Concave Lenses are used to move the focus point back so it lands exactly on the retina.
A myopia-correcting contact lens had rear surface curve that matches the front curve of the cornea, and is thinner in the center than in the periphery.
Laser treatment works by optically ‘sculpting’ the desired correction into the collagen layer of the cornea. For myopia correction, more sculpting is preformed in the center of the treatment than in the periphery. This results in the removal of a convex-lens-shaped portion of tissue, which is optically equivalent to adding a concave lens to the eye’s optical scheme.
Nearsightedness (myopia) is the most common optical condition in adults worldwide, affecting about 35% of the population. In the nearsighted eye, light from distant objects focuses in front of the retina, not on it; so a blurry image is perceived. Concave lenses are used to correct this condition.
Correcting Nearsightedness by laser treatment involves precisely sculpting the desired correction into the cornea. Glasses and contacs work by adding a concave lens to the eye, whereas laser treatment works by evaporating or subtracting a convex lens shape from the cornea.