by Jamie Bartlett January 29, 2021 4 min read
Avoid the inspector look.
Instead of weirdly magnifying your eyes, choose lenses which flatter them.
This guide explains the differences of aspheric, spheric and high index lenses to help you decide which are best for you.
Aspherical spectacle lenses use varying curves across their surface to reduce bulk and make them flatter in their profile. Spherical lenses use a singular curve in their profile, making them simpler but bulkier, especially in the centre of the lens.
Example of a + (convex) shaped lens for correcting hyperopia (far-sightedness) in both a spherical and aspherical profile. Notice the flatter and thinner shape of the aspherical lens using the varying curvatures.
Aspheric lenses are beneficial if you require more than +/- 4.00 dioptres in your prescription.
Far-sighted (+) spectacle lenses are thickest at their centre; therefore, the flatter aspheric profile is much more flattering on your eyes.
Great news if you have a strong + prescription.
Flatter and thinner aspheric lenses will fit a broader variety of frames, giving you more choice for your next pair of glasses.
Inversely, near-sighted (-) spectacle lenses are thickest at their edges. This doesn’t mean that aspheric lenses aren’t for you.
They’ll still reduce edge-bulk and appear flatter than a spheric equivalent. Ideal for reducing the weight of your lenses overall.
Thanks to their clever curves, aspheric lenses reduce the aesthetic magnification of your eyes for a more natural sort of look.
No inspector glasses for you.
If you’re far-sighted, this is especially helpful as your lenses are thickest in their centres.
If your prescription is fairly mild, say less than + / - 2.75 dioptres, aspheric lenses won’t be that much thinner.
However, they’ll look flatter and sleeker.
I like your thinking.
Simply put, high index lenses refers to it's thickness, whilst spheric or aspheric lenses refers to it's profile.
Delving deeper, here's the geeky bit...
Refractive index denotes a lenses' efficiency at bending light. The higher the refractive index, the better it bends light, the thinner a lens can be.
In a strong prescription, 1.67 high index lenses will be thinner than 1.50 standard index lenses.
With me so far?
Spherical or aspherical denotes the profile of a lens.
Spheric lenses use a single curve in their profile, whilst aspheric lenses use varying curves.
These varying curves make your lenses thinner and generally flatter which makes them look nicer and prevents your eyes being magnified.
Combining high index & aspheric.
Say you need +6.00 dioptre.
High index 1.67 lenses will be thin, but aspheric high index 1.67 lenses will be even thinner and look visually flatter.
As a rule of thumb, the stronger your prescription, the higher refractive index you’ll need.
For a guide on choosing lens indexes, check out my handy blog post.
Progressive (varifocal) lenses provide a spectrum of focal power from the top the lens to the bottom. This is achieved from varying curvatures and thicknesses within the lens, therefore they’re all considered as aspheric.
Double aspheric lenses (bi-aspheric) are designed for high - minus prescriptions which use aspheric curvatures on both their front and rear surfaces.
These lenses have an enlarged field of view which provides greater vision and reduced distortion at the edges of your lenses.
Slightly more costly than single aspherics, these lenses are even thinner and even lighter weight.
Ideal if you’re heavily near or far-sighted and your prescription is stronger than + / - 6.00.
For more information on double aspheric lenses, click here.
Aspheric lenses are more expensive due to how they’re made. Becuase they use more complex curvatures, aspheric lenses are more difficult to produce than spheric ones, hence their increased cost. (Around 20%.)
In 2022, 1.61 index, CR39 aspheric lenses cost approximately £40 including anti-scratch and anti-glare coatings.
For a personal quotation to suit your prescription and lifestyle, please get in touch.
If you have a strong prescription, aspheric lenses will be flatter and thinner than spheric ones. However, they’re more costly due to their more complicated production.
Aspheric versions of high index lenses are even thinner but have the aesthetic benefit of looking flatter and sleeker.
Aspheric lenses are approximately 20% more expensive than spheric equivalents, whilst double aspheric lenses are approximately 50% more expensive.
Aspheric lenses use varying curvature on the front of the lens to reduce bulk, whilst double aspheric lenses do this on both the front and the rear of the lens.
Aspheric lenses are more prevalent in high indexes such as 1.61, 1.67 and 1.74 designed to reduce thickness for strong prescriptions.
Aspheric lenses are commonly available in lightweight materials such as polycarbonate and Trivex, but can also be made from CR39 (regular lens plastic.)
As you can tell, there are a lot of options to choose from, so feel free to get in touch about your ideal set of lenses.
Hopefully you found this article useful.
Thanks for stopping by.
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