My Online Glasses Do Not Work – Why?

April 21st, 2009 by andum | Posted in Buying Online, Save Money, Vision Care, Wealth Enjoyment, Wealth Preservation

photo credit: net_efekt

Some visitors have found my previous post on buying eyeglasses online because they were searching for help in figuring out why they could not see with the glasses that they had purchased online or they wanted help with measuring their PD.  In this post I will list some of the reasons why your vision might not be best with your new glasses and help you troubleshoot.  I also have included some links at the end of this post that will help you measure your PD accurately.

Before you read further … it is always a good idea to figure out if your vision is poor with one or both eyes.  To check this, alternately cover each eye and compare the vision with each eye while looking at distance or near – where ever you may be having a problem.

Prescription is Not Correct

Consider this a possibility if the new pair of glasses is your first pair with the new prescription.  If there was an error in determining your prescription or when writing it down, it is more likely that one eye is wrong than both eyes.  If you suspect that the prescription is wrong, you will have to return to the eye doctor that provided you with the new prescription or find a new doctor.

Glasses Not Made Correctly

Eyeglasses sold in the United States have to be prepared to documented accuracy standards.  Of course, people make mistakes when fabricating glasses that are not caught during the inspection process or purposely release the glasses thinking that the error is either not significant or will not be noticed by the patient.  It is more likely that the error will be made with one lens rather than both lenses.  One way to check this error is to find an optician or eye doctor’s office with a dispensary and ask them to verify the glasses against the prescription.  I would suggest that you return to the doctor’s office that provided you with the prescription – they might not like that you did not buy your glasses from them but they will still want you as a patient.

Distance PD is Not Correct

The PD is the measurement that specifies the point in the lens that you will be looking through when looking straight ahead.  Since the PD is not routinely provided with your prescription, many patients will have to figure out how to measure their own PD in order to complete the prescription (see links below).  I reviewed the difficulty in getting this correct in my earlier post linked above.   Please note that this is an issue more likely to effect patients with higher prescriptions or when ordering no-line bifocals.  To summarize, errors can occur when measuring your PD, in fabrication or when the PD for each eye is not identical and the online form assumes that the PD for each eye is equal.

Here is one way for you to check to see if the PD is incorrect.  Cover one eye and look a little bit to the left and then right and see if your vision improves.  If it does, this may mean the prescription is correct but the PD is wrong for one or both eyes.  If your vision does not improve, either re-measure your PD and compare against the values that you provided when ordering the glasses or have the PD of your glasses verified.

Near PD is Not Correct

The near PD is used when ordering reading glasses.  If you have ordered reading glasses and you have a high prescription and you have provided your distance PD, then you will not be looking through the optimal point of the lenses.  On average the near PD is 1.5 mm less than the distance PD for each eye or 3 mm for both eyes (binocular).  Most bifocal eyeglass orders do not require a near PD.

Fitting Height is Wrong

This only applies if you have purchased bifocals.  It is somewhat easy to check and see if the fitting height is incorrect – simply move your head up and down and see if your vision improves.  If your vision improves when tilting your head down, the fitting height is too high (number too big).  If your vision improves when you tilt your head back, then the fitting height is too low (number too small).

PD Measurement Links

Although most of the online eyeglass retailers provide assistance in measuring your PD, not all provide a method that is very accurate.  Below is a link for printing your own millimeter ruler and two links to help your friend measure your PD (I don’t recommend trying to measure your own PD).  I suggest that you follow the directions in both links and compare the results.

• printable millimeter ruler
• good description for having friend measure PD
• near PD measurement method – add 3 mm for distance PD

I have reviewed some of the more common reasons  for having trouble with new eyeglasses – there are others.  If you have questions or want advice, please post a comment and I will reply as soon as possible.

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