Sometimes ordering contact lenses online can be confusing because we have to decipher our optometrist’s contact lens prescription. A common question we’re often asked: “Is my glasses prescription the same as my contact lens prescription.” The answer is no. The power of your glasses and contact lenses may sometimes be the same however your contact lens prescription will have details about the brand, base curve and diameter of the lens prescribed. Because there are so many different brands of contact lenses available your optometrist has the task of weeding out all the brands which aren’t suitable and to fit you with the optimum lens. If you are just long or short sighted your prescription is relatively simple. You will only have details about the; Brand, Diameter, Base Curve and Spherical Power. For example it may be written as:
Acuvue Moist / 14.0 / 8.5 / -2.00
People who have astigmatism will have additional parameters in their contact lens prescription including the Cyl Power and Axis. An example of how this is may be written is:
Acuvue Oasys for Astigmatism / 14.0 / 8.6 / -2.00 / -1.25 x 180
The -1.25 x 180 is the Cyl power and axis of the lens.
If you need to wear spectacles for reading or have both a distance and near prescription your optometrist may prescribe a multifocal contact lens. Usually a multifocal contact lens prescription will contain a parameter called the ADD. The ADD is how much additional power you require for near. Some brands of multifocal contact lenses will have a limited range of powers for the ADD such as +1.00, +1.50, +2.00, +2.50 and so on. Other brands of multifocal contact lenses will may have the ADD written just as; High or Low. An example of how a multifocal contact lens is written may be:
Purevision Multifocal 14.0 / 8.6 / -3.00 DS High ADD
The +1.00 denotes the distance prescription and is the sphere power. The ADD for the multifocal contact lens in this prescription is HIGH.
Have you ever wondered why your contact lens prescription is not always the same as your glasses prescription? This is usually the case with people who have high prescriptions or have some astigmatism. If you have a prescription which is larger than 4.00 Dioptres your contact lens prescription may be slightly different. This is because a contact lens is placed directly on the eye whereas the lenses on glasses are positioned a small distance from your eye. This distance is known as the vertex distance and affects the effective power of the lens. If you have astigmatism and your optometrist has chosen to fit you with a spherical lens than your contact lens prescription will be different to your spectacle prescription. Usually your optometrist will use the ‘Spherical equivalent’ of the astigmatic prescription which is calculated by halving the cyl power and adding it to the sphere.
If you are unsure of how to read your contact lens prescription please email us, we’re always happy to try clear things up and make the ordering process simpler.