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.
Retina is located at the back of your eye and contains light sensitive cells that send electrical signals to the brain along the optic nerve. These signals are used by the brain to interpret what you are seeing.
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.