Infantile-Onset Saccade Initiation Delay in a Child with a Thin Intercollicular Commissure

Infantile-onset saccade initiation delay (ISID), also known as congenital ocular motor apraxia, is an uncommon condition characterized by an inability to trigger horizontal volitional saccades.[1][2][3] Vertical saccades and smooth ocular pursuit are usually preserved.1,3 Reflexive saccades may be impaired.1,[4][5][6] Saccade initiation delay is a clinical finding and not a specific disease.7 The diagnosis is usually made after head control is achieved in infants between four to six months-of-age, when characteristic head thrusts appear.The infant initially makes use of head thrusts and later on uses eye blinks to rapidly shift the direction of gaze to overcome the difficulty in initiating saccades.8,9 Infantile-onset saccade initiation delay is often associated with developmental delay in the areas of fine motor, gross motor, speech, and language development.3,8,[10][11][12][13][14] Neuroradiological findings in ISID are diverse and include various abnormalities involving hindbrain structures or agenesis of the corpus callosum.3,6,[13][14][15][16][17] The etiology of ISID is unknown, but it has been suggested that the abnormality lies in the midbrain, 3 or cerebellum.8,15 In this paper we present a child who has difficulties initiating horizontal saccades and describe his videotaped eye movements and unique brain MRI findings in detail.We then suggest a mechanism for the pathogenesis of saccade initiation delay. CASE REPORTA three-year-old boy was referred for an assessment of his abnormal head movements.He was noted to make horizontal head thrusts when looking at objects since the age of one year.Pregnancy and delivery at full term were normal.He sat at eight months and walked at 18 months, suggesting mild motor delay.His language development was also delayed.He spoke his first words at 18 months and made two-word sentences at 30 months.Past medical history was significant for iron-deficiency anemia at age two years, which was treated with iron.The family is Aboriginal Canadian from Northern Ontario.His mother is Ojibway-Cree and his father is Ojibway.No relevant family history was elicited.On initial assessment, his general physical exam revealed no neurocutaneous stigmata or dysmorphic features.Visual acuity was normal bilaterally.Pupils were equal and reactive to light.His fundi were normal.He used intermittent horizontal head thrusts when asked to look at objects to the right or left of his visual fields.He was noted to make spontaneous small amplitude saccades intermittently in all directions.Horizontal smooth pursuit was slightly saccadic but within normal limits for age.Vertical saccades and smooth pursuit were normal.The oculocephalic maneuver (low frequency vestibulo-ocular reflex)

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