Refractive error means that the shape of your eye does not bend light correctly, resulting in a blurred image. The main types of refractive errors are myopia (near sightedness), hyperopia (far sightedness), presbyopia (loss of near vision with age) and astigmatism.
Cornea is the clear, protective outer layer of your eye. Diseases, infections and injuries that affect cornea can result to scars that affect your vision by blocking or distorting light as entering your eye.
Glaucoma causes irreversible BUT preventable blindness. It is a condition that is caused by an abnormally high pressure in the eye that damages the optic nerve leading to loss of vision.