Reach Kinematics During Binocular Viewing in 7- to 12-Year-Old Children With Strabismus

Abstract

Purpose: Eye-hand coordination is essential for normal development and learning. Discordant binocular experience from childhood strabismus results in sensory and ocular motor impairments that can affect eye-hand coordination. We assessed reach kinematics during visually guided reaching in children treated for strabismus compared with controls.

Methods: Thirty-six children aged 7 to 12 years diagnosed with esotropia, a form of strabismus, and a group of 35 age-similar control children were enrolled. Reach movements during visually guided reaching were recorded using the LEAP Motion Controller. While viewing binocularly, children reached out and touched a small dot that appeared randomly in one of four locations (±5° or ±10°). Kinematic measures were reach reaction time, total reach duration, peak velocity, acceleration duration, and deceleration duration. Touch accuracy and factors associated with impaired reach kinematics were evaluated.

Results: Strabismic children had longer total reach duration (545 ± 60 ms vs. 504 ± 43 ms; P = 0.002), had longer deceleration duration (343 ± 54 ms vs. 312 ± 45 ms; P = 0.010), and were less accurate (93% ± 6% vs. 96% ± 5%, P = 0.007) than controls. No differences were found for reach reaction time, peak velocity, or acceleration duration (all Ps ≥ 0.197). Binocular dysfunction was more related to slow reaching than amblyopic eye visual acuity.

Conclusions: Strabismus affects visually guided reaching in children, with slower reaching in the final approach and reduced endpoint accuracy. Binocular dysfunction was predictive of slow reaching. Unlike strabismic adults who show longer acceleration duration, longer deceleration in the final approach in strabismic children indicates a difference in control that could be due to reduced ability to use visual feedback.

Figure 1.

Experimental setup. Children held onto a stick placed 5 cm in front of them and, with both eyes open, fixated a cross displayed on a computer monitor at a viewing distance of 35 cm. Once the cross disappeared, a small white dot appeared on the left or right displaced 5 or 10 degrees from fixation. The child was instructed to reach out and touch the dot as quickly and accurately as possible and then return to the stick. The LMC recorded hand movements and was placed 10 cm from the hand's initial starting position.

Figure 2.

Data from a typical reaching trial. (A) Position trajectory of the index finger (cm). At the beginning of the trial, the child holds a stick, and then the target white dot appears on the screen (time point 0 ms) and the child reaches out to touch the dot. (B) Velocity trajectory of the index finger (m/s). Reach kinematic measures identified based on velocity thresholds (dotted lines) of the index finger. Light blue line is raw LMC data, and dark blue line is resampled, filtered LMC data. Blue circle, reach initiation; red circle, peak velocity; green circle, reach termination.

Figure 3.

Examples of one visually guided reaching trial for a child with strabismus (dashed curve, solid circle) and a control child (solid curve, open circle). The child with strabismus had a longer reach duration than the control child, slowing down (i.e., constant velocity at terminal deceleration), which indicates a more cautious approach.

Figure 4.

Mean reach kinematic measures for strabismic children (dark gray) compared with controls (white). Strabismic children were similar to controls for reach reaction time (A), acceleration duration (C), and peak velocity (E) but had significantly longer total reach duration (B) and deceleration duration (D). Errors bars: ±1 SE. *P < 0.05.