The Normal Eye
Normal vision, otherwise known as emmetropia, is where light from an object forms a perfect image by focusing directly onto the retina
Myopia is the most common refractive error seen in children. A myopic person will notice objects close to them appear clear while distant objects appear blurred and may cause headaches and/or eyestrain.Commonly known as short sight, myopia is where light from a distant object forms an image in front of the retina, either because the eye is too long or because the cornea or crystalline lens bends the light too steeply. Glasses or contact lenses help to correct myopia by moving the image back onto the retina.
Commonly known as long sight, hyperopia is where light from a distant object forms an image behind the retina, either because the eye is too short or because the cornea or crystalline lens does not bend the light enough.
A hyperopic person will notice objects in the distance appear clear while objects closer to them appear blurred and may cause headaches, eyestrain, and/or fatigue. Children with hyperopia often exhibit signs such as squinting, eye rubbing, and difficulty reading. Glasses or contact lenses help to correct hyperopia by moving the image forward onto the retina.
Astigmatism refers to there being more than one point of focus. It occurs when the cornea (the clear window at the front of the eye) or the lens (the clear structure that lies just behind the pupil) is shaped like a rugby ball. An astigmatic person will have distorted vision. Glasses or contact lenses with cylindrical correction will bend the light more in one direction than the other giving clear vision at both distance and close up.
Presbyopia is the gradual decline in the eyes’ ability to change focus from distance to close-up. Although the process begins in early adulthood, most people first notice the problem when they reach their mid-forties, when they can no longer focus on objects at their normal reading distance.