Optometry & Visual Performance 268 Volume 13 | Issue 4 | December 2025 Third, our study adopted a single, well-defined forward head posture. During an eye exam, patients may adopt their own postures that may be more complex and could be investigated in future studies. During subjective refraction, many changes are made to the lens powers in the phoropter or trial frame, and hence, constant changes in accommodation demand are found. However, in our apparatus, it would have been difficult to introduce lenses quickly due to the small space between the subject’s eyes and the housing of the autorefractor. Many previous studies examined a causative direction from accommodative to neck physiology, whereas this is one of the first studies, apart from Han and Lennerstrand’s,15 that examined a causative direction from neck to accommodative physiology. However, Han and Lennerstrand15 used highfrequency vibrations (70 Hz) on the shoulder to stimulate muscle proprioceptors and did not include actual changes in neck posture. With some limitations, the current study does not favor a hypothesis in which neck physiology causatively influences accommodative physiology. The current study is the first to address Richter’s observation8,14 that although a close functional relationship has been documented from oculomotor load to the activation of the neck and scapular muscles, little formal research has investigated the coupling mechanism of the two systems. The presence of a refractive error, specifically myopia, was found in one observational study to be uncorrelated with neck posture and cervical range of motion.32 Another study suggested that trapezius and sternocleidomastoid activity differs between myopic and non-myopic individuals as a function of cardinal direction of gaze.33 However, in that study, no statistical analysis was performed, and it was not stated whether subjects wore a correction during testing. Overall, this is an area needing more research because there are multiple mechanisms by which refractive error could potentially influence neck posture. These include the level of correction or under-correction, which could lead to blur and/or binocular imbalance; the typical working distances in daily tasks; and the type of correction worn. In the case of spectacles, prismatic effects and spectacle magnification could influence the coordinated eye– head movements. According to our data, there was no significant interaction between neck posture and eye. This interaction effect was included to determine whether posture might affect one eye more than the other. The lack of an effect demonstrates that no postureinduced aniso-accommodation occurred. However, we compared the right eye versus the left eye, not dominant versus non-dominant eye. Thus, we cannot say anything regarding eye dominance. Nevertheless, future studies could investigate left and right eye differences more closely. In our group, left-eye accommodation data had significantly greater between-subject variance than the righteye accommodation data. However, there were no significant differences in microfluctuations between eyes. These findings mean that while each individual has equal accommodative microfluctuations in right and left eyes, the left-eye mean accommodation responses in a group are less consistent between individuals than their right-eye responses. The potential role of ocular dominance in these findings could be investigated in a future study. Craniovertebral angle There was a significant effect of neck condition on the actual craniovertebral angle achieved, although no change in craniovertebral angle was found between the start and end of the trial. Thus, the experimental procedures for obtaining neck postures were effective and did indeed place the craniovertebral angle in the desired direction. A wide range of craniovertebral angles was obtained in our subjects, and so we analyzed the correlation between posture-induced change in craniovertebral angle and change in objective accommodation. Individuals who stretched their necks forward more did not demonstrate greater changes in accommodation. This regression finding further supports the conclusion of no effect of forward neck posture on accommodation. According to previously published works, a craniovertebral angle less than about 48° is considered a forward neck state.21,34,35 Subsequently, a craniovertebral angle greater than about 48° is considered a neutral neck state. However, our data were quite different. The mean craniovertebral angle in the Neutral condition was 37.2°, much less than the cited range. The mean craniovertebral angle in our Forward condition was 23.8°, also much less than in the cited studies. On the other hand, the mean change in craniovertebral angle between conditions was 13.5°. This change is larger than the 6.7° difference Lau et al.34 found between individuals with and without neck pain. Thus, although the ranges of craniovertebral angles in the previous study do not match our current conditions, it was found that the experimental conditions in the current study
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