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Understanding your optical prescription

Ever wondered what the information on your prescription means? Here’s a brief overview:

Sph (sphere) shows the amount of long or short light that is present. The larger the number the stronger, and therefore the thicker the spectacle lens will be. Plus lenses are used to correct long sight and minus lenses are used to correct short sight.

Patients commonly fall within the -25.00 or +25.00 range with most falling between +4.00 or -4.00.

Cyl (cylinder) shows the amount of astigmatism that is present. Astigmatism is caused when the eye is not completely spherical (like a football) but is shaped more like a rugby ball. This causes the vision to be distorted for both distance and near objects. The cylinder may be plus or minus regardless of whether the sphere is positive or negative.

Axis shows the orientation of the cylinder (from 0-180 degrees) and is the precise angle at which the lens must be set into a spectacle frame.

VA (visual acuity) refers to how clearly you can see shapes and detail measured from a set distance away (six metres in the UK), with your glasses on if you wear them. It is shown as a fraction and the higher the number, the better your visual acuity. For example, if you have a VA of 6/6, you can see clearly and if your VA is 1/6, it means that you need to be a metre away from an object to see it as clearly as people can normally see from six metres away.

Prism is the correction needed (if any) to align the eyes, so that they are looking straight and working well together. A prism is a lens that bends the path of light without altering its focus. Different prisms may be required at distance or near. Prisms are also used at times to help spatial awareness.

NV. Add (reading addition) shows the additional positive power that is needed to enable the eyes to focus for close work. If a reading addition is stated, this means you need different spectacle prescriptions for reading and for distance - they may be combined into one frame as varifocal or multifocal lenses.

Following your eye examination, your optometrist will share your prescription with one of our qualified Dispensing Opticians who will help you choose both your frames and the most appropriate lenses.

If you are due your next eye examination, please click here to book an appointment.