Asthenopia is the formal term for describing what is usually called eye fatigue. While eye fatigue has been around long before computers, spending many hours in front of computer monitors certainly causes eye fatigue for a lot of people. I’m keenly interested in understanding eye fatigue and what can be done to prevent it.
Surprisingly when you go to an eye doctor today, there are no direct tests of eye fatigue in the same way that there are tests for high blood pressure. Instead you’re asked to respond to questions like: Do you have blurred vision? Do you feel ache or pain around the eyes? Do your eyes feel tired at the end of the day? If you answer yes frequently enough, then you have eye fatigue.
The pain associated with eye fatigue can be felt in a variety of different ways. Some people feel eye fatigue as ache, strain, and/or headache, typically coming from the back of the head. Other people feel it as burning, irritation, and/or dryness in front of the eye. Others experience vision problems like double vision and blur. These would all be called eye fatigue.
There are many situations that are known to cause eye fatigue, and reducing these factors is a good strategy for reducing eye fatigue. Some factors are related to common office arrangements such as the computer monitor requiring an upward gaze because it is above eye level, a glare sources directed at the user’s eyes, or a flickering light in the environment. Text read from too short a distance which forces your eyes to turn in towards each other (e.g. 15cm) or text that is too small for a user will both cause eye fatigue. Eye fatigue can also result from vision problems such as uncorrected astigmatisms or the inability to adequately change lens power enough to focus on the reading material.
Sheedy, Hayes, & Engle investigated if different factors known to cause eye fatigue were more likely to result in particular kinds of symptoms. To test this they had study participants read text while they intentionally induced eye fatigue. Participants would read text in a variety of unpleasant situations including having a bright light pointed at their face, with a strobe light in the room, with too small text, with text placed close to their face, and while wearing glasses that simulated astigmatism. After each condition the participants answered questions about which eye fatigue symptoms they experienced.
They found that reading with difficult environmental conditions such as upward gaze, glare, flickering light, or small text caused the participants to report symptoms of burning, irritation, and dryness. While reading with internal problems like having to turn your eyes inward, astigmatism, and stress on the focusing lens caused the participants to report ache, strain, and headache.
There is more than one kind of eye fatigue. Understanding the physiological mechanisms that cause eye fatigue can help us reduce its effects.
Sheedy, J.E., Hayes, J., & Engle, J. (2003). Is all Asthenopia the Same? Optometry and Vision Science, 80 (11), 732-739.