. Subjects were classified as having unilateral INO if the abduction: adduction slope was >0.7 in one eye, and bilateral INO if the slopes were <0.7 in both eyes. One subject, recorded from twice, had bilateral INO on first visit and improved to unilateral INO on the second visit. Instability of fixation was also measured in primary position. Full orthoptic assessment was performed. Results: Using the criteria established 6 subjects were classified as unilateral and 8 subjects as bilateral INO (repeated subject in both groups). Three subjects, who showed either severe bilateral adduction deficit or vertical eye movement instability (nystagmus) in primary position, found reading almost impossible and took >40s to read a line. Four subjects with unilateral INO read more quickly with affected eye (mean = 4.2 sec/line) than the unaffected eye (mean = 6.6 sec/line). They found it relatively easy to read with both eyes open (mean = 5.9 sec/line) but preferred monocular reading. Five subjects with bilateral INO read at similar speeds with either most affected (mean = 8.3 sec/line) or least affected eye (mean = 8.9 sec/line) open but worse with both eyes open (mean = 11.2 sec/line). Two subjects, who had poor visual acuity in one eye due to either optic neuritis or amblyopia, found reading with both eyes open as easy as monocular reading. Conclusions:We found that most subjects with INO could read better during monocular viewing compared to binocular viewing due to incomitant eye movements. Possibly occlusion of one eye, botulinum injection or surgery could be used as potential therapies to assist reading.
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