Eyeglass prescriptions are given to children for a variety of reasons.
Myopia or nearsightedness, which refers to difficulty seeing in the distance, is one of the most common conditions requiring glasses. Myopia typically appears around the age of nine or ten and in its early stages often does not need correction. The typical course, however, regardless of whether glasses are prescribed initially, is for the myopia to increase as the child grows. The age of onset and the final level of nearsightedness are hereditary to a large degree.
Astigmatism refers to the eye being out of focus because the cornea or the front surface of the eye is not perfectly round. Glasses can easily compensate for this distortion and are prescribed based on the amount of astigmatism and the age of the child.
Hyperopia or farsightedness is another condition which may require glasses. Whereas hyperopia in adults may cause blurring, some amount of hyperopia is normal in children. Unless the amount of hyperopia is very high, children’s eyes can focus clearly despite hyperopia. Therefore, glasses may not be necessary. However, if the farsightedness is associated with crossing of the eyes (see Accommodative Esotropia), farsighted glasses would be required to maintain straight alignment of the eyes.
Another reason to prescribe glasses is to treat amblyopia or a “lazy eye.” Amblyopia is a condition where the vision pathways between the eye and the brain do not develop fully because one or both eyes do not receive the proper visual stimulation. One cause for this is one eye being out of focus in relation to the other. For example one eye may have astigmatism while the other does not. In this instance, vision would be clear with both eyes open because one eye is perfectly focused. Glasses, therefore, would be needed to prevent or treat the amblyopia in the eye which is out of focus.