The over-worked muscles
The ciliary muscles control focus by changing the shape of the lens. Looking at near objects for extended periods of time strains the ciliary muscle, leading to a ciliary spasm. This muscle is most relaxed when looking far in the distance.
Extraocular muscles control the movement of the eye and the eyelid. These muscles may tighten during intense visual work or when the body perceives a threat. When tightened, a person may appear to be scowling or squinting. Closing the eyes and massaging around the eye can temporarily relax these muscles, but they will quickly tighten again if the core problem is not addressed with better habits. In addition to causing discomfort, strained extraocular muscles will result in a wrinkly, unpleasant facial expression.
Causes and solutions
Blur from uncorrected vision causes eye strain. This problem is solved by wearing the differential or normalized lenses that are most appropriate for the situation. Good ambient lighting will also go a long way to help avoid eye strain. More light means better vision, and natural light is the best light.
Staring at a computer monitor or other electronic screen for extended periods of time may cause eye strain under certain conditions:
- The screen contrasts with the environment. The color temperature and brightness of the screen should be adjusted to match the surrounding environment. Or, the lighting in the room may need to be adjusted to better match the screen. Having the lights off in the room while staring at a screen is never a good idea.
- The screen is too close to eyes. The screen should be at least an arm's length away from the eyes. With tiny phone screens, this is impractical; the bad habit of doing everything on the phone should be replaced with a good habit of doing as much as possible on a desktop or laptop computer at a healthy distance from the eyes.
- The staring is being done without reasonable breaks. At the very least, the eyes should be given a short break every 20 minutes and a long break every 60 minutes.
- The screen is low-quality or uses old technology. The old CRT technology is rarely used now, but be aware that its inherent flicker strains the eyes. The human eye certainly struggles when viewing light that flickers on and off 60 times per second! Unfortunately, even the current display technology, LCD, can flicker. Low-quality LCDs use PWM dimming, where the backlight is switched on and off hundreds of times per second. High-quality LCDs are designed with DC dimming, where the light is constant.