Head-Eye Coordination Increases with Age and Varies across Countries

Abstract

Purpose: Head movements in older people may contribute to their dizziness and equilibrium problems. Head gain is the ratio of head movement to total movement (head + eye) when executing a saccade to an eccentric target. Two studies have investigated the relationship between head gain and age but have provided conflicting results.

Methods: We report head gain data collected from research laboratories and optician stores. Our sample sizes are much larger (n = 657 for laboratory, n = 64,458 for optician stores), permitting more detailed analyses.

Results: The head-eye coefficient, expressed as 100 times the square root of head gain, was bimodal with one mode of primarily eye movers and one mode of eye-and-head movers. Head-eye coefficient increased with age and was invariant with eye correction and gender. We also found an effect of nation that seemed associated with gross domestic product or by latitude (in the northern hemisphere) and log population density.

Discussion: Assuming that head movements and visual distortions contribute to dizziness and equilibrium problems, our study suggests that customizing eyewear based on age and country may help in reducing the prevalence of problems associated with head and/or eye movements.

FIGURE 1

The VPS used to measure individual head-eye coordination strategy. A color version of this figure is available online at www.optvissci.com.

FIGURE 2

Histogram plots for variables at two bin scales (fine scale, no symbol; broad scale, black circles): (A) sphere, (B) cylinder, (C) axis, (D) bifocal power, (E) HEC, (F) SD of HEC, and (G) age.

FIGURE 3

Mean HEC for various subgroups. Participants were subdivided by age (A, C, and D) and/or correction (B to D). Specifically, panels show mean HEC as a function of (A) age, (B) addition (grouped by rounded value), (C) age for only participants without addition correction (younger n = 174; older n = 112), and (D) age and addition.

FIGURE 4

(A) Age distribution of male and female subjects in our sample. (B) Head-eye coefficient as a function of age and gender (female, thin line; male, thick line).

FIGURE 5

Mean HEC as a function of age and location.

FIGURE 6

Head-eye coefficient as a function of (A) latitude, (B) log population density, and (C) GDP per capita for each of the 12 subsamples. Laboratory samples are indicated by squares. Nations are North America (empty black symbols), Europe (filled black symbols), and Asia (empty gray symbols). Also shown in D is HEC as a function of latitude and log population density as analyzed jointly in a regression analysis.