Prescription Guide for Eyeglasses

The eyeglass prescription is written by an ophthalmologist, optometrist, or an orthoptist. There are many symbols in the eyeglass prescription which explain different aspects of your eye condition and the specific type of prescription eyeglass that you need for a clear and comfortable vision. Let’s take a look at those symbols and their meaning.

OS and OD

OS and OD are Latin abbreviations. OD stands for ‘oculus dextrus’ which means the right eye and OS stands for ‘oculus sinister’ which means the left eye. Sometimes, you can also witness the term OU in your prescription, OU indicates any condition which involves both eyes.

SPH (Sphere)

A + sign in the box indicates that the patient is long-sighted. This means that the patient faces difficulties in viewing close or near objects. A - sign in the box indicates that the patient is near-sighted, which means that the patient finds it hard to view distant objects. The number can be extremely small, such as 0.25, or it can be really large, such as 7.00. The higher the number, the more severe is the eyesight problem, and the patient requires stronger lenses to rectify the vision. This number can also influence the selection of frame by the patient. If the number is higher, the patient requires an eyeglass lens with a greater curve.

CYL (Cylinder)

This symbol indicates the amount of visual distortion or astigmatism. This astigmatism is caused due to an irregular shape of the cornea. In case of an empty box, the patient’s eyes are precisely spherical and there is no sign of visual distortion. In case of a low number such as 0.3, the patient’s eyes are almost round but not perfectly spherical. In case of a high number, such as 4.00, the patient’s eyes are far from round and greatly oval in shape.


Prism indicates that both eyes are not working properly as a pair. This happens because of muscular imbalance between the eyes. In such cases, prism lenses are recommended which provide the much-needed visual correction to prevent the occurrence of double vision and headaches.


Axis is a specific number between zero and 180 degrees. Axis measures the direction of visual distortion i.e. astigmatism, in degrees. This number is not related to your visual abilities but helps the opticians in determining the right position of the lenses in your eyeglass frame.


This number is also not related to your vision. It tells the opticians or other optical laboratory specialists about the right positioning of prism in your eyeglasses.


ADD is known as reading addition and relates to the amount of extra correction needed to view or focus at close distances. If there is a number in this specific section, it indicates that the patient requires extra vision power correction. In such cases, a bifocal or progressive lens is needed by the patient for a clear and comfortable vision. The number indicated is the power needed on the lower part of the glass.