You are able to see because the front part of the eye, the cornea, is able to bend (refract) light and direct it to the retina, the back part of the eye. When your eyes are functioning well, the point of focus on a distant object will fall on the retina at the back of the eye (emmetropic vision).
Symptoms of eye problems can vary considerably but can include blurred vision, squinting, tired or red eyes, headaches, difficulty reading, tilting of the head, exaggerated blinking and light sensitivity. Other common eye conditions include:
Astigmatism occurs when the eye is no longer round or spherical. When the curve of the eye is somewhat flattened, sharp focus is no longer possible.
Presbyopia results from natural aging of the eyes. The crystalline lens of the eye hardens, which necessitates reading glasses, bifocals, or progressives.
Amblyopia or lazy eye is an eye that has reduced function due to a strabismus (turned eye) or a very different prescription from one eye to the other. It must be treated early in life, before the age of three, with glasses or the wearing of a patch over the good eye, to strengthen the weaker eye.
Strabismus or crossed-eyes occur when eye muscles direct one or both eyes the wrong way. Some cases can be controlled with eyeglasses; others require surgery.
Muscle imbalance is a micro-turned eye where the two eyes do not co-ordinate together perfectly; this can be corrected with special lenses.