Deciphering a prescription can be easy once you know what to look for. The prescription contains various details that determine how the lenses should be adjusted to the specific needs of your eyes. The details are expressed in diopters. This is a test performed by the ophthalmologist to measure visual acuity, usually from 0 to 10, or sometimes even more after laser treatment.
1. Sph (Spherical):
The first value is the spherical power of the lens. A “+” means you are hyperopic (nearsighted, or an eye that is too short or has a cornea that is too flat). A “-” means you are nearsighted (an eye that is too long or has a cornea that is too convex). If the value is “0”, no correction is needed.
2. Cyl (Cylindrisch):
The second value, in brackets, is the cylindrical power of the lens. This is for the correction of astigmatism, which means that the cornea has an oval shape. One axis is flat and the other is more convex, with a difference of 90°. Sometimes no correction is needed. The value can be negative (usually used by doctors) or positive (usually used by opticians), but this does not change the meaning.
3. Axis (Axis):
The third value is the axis of the cylinder, which is expressed in degrees. This indicates the direction of rotation, in relation to the horizontal line. This is essential for correcting astigmatism, so that the correction is applied correctly.
PD (Pupillary Distance):
This is the distance between the centre of both pupils. It is important that this is measured correctly in order to properly place the lenses in the frame.
The prescription helps to choose the right lenses that correct the patient's visual problems. Your ophthalmologist or optician will explain to you how the prescription works and how it affects the quality of your vision.