The Different Ametropias
Myopia, hyperopia, astigmatism, presbyopia, anisometropia and other ametropias are often confused or wrongly interpreted. In opposition to emmetropia, which defines an eye with no optical defect, ametropia means that the eye shows some optical error. Anisometropia is when the optical defect is not of equal value in both eyes. Antimetropia means that one eye is myopic and the other is hyperopic.
Presbyopia and hyperopia
Presbyopia is an age-related phenomenon that usually appears during the early forties when the lens of the eye loses its flexibility and needs to be helped by glasses when reading. Comparatively, hyperopia can be found at any age. In this condition the lens of the eye has to work harder than usual all the time, which is why wearing glasses makes every task easier, whether looking at near or far. Someone can therefore suffer simultaneously from hyperopia and presbyopia or myopia and astigmatism and presbyopia. Evidently hyperopia becomes more disturbing with age as the lens gradually becomes less able to do the extra work this condition requires. That is why we often see people who have long enjoyed good distance vision complaining of a relatively rapid onset of symptoms. This phenomenon actually happens gradually over time, but is not always noticed in the early stages of deterioration.
Myopia is probably the most famous ametropia and means that the eye is slightly too long and therefore focuses light in front of the retina. A simple variation in length of one millimetre leads to a defocusing of three diopters. This stretching of the eye affects the tissue starting at two millimetres and over (myopia of six and more) and can cause enough thinning to induce tearing and, eventually, a detachment of the retina.
Astigmatism is when the eye focuses unevenly lines that are oriented differently. Horizontal lines can therefore be seen as clear while vertical ones can be blurred or vice-versa depending on the focusing effort. This optical defect causes discomfort in both far and near vision. It is often described as a football-shaped eye. This problem can occur alone or associated with myopia, hyperopia or presbyopia.
It is important to remember that, even if they affect your visual performance, most of these vision problems are harmless for your eyes’ health. Do no hesitate to meet with your Opto-Reseau optometrist to learn more about these different optical problems. He will be pleased to inform you.