Because a contact lens is a medical device and if it is not prescribed properly, you may not see well. Specially if it is made from a not well-suited to your eyes materials which can lead discomfort or inflammation or another problems that could result to permanent blindness.
Prescription contact lenses are valid for a minimum of one year or the minimum required by every state law whichever is higher. You cannot buy additional lenses until your Optometrists give you an updated prescription when your first prescription given expires. You have the right to get a copy of your prescription after you undergo the eye examination.
The parameters specified in a contact lenses prescription may include:
1. The Materials Used.
a. Soft contact lens- are made of pliable hydrophilic plastics called hydrogels and can be processed by either a lathe cutting process or an injection molding process.
b. Rigid gas permeable contact lens- are made of oxygen-permeable plastic polymers containing silicone and fluorine.
2. Base Curve Radius. It is a parameter of a contact lens that show how much the lens should curve to match your cornea’s back curvature. Contact lenses must fit well to the wearer’s cornea in order to be comfortable and to facilitate tear exchange and oxygen transmission.
3. Diameter. It is how far in millimeters it is across the lens from one edge to the other.
4. Power in dioptres – Spherical, Cylindrical and/or reading addition.
5. Cylinder Axis. This is necessary if your lens correct for astigmatism.
6. Center thickness (CT)
7. Brand. Prescription contact lenses may indicate a specific brand.