Dr Moïse Tourabaly · Key points
A prescription gives one line per eye (RE: right eye, LE: left eye). Choose an item to see what it means.
Sphere (S). The main correction. A negative number indicates short-sightedness (myopia), a positive number long-sightedness (hyperopia). Here: short-sighted by 2.50 dioptres.
Cylinder (C). The strength of the astigmatism, in dioptres. It can be written as negative or positive depending on the convention: the two notations are equivalent once converted.
Axis. The orientation of the astigmatism, from 0° to 180°. It always goes with the cylinder: a cylinder without an axis cannot be made.
Addition (Add). A positive extra for near vision, which compensates for presbyopia. It is the same for both eyes.
Here, the left eye is short-sighted by 2.50 dioptres, with astigmatism of 1.25 dioptres oriented at 170°. Dioptres measure the correction; they do not tell you the visual acuity.
Educational diagram · Dr Moïse Tourabaly, ophthalmologist. It does not replace a consultation.