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The degree from which you do not have normal vision, is normally measured in diopters. A diopter is usually represented by a capital “D” in a prescription. Normal vision is referred to as “plano”, often represented as “pl”. The greater the error, the larger the number for sphere and cylinder.

A typical optical prescription would look like:

      sphere  cylinder  axis
OD: -1.75    -1.25     x35
OS: pl          -1.75     x45

OD is an abbreviation for right eye.
OS is an abbreviation for left eye.
The first number is the sphere. A negative number indicates myopia (shortsightedness). A positive number indicates hyperopia (longsightedness).
The second number is the cylinder (astigmatism).
The third number is the axis of the cylinder component. This is the location of the irregularity. If the patient has no cylinder, then the last two columns may remain blank, or occasionally “DS”

This prescription shows that the patient has 1.75 diopters of myopia with 1.25 diopters of astigmatism at an angle of 35 degrees in the right eye, and the left eye is plano with 1.75 diopters of astigmatism at an angle of 45 degrees.

Below are some other terms you might see on optical prescriptions:

BC Inside curve of your contact lens (8.0, 8.1, 8.2, etc.)
Diameter Size of your contact lens (13.8, 14.0, 14.2, etc.)
Power [Pow] Strength of your corrective lens (-1.00, -2.75, +2.25, etc.)
Add Bifocal plus power for near distance (+1.00, +2.00, etc)

Our Prescription Swim Goggles are only suitable for those with Myopia (shortsightedness). We are unable to supply correction for Astigmatism.

Our Range of Prescription Swimming Goggles runs from -1.5 to -8.0 in 0.5 Diopter increments. You should choose the nearest diopter measurement for your particular prescription. If your Prescription is out by 0.25 diopters you should choose the next lowest lens. e.g., if your prescription is for -1.75 you should choose -1.5 instead.