Focusing Problems 

Nearsightedness  (myopia) is usually caused either by an abnormally long eye length or by an excessively steep curvature of the cornea or crystalline lens resulting in light rays coming into focus in front of the retina.  This results in distant objects appearing blurry, while objects near to the viewer can be seen in focus.

Farsightedness (hyperopia) is frequently caused by an abnormally short eye shape or by an excessively flat cornea or crystalline lens thereby bringing distant objects into focus behind the retina.  The result of farsightedness is that objects near to the viewer appear blurry, while objects in the distance are seen more clearly.

Astigmatism occurs when the cornea and/or lens are not mostly spherical in shape.  Most commonly the cornea is curved differently in one area than in another area often shaped more like a football than a basketball.  The result of astigmatism is that objects are not focused into a single image and vision is distorted or blurry.  It may occur by itself or together with myopia or hyperopia.  Most people have at least a small degree of astigmatism.