How to read your optometrists Contact Lens Prescription
You will find various parameters on your prescription, outlining the refractive powers for your eyes. The are 2 specific parameters that refer to your eyes: "OD" (Right eye) and "OS" (Left eye).
Base Curve or (BC)
The base curve measures the millimeters needed to fit in with the backside of the eye and its curve.
To increase wearing comfort of the contact lens, and to allow for tear and oxygen exchange, its matched with your cornea (front surface of your eye). Usually contact lenses range from 8 to 10 millimeters.
Diameter or (DIA)
The diameter measures the axial distance of the lens in millimeters and determines the contact lens resting place on the edges of your eye.
Refractive Power or (PWR)
This parameter is measured in units of dioptre. The number outlines the corrective refraction neccessary to restore the person´s 20/20 or normal vision.
You might see that there is a + or a - in front of the number, specifying nearsightedness or farsightedness.
The lower the number, the steeper the curvature of your eye´s cornea.
Cylinder (CYL)
The cylinder expresses the degree of astigmatism in dioptre. If you are astigmatism patient, you will see a value in this field of your contact lens prescription.
The cylinder (CYL) of a contact lens is shaped to correct the astigmatism by eliminating the curvature caused by it.
You may find a + or – sign in front of the value on your prescription. A negative value means you are nearsighted and a positive value means you are farsighted.
The value is a means of expressing the corrective power need to re-establish normal vision.
Axis
The axis is measured in degrees between one and 180 and expresses no cylinder value for correction of astigmatism. Half of 180 degrees, 90 references the vertical zenith of the eye and 180 refers to the horizontal zenith of the eye. The axis is the contact lens vertex 90 degrees distant to the vertex of the cylinder (CYL).
Add
Add power is prescribed for patients with bifocal contact lenses having difficulties seeing close objects like reading books and is meant to correct the effects of presbyopia. The value that you may see in your prescription is always a positive one and between 0.75 dioptre and 3 dioptre and both eyes are marked the same value.
Color
In case you are prescribed colored contact lenses, your color will appear in this field of your contact lense prescription.
Brand
The brand name of your prescribed contact lens.
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