Capturing saccades in multiple sclerosis with a digitized test of rapid number naming

The King–Devick (K–D) test of rapid number naming is a visual performance measure that captures saccadic eye movements. Patients with multiple sclerosis (MS) have slowed K–D test times associated with neurologic disability and reduced quality of life. We assessed eye movements during the K–D test to identify characteristics associated with slowed times. Participants performed a computerized K–D test with video-oculography. The 25-Item National Eye Institute Visual Functioning Questionnaire (NEI-VFQ-25) and its 10-Item Neuro-Ophthalmic Supplement measured vision-specific quality of life (VSQOL). Among 25 participants with MS (age 37 ± 10 years, range 20–59) and 42 controls (age 33 ± 9 years, range 19–54), MS was associated with significantly longer (worse) K–D times (58.2 ± 19.8 vs. 43.8 ± 8.6 s, P = 0.001, linear regression models, accounting for age). In MS, test times were slower among patients with higher (worse) Expanded Disability Status Scale scores (P = 0.01). Average inter-saccadic intervals (ISI) were significantly longer in MS participants compared to controls (362 ± 103 vs. 286 ± 50 ms, P = 0.001), and were highly associated with prolonged K–D times in MS (P = 0.006). MS participants generated greater numbers of saccades (P = 0.007). VSQOL scores were reduced in MS patients with longer (worse) K–D times (P = 0.04–0.001) and longer ISI (P = 0.002–0.001). Patients with MS have slowed K–D times that may be attributable to prolonged ISI and greater numbers of saccades. The K–D test and its requisite eye movements capture VSQOL and make rapid number naming a strong candidate efferent visual performance measure in MS.