Eyeglass Lens Materials: What Makes Lenses Thick + Which Is Best for Your Prescription
When you’re buying eyeglasses, the lens material matters way more than you might think—it affects how thick your lenses are, how comfortable they feel, and even how safe they are. But with terms like “refractive index” and “polycarbonate” thrown around, it’s easy to get confused.
We’re breaking this down simply: first, what causes lenses to be thick (and how to fix it), then the most common lens materials—their pros, cons, and who they’re best for. No jargon, just straightforward advice to help you pick the right lenses.
4 Key Factors That Make Eyeglass Lenses Thick
Lens thickness isn’t random—it’s determined by four things. Knowing these helps you choose lenses that feel light and look sleek, even with a strong prescription.
1. Lens Power (Your Prescription Strength)
This is the biggest factor.
Nearsightedness (myopia): Lenses are “concave” (thicker at the edges, thinner in the center). The stronger your prescription (e.g., -5.00 vs. -1.00), the thicker the edges will be.
Farsightedness (hyperopia): Lenses are “convex” (thicker in the center, thinner at the edges). A stronger prescription (e.g., +4.00 vs. +1.00) means a thicker center.
In short: The worse your vision, the thicker your lenses will be—unless you choose a high-refractive-index material (more on that next).
2. Lens Diameter (Tied to Your Frame Size)
Lens diameter is directly linked to the size of your frames. Bigger frames mean bigger lenses, and bigger lenses = thicker edges (for myopia) or thicker centers (for hyperopia).
Pro tip: If you have a strong prescription, skip oversized frames. Smaller, more compact frames let your optician cut smaller lenses—resulting in less thickness.
3. Lens Shape (Concave vs. Convex)
This ties back to your prescription:
Myopia = concave lenses (thick edges, thin center).
Hyperopia = convex lenses (thick center, thin edges).
You can’t change this—your prescription dictates the lens shape—but you can choose a material that minimizes thickness.
4. Refractive Index (The Factor You Can Control)
Refractive index is the “secret weapon” for thin lenses. It measures how much light bends when passing through the lens.
Higher refractive index = thinner lens (for the same prescription).
Lower refractive index = thicker lens.
Common indexes you’ll see:
1.50 (standard plastic, CR-39)
1.586 (polycarbonate)
1.595 (polyurethane)
1.70 (high-index glass/plastic)
For example: A -5.00 myopia prescription in 1.50 index will have thick edges, but the same prescription in 1.70 index will be noticeably thinner.
Common Eyeglass Lens Materials: Pros, Cons & Who They’re For
There are two main categories: glass (traditional, less common) and plastic (mainstream, more versatile). Here’s how they stack up.
1. Glass Lenses (Traditional, But Rare Now)
For centuries, glass was the only lens material—but it’s been overtaken by plastic for good reason. Most modern glass lenses are made from crown glass, a durable type of optical glass.
Pros
Minimal color distortion (called “chromatic aberration”): Great for people who need precise color vision (e.g., artists, graphic designers).
Super scratch-resistant: Won’t get scuffed easily, even with daily use.
High-index options: 1.70 index glass is ultra-thin for strong prescriptions.
Cons
Heavy: Glass lenses are twice as heavy as plastic—wearing them all day can leave red marks on your nose.
Shatterable: Drops or impacts can break the glass, risking eye injury.
Who They’re Best For
Only people who prioritize perfect color accuracy over comfort and safety. Most people (especially kids and active adults) should skip glass.
2. Plastic Lenses (The Mainstream Choice)
Plastic lenses are lightweight, affordable, and safe—they’re the go-to for 90% of people. There are two main types: standard and high-refractive-index.
A. Standard Plastic (CR-39: Columbia Resin-39)
This is the “basic” plastic lens—used for mild prescriptions.
Pros
Lightweight: Half the weight of glass, so they won’t weigh down your nose.
Good scratch resistance: More durable than high-index plastics.
Affordable: The cheapest plastic option, great for budget shoppers.
Cons
Low refractive index (1.50): Lenses get thick fast with strong prescriptions (e.g., -3.00 or +3.00 and above).
Who They’re Best For
People with mild prescriptions (myopia/hyperopia under -3.00/+3.00) and anyone who wants an affordable, low-maintenance option.
B. High-Refractive-Index Plastic (For Strong Prescriptions)
These are designed to fix the “thick lens” problem for people with strong vision needs.
i. Polycarbonate (Refractive Index: 1.586)
Polycarbonate is the most popular high-index material—it’s a favorite for kids and athletes.
Pros
Thin and lightweight: Cuts down on edge thickness for myopia (or center thickness for hyperopia).
Shatterproof: Impact-resistant, so it won’t break if dropped (safe for kids and sports).
UV protection: Blocks 100% of harmful UV rays (no extra coating needed).
Cons
Slight image distortion: Some people notice mild “aberration” (blurriness around the edges of the lens) at first.
Softer than CR-39: More prone to scratches—you’ll need an anti-scratch coating.
Who They’re Best For
Kids, athletes, people with strong prescriptions (-4.00/+4.00 or more), or anyone who wants durable, thin lenses.
ii. Polyurethane (Refractive Index: 1.595)
Polyurethane is similar to polycarbonate but with a slightly higher index.
Pros
Even thinner than polycarbonate (for the same prescription).
Lightweight and impact-resistant: Same safety benefits as polycarbonate.
Cons
Same distortion and scratch issues as polycarbonate.
Slightly more expensive than polycarbonate.
Who They’re Best For
People with strong prescriptions who want lenses a little thinner than polycarbonate, and don’t mind the extra cost.
iii. High-Index Specialty Glass (Refractive Index: 1.70)
This is a hybrid: it’s glass, but with a high refractive index to keep lenses thin.
Pros
Ultra-thin for very strong prescriptions (-6.00/+6.00 or more).
Better scratch resistance than polycarbonate or polyurethane.
Cons
Heavier than plastic high-index lenses: Still feels bulkier than polycarbonate.
Breaks easier than plastic: Not as safe for kids or active use.
Who They’re Best For
People with extremely strong prescriptions who need the thinnest possible lenses, and don’t mind the extra weight.
FAQ: Choosing the Right Lens Material
Q: Which material is best for high myopia (strong nearsightedness)?
A: Polycarbonate (1.586) is the best balance of thinness, lightness, and safety. If your prescription is over -8.00, go for 1.70 high-index glass or plastic.
Q: Are high-index lenses worth the extra cost?
A: Yes—if you have a strong prescription. For mild prescriptions (under -3.00), high-index lenses won’t make a noticeable difference, so save your money on CR-39.
Q: Do I need an anti-scratch coating?
A: Yes—for polycarbonate or polyurethane. These materials are soft, so scratches show easily. CR-39 and glass lenses don’t need it as much (they’re more scratch-resistant).
Q: Can kids wear polycarbonate lenses?
A: Absolutely—they’re the safest choice for kids. Polycarbonate is shatterproof, so it won’t break if your kid drops or throws their glasses.
Final Tip: Match Material to Your Needs
The best lens material depends on three things:
Prescription strength: Mild = CR-39; Strong = polycarbonate/high-index.
Lifestyle: Active/kids = polycarbonate (shatterproof); Artists = glass (color accuracy).
Budget: CR-39 = cheapest; 1.70 high-index = most expensive.
Don’t let thick lenses hold you back—with the right material, even strong prescriptions can feel light and look sleek. Talk to your optician about your needs, and they’ll help you pick the perfect fit.
