Timing of surgery for infantile esotropia in humans: effects on cortical motion visual evoked responses

Abstract

Purpose: Infantile esotropia is associated with maldevelopment of cortical visual motion processing, manifested as directional asymmetry of motion visual evoked potentials (mVEPs). The purpose of this study was to determine whether early surgery at or before age 11 months could promote the development of cortical visual motion processing in human infants, compared with standard surgery at age 11 to 18 months.

Methods: Sixteen children with a constant, infantile esotropia >or=30 prism diopters and onset before age 6 months were recruited prospectively. Eight of them underwent early surgery at <or=11 months of age, and eight underwent standard surgery at 11 to 18 months of age. Seven age-matched normal subjects served as the control. At 2 to 2.5 years of age, mVEPs were measured during monocular viewing of a grating that shifted between two positions with a lateral displacement of 90 degrees at 10 Hz. Nasotemporal mVEP asymmetry was assessed by an amplitude asymmetry index and by the presence of a significant interocular phase difference.

Results: The mean asymmetry index and interocular phase difference in the early surgery group were comparable to that in age-matched control subjects, and they were significantly lower than those in the standard surgery group.

Conclusions: Early surgery for infantile esotropia promotes the development of cortical visual motion processing, whereas standard surgery is associated with abnormal mVEPs. The results provide additional evidence that early strabismus repair is beneficial for cortical development in human infants.

Figure 1

Polar plots of mVEP amplitude (4 μV, full scale) and phase in normal control subjects (top) and in patients who underwent early surgery (middle) or standard surgery (bottom). Each vector is an individual response from a 10-second trial while viewing monocularly with the right or left eye. The length of the vector depicts amplitude (in micro-volts) and the direction indicates phase (0–360°). F1, first harmonic response; F2, second harmonic response. Control subject and patient with early surgery had smaller F1 but larger F2 responses, with the phases of the responses for the right and left eyes congregated in roughly the same direction. Patient with standard surgery had larger F1 but smaller F2 responses, with the phases of the response for the right and left eyes in opposite directions (approximately 180° out of phase).

Figure 2

Asymmetry indices in patients with early and standard surgery. (▲) Mean value of asymmetry index in each subject. Short horizontal lines: mean asymmetry index for each group. Shaded area: 95% CI in normal control subjects.

Figure 3

Interocular phase differences in patients with early and standard surgery. (▲) Mean value of interocular phase difference in each subject. Short horizontal lines: mean phase difference for each group. Shaded area: 95% CI in normal control subjects.