Abnormal Vestibulo-Ocular Reflexes in Autism Spectrum Disorders

Background: Although not diagnostic for the disorder, altered sensory-motor function has been frequently observed in children with ASD. Some of these alterations (e.g., decreased postural stability, altered vestibulo-ocular reflexes) depend upon adequate processing of vestibular sensory input. The rotational vestibulo-ocular reflex (rVOR), which functions to maintain stable vision by generating compensatory oculomotor responses to angular rotation head movements, may be useful for studying vestibular related sensory motor processing in ASD. The primary measures of the rVOR (time constant of decay, gain, symmetry) provide information about the functional ability of peripheral vestibular anatomy or central processing of vestibular sensory information. Abnormalities in rVOR beyond these standard measures have been noted, but not systematically studied, in children with ASD. rVOR eye movements are composed of nystagmus beats (i.e., slow phase eye excursions followed by a quick phase reset to center), that occur during and after continuous whole body rotation in the earth-horizontal plane. Typical horizontal nystagmus occurs in a linear and periodic fashion, without vertical or torsional intrusions.

Objectives:  The primary objective of the present study was to investigate differences in the temporal dynamics of rVOR between ASD and typically developing children using video-oculography techniques.

Methods:  Children diagnosed with ASD (n=15) and typically developing (TD) children (n=16) ages 6-12 matched on age, sex, and IQ participated in the study. Rotary chair testing was completed using a computer-controlled, motorized rotary platform and binocular video-oculography goggle (VOG) system (Neuro-Kinetics). Post rotary rVOR eye movements were recorded for 30-50 seconds in the dark with eye position sampled at 100 Hz. Eye movement tracings during the first 20 seconds that followed cessation of rotation were evaluated using time series models (Approximate Entropy and spectral analysis) designed to assess regularity or periodicity in eye position.

Results:  Children with ASD exhibited rVOR eye movements that differed markedly from TD children. Visual inspection of eye position tracings of TD children showed the expected horizontal, periodic eye movements whereas those of ASD children were markedly irregular. Moreover, unlike TD children, ASD children showed numerous vertical eye movements. Quantitative measures of regularity or periodicity (ApEn, spectral analysis) confirmed these group differences.

Conclusions:  Beyond changes in standard measures of rVOR, ASD children exhibited clear differences in post-rotary nystagmus. The marked irregularity of horizontal nystagmus and novel identification of frequent vertical intrusions suggest cerebellar deficits. Vertical intrustions exhibited by ASD children likely disrupted the regularity or periodicity of horizontal nystagmus. If rVOR alterations are selective for ASD, this reflex which can be measured in infants, could be a potentially important early biobehavioral marker in ASD.