straining your eyes

I always wondered why, when my grandfather would tell me "Don't read in the dark its not good for your eyes, it will strain them" how that worked.

As I grew older the question became clearer. Muscles and muscle groups need to be exercised. The more exercise the better. When you lift weights you are straining your biceps to make them stronger. When you do cardio exercise, you are straining your heart to make it stronger. Unless it's extremely overdone, typically, muscles adapt well to  exercise and actually need exercise. When a muscle is not used for even a short period of time it starts to atrophy quickly. Why are the eyes different? Why not strain your eyes and try to read in the dark to make them stronger? try to peer into the distance to work-out and strengthen your eyesight?

Some experts today actually question the conventional wisdom and say that the concept of straining your eyes is a myth. However many researchers, and much circumstantial evidence points to the fact that straining ones eyes definitely has a detrimental long-term effect on eyesight.

The Rambam in Moreh Nevuchim In Chelek 1, Perek 32 brings out  an interesting point. The Rambam discusses the Mishna and Gemarah in Chagiga 11B which states:

כל המסתכל בארבעה דברים רתוי לו כאילו לא בא לעולם מה למעלה מה למטה מה לפנים ומה לאחור

The question the Rambam, as the great rationalist he is, seems to be grappling with, is, why and how do Chaza"l feel that we should be limiting people's intellectual pursuit of anything. The Torah wants us to think for ourselves. Obviously the Torah directs us where we need direction and there are basic truths that we have to assume based on faith and mesorah/kabbalah. However, why should we be limited in what we can think about and research. Mind control is not a Torah or Jewish practice, it is the practice of other religions. 

The Rambam explains with an analogy. He says that there is a parallel between the physical body and the mind in many ways. He continues by saying (I Paraphrase): Just like when a person strains his eyes it will ruin his eyesight and the more he strains the weaker his eyesight will become so to is it with a person who delves into THESE intellectual pursuits, the deeper he delves the weaker his mind will become. 

The Rambam in his brilliance understood that in normal circumstance exercise is good for the body and of course good for the mind. However there are exceptions to that rule. The Rambam found the one exception to that rule in the physical/body realm and makes a brilliant analogy in the spiritual/mind realm. 

The researchers explain that the reason for the detrimental effect straining has on eyesight is because as it is explained:

"The study shows that the strain of reading, and especially of reading in the dark, could give undeveloped eyes a signal to grow in the wrong way; how eye shape develops is important because nearsightedness occurs when the eye grows overly elongated. to read you may have to pull the book closer to your eyes. As you do this, the ciliary muscle around the lens of your eye contracts, reshaping it so that light flooding in is redirected to a focal point at the back of the eye this affects which light penetrates the eye and lands on the point of highest acuity in the back of the eye (the fovea). Especially during the first decade of life, the eyes change slightly in shape and size, significantly impacting how the eye focuses."

Because eyesight is continuously developing (definitly during formative years) and there are various muscle groups interplaying with each-other the effect of over straining will cause the eye to become imbalanced and the eye will not learn how to focus when the light is right causing generally bad eyesight. 

The Rambam says the same thing applies to the mind. When one delves into intellectual pursuits that are beyond his capabilities of understanding to the point where  he will strain aspects of his mind one way while other aspects of his mind will be twisted in another direction the result will be that even simple intellectual pursuits that he was capable of prior will become to hard for him to the point where he will actually go mad. Only Rabbi Akiva or people of similar capacity that are totally balanced and know when and how to strain their minds and don't ever start twisting their minds because the are fully balanced can enter PARDES in Shalom and leave Be'Shalom.