Your prescription drives everything we do for you, as an optician. It steers us through which lens design might be best for you, which frame is suitable for you, and when you should wear your glasses. But, we often make assumptions in our field, that you understand what the numbers and terms mean. I’m hoping to clear the air and help you understand what it all means.
Demystifying the Mystery
The names used for the different parts of the prescription can be confusing to the uninitiated but, there is no need to be afraid or confused, with a little bit of tender guidance. The terms can actually be quite self-explanatory, once you have a grounding in some basic facts about how lenses work. In the end, it all comes down to how Light is bent by the shape of the lens, and how this corrects for the wrong shape of your eye.
Basically it all comes down to correcting the fact that an eye that needs glasses is the wrong shape. We put a prescription lens in front of the eye to help bend the light towards the correct path.
If you are corrected for Myopia, or nearsightedness, you wear a “minus” power lens. This indicates that your lens is concave (i.e. relatively flat on the front surface and steeply curved on the inside surface). This means, in practical terms, that your lens will be thickest on the outside edge.
Conversely, if you are corrected for Hyperopia, or farsightedness, you wear a “plus” power lens, indicating that your lens is convex (i.e. relatively steeper curve on the front surface of lens than on the inside surface). This means, in practical terms, that your lens will be thickest right in front of your eye.
The Confusing Part
Astigamtism takes a little more time to explain, so bear with me. Astigmatism, is essentially a lack of roundness to the eye. The eye is more egg, or football, shaped than someone who has good vision. But this is where it gets a little complicated. Think of it, more like the egg is standing on it’s end, rather than laying on a counter like you’re used to seeing them. It’s oblong, vertically, rather than horizontally.
This lack of roundess to the eye is corrected with Cylinder. Cylinder is actually rather self-explanatory. A cylindrical lens is exactly that, a lens that is made by taking the side of a cylinder, rather than a end/sphere. This also explains the final column in your prescription. A cylinder can be set on different angles to correct for which angle your egg-shaped eye is standing on. So your astigmatism correction is both the Cylinder AND Axis. This explains the most common components of a Single Vision Prescription. There are other components, but I will save them for an addendum very soon.
I hope after this brief explanation of the three basic componenets of your prescription has helped you understand the basics of why we choose the frames we do for you, and how we can help make sure your glasses can look as good as possible.