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Updated: Jul 12, 2026
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Measuring the Behavioral Effects of Intraocular Scatter
Published on: February 18, 2021
Objective measurements of lower-level visual stress.
Niru K Nahar1, James E Sheedy, John Hayes
1College of Optometry, The Ohio State University, Columbus, Ohio 43210, USA. nahar.2@osu.edu
Summary
Electromyography (EMG) of the orbicularis oculi muscle shows sensitivity to visual stress, particularly in conditions benefiting from squinting, like glare and refractive error. Blink rate may be a better objective measure for visual discomfort not benefiting from squint.
Area of Science:
- Ophthalmology
- Neuroscience
- Human Factors
Background:
- Visual discomfort, or asthenopia, is a common complaint during prolonged screen use.
- Objective measures are needed to quantify visual discomfort and its underlying mechanisms.
- The orbicularis oculi muscle's electromyography (EMG) response and blink rate are potential indicators.
Purpose of the Study:
- To assess the sensitivity of orbicularis oculi muscle EMG to low-level visual stress.
- To determine if EMG can serve as an objective measure of visual discomfort.
- To differentiate responses between visual conditions that benefit from squinting and those that do not.
Main Methods:
- Thirty-one healthy adults with normal vision participated.
- Subjects read under various low-level asthenopic conditions (font size, type, contrast, refractive error, glare) for 5-minute trials.
- Orbicularis oculi muscle activity was measured using surface EMG, alongside blink rate and subjective discomfort ratings.
Main Results:
- Conditions benefiting from squinting (refractive error, glare) significantly increased orbicularis oculi EMG power and blink rate.
- Conditions not benefiting from squinting (small font, low contrast) showed no significant EMG response but decreased blink rate.
- All tested conditions induced significant visual discomfort, with varying statistical significance.
Conclusions:
- Squint-beneficial visual stress likely involves local mechanisms, including orbicularis oculi contraction and increased blinking.
- Non-squint-beneficial visual stress may involve central inhibition of blinking, decreasing blink rate without engaging the orbicularis oculi.
- Orbicularis oculi EMG is a sensitive objective measure for squint-beneficial visual stress; blink rate may be more sensitive for non-squint-beneficial conditions.
