Need to convert your contact lens prescription to glasses? It's very simple to do. First note that below -3.50 diopters you don't need to make any changes to the diopters between glasses and contact lenses. So a -4.00 glasses prescription is roughly equal to a -3.75 contact lens prescription.
Is my contact lens prescription the same as my glasses?
Contact lens prescriptions and eyeglass prescriptions are not the same. They are significantly different because eyeglass lenses are positioned approximately 12 millimeters from your eyes, whereas contact lenses rest directly on the surface of your eyes.
Can I use my contacts prescription for glasses?
The answer is no. While they both have the same objective — to correct what eye doctors call “refractive errors” that prevent you from seeing correctly — prescriptions for eyeglasses and contact lenses are distinctly different.