Impact of Font Size on Static and Dynamic Aspects of Accommodation among Digital Eye Strain Subjects

Purpose: This study investigated the short-term effects of text size on an OLED display on the accommodation and pupillary responses of individuals with pre-existing digital eye strain. The hypothesis was that text size would affect the dynamics of accommodation and pupillary response.Design: Prospective Qasi-experimental study (non-randomized clinical trial)Methods: This study was conducted in a single hospital setting. A total of 324 patients were screened for digital eye strain using a validated questionnaire. Forty-six participants who met the inclusion criteria were enrolled, including having no history of digital eye strain, being young, and having no ocular problems contributing to binocular vision or digital eye strain. The dynamic accommodative response and pupillary motility of the participants' dominant eye were continuously measured using an automatic refractometer as they read text passages of three different font sizes, each for two minutes. The study was conducted under normal office lighting conditions of 400 lux, with screen brightness maintained at 400 lux and 100% letter contrast. Participants viewed the text from a fixed distance of 50 cm.Results: Repeated-measures ANOVA was used to examine whether accommodation response and pupillary response differed across the three different font sizes. Results showed that font size significantly affected both pupillary dynamics and accommodation response, with statistical significance at p < .001. Specifically, larger font sizes were associated with shorter accommodation latencies and better pupil responses, while the smaller font size of 12 points resulted in higher accommodation latencies and poorer pupil responses.Conclusion: Using larger font sizes on digital displays may improve eye function for people with digital eye strain. This may reduce their symptoms, as accommodation lag is a major cause of eye strain. Smaller text sizes increase eye strain because accommodation lag is worse with smaller fonts. Adjusting font size is an important way to manage digital eye strain.