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Contact Lens Prescriptions 

The prescribing of contact lenses is usually restricted to appropriately qualified eye care practitioners. In countries such as the United States (where all contact lenses are deemed to be medical devices by the Food and Drug Administration), the United Kingdom and Australia, optometrists are usually responsible. In France and eastern European countries, ophthalmologists play the major role. In other parts of the world, opticians usually prescribe contact lenses. Prescriptions for contact lenses and glasses may be similar, but are not interchangeable.

The practitioner or contact lens fitter typically determines an individual's suitability for contact lenses during an eye examination. Corneal health is verified; ocular allergies or dry eyes may affect a person's ability to successfully wear contact lenses. Especially above the age of 35 years dry eyes often makes wearing contact lenses too risky, especially soft lenses.

The parameters specified in a contact lenses prescription may include:

Material (eg. Oxygen Permeability/Transmissibility (Dk/L, Dk/t), water content, modulus)
Base curve radius (BC, BCR)
Diameter (D, OAD)
Power in dioptres - Spherical, Cylindrical and/or reading addition)
Cylinder axis
Center thickness (CT)

Many people already wearing contact lenses order contact lenses over the internet at their own risk. It is also possible to convert the power of a glasses prescription to the power of contact lenses with the following formula:


d is the distance of the glasses to the eye and
F = 1 / D are the focal length of the contact lens and the glass,
D is the lens power in diopters.
The formula above is implemented in this online calculator.

The Fairness to Contact Lens Consumers Act, which became law in February, 2004, was intended to ensure the availability of contact lens prescriptions to patients. Under the law consumers have a right to obtain a copy of their contact lens prescription.