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A Glasses Prescription is NOT a Contact Lens Prescription

A glasses prescription is NOT a contact lens prescription.

And I'm not just saying that so you have to hand over more money to receive your contacts RX.

Truthfully, the prescription for your glasses is similar, but is not the same as your eyeglass prescription.  Let's look at what's different:


Your glasses sit 12 mm from your eyeball. Your contacts sit ON your eyeball. Believe it or not, that makes a difference. The higher your prescription, the more the change in your glasses and contacts.


Not all eyeballs are the same size.  Some corneas curve more than others.  Getting the curvature of your eye correct does not just mean a contact that feels better, it also means a cornea that is less likely to have corneal damage.  A contact lens that is too tight can cause severe corneal issues especially if worn repeatedly.  These measurements, called the base curve (BC) and Diameter (D) are a vital part of your contacts prescription.  These are NOT measurements included on a glasses prescription.  

And how exactly is BC and Diameter determined? Initially, our technician or doctor guesses. That's right they GUESS. They make an EDUCATED GUESS, but they need to follow up to make sure they were right.  An experienced contact lens tech or doctor will be right more often than not, but each and every time the lens needs to be verified with a CONTACT LENS FITTING AND/OR FOLLOW-UP.  This is an exam where the tech or doctor quickly looks at your eye with your new lenses in to see how they fit.  This is best done after you've een wearing your lenses for a week or two because, just like a pair of new shoes, the lenses may appear to fit well initially, but after a bit of wear they can cause your corneas to swell or develop an ulcer.


Lenses that correct for astigmatism will also have a Cylinder and Axis measurement, like a glasses prescription.  This number may or may not change from your glasses prescription, but only actually wearing your lenses and having a follow-up will determine if the number your eyecare provider came up with is correct.

Contact lens prescriptions are not as easily determined as glasses prescriptions and the repercussions of a bad glasses prescription are not as serious as a bad contact lens prescription.  Determining a contacts prescription that is appropriate for YOUR eyes is time-consuming.  Your provider will guess on a lens based on your glasses prescription and then will order (usually) trial lenses, maybe several, for you to try out.  Your provider will want to see you for at least one follow-up before ordering your real lenses. 

Each of these appointments and the time to order and receive and calculate require an experienced provider, not just a front desk assistant.  In order to pay for the time and costs associated with contact lenses, a contact lens fitting and follow-up fee is generally charged. Not just from our office, but most eye doctor offices. Very few insurances cover these fees. Why? Because contacts are considered cosmetic and because insurance likes to pay for as little as they can. That's just how it is. We aren't trying to just get more money from you by charging you these fees. In fact, our office just barely breaks even on contacts related services. 


So now we've discussed the basics of contact lenses but we haven't talked about some of the problems that are related to contact lens wear. Come back next week and we'll talk about those issues.