Ametropia (refractive disorders)
To see clearly the image must be focused on the retina. In myopia (short/ near sight) the image is focused in front of the retina and in hypermetropia (long/far sight) the image is focused behind the retina. Astigmatism results from uneven focusing power at different meridians, causing image distor-tion. Children are usually born a little long-sighted and the refraction nor-malizes as the eyes grow. Ametropia may lead to squints and amblyopia. Quick rule of thumb: convex lenses (for long sight) magnify; concave lenses (for short sight) minify an image.