If you select a prescription lense in your order, you will need to complete the prescription form in the product details. Your prescription must be written by your doctor. Your prescription provides your doctor’s (an ophthalmologist or optometrist) advisement for clear vision. It specifies the refractive power needed in eyeglasses to correct blurred vision due to ailments such as myopia, hyperopia, astigmatism and presbyopia. Blurred vision is the result of light incorrectly focused on the retina. The hardening of the lens in your retina is a continuous process, not something that suddenly happens in middle age. It has been occurring your entire life. However, it is around 40-45 when the process progresses to the point where it interferes with reading. Most people need glasses for reading starting around 40-45 years old.

Your prescription is typically measured by a phoropter or an automated refractor.
CYL (cylindrical): astigmatism correction by adding or subtracting strength along the horizontal axis, the vertical axis or a diagonal axis. Sometimes doctors indicate a plus or minus value. The plus value magnifies an object and the negative value reduces it. A cylindrical correction assists reading wide columns of print because the surface of the lens magnifies only height and not width. The CYL puts an optical system in focus and reduces blur in only one direction. Sometimes this part of the prescription is blank.

SPH (spherical): correction by adding or subtracting the same refractive strength along both the horizontal and vertical axis; considered the overall power. The positive and negative powers magnify and reduce objects as mentioned above. The ailment is equally blurred vision in all directions.

DV (distance vision): the part of the prescription designed primarily to improve far vision. In a bifocal lens, this generally indicates what is to be placed in the top segment. For most people under forty years of age, this is the entire prescription.

NV (near vision): indicates reading work. some doctors will write the reading prescription separately, in its entirety. If this is the case, enter the power in the BOTTOM half of the form only. Sometimes NVO is written for near-vision-only and your doctor is recommending “reading-only” glasses.

OD (oculus dexter): right eye

OS (oculus sinister): left eye

OU (oculi uterque): both eyes

X (axis): is the horizontal, vertical or diagonal angle of the cylindrical correction. The axis is measured in a clock face that starts with zero degrees in the 9 o’clock direction, and increases through 90 and 180 degrees in a counter-clockwise direction. The total power of a CYL lens varies from along it’s main axis to its maximal value along the axis 90 degrees away. The total power of a lens with a spherical and cylindrical correction changes accordingly: along the axis specified on the prescription it is equal to the value listed under “spherical”, and it reaches the sum of “spherical” and “cylindrical” along the axis perpendicular to the one listed on the prescription. Written in a prescription X 90 means Axis 090.