I doubt very much that playing is the cause of your vision difficulties.
Do you currently wear glasses or contacts? Have you gotten your vision checked recently (adults should have their vision checked every two years).
I have found that when I ‘graduated’ from normal glasses / contacts (I used to be simply near-sighted) to varifocal lenses (many people as they get older begin to have trouble seeing / reading up close) I now sometimes have a bit of depth perception issues on the lower strings of the harp and also have trouble when lighting conditions are on the ‘too dark’ side (like at open mic nights, etc.)