The process of straining the eye muscles is used to change the shape of the lens. This can actually improve near OR farsightedness
due to the degree of change of the lens shape. As we age, the lens become less flexible and taken to the extreme, may form cataracts
The reason pinhole boards work is that the send light through just the CENTER portion of the lens, and prevent refractive error from the edge of the lens, which becomes distorted more rapidly than the central portion of the eye. This refractive error is prevented by taking the full light source down to a very narrow band through the pinhole and sending it through just the CENTER of the crystalline lens.
You should understand something unique about the eye's lens. It is the ONLY tissue in the human body that lays down new cells on the OUTSIDE, so that the older, more senescent cells are trapped. This is what makes the lens thicker and less pliable as we age, and leads to presbyopia
In the skin we flake off dead skin. In the GI tract, we shed off mucosa and pass it out as waste. With the eye lens, that cannot happen and thus the new cells are laid down in a somewhat uneven pattern, causing the refractive error mentioned above.
Plenty of people who have near sight strain to see things far away. The ciliary body has opposing fibers and can both collapse and expand the eye's lens. I'm doing it at this very moment looking out my window as I try to focus on a distant bird without my glasses
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