Bring your prescription
Prescriptions for eyeglasses are not interchangeable for contact lenses or other glasses. Prescriptions can be different.
The sphere is a general designation for correction of the eye. It’s called the “dioptre” in medical terms. To correct for myopia we obtain a negative dioptre; for hyperopia, the dioptre is positive. There is no particular limit to the degree of correction for your eyes, i.e., you could have a -12 myopia (per eye) and a +12 hyperopia (per eye).
Cylinder and Axis
Together, the cylinder and axis correct astigmatism. The cylinder designates strength while the axis designates the direction of the astigmatism that must be corrected. Astigmatism is the most common additional defect in eyesight, i.e., in addition to having myopia, hyperopia or presbyopia, one could also have astigmatism. The value for the cylinder is usually expressed in parentheses and the value for the axis is almost always expressed in degrees.
The addition is used only for correcting presbyopia and hyperopia. It is an “additional” value that must be added to farsightedness to make close-up vision (approximately 40 cm from the face) clearer. This value has to be indicated when you need bifocal or progressive lenses.
Here’s what your optician adds…
Pupillary Distance (PD)
The pupillary distance is the space between the two pupils of your eyes. It is different for each person and must be calculated by an optical professional.. The PD is indispensable in making the lenses and installing them properly in your glasses; it lets the optician know exactly where the lenses should be centred. In order to obtain complete accuracy, fit and comfort, an optician at The Canadian Optical Warehouse will take up to four PD measurements.
To ensure accurate adjustment of progressive lenses, the “height” must be calculated to precision in order ensure proper adaptation to the progressive vision of your glasses. This measurement is obtained when you choose a pair of frames and lenses as progressive lenses are made to each person’s frame choice and prescription. Note: Frames require a minimum depth to accommodate progressive lenses.