Effect of One Hour of Smartphone Reading Under Different Illumination and Body Positions on Accommodative Function in Healthy Young Adults

Background: Prolonged smartphone use has become increasingly common among young adults and is associated with accommodative stress and digital eye strain. Body posture during smartphone use may further influence accommodative performance.

Objective: To evaluate the effect of one hour of smartphone reading on accommodative function in erect and supine positions under bright illumination among healthy young adults. Methods: This prospective experimental study included 31 healthy participants aged 18-30 years. Baseline accommodative parameters, including Near Point of Accommodation (NPA), Amplitude of Accommodation (AA), Negative Relative Accommodation (NRA), Positive Relative Accommodation (PRA), Accommodative Facility (AF), and accommodative convergence to accommodation (AC/A) ratio, were assessed using standard clinical procedures. Participants then read the same novel on a smartphone for one hour under bright illumination in erect and supine positions, followed by reassessment of all accommodative parameters.

Results: The mean age of participants was 20.48 ± 1.34 years. Following smartphone use, NPA increased from 5.94 ± 1.29 cm at baseline to 6.58 ± 1.39 cm in the supine position, while AA decreased from 17.51 ± 3.19 D to 15.81 ± 3.13 D. NRA showed a slight reduction, whereas PRA demonstrated a modest increase. The AC/A ratio and accommodative facility exhibited minimal changes.

Conclusion: One hour of smartphone reading produced measurable alterations in accommodative function, particularly in the supine position. Maintaining an upright posture, appropriate viewing distance, adequate illumination, and regular visual breaks may help reduce accommodative stress and improve visual comfort during prolonged smartphone use.