Frequency characteristics of accommodation in a patient with agenesis of the posterior vermis and normal subjects.

AIMS To clarify the cerebellar control of accommodation in humans, the frequency characteristics of accommodation were studied in a patient with agenesis of the posterior cerebellar vermis and four age matched normal subjects. METHODS Magnetic resonance imaging of the brain of the 29 year old patient showed agenesis of the vermis and paravermis of lobules VIII-X and hypoplasia of the vermis and paravermis of lobules I-VII, the cerebellar hemisphere, and the cerebellar nuclei. The gain and phase lag of accommodative responses for sinusoidally modulated blur stimuli were calculated for the patient and four normal subjects. The blur stimuli consisted of predictable simple sinusoids of 3.0 dioptres at a frequency of 0.05, 0.1, 0.2, 0.3, 0.5, or 1.0 Hz. RESULTS The frequency characteristics of accommodative responses in the patient have a larger phase lag and a smaller gain at higher frequencies than those in the four normal subjects. CONCLUSIONS These findings suggest that the cerebellum contributes to the control of accommodation by improving the frequency characteristics at high frequencies.