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Understanding my Degree

What is a degree?

Having a degree/prescription for glasses means that the eye is not able to perfectly focus light for crisp clear vision either for far or near or both. If a degree is present there are associated numbers which represent the severity and type of degree and these are measured in a unit called Dioptres (D).

Sphere Cylinder Axis Add Prism & Base VA
Right (OD)
2 base in
Left (OS)
1 base up
Our eyes are not always exactly symmetrical therefore our right and left eye may have a different degree/prescription. This is quite normal. Usually this is clearly indicated on your prescription as “Right” and “Left” however it is sometimes noted as the abbreviation ”OD” which stands for right and “OS” for left.


Sphere represents the power/strength of the degree lens (in Dioptres) which corrects either long or short-sightedness.

  • Short sighted (Myopia) is represented by minus (-)
  • Long-sighted (Hyperopia) is represented by plus (+)
  • Having no degree (Emmetropia) is record as “0.00” or “Plano”

The higher the number, the more severe the degree and therefore the worse the vision without glasses/contact lenses correction. The degree is recorded in 0.25 steps e.g. 0.00, +0.25, +0.5.

In the above example this patient’s Right eye is long-sighted whilst the Left eye is short-sighted.


Cylinder represents the amount of Astigmatism present (in Dioptres). If this box is empty this means there is no astigmatism in the eye. Again this is recorded in 0.25 steps and is usually written in the negative power format (e.g. -0.75) but this negative does not indicate myopia as above. If you receive a prescription with one eye Cyl as – and the other eye as + there is an error and you should confirm with your Optometrist.


Axis represents the rotation or angle of the Cylinder lens and is measured in Degrees from 1-180° where 90 represents vertical and 180 represents horizontal. The higher the number does not indicate a stronger degree, it only describes the position of the astigmatism in the eye. If there is no Cylinder power then there is no Axis and if there is a number recorded in Axis but not Cylinder then there is an error and you should confirm with your Optometrist.


Add stands for “Addition” which is when there is Presbyopia present. Add represents the difference in power from the far and near vision degrees. If there is no add this means a second separate degree is not given for near vision.

Prism & Base

Some patients with more complex eye health/prescription issues require a special type of lens with a Prism. Prisms bend light and prescribing prisms requires further checks beyond that of a regular degree assessment. It is best to ask your Optometrist regarding prism if this is necessary.


VA stands for Visual Acuity and this is a measurement of vision level. “6/6” is commonly considered “perfect vision” and can also be recorded as “20/20”. Usually, as the second number increases this represents poorer vision e.g. 6/9 vision is worse than 6/6 vision.