When the eyeball is too long or the corneal curvature is greater than usual, then the light entering the eye is not focussed on the retina. This gives rise to a blurred image of the viewed objects. Myopia is a refractive condition in which the vision is blurred while viewing far-off objects whereas closer objects can be seen clearly without any strain on the eye. It can be a simple myopic error which is of a low to moderate degree or can be of the progressive type in which the power keeps increasing gradually till the patient reaches 23-25 years of age.
It is the latter that can result in poor vision even with the best correction. The likelihood of such an error is more if both the mother and father of the child are highly shortsighted. Heredity has a strong role to play in case of myopia.
It is very common, particularly in children of school-going age. Some cases are present at birth which are usually progressive in nature associated with changes in the retina.
It is not possible to totally eliminate the error. But the rays can be brought to a focus on the retina to make images of objects clearer by the use of (-) minus lenses in the form of glasses or contact lenses.
Children with short sight have trouble seeing distant objects like blackboard, movie screens or TV clearly. They may also sit close to the TV or hold books too close to the eyes which is often noticed by the parents.