As we age, the natural lens of the eye loses flexibility. Its called presbyopia.
A perfect powered eye can see 20/20 or better. When a kid, that eye can focus to a few inches. As we age the nearest clear distance an eye can focus gradually increases because it gets stiffer and we cant focus as close.
A perfect eye can focus at 16 inches only until about age 44 where it could focus at maybe 8 inches at age 35.
Focusing ability is age related.
At 44 with perfect eyes we need help to focus to read as we are using all our focusing ability to see clear at 16 in.
I am old. I can see perfectly at 16 inches without specs because i am Near Sighted (myopic) approximately the correct amount to see up close (2 Diopters).
If i were highly myopic (6 D) i would need glasses to see clearly at 16 inches or i could see clearly at about 6 inches without specs.
After age 44 a perfect eye needs slightly more help to see clear at near as we age because we are able to focus our hardening lens
less as we age.
By age 58 or so we have no focusing ability left and need 2.50 diopters of lens power to focus at 16 in if our eyes are perfect (emetropic- meaning no refractive error at distance).
Farsighted folks need + power (biconvex) to see at far without straining. Young folks or kids who are a little farsighted can strain, focusing to see at far as perfect eyes do to see at near.. Problem one, they have to focus more and strain more to focus enough to see up close.
Those with low or moderate farsighted eyes (hyperopic) strain more to see clear without an rx as they age because the lens hardens. This normally leads to kids getting eyestrain and tired eyes after near work. They are the kids mom says likes to play outdoors and hates studying.
The danger of them aging without vision correction is that they also strain more and more to see clear at distance as they age and tiredness driving increases as they age and this can result in highway hypnotism and sleep while driving.
They need correction to help focus at distance with out them focusing. They then focus normally to see at near-until after, again, age 44 or so when they also need additional focusing power at near to see clear at near -bifocals.
Me being a senior and able to see clear at near with no rx, i see blurred at far and need myopic correction. Now, when i use an rx to see clear to drive, when i wear it, my vision is clear at distance but i cant then see clear at near because i am presbyopic and cant focus my hard lenses in my eyes to see at near. Answer, bifocals to focus the near vision,
Last edited by jaguartx; 02/27/17.
