Smooth ocular pursuit in Chiari type II malformation

Area of Science:

• Neuroscience
• Ophthalmology
• Developmental Biology

Background:

• Chiari type II malformation (CII) is a congenital anomaly affecting the cerebellum and brainstem.
• These brain structures are crucial for smooth pursuit (SP) eye movements.
• CII is frequently associated with myelomeningocele and hydrocephalus.

Purpose of the Study:

• To investigate the impact of Chiari type II malformation on smooth pursuit eye movements.
• To determine if spinal lesion level, shunt revisions, nystagmus, or brain dysmorphology influence SP in individuals with CII.

Main Methods:

• Smooth pursuit eye movements were recorded using an infrared eye tracker in 21 participants with CII (ages 8-19).
• Participants tracked a sinusoidal visual target horizontally and vertically at varying frequencies.
• Data were compared to 38 healthy children.

Main Results:

• Children with CII and nystagmus exhibited abnormal SP gains (ratio of eye to target velocities).
• No significant correlation was found between SP gains and the number of shunt revisions, brain dysmorphology, or spinal lesion level.
• Abnormal pursuit was evident in the CII group, especially those with nystagmus.

Conclusions:

• Smooth pursuit eye movements are impaired in children with Chiari type II malformation, particularly when nystagmus is present.
• The findings suggest that abnormal pursuit is primarily related to the underlying cerebellar and brainstem malformation in CII, rather than secondary effects like hydrocephalus or surgical interventions.
• The lack of correlation with shunt revisions supports the primary role of brain dysgenesis in visual tracking deficits.