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Helpful Eyesight Definitions to Understand Eyeglasses and Your Eye Problem

May 22, 2017Eyeglasses
helpful eyesight definitions

Eyesight problems are varied and personalized. This leads to an influx of information that you must filter through to learn about your particular situation. Here is a compiled list of helpful eyesight definitions that will make understanding your current eye problem easier, as well as how to remedy it.

  1. Myopia ( or nearsightedness): when a distant object appears blurred because the image comes into focus before it reaches the retina. It can be corrected with a minus lens, which moves the focus farther back.
  2. Hyperopia (or farsightedness): when a nearby object looks blurred because the image does not come into focus before it gets to the retina. It can also occur as people age, but can be corrected with a plus lens.
  3. Astigmatism: caused by a distortion in the cornea that results in a second focal point in the eye. It can be corrected with a cylindrical curve.
  4. Aberrations: ghost images, halos, waves, or rainbows caused by imperfections in the eye curve or lens surface.
  5. Index of refraction: a ratio used to compare refractive power.
  6. Plus lens (+): a lens that is thickest at the center, which moves the focal point forward.
  7. Minus lens (-): a lens that is thinnest at the center, which moves the focal point backward.
  8. Focal point: a point in space where refracted light meets. This may be actual (plus lens) or assumed (minus lens).
  9. Pupillary center: the point on a lens that is directly in front of the pupil.
  10. Bifocals: a pair of eyeglasses that have lenses with two parts, each with different focal lengths. They can help a farsighted person read or do close work.
  11. Segment: the portion of a lens added for reading (bifocal or trifocal). It may be added separately to the lens blank, but it can be formed as a blended curve onto the base as well.
  12. Compound lens: a lens that has both a spherical and a cylindrical component.
  13. Cylindrical curve: a curve that radiates along a straight line, similar to a pipe cut lengthwise.
  14. Spherical curve: a curve that is the same in all directions, like a basketball cut in half
  15. Base curve: a simple spherical curve; the primary lens curve
  16. Diopter (D): the refractive power of a lens. The higher the number, the stronger the lens will be.
  17. Refraction: the bending of light.
  18. Lens blank: a basic spherical lens. The lab grinds the back of the blank to match a particular prescription.
  19. Optical center: a point on a spherical lens where light enters at a 90-degree angle to the lens plane.
  20. Generator: a compound surface grinder used to grind curves into the surface of the lens.
  21. Induced prism: a technique that moves the optical center away from the pupillary center.