Optometry & Visual Performance 263 Volume 13 | Issue 4 | December 2025 Apparatus Accommodation was measured using a Grand Seiko WAM 5500 open-view autorefractor.19 This autorefractor provides accurate and repeatable measures of accommodation.20 Accommodation was recorded separately in right and left eyes at a 5 Hz sampling rate. To maintain stable head, neck, and trunk posture, subjects sat at the chin and headrest of the autorefractor on a chair with fixed legs and adjustable seat height. The chair sat on a carpeted floor. This, along with the fixed legs, meant that the chair legs did not move during each trial. A Velcro band on the headrest of the autorefractor was used to ensure that the subject’s head remained in a steady erect position. The height of the table securing the autorefractor and the height and placement of the chair were adjusted to specific marked positions to obtain the correct posture for each condition on repeated trials (consult Procedures sub-section). Photographs of the neck and head posture were taken using a Samsung 12.2 Mega Pixel digital camera mounted on a tripod. A paper grid was placed on the wall to help attain the correct positioning of each subject and was visible in all photographs (Figure 1). The grid had gravitationally vertical reference lines. Experimental design The main trials in the study were constructed as a two-factor, within-subjects experimental design. The first factor was Neck Posture, the second factor was Eye, and the single dependent variable was the Distance Accommodation Response under lighted conditions. Neck posture The first experimental factor was Neck Posture, which had two levels: Neutral and Forward. Forward head posture refers to the position of the head relative to that of the upper trunk and is measured within clinical research using the craniovertebral angle.21 The craniovertebral angle is defined22 as the acute angle between two lines. The first line is gravitationally horizontal and passes through the skin over the C7 spinous process. The second line passes through the skin over the C7 spinous process and then to the middle of the tragus of the ear (consult also Figure 1 of Shaghayeghfard et al.21) The greater Figure 1. Sample photographs of the (left) forward and (right) neutral neck postures. The subject sits at the chin and head rest of the autorefractor. The C7 process is marked with a piece of tape. A red plumb line and paper grid in the background provide gravitational vertical for reference.
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