How to select correct contact lens?

Question

I have hetherto consulted many Ophthamologists. Some doctors advise to buy the contct lens of the same number as the spectacles are. On the other hand, some other doctors advise to buy contact lens of 0.25 less degree of the numbers specified for the spectacles. Can please anybody guide me the correct method? I am confused.

Answer 1

I don't know the ins and outs, but contacts are DIFFERENT prescriptions to your glasses, because glasses sit further from your eyes, therefor you are looking from a different view point. Make sure you don't get the same prescription, as you'll have fuzzy vision and it might end up giving you headaches or a squint.

Answer 2

It's nothing like as simple as that, and in any case that should be done for you by the person providing your contact lens Rx

A spectacle Rx is not a contact lens Rx. They may be the same, similar or distinctly different in their optical power in individual cases, and the contact lens Rx should also specify the lens parameters (often by brand and type) as the material and other non-optical details can sometimes appreciably affect the final effective Rx.

At the bottom of the page below is a vertex chart, showing a guide (usually but not always valid) to the power equivalent between spectacle and contact Rx's.

If the spectacle Rx is +5.00, tested at 12mm from the eye, the contact lens equivalent is: +5.25. If -5.00 it is -4.75.
If the spectacle Rx is -8.50, the correct lens will be -7.75 or -7.50 depending on vertex distance.
(and that can easily be more than 13, causing a greater disparity!)

With high power lenses, the final Rx should always be determined with an over-refraction of lenses of the right type and approximately correct power.
(often the patient's existing lenses, if they are not so old or fouled as to make their effective power uncertain!)
Anything else is guessing. Informed guessing, perhaps, but guessing.