Below are three examples showing what your typical prescription may look like, this is followed by an explanation of the different terms found on your prescription.
| Sph | Cyl | Axis | Prism | Base | |
|---|---|---|---|---|---|
| Right | +0.75 | -0.50 | 180 | ||
| Left | +1.50 | -0.25 | 175 |
| Sph | Cyl | Axis | Prism | Base | |
|---|---|---|---|---|---|
| Right | -1.50 | -0.50 | 90 | ||
| Left | -1.75 |
| Sph | Cyl | Axis | Prism | Base | |
|---|---|---|---|---|---|
| Right | +2.75 | -0.50 | 90 | 3 | UP |
| Left | +0.50 |
The Sphere power of your prescription is used to measure the required lens power, which will compensate for short-sightedness (Myopia) or long-sightedness (Hyperopia). Basically the power starts at 0.00, which means that no adjustment is required, and increases in increments of 0.25, so the higher the figure, the stronger the required lens.
If the power is negative (has a - sign next to it), this specifies a concave lens and indicates that you are short sighted.
If the power is positive (has a + sign next to it), this specifies a convex lens and indicates that you are long sighted
Cyl power corrects astigmatisms, a condition which around one in three of us suffer from. The simple explanation for astigmatisms is that the eye, instead of being shaped like a golf ball in the normal eye, is shaped more like a rugby ball. The resulting defect is that the incoming light rays fail to meet at the right point in your eye (the retina) resulting in a blurred and imperfect image.
Cylinder power is incorporated into the lens to stretch the image across an axis. This corrects the defect within the cornea or lens within the eye. Like Sphere power, Cylinder power increases in increments of 0.25, and if you do not require it, nothing will be written on this part of the prescription.
To graphically demonstrate a cylinder lens imagine it being cut from a rod.
If your lens does incorporate a Cyl power, then the actual shape of the lens will be the combination of the Sph and Cyl powers.
The Axis is the angle at which the Cylinder power of your lens sits. This angle is measured in degrees (1 degree through to 180 degrees).
At the time of sight testing, the optician may notice a slight imbalance between the muscles in the eyes. It is usually only prescribed by the optician if a customer is suffering from eyestrain, headaches, blurred or double vision. Prismatic power can be prescribed for a couple of reasons:
Prisms are prescribed in a measurement called prismatic dioptres.
The base is simply the direction from the pupil, at which the prism sits. The measurements are UP, DOWN, LEFT or RIGHT.
