Understanding Your Prescription

First, a crash course in Vision 101:

  • Light enters the eye at the pupil and strikes the back of the eye at the retina.
  • The retina takes in that light and sends off signals to the brain
  • The brain interprets those signals and constructs a mental conceptualization that we experience as “vision”.
  • Vision is made possible by the eye, but it only exists in the mind.

Your prescription fixes a problem

Your optical prescription is like any other prescription you may receive, and the ultimate goal is to restore a deficiency or remedy a disorder of some sort. In this case, the deficiency in our inability to see well.

There are many, many reasons why a person may not see well (eg. concussion, stroke, pathologies), but generally when we think of a visual deficiency we’re really thinking of “refractive errors”, which is simply the inability of the eye to properly focus the incoming light onto the retina.

And that’s where lenses come in!

Using lenses, we can help the eye out by bending the light to where it should be on the retina. Your prescription is a recipe for how the lenses are made, as follows:

  • Sphere:
    This is the power required to correct your basic near-sightedness or far-sightedness.
  • Cylinder:
    If you have Astigmatism, you will need Cylinder to “tweak” your Sphere power to sharpen the image.
    • What is Astigmatism?
      Instead of all the rays of light being equally blurry, some light rays coming in from one angle are slightly blurrier than light rays coming in from another angle. Cylinder provides the extra power (but only where it is needed) to bring the entire image back into equal focus.
  • Axis:
    This is the angle from the horizontal at which the cylindrical power starts to get added to the Sphere (only if you have Astigmatism).
  • ADD:
    This is the additional power required (added to your Sphere power) to allow you to read. This becomes necessary in our mid-forties when our ability to see up close is compromised with age.
  • Prism:
    This is only required when the patient has double vision. The prism in the prescription shifts the images from your left and right eyes causing them to overlap and properly form one image instead of two.