HELP FOR PRESCRIPTION GLASSES
The prescription you have for your
glasses cannot be used to buy
contact lenses. The parameters for
contact lenses can only be determined in consultation with an optometrist or ophthalmologist.
What does each parameter mean in the purchase of prescription glasses? Sphere (SPH) is the measurement in dioptres (D) of the spherical power of a lens. Normally, lenses are graded in increments of 0.25D.
- If the measurement of spherical power is preceded by a negative sign (-), the lens is concave and corrects myopia (nearsightedness). Concave lenses are thicker along the edges and thinner at the centre.
- If the measurement of spherical power is preceded by a positive sign (+), the lens is convex and corrects hyperopia (farsightedness). Convex lenses are thicker at the centre and thinner along the edges.
Cylinder (CYL) is the measurement in dioptres (D) of the cylindrical power of a lens. The CYL parameter applied to a prescription lens corrects for astigmatism. If you do not have astigmatism, the boxes on your prescription corresponding Cylinder (CYL) and Axis (AXIS) should be specified as 0 (the default parameter).
Axis (AXIS) is a parameter filled out in a prescription with CYL to provide the necessary lens values to correct for astigmatism.
AXIS values range from 0 to 180 degrees.
Anti-reflective coating allows for clearer vision. The coating covers the lens with a series of anti-reflective layers that allow almost all light to pass through the lenses, thereby eliminating most glare and reflection. The coating is recommended for all prescription glasses.
Mid and high-index lenses are more comfortable and fashionable than standard lenses, due to their reduced thickness and weight. Additionally, when a prescription is particularly strong, mid or high-index lenses are necessary, since the required thickness of a standard lens would make it impossible to fit properly into the frame.
