When your eye examination is complete you’ll be given a prescription.
Sphere (Sph) represents the amount of dioptric power required to correct your long or short sightedness. If the number is positive (+) you are longsighted ( hypermetropic), if it is negative (-) you are shortsighted ( myopic).
The term “sphere” means that the correction for nearsightedness or farsightedness is “spherical,” or equal in all meridians of the eye.
Cylinder (Cyl) indicates the amount of astigmatism, this is usually a negative number. If nothing appears here or the letters ‘DS’ after the Sphere it means that there is no astigmatism. Most people have some degree of astigmatism. 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 term “cylinder” means that this lens power added to correct astigmatism is not spherical, but instead is shaped so one meridian has no added curvature, and the meridian perpendicular to this “no added power” meridian contains the maximum power and lens curvature to correct astigmatism.
Axis represents the orientation of the cylinder (from 0-180 degrees) and is the angle at which the lens is set into the frame. If a prescription includes cylinder power, it also must include an axis value, which follows the Cyl power.
V.A stands for Visual Acuity which is the best attainable vision achieved with your spectacle lenses. In the U.K visual acuity is conventionally measured at six metres, so the numerator is 6 (e.g. 6/6). In the US, VA is measured at 20 feet (e.g. 20/20). The larger the denominator, the worse the eye sees, so a VA of 6/12 is half as good as 6/6. 20/20 or 6/6 vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 feet (6m). If you have 20/20 vision, you can see clearly at 20 feet (6m) what should normally be seen at that distance. Near VA represents the smallest sized print that can be read. N5 is the smallest sized type that you will normally find and N8 is approximately the size of normal newsprint.
Addition – This is the added magnifying power for reading. The number appearing in this section of the prescription is always a “plus” power. Generally, it will range from +0.75 to +3.00 D and will be the same power for both eyes. It is usually only needed for patients over 40-45 as focusing ability declines as we get older (presbyopia). If a reading addition is stated, this means you need different glasses prescriptions for reading and for distance.
Prism – This is the amount of prismatic power prescribed to compensate for eye alignment problems. Only a small percentage of eyeglass prescriptions include prism.
Spectacle and contact lens prescriptions aren’t the same. A spectacle prescription is for the purchase of glasses only. It does not contain certain information that is crucial to a contact lens prescription and that can be obtained only during a contact lens consultation and fitting.
A prescription is usually valid for two years, but your optometrist may recommend that you have your eyes examined more frequently, depending on your particular circumstances.
Your prescription can be dispensed wherever you choose. However, prescribing and dispensing of glasses are closely linked, so it is best to have your glasses dispensed where you have your eyes examined. It is often more difficult to resolve any problems you may have with your glasses when prescribing and supply are separated.