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    What do the eye prescription numbers mean?

    Written by Miss Linda Ficker, Consultant Ophthalmic Surgeon
    • Eye prescription numbers are the results of refraction test
    • What hyperopic, myopic and astigmatism mean
    • How to correct your prescription

    Eye prescription

    When you go for an eye test, you end up being given a set of figures known as a prescription. The test is called a refraction, and the results are expressed in a standard format:


    Refraction testing measures the strength of spectacle lens needed to give you a clear distance focus.

    If you need spectacles or contact lenses, the power of these lenses is measured in units called dioptres, usually expressed as “D” in the prescription. There is a range of lens powers and lenses can either increase or reduce the focusing power of the eye.

    If you are hyperopic or “long-sighted” you need extra focussing power. Lenses which increase the focusing power of the eye are convex in shape and have a plus (+) sign before the number, saying how strong they are.

    If you are myopic or “short-sighted” you need to reduce the focussing power of the eye. Lenses which reduce the focusing power of the eye are concave and have a minus (-) sign.
    Most eyes are not perfectly spherical but have a degree of irregularity called astigmatism. This is often compared to the difference between a football which is spherical and a rugby ball which has two different curvatures. The amount of long or short sight is measured in the first (X.XX) number of your spectacle prescription, and the amount of ‘rugby ball shape’ or astigmatism is measured in the second number.

    To correct astigmatism, the rugby ball shape lens has to be in the right orientation in your glasses. This orientation is expressed in degrees (0-180°) and is the third number (xZZ) in your spectacle prescription.Female doctor assesing male patient

    Reasons for choosing Moorfields Private Eye Hospita

    Most young people have enough natural additional focusing power for near vision. This flexibility of focus is called accommodation, and is based on flexibility of the natural lens within the eye.

    If you are in your mid-forties or older, you will start to need additional (+) focusing power to help bring near objects into focus. This is because older people have a less flexible lens in the eye, and a less flexible focus. The strength of the extra (+) lens is called the reading addition. The reading addition can either be put into the bottom segment of bifocal or varifocal glasses, or worn separately as a dedicated pair of reading glasses.

    At Moorfields Private, we offer the full range of laser and implant techniques for correcting your spectacle prescription. Whether you are younger or older, short-sighted or long-sighted, have astigmatism, or need reading glasses, we will be able to advise you which treatment will safest and most effective for you.

    Or speak to the New Patient Enquiry Team:
    0800 328 3421



    Miss Linda Ficker

    Written by Miss Linda Ficker

    Consultant Ophthalmic Surgeon