Spherical Contact Lens
A soft contact lens fitting takes into account your eyeglass prescription, the curvature of your cornea and tear film quality.
One difference in the prescription between glasses and contacts is the distance from the glasses to the eye is about 12 millimeters versus a contact lens that sits right on the eye. The doctor needs to account for that difference in the prescription. Oftentimes your contact lens prescription will have more plus in the numbers or account for a small amount of astigmatism in your eye.
The reason a contact lens prescription includes the brand is that each brand is made of a different plastic material that interacts with your tear film in a unique manner. For example, some brands are made to help with dry eye symptoms or help with symptoms of patients who are high depositors. Both problems need to be addressed by the doctor to help the contact lens wearer continue to use lenses safely.
Each different brand has a different curvature, diameter, and type of lens material that must work properly for the patient. That is why a contact lens prescription always includes a brand and prescription and it is not readily substituted without an Optometrist’s contact lens exam.