These are questions that eye doctors are frequently asked. It can be confusing when there are common terms for medical conditions.
Myopia or Nearsightedness
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, even though their distance vision is blurry and requires glasses or contact lenses to make it clear.
Hyperopia or Farsightedness
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 an intra-ocular lens. As we get older it becomes more difficult for the eye to accomplish this auto focusing. Because of the eye's ability to focus, farsighted people often do not 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.
A person is presbyopic when the crystalline lens in the eye can not longer focus well at near, making reading glasses or bifocals necessary. A person can be both farsighted and presbyopic or nearsighted and presbyopic. Presbyopia typically begins in our early 40s. The older we get the more difficult it is for our eyes to focus at near. The effects of presbyopia level off in our mid to late 60s.
Many people feel astigmatism is a bad, progressive disease. Actually astigmatism is caused when light focuses in two points in the back of the eye because it is not in the shape of a sphere. An eye with astigmatism has often been described to be in the shape of an egg or football, to some degree that is true, although an astigmatic eye is not exaggerated to that degree. Most people have some astigmatism. Visually, a person with uncorrected astigmatism will often see a flaw shadow on letters or objects.
A person is emmetropic when an image focuses clearly on the retina without the eye doing any focusing itself. A person that is emmetropic has uncorrected "normal vision".