| Sumario: | Background: While many studies have shown an effect of accommodation on neck muscle activity, none have studied the causal effect of neck posture on accommodation. In addition, some Postural Restoration Institute (PRI) physical therapists believe that neck posture can influence subjective refraction. Methods: Twenty-four young adult subjects (19-35 years) participated. Subjects adopted a neutral or forward neck posture while viewing a letter chart binocularly at 3 m during 2-minute sessions. Accommodation was recorded in the right and left eyes using a Grand Seiko WAM 5500 open-view autorefractor. Digital photographs of neck posture were taken before and after each trial to calculate the craniovertebral angle. Results: Any accommodative differences due to neck posture or between eyes were minimal and statistically non-significant. Analysis of craniovertebral angle demonstrated a significant difference between the neutral and forward postures, but no effect of before or after the trial, and no significant interaction of these two factors. Additionally, the accommodation change from neutral to forward head posture was not greater for those subjects who could bend their necks more than the others. Conclusions: There was no significant effect of a forward neck posture on accommodation in our study. The individual change in craniovertebral angle between postures did not predict the observed changes in accommodation. These data do not support the PRI hypothesis that neck posture could affect subjective refraction. However, future studies could consider a longer duration for neck posture, and they could document actual patient postures to determine whether these affect accommodation.
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