Changes in corneal astigmatism and near heterophoria after smartphone use while walking and sitting

Abstract

Background/aims: Smartphone use has become an indispensable part of our daily life. The handy design and powerful processor allow smartphone users to perform diversified tasks even when walking. This study aimed to investigate and compare the optical aftereffect and vergence adaptation of using a smartphone while walking and sitting.

Methods: Twenty-nine young healthy adults (aged 19 to 24 years old) with normal binocular and accommodative functions were recruited. Participants were asked to watch a movie for 30 minutes using a smartphone while either walking on a treadmill or sitting on a chair. Corneal aberrations and near heterophoria were measured before and after smartphone use by a corneal topographer and modified Thorington heterophoria test, respectively.

Results: Using the smartphone while walking induced a change in corneal H/V astigmatism, becoming 0.11±0.03 μm less negative (two-way ANOVA repeated measures, Bonferroni post-hoc test, p = 0.001). This optical aftereffect was significantly higher than after smartphone use while sitting by 0.10±0.03 μm (paired t-test, p = 0.003). Although smartphone use did not result in a significant change in near heterophoria (Bonferroni post-hoc test, p > 0.15), the vergence adaptation showed relatively more eso- or less exo-deviation by 0.79±0.36Δ in the walking than the sitting condition (paired t-test, p = 0.037).

Conclusions: Eyecare practitioners should be cautious of the potential optical after effect and vergence adaptation after prolonged smartphone usage.

Fig 1. Optical aftereffects following 30 minutes of smartphone use.

A) Results for subject S01: The change in corneal wavefront was more obvious after smartphone use while walking than sitting. B) Corneal H/V astigmatism: The corneal H/V astigmatism became significantly less negative after smartphone use while walking, but no significant change was found while sitting. C) Corneal H/V astigmatism: The change in H/V astigmatism was significantly more positive while walking than sitting. D & E) Corneal oblique astigmatism: The optical aftereffect for the corneal oblique astigmatism was not statistically significant, and no significant difference in the change in oblique astigmatism was found between groups. Red symbols: Walking; Blue symbols: Sitting. Bonferroni post hoc test or paired t-test: ** p < 0.01.

Fig 2. Vergence adaptation following 30 minutes of smartphone use.

A) In the post-smartphone use session, near heterophoria showed significantly less exo-deviation (i.e., less positive) after walking than sitting, while no significant difference was found at the baseline. B) Change in near heterophoria showed significantly less exo-deviation (or more eso-deviation) for walking than sitting. Positive: Exo-deviation; negative: Eso-deviation. Red symbols: Walking; Blue symbols: Sitting. Bonferroni post hoc test: ** p < 0.01, paired t-test: * p < 0.05.