Analysis of head position used by myopes and emmetropes when performing a near-vision reading task

The aim of the study was to compare head posture in young, adult emmetropes and corrected myopes during a reading task. Thirty-two (32) myopes (mean spherical equivalent: -3.46±2.35 D) and 22 emmetropes (mean spherical equivalent: -0.03±0.36 D) participated in the study. Of the myopes, 16 were progressing (rate of progression ⩾-0.5D over the previous 2 years), 12 were stable (changes of -0.25 D or less over 2 years) and four could not be classified. Seated subjects were asked to read a text binocularly in their habitual posture. To measure head posture, two simultaneous images were recorded from different directions. In a separate study with the same subjects and conditions, a motion monitor was used to track head posture for 1 min. The habitual reading distance was measured in both studies, together with the stereoscopic acuity and fixation disparity for each subject. The results of the photographic study showed no significant differences in head posture or reading distance between the myopic and emmetropic groups (p>0.05) but there was some evidence that downward pitch angles were greater in progressing myopes than in non-progressing myopes (p=0.03). No correlations were observed between the binocular parameters and head posture. Reading distances were systematically shorter with the helmet-mounted eye tracker and it was concluded that posture was affected by the weight of the equipment. With this reservation, it appeared that the rate of change of downward pitch angle over the 1-min recording session increased with the subject's rate of myopia progression (correlation between myopia progression and slope of pitch: r(2)=-0.69, p=0.001), implying a greater reliance on head movements when reading down a page. Overall, while no differences in mean head posture were found between myopes and emmetropes, there was some evidence that head posture and movement during reading may differ in progressing myopes.