Reading disability due to an ocular motor disorder: A case of an adolescent girl with a previous diagnosis of dyslexia.

Dyslexia is a reading disability characterized by difficulties with accurate and/or fluent word recognition, which are thought to stem from a phonological processing impairment. Herein we report the case of a 13-year-old girl who received the diagnosis of dyslexia at age 12 years. We considered this diagnosis to be incorrect because her reading difficulty was caused by a spontaneously repeated eye movement toward the vertical direction; the eyes were likely to show slow, upward drifts followed by quick downward movement at the physical examination, and the amplitude of the downward movement was increased when she changed eye positions to look at the upper direction in the evaluation of the eye tracker. Although we considered there was the possibility that the spontaneously repeated eye movement was classified as the spontaneous downbeat nystagmus, the eye tracker showed the transition of the gaze starting from and returning to was inconsistent with nystagmus, and we concluded that the term of nystagmus like abnormal eye movement was appropriate for the expression of the spontaneously repeated eye movement. There was no apparent abnormality on head magnetic resonance imaging (MRI), and whole exome sequencing showed no known candidate genes to explain the cerebellar dysfunction. An accumulation of similar cases in the future should help elucidate the pathomechanism observed in this case, and we should fully pay attention to evaluate the neurological aspects of the patients before settling on the diagnosis of dyslexia.