Eye and Head Movements for Changes in Gaze in a Presbyopic Population

Abstract

Abstract: : Purpose: To determine in a presbyotic population the contribution of eye and head movements during the fixation of lateral targets in near vision, and to determine whether the respective contributions can be influenced by age, ocular refraction or previous type of ophthalmic lenses. Methods: A group of 175 healthy presbyopes (58 males, 117 females) with normal binocular vision was evaluated. Age varied from 42 to 79 years (mean = 53.5, SD = 7.5). Spherical equivalent of refraction ranged from – 9.13 to + 5.75 D (mean = – 0.33, SD = 2.5). Progressive lenses were the type of correction used by 69% of the subjects. Head movements were measured with electromagnetic sensors (Polhemus system) incorporated in a head-set. The subject had to fix alternatively a reference LED, located at 40 cm in front of the subject and one of two lateral LEDs randomly presented with an eccentricity of 40° on each side of the central one. The ratio between the amplitude of head rotation and the eccentricity of the lateral LEDs (40°) was computed after 25 presentations of these targets. Results: The measurement of the ratio, evaluated twice in a subset of 50 subjects, shows a significant repeatability (intraclass correlation coefficient = 0.807). This ratio has a mean value of 0.2527 and a SD of 0.2259 with a range from 0 (eye mover behavior) to 0.98 (head mover behavior). A Kolmogorov-Smirnov test shows that the distribution of this ratio in the presbyopic population differs significantly (p > 0.001) from a normal distribution or from an exponential distribution. The first quartile of the distribution has a ratio of 0.04 or less (head movement less than 2°). Half of the subjects present a head rotation lower than 10°, and 15% of the studied population have a head movement of 20° and more (head movers). There is no significant correlation between the magnitude of head rotation and gender, age, refraction, addition or type of presbyopia correction. However, there is a significant but moderate correlation (Rs = 0.309 p > 0.001) between the head rotation and the duration of progressive lenses wear. Conclusions: The respective contribution of eye and head movements during the fixation of a lateral target does not show a predictable distribution in a presbyopic population. Subjects with an eye mover behavior are more numerous than those with an head mover behavior. This factor has to be considered in the design of progressive lenses for a better adaptation to this type of correction.

Keywords: physiological optics • aging: visual performance • eye movements