Why do small fonts strain the eyes?

[Ganesh Ujwal]

I understand that too much close reading will strain the ciliary muscles of the eyes. But what about small fonts? The contraction of the ciliary muscles is dependent on the distance not font size.

In other words, it is better to read from a closer monitor with bigger font or from a further monitor with smaller font?

[Dekan]

It's probably better to read from the further monitor. Because the monitor's increased distance, reduces the strain on the ciliary muscles. These muscles have to "squeeze" the eye-lens, in order to make it more convex. So that it can bring the incoming light-rays - from a viewed object - to a sharp focus on the retina. And thus transmit a sharp optical image to the brain.

 

The amount of "squeezing" this requires, depends essentially on how far away the viewed object is. If the object is quite close, say only a couple of feet away, the muscles will have to squeeze quite a lot. Thus exerting a continual strain on them. Which is bound to stress them - and so cause eye-strain. Such as results from a viewing a small computer monitor screen, at close range.

 

Viewing is much easier if the screen is bigger, and further away. The increased distance means the eye-muscles don't have to squeeze so much. They can be more relaxed. They don't get so stressed. A big screen at a big distance, is easier on the eyes. For example - when you go to watch a film at a cinema, isn't the screen extremely big, and 30 or 150 feet away?

 

Of course, this analogy may not be entirely appropriate. Other factors can come into play when we're considering computer monitors. Especially their "fonts" - to go back to Ganesh's OP.

All fonts are made of "dots". And there are more dots in some fonts than others. This can obviously affect their intrinsic "readability" - from any distance.

 

Nevertheless, I think that as a general rule - "big screen - big distance" is optically preferable to its converse.

Edited December 13, 2014 by Dekan