Effect of tongue stimulation on nystagmus eye movements in blind patients

Abstract

We have observed dramatic effects of tactile tongue stimulation on nystagmus eye movements in patients with acquired blindness, and we report these results. Six adult subjects (3 subjects with light perception or worse vision and 3 normal subjects) were included in this study. Causes of blindness included traumatic explosion, anterior ischemic optic neuropathy, and central retinal artery occlusion. Duration of blindness was 15, 3 and 1.5 years, respectively. A video eye tracking system (Eyelink 1000) was used to record eye movements. The eye movement recording (EMR) was repeated four times in a span of 20 min. Two of the EMRs were performed without tongue stimulation and two with tongue stimulation in randomized order. A tongue stimulus was applied to the surface of the tongue using a Brainport device that produces an electrical tactile stimulus. The nystagmus waveform characteristics and frequency were analyzed. We found that all blind subjects showed continuous jerk nystagmus with slow and quick phases, mainly in horizontal plane in their primary eye positions. The recorded nystagmus waveforms were jerk with linear velocity slow phases. When the tongue stimulus was applied, the frequency of nystagmus was significantly reduced by 47, 40, and 11%, and relative amplitude was reduced by 43, 45, and 6% for three blind subjects, respectively. In conclusion, we think our results that tongue stimulation influences nystagmus eye movements support a link between non-visual sensory input and ocular motor activity.

Neurological Basis for Eye Movements of the Blind

“…Prior studies of individuals who have visual loss showed that, during attempted fixation, gaze is unstable due to eye drifts, which may be disjunctive or even in opposite directions [16]–[21]. Some of these ocular drifts are pendular, but others are unidirectional with corrective saccades, thereby giving rise to jerk nystagmus.…”

A nonvisual eye tracker calibration method for video-based tracking

“…Using a replacement stand-in to perform the calibration for the blind or visually impaired person is the easiest way around the calibration problem at the moment. With the exception of Schneider et al (2013) who used search coils, which are calibrated without the involvement of the participant, previous studies investigating eye movements in the blind have either not transformed eye movements into gaze coordinates (Hall et al, 2000), transformed with an average calibration factor determined from a group of sighted participants (Nau, Hertle, & Yang, 2012;Sherman & Keller, 1986), or transformed with an approximate calibration with an unknown degree of error (Kömpf & Piper, 1987;Leigh & Zee, 1980). Although determining an average calibration factor from a large group of people is an excellent alternative to visual calibration, not all eye trackers will accept an input for calibration (e.g., EyeLink 1000 Plus).…”

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“…Regarding skill practice, evidence for functional task training is generally positive in individuals with neurologic deficits, including those with stroke and cerebral palsy. Because these neuromodulatory devices are relatively new and no studies have identified their long-term effects, 16,29,30 longitudinal studies should be undertaken to monitor the long-term therapeutic benefits of using these devices. The Brainport device may have served to augment information for postural orientation, and the CN-NINM device may have increased the neural receptivity or connectivity to support learning and neuroplastic change.…”