Some years ago there was a rush by website developers to offer online spectacles and we often get asked why we don’t have an online spectacle shop as well. The answer is quite simple, one of the most fundamental parts of getting accurate spectacles made is the facial measurements and we can’t get those via an online shop. Our primary concern is the accuracy and suitability of your spectacles so that you maintain good ophthalmic health and functional vision.
In order to make a functional pair of spectacles there are several key components:
- Lens design
- Facial measurements
- Fitting compensations
No matter how sophisticated the system may be for a website they will never be able to deal with the last two points, most websites claim that they can deal with the frame fitting as well, but this is really only something that can be done ‘face to face’. In fact, even the lens design is nearly impossible to get perfect without having a detailed discussion with the patient, so let’s be frank, all an online seller of spectacles will be able to do is make something that duplicates your prescription without any regard to usage or appropriateness (we’ve checked, and they even have a disclaimer saying that their spectacles are not guaranteed to be usable!).
In order to correctly select and fit a spectacle lens to a frame we need to know the dimensions of the patients face and relative eye positions, and no, that is not just the ‘PD’. There are also heights, vertex distance, tilt, working distance and so on. What they determine, indeed what is most important, is the centre of rotation of the eye. This is vital to position the lens correctly so that the patient does not experience unwanted aberrations. It is also impossible to obtain these various measurements without either a great deal of skill or specialised equipment. None of these measurements are possible via an app and most certainly can’t be obtained in the absence of the frame!
Once this information has been determined the practitioner will make compensations to the measurements to ensure that the lenses present precisely the same powers to the eye as were measured by your Optometrist in the eye test. Patients are often amazed by the large impact that a tilt or shift in centration can have on their perception of the world and it is this role that your practitioner plays almost unseen to the public, the interpretation of the prescription.
This is why many practitioners decline to offer facial measurements to their patients when asked, it is not meant as an insult, rather it is an indicator of their level of concern for your ongoing optical health.
With ever greater advances in lens design these measurements become increasingly vital, in some cases an error of even 1mm will render your lenses effectively useless. Going online means that you may be getting far less than you paid for.
For further information on public policy on this and other issues relating to Optometry please visit the following sites from Optometry Australia