Phoenixville Eye Care Optical Shop

Glossary of Refractive Terminology

Emmetropia - The scientific term for normal vision. When the cornea and lens of the eye focus an image directly on the retina, clear vision is the result:

Astigmatism - is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance.

In Hyperopia, or Farsightedness, vision is usually better for distance objects than for near. It results from the eyeball being too short from front to back, causing images to be focused behind the retina. Children are often hyperopic, which may lessen as an adult.

Myopia - Nearsightedness - Nearsightedness, or myopia, as it is medically termed, is a vision condition in which near objects are seen clearly, but distant objects do not come into proper focus. Nearsightedness occurs if your eyeball is too long or the cornea has too much curvature, so the light entering your eye is not focused correctly.

Nearsightedness is a very common vision condition that affects nearly 30 percent of the U.S. population. Some evidence supports the theory that nearsightedness is hereditary. There is also growing evidence that nearsightedness may be caused by the stress of too much close vision work. It normally first occurs in school-age children. Because the eye continues to grow during childhood, nearsightedness generally develops before age 20.

Presbyopia - (aging of the lens in the eye and the muscles that control the shape of the lens) commonly occurs after age 40, when the lens of the eye becomes more rigid and does not flex as easily. The result is that it is more difficult to read at close range. The normal aging process of the lens can be combined with all the other refractive errors. Treatment is reading glasses or bifocals

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