Getting eyesight is nothing but your lens in your eye got disturbed. As you stress or try to focus more on something with your eye which you see blurry or different than normal your eyesight increases.
In order to avoid damaging your eye, take a good spectacles and wear, it makes you to see objects clear and as a result it reduces strain on eye.
 Spectacles would not decrease your power but it rather stops it to increase.
Food is the most important one that increases your vision.

1) Take carrots and foods rich in Vitamin A, Vitamin C, lutein and beta carotene as they help repair the eyes,
2)Don't take sugary foods

-Get proper rest and do eye exercises 
-Stay hydrated( Take more drinking water and wash your eyes after a long work)..