The fun part! We're comparing the thickness of the center of the lens. Remember, minus prescriptions are thinnest at the center.

Eyeglass Tyler covers the highly technical topic of lens thickness; going over how we determined the thickness, what the thickness was in several points of the lens, then compares the weight of each lens.

To ensure consistency when possible, we measured lens thickness using the same frame and pupil distance (PD) measurement and a few different prescriptions.

As you can see from the graphic, with a -3 prescription the CR-39 lens is thickest but they're all fairly close. This is because impact-resistant lenses can go as thin as 1.5mm. Since CR-39 is not impact-resistant, the thinnest it can go is 2mm.

Before we get started, we also want to note that there are many variables that affect lens thickness, so we can only give a ballpark estimate on how thick your lens will be. However, knowing the trends that different lens materials follow is still a good rule of thumb to use.

Tyler was surprised to discover that the weight is pretty much the same across the board despite different prescriptions and lens materials. Aside from CR-39, which was slightly heavier, we can determine that weight isn't a huge factor in what lens material you pick.

One other thing to note is that we performed these tests with a cosmetic pair of eyeglasses, as opposed to a wraparound sports frame. Keep your eyes peeled if you love this technical stuff—we may repeat this experiment while accounting for a higher base curve!

You thought you'd have your hands full picking what sort of lens features you want, and now you have to pick a lens material too. What's up with that? Stick with us to learn more about the nitty-gritty of lens material thickness.

There's almost 1mm difference of thickness just between CR-39 and Trivex, and almost 2mm between CR-39 and High Index 174.

The + represents the geometric center, while * is the OC. Additionally, the placement of the E and e can change based on your prescription and axis, so they won't be in the same place every time. Essentially, this means that one side of the lens will be slightly thicker than the other.

1. What to Expect 2. The Setup 3. Prescription Thickness 4. Center Thickness 5. Thickest Edge 6. Weight 7. Tyler's Takeaway 8. Prescription Glasses at SportRx

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There's a pretty large difference of 2mm between the thinnest and thickest in this, but the others are still fairly close. However, many more comparisons to go!

Now we're comparing the thickest of the lens edges. As you'll remember from earlier, a minus prescription means the lens will have thicker edges.

We selected this frame because not only is it a great look, it has a fairly large lens and a square lens shape. These are both factors that influence the lens thickness as well.

As an optician for 15+ years and one with prior experience in a lens-making lab, Tyler's main takeaway from this comparison is that the weight of the lens will be pretty consistent no matter which lens material you choose.

Another important factor in prescription lenses is the OC, or ocular center. This refers to the clearest part of the lens and is based on your PD as well as the frame shape. Note that the OC rarely ends up in the "geometric center" of the lens, or what you can also think of as the true center point, as shown in the graphic below.

The field of view (FOV, also called angle of view) is the width of the scene that a camera detects on its sensor. It is determined by the focal length of the lens in relation to the sensor size. Longer lenses or smaller sensors produce narrower fields of view, while shorter lenses or larger sensors produce wider fields of view. A smaller field of view means that a camera is more “zoomed in” (to use a term that most people are familiar with). For example, a camera with a 90° horizontal field of view (HFOV) will see a 1000m wide section of a wall that is 500m in front of it. If you then adjust that camera’s HFOV to only 1°, it will fill the screen with an 8.7m wide portion of that same wall. This second “zoomed in” field of view is what customers are looking for when they want a camera that can see a long distance. They want a narrow field of view.

As you can see, CR-39 is the thickest again. Comparing this to the -3, we don't usually recommend a thinner lens material for a weaker prescription because it doesn't make much of a difference.

However, it's important to note that this blog post concerns itself primarily with lens thickness rather than the pros and cons of each material. There's no one material that's best for you, as it all depends on what you use your glasses for. Feel free to reach out to us if you have more questions on which type of lens you should get.

Again, our thickness measurements are only an estimate for your glasses because there are so many other factors that influence the exact measurements. Our examples are just to show general trends.

There is almost 4mm of difference between CR-39 and high index 174. From these examples, we can confidently determine that when dealing with a stronger Rx, lens material makes a huge difference.

You lose over 1mm of thickness from the lens by using a high index material, so though it's a difference, it's not huge.

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