What are lenticular lenses?
You may have seen lenticular lenses and not known what they are. From the outside, they look like clear fried eggs, with a flat disk for most of the lens but a round bulge in the middle. This creates a kind of 3D effect, which might make a person's eyes seem really big from some angles and reflect light in odd ways from others. These are actually really cool pieces of technology, and the science behind them goes pretty deep. They're also pretty helpful for people with serious vision issues. So, let's take a look (if you'll pardon the pun) at lenticular lenses, learn how they work, and get a feeling for why your eye care professional might say you need them.
Introduction to lenticular lenses
The word lenticular means, basically, bean-shaped. The defining feature of lenticular lenses is the large, bean-shaped bulges in the middle of them. These are helpful for people who can't focus up close, but they also have some pretty cool effects for camera work and special effects in movies. The key to the whole design is those center bulges. To understand why they have these, it's helpful to dip into the physics of light and the way lenses work generally.
The science behind lenticular lenses
Your eyes have natural lenses that bend light into a tight focus. The place where the images have the least blur is called the focal point, which should be right on the light-sensitive part of your eye, called the retina. When your eyes' lenses are focusing too near or too far to make that target, you might need contact lenses or glasses to correct the issue. People who can see things far away but struggle to see up close are said to be farsighted, which happens when your lenses' focal point is behind the retinas.
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Principles of lenticular lens technology
Lenses can be ground so they bend light a lot, which is called having a high refractive index. This pulls the focal point forward, hopefully onto your retinas and back into clear-vision territory. If you need more than a little bit of correction, the glass usually has to get thicker. There's an upper limit to this, since the bridge of your nose can't carry unlimited weight from ultra-thick lenses. So the compromise is to make most of the lenses thin and light, but with a low refractive index, and just bulge out the middle part to pull focus the way you need for reading.
Construction and composition of lenticular lenses
In a perfect world, your lenses would just be ground in such a way that their refractive index varies continuously across their entire area. This really can't be done, though, since a single piece of glass will have basically one refractive index. To get variable indices, lens makers have to layer multiple sheets of glass (or acrylic), each with its own index. This gets complicated fast, so for people whose only issue is seeing up close, it's usually easier just to make regular glasses with no prescription, then drop the bulgy lenses in the middle of them, right at the point you look through to read, sew or do other close-up work.
Are lenticular lenses the same as bifocals?
In practice, lenticular lenses act a lot like bifocals. In traditional bifocals, you've got regular glasses to help you see things at a distance, then a little area in the lower part with a higher refractive index for reading. This may be an obvious section that's visible to others, or the area might be blended a bit to conceal the second lens.
The blending option really isn't there for lenticular lenses. The bean in the middle has to have a really high index for really serious farsightedness, so it usually has to be big. The person wearing the glasses might not even need help seeing things far away, so the rest of the lens can usually just be low-index glass. So while they might do double duty as sort of extreme bifocals, it's just as likely your lenticular lenses only have one prescription and only help with close-in focus.
Do you need lenticular lenses?
If you have moderate to severe farsightedness, you might be a good candidate for wearing lenticular lenses. Only a trained professional can diagnose your vision issues, and that is only after a proper eye exam. If you have any issues with seeing at all, or even if you're not sure, schedule an eye exam when you can and make it part of your annual health checkup routine. You'll be glad you did.
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FAQs
What's the difference between traditional and lenticular lenses?
Traditional eyeglass lenses have a relatively low refractive index that's the same across the whole lens. Bifocals and trifocals may have small areas where another lens has been added for better focus. Lenticular lenses are like normal glasses, or might even have no prescription at all in most of the lens, but with a center area that bulges out and has a high index for focusing up close.
How durable are lenticular lenses?
Lenticular lenses are made from the same glass or acrylic as other glasses, so they scratch and crack in basically the same way if they're not treated right. The thick central part is actually a little tougher than regular glasses, if only because it's thicker. Still, take good care of your glasses no matter how they're made.
Can you get lenticular lenses in any frames you want?
Usually, yes. It should be no problem to fit new lenses into any frame you want. There's an "if" there, though. When you get your eye exam, your eye care professional should tell you if your lenses have any limitations on frames. Most of the time, you can just pick new frames and still get the look you want.