Myopia is a refractive disorder of the eye in which light rays do not focus on the retina, but at some point in front of the retina. For this reason, the nearsighted cannot clearly see objects far away.
Myopia is divided into simple and pathological. Simple myopia occurs in childhood, usually between 5 and 12 years of age and is either hereditary or due to significant amounts of near work (reading in bad light, very close etc). The pathological myopia appears at puberty and worsens later.
Myopia is corrected by using glasses (lenses) that have a negative optical power which compensate the excessive positive diopters of the myopic eye, contact lenses or laser surgery with LASIK or PRK.
Usually myopia is measured in diopters and is divided into:
Mild myopia up to three diopters,
Moderate, from three to six diopters,
Large, six diopters or more. People with high myopia are more likely to suffer from retinal detachment or experience other symptoms like fleeting shadows (as “floaters”).
Hypermetropia is a refractive defect of the eye in which light focuses at a point behind the retina. The patient can distinguish objects at great distance, but has trouble distinguishing them clearly within walking distance.
Hypermetropia is divided into two main categories:
Refractive (when the length of the eye is normal but the optical powervalidity is too small) and
Axial (when the power of the eye is normal but the eye’s axial length is too short)
Hypermetropia is corrected by using glasses (lenses) that have a positive optical power which compensate the excessive negative diopters of the hyperopic eye, contact lenses, or surgery laser LASIK or PRK.
Astigmatism is a very common refractive problem in which the surface of the cornea has an asymmetrical curvature so objects near or far are displayed distorted.
Usually astigmatism coexists with nearsightedness or farsightedness. The term comes from the Greek α- (a-) meaning “without” and στίγμα (stigma), “a mark, spot, puncture”.
When astigmatism is regular, the correction is done with glasses or contact lenses. In the opposite case e.g. caused by trauma (irregular astigmatism) is corrected either by the use of hard contact lenses or in some rare cases with corneal transplantation.