Nearsightedness occurs if light rays from distant objects meet before they reach the retina.
In most cases, distance vision is blurred, but near vision is sharp. The glasses that are used to correct this are concave lenses. Concave lenses expand the light rays before they enter the eye. When the light rays then enter the eye lens, the converge correctly to a focus point on the retina. This results in sharp distance vision but blurry near vision.