Why your eyes are strained more reading from a computer screen than reading from the printed page:

Your eyes focus differently on characters in printed material than characters on the computer screen. Letters on printed material form smooth, dense, black lines with edges that are well defined. 

Printed letters

Computer Screen Letters

The letters generated on your screen are known as Gaussian images. They are brightest, and have the clearest definition at their centers, while their edges fade and are less distinct.

Because the characters on the computer are the brightest in the middle and then fade out, the eyes have difficulty focusing on them. 

Dark Focus
Our eyes have what is called a "dark focus." This is the point in space where your focus would be if your eyes were totally relaxed. Imagine a pitch black room. In such an environment, where you can't see anything, your eyes are actually focusing on a fixed point in space, that is why it is called the "dark" focus. 

This focus is known as the Resting Point of Accommodation (RPA) and is unique to every individual, but it usually rests more than three feet away from your face (and does not depend on time of day or age). 

When you look at something, your eyes exert effort to move their focus away from the RPA and towards the object that you are looking at. The difference between your RPA and what you're focusing on is known as the lag of accommodation.

The computer screen plays a tug-of-war with your focus. The characters on a computer screen actually force your eyes towards the dark focus. It isn't that your focus is pushed to the RPA that causes a problem; it's your brain's attempts at pulling the focus back to the plane of the computer screen that results in the tug-of-war that causes eyestrain. 

Someone who uses a computer eight hours a day will do this constant re-focusing up to 25,000 times.

Home  Emotional  Forum  Intellectual  Physical  Resources  Site Map  Social  Spiritual