Figure. Effects of dalfampridine in 3 patients with multiple sclerosis with bilateral internuclear ophthalmoparesis.

(A, B) Eye position records of a representative leftward and rightward saccade made by patient 1 before and after taking dalfampridine. Note that his baseline leftward saccade (A) is hypometric in the right, adducting eye and requires a series of saccades to reach the target with corresponding larger movements and nystagmus in the left, abducting eye; after taking dalfampridine (B), his right eye is almost able to reach the target with 1 saccade, a normal response, and the nystagmus in the left eye is decreased. Conversely, there is a mild decrease of the amplitude of his baseline left eye hypometric adducting saccade following dalfampridine (A, B). Positive values indicate rightward movements; the initial leftward target jump occurs at the beginning of the record (not shown). (C–E) Abducting/adducting eye peak velocity ratios of the saccades for patients 1–3 before and after taking dalfampridine as box plots; percentiles are indicated in C. In our laboratory the mean ratio (±SD) is 1.04 ± 0.08 for healthy subjects.⁴ L/C = leftward movements during control period; L/D = leftward movements after dalfampridine; R/C = rightward movements during control period; R/D = rightward movements after dalfampridine. Note that in each case, the INO that is worse (larger ratio) at baseline improves with dalfampridine, whereas the milder INO shows a small ratio deterioration for patients 1 and 2. Asterisks indicate a significant decrease of peak velocity ratio compared with the corresponding control condition.