Thinner Vs. Thicker Lenses
When ordering your prescription lenses, you will often be asked what thickness you would prefer them to be. It can be a little complicated, so here's a quick breakdown of what the heck things like the refractive index are. Knowing this will give you a good idea of what you're actually spending your money on. If any of the following seems unclear, our in-house optometrists will happily answer any questions you may have over a remote consultation.
The majority of people who wear spectacles are short-sighted, with their spectacle lenses being thin at the centre and thickner at the edge. Long-sighted people require lenses which are thicker in the centre of the lens, and thinner at the edge.
Frustratingly, the higher the prescription, and the larger the size of the frame, the more thickness the lens edge (or centre) will have. This results in thicker, heavier spectacles.
If you chose a spectacle frame that has quite a chunky edge profile, then the chances are, they will mask the extra thickness of your lenses, however the overall weight could be uncomfortable on your face.
If your prescription is +/-2.25DS or above, you could benefit from having a higher index lens. These lenses are more dense, and are able to deliver the same prescription with a thinner lens profile. These lenses are also less heavy due to there being less overall material (applicable to plastic lenses, however this is not the case with glass which is more heavy).
Many of the high index lenses also have an aspheric design, which reduces the magnified eye look that higher, long-sighted prescriptions cause.
Standard, entry level plastic spectacle lenses are usually made from a material called CR39, and have a refractive index of 1.49. The higher the refractive index, the thinner the lens will be, and more expensive. It’s important to consider this, and discuss with your optician to understand which refractive index is most appropriate for your prescription, and the desired outcome you have.
As a general guide, you can reference the following for cosmetically appealing and lightweight lenses:
|Prescription (+/-)||Refractive Index|
|0.00 to 2.00DS:||1.50|
|2.25DS to 4.00DS:||1.60|
|4.25DS to 6.00DS:||1.67|
Please always consult an optician where possible however, as astigmatism can increase your lens thickness as well as flattening it, depending if you’re long or short sighted. Your optician can guide you through how your prescription will appear aesthetically in your chosen frame, and help you make a refractive index selection based on your needs and budget.
Now that you've got a better understanding about the thickness of prescription lenses, ordering a new pair of frames will be easier than ever!