The Common Refractive Terms Define
These are questions eye doctors are frequently asked. It can be confusing when there are common terms for medical conditions. Here we will discuss and define the terms for the common refractive conditions, myopia, nearsightedness, hyperopia, farsightedness, astigmatism, and presbyopia.
Myopia or Nearsighted
A condition where a person’s uncorrected vision is only clear up close. Instead of the light focusing on the retina, it focuses in front of the retina. A myopic person can read a magazine; however, their distance vision is blurry and requires glasses or contact lenses to make it clear.
Hyperopia or Farsighted
Hyperopia commonly referred to as farsightedness, is when a person sees better in the distance than at near. Light entering the eye focuses behind the retina placing a blurry image on the retina. For a hyperopic person to see clearly at any distance a muscle, inside the eye called the ciliary body, must focus the intra-ocular crystalline lens. As we get older it becomes more difficult for the eye to accomplish this autofocusing. Because of the eye’s ability to focus, moderately farsighted people often don’t need glasses until their 30s or 40s. Uncorrected farsightedness, however, may cause a person to experience eyestrain or an eye turn (strabismus), depending on the degree of farsightedness and the patient’s age. The younger we are the easier it is for the eye to compensate for farsightedness. Uncorrected farsightedness can lead to amblyopia. Farsightedness and presbyopia are often confused.
Many people feel astigmatism is a bad, progressive disease. Actually, astigmatism is caused when light focuses at two points in the back of the eye because the eye is not in the shape of a sphere. An eye with astigmatism is often described as being in the shape of an egg or football, to some degree that is true, though an astigmatic eye is not exaggerated to that degree. Most people have some astigmatism. Visually, a person with uncorrected astigmatism will often see a faint shadow on letters or objects.
A person is emmetropic when an image focuses clearly on the retina. A person that is emmetropic has uncorrected “normal vision”.