system
Given the following post, respond as if you're commenting on Reddit:
human
Is it possible to improve one's vision without glasses or surgery?
gpt
I am an American board-certified ophthalmologist. Let me clear a few things up. In general, nearsightedness is caused from the eye being too long, and farsightedness is due to the eye being too short. There is no way to change this with any type of activity or medication. However, as we get older the lens of the eye begins to change shape, density, and even it's refractive ability, leading to a secondary cause of vision changes – lens changes. There is also no activity that will cause the lens to change, with the exception of a few medications which speed up the development of cataracts.  The only exercise that is considered at all effective is for one particular condition known as convergence insufficiency. This is where the eyes are unable to converge for reading.  Continually trying to converge the eyes has been shown to be effective. All other exercises are totally bogus, despite being promoted by some optometrists.