ELI5: If the eye focuses with muscles, how can/why can’t those muscles train to work without glasses again?

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A lot of vision issues have to do with the shape of different parts of the eye (~~astigmatism is~~ when the eye is more oval than round, some vision things are caused by the lens being different shape/thickness/flexibility or cloudy due to age or disease). Even with more muscle control in the iris and ciliary muscles of the lens, you can’t change the physics of how the light strikes the lens and then retina to form an image or change the shape of the anatomy without intervention.

Joonami

Eye doc here: Think of the eye as a complete system for bending light. The goal is to have the light in focus on the back of the eye (retina). The main focusing factors are the curvature of the cornea (fixed/doesn’t change), the curvature of the lens (not fixed/can add (+) power only), and the length of the eye (decides if the other two are doing it good enough or not enough. If you are near sighted that is a way of saying your entire system has too much power for the length of your eye…which means you have built in reading (near power) so we use minus powered lenses to correct that light to focus on the retina. In a near sighted person the lens in the eye is relaxed because adding even more power would just make things more blurry. If you are far sighted the eye is under powered for the current length of your eye, so adding more (+)power is needed, which the lens in your eye can do…in other words the lens can act “like a pair of glasses” for a far sighted person…except straining all the time like this can cause headaches and eye strain. The ability of the lens in the eye to bend is deteriorated over time regardless of “muscle strength” which is why it wouldn’t help to do eye exercises. Eye exercises are beneficial to folks who can’t bend their lenses as well as others in their young age group (younger than 40) The reason LASIK works is the front curvature of the cornea is reshaped to match the length of the eye so things are in focus for the distance. To see things up close the lens in the eye still needs to bend and flex, which is why after age 40 those people with LASIK still need to wear reading glasses. (Reading glasses give the (+) power needed that the lens bending used to give but no longer can)

chemical_refraction

You can in certain cases. My eye issues stemmed from my brain essentially getting stuck in survival mode after I had meningitis. I went to a year of vision therapy to help retrain my brain how to properly use my eyes and now I am back to approximately 20/20 vision (except at night. I lost my night vision to meningitis, can’t see a damn thing if there is no source of light or very little light)

CinderLupinWatson

Myopia (~~far~~nearsightedness) is the eye being too long for light focusing. The muscles on the lens pull it to shorten the focal length or relax to elongate it. The muscles can’t train to relax even further than all the way, so farsighted people remain far sighted. Presbyopia (~~near~~farsightedness) usually comes with age and is the lens losing is stretchyness. So no matter how you train the muscle, they can’t fix the fact that that the lens is no longer stretchy. Astigmatism is the misshapenness of the eye that caused a distortion in the visual field. So the muscles which pull in the lens can’t fix that either. But yes, other smaller defects can get fixed by the muscles adjusting.

fox-mcleod

The comments here are focusing on the lens of your eye, but you are asking about the muscles of your eye. Basically, there are two main muscle pairs that control eyesight: the cilliary and pupillae muscles. These muscles are smooth muscles that are controlled by the autonomic nervous system, which basically means they require no voluntary movement like arms and legs. Therefore, you can’t really train them as you can with arms and legs since skeletal muscle and smooth muscle have different properties. The ELI5 answer: It’s the equivalent of asking “Why can’t I make my stomach turn food into poop faster?”. Well can you control how your stomach moves? No? That’s why. Source: med school

RT_Frank