Dangers of monitor too high
Conventional wisdom is to place the monitor high enough to maintain an upright neutral neck posture. This upright posture and high viewing angle with a high monitor causes extra eye strain, and may result in neck extension (bending back) to relieve the eye strain. Neck extension in general puts more strain on the neck muscles than flexion.
Optimal eye positioning – looking down a little
There is common thinking that the eyes need to look straight at an angle perpendicular to the spine. The small muscles surrounding the eyes control the visual system and must work actively to focus the eyes. If the reading material is too close or too high, these eye muscles can be strained:
- Eye strain from visual accommodation. Viewing objects closer than about 100 cm requires the muscles surrounding the eyes to contract to maintain focus, increasing the strain from accommodation.
- Eye strain from convergence. The eyes converge or turn in towards each other for near viewing, preventing double vision. Viewing close objects increases eye strain from convergence. Convergence is much easier for the eyes with a downward gaze angle. Convergence is much harder with an upright horizontal viewing angle.
- Eye strain from dry eyes. Horizontal viewing results in the eyes opening very wide. The eye lids have further to travel to close, resulting in an incomplete blink and more of the eye exposed to dry in the air.
How to choose the right monitor height
- Aim for a nearly upright neutral neck and head posture
- Allow for a downward gaze to reduce eye strain
- Keep monitor distance further than 65 cm to reduce the strain of accommodation
- Zoom in to increase text and image size to allow comfortable viewing from a greater visual distance
- Change positions, get up and move both your neck and your eyes!
- Use the 30-30-30 rule:
Every 30 minutes
Take a 30 second break and
Look 30 meters away.
As shown in the diagram:
- a 35-degree downward gaze angle from the horizon
- Optimal monitor placement is +/- 15 degrees from this resting angle.
- The screen should be between -20 degrees and -50 degrees relative to the horizon.
Smartphones and vision problems
Frequent phone use, computer use, and TV-watching can all lead to eye strain, which can be called Computer Vision Syndrome.
It’s estimated two thirds of us will experience eye strain caused by excessive phone use.
Symptoms can include:
- Blurred vision
- Dry eyes
- Sore eyes
Causes of eye strain from smartphone and screens
Blinking keeps the eyes moist, stops them getting dry, and is a natural defence to dust and sunlight. We should blink about 15 times per minute. This is halved when using a smartphone.
Squinting at on-screen text and videos overworks your muscles around your eyes, neck, and shoulders, and is a major cause of eyestrain and blurred vision.
Excessive glare can cause eye strain. Our eyes should not look directly at light for long periods of time.
Macular degeneration is linked with blue phone light which produces a substance called retinal that can cause the eye’s photoreceptor cells to die. Sun also produces blue light and is the greatest cause of macular degeneration, but long hours of phone use especially at night cannot be healthy.
Reduced melatonin production can occur with spending time on the phone, making it harder for you to fall or stay asleep.
Protecting eyes from mobile screens
- Turn down the glare. Reduce your smartphone’s brightness. This will make the phone easier on your eyes (and saves battery life). Simply access your phone’s settings and adjust the brightness to a lower, more comfortable level.
- Using your phone in the dark is worse, please set phone to night-time mode with more yellow light.
- Adjust your text size: make the default font larger to prevent squinting.
- Remember to blink: as strange as it sounds, developing a good habit to blink while using your smartphone reduces eye strain and helps keep your eyes moist and fresh.
- Take breaks: This is our most important tip!
Adapted from D. R. Ankrum and the www.office-ergo.com web site. This is an updated version of content originally published in The Ergonomics Report™ on July 19, 2011.
Originally published on ergoweb.com September 2, 2014.
International Standards Organization (ISO ergonomics standards 9241-5)