What does the prescription on my glasses card actually mean?
The numbers, measured in dioptres, describe how much and in what direction light needs to be bent to focus on your retina. A minus value means short sightedness, a plus value means long sightedness, and a cylinder value describes astigmatism.
- Subject
- Vision correction
- Topic
- Refractive surgery basics
- Kind of question
- What is…
- Last reviewed
- 22 September 2026
In more detail
The axis number alongside the cylinder describes the direction of the astigmatism, and two different sets of readings from two different optometrists can both be correct, because refraction depends partly on how you respond during the test.
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It is one of 483 answers in the vision and eye health knowledge base, filed under Vision correction & laser eye surgery in Refractive surgery basics . The subject page carries the answers either side of it, and the hub is searchable.
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This information is for educational purposes and does not replace an examination by a qualified eye-care professional.
General answers cannot tell you what is happening in your own eyes. Only an examination by a qualified ophthalmologist can do that.