What’s in a Prescription?

It seems like contact lenses and glasses would use the same prescription. After all, the idea is that your eyes don’t see quite right, so you use a lens to change the view, and then you see clearly, right? Well, the two prescriptions are quite different. Few patients check the numbers or notice any change during the exam process, but the prescriptions are not the same because of where the lenses sit in relation to your eye.

The lens of your glasses rests about twelve millimeters from your eye. Contact lenses, on the other hand, are placed directly on the surface of your eye. Why would this make your prescription different? Well, think about holding a magnifying glass out in your hand. When you hold it far away and look through, the view you see is much different than if you try to hold the magnifying lens up close to your eye. The same principle is in play when you consider glasses in contrast to contact lenses.

Not all contact lens prescription powers are drastically less than the glasses prescription for the same person, but usually the power used for contact lenses is less. In addition to the powers being different, our doctors will need some additional measurements to evaluate you for contact lenses because the specifications for fitting contact lenses is much more involved than the prescription for glasses.

Specifications include an accurate eyeglass prescription compensated accordingly for contact lenses; corneal curvature measurements; dimensions and curvature of the contact lenses themselves, and assessment of the correct brand of lenses that will work best for you.

Please ask us if you have any questions about your prescription or are considering contact lenses.

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