The Complete Guide
to Thinner Lenses
Thick lenses are one of the most common concerns our patients bring to the dispensing table. This guide explains the science behind lens thickness, which materials genuinely make a difference, and — crucially — when upgrading to the highest index is worth the extra cost and when it is not.
The honest headline: Frame choice can reduce lens thickness more than changing from standard to ultra-high-index material. A strong prescription in a small, well-chosen frame will always beat the same prescription in a large fashionable frame — even with 1.74 ultra-high-index lenses. We cover both in full below.
Section 01
Why Lenses Get Thick
Every spectacle lens works by bending light. The stronger the bending required, the steeper the curvature — and steeper curves mean more material.
Minus lenses (short-sight)
Minus lenses are thin at the centre and thick at the edge. The thickness problem is at the rim — where the lens meets the frame. The higher the minus number, the thicker the edge.
They also produce a minification effect — the eyes appear slightly smaller than they are, more noticeable at higher powers.
Plus lenses (long-sight)
Plus lenses are thick at the centre and thin at the edges. The central dome is the problem — it adds unwanted weight and produces a "magnifying glass" appearance, making eyes look larger.
Varifocal wearers should note: your near ADD power adds to the effective plus power. A +2.00D distance prescription with a +2.50D add means the near zone is effectively +4.50D — relevant for thickness calculations.
The critical insight about frame size: The thickness of a lens grows with the square of the lens diameter. Doubling the width of a frame doesn't double the lens thickness — it quadruples the depth of curvature required. This is why a smaller frame is often more effective at reducing visible thickness than upgrading to a higher-index material.
Section 02
Refractive Index — What the Number Means
The refractive index (n) of a lens material determines how efficiently it bends light. A higher number means more bending per unit of curvature — so the same prescription can be achieved with a flatter, thinner lens.
| Material | Index | Abbe Value | Thickness vs 1.50 | Impact Resistance | Best For |
|---|---|---|---|---|---|
| Standard Plastic (CR-39) | 1.50 | 58 Excellent | — | Moderate | Low-moderate prescriptions; best optical clarity |
| Polycarbonate | 1.586 | 30 Poor | ~15% thinner | Very high | Safety/sport; where 1.67 not available |
| Mid-Index | 1.60 | 36–42 Good | ~20% thinner | Moderate+ | ±2.50D to ±4.50D; sweet spot value |
| High-Index | 1.67 | 32 Acceptable | ~30% thinner | Moderate | ±4.00D and above; most recommended premium step |
| Ultra-High-Index | 1.74 | 33 Acceptable | ~40% thinner | Low Fragile | ±7.00D and above only; full-rim frames only |
The Abbe Value — the trade-off nobody tells you about
The Abbe value measures chromatic aberration — how much the lens disperses different wavelengths of light, creating colour fringing or a subtle "rainbow" effect at the periphery of vision. A higher Abbe value means better optical quality and less fringing.
Key insight: Standard CR-39 at Abbe 58 is optically excellent. Ultra-high-index at Abbe 33 is noticeably lower. Most patients at moderate prescriptions don't notice this difference — but some do, particularly in peripheral vision. A knowledgeable independent eyewear studio considers both factors, not just thickness.
Real-world thickness: –6.00DS prescription, 50mm frame
Approximate values for a –6.00DS prescription in a 50mm round frame. Actual thickness depends on frame shape, optical centre placement, and minimum centre thickness.
Section 03
Which Prescriptions Benefit Most
Not every prescription gains meaningfully from high-index lenses. Here is an honest guide to where the upgrade genuinely makes a visible, worthwhile difference.
Clear Benefit
Moderate Benefit
Minimal Benefit
Section 04
Lens Materials — A Full Comparison
Each material has a specific profile of optical quality, thinning, impact resistance, and weight. The right choice depends on your prescription, your frame, and your priorities.
1.50 Standard Plastic — CR-39 Best Optics
The benchmark material — developed in the 1940s and still the optical quality leader. CR-39 has an Abbe value of 58, meaning chromatic aberration (colour fringing) is minimal. If optical clarity is the priority and the prescription is moderate, this is often the best choice.
It accepts all coatings beautifully — AR, photochromic, tint, and hardening systems are all optimised for CR-39. It is also the most cost-effective option.
1.586 Polycarbonate — Impact-Resistant, with Caveats Low Abbe
Polycarbonate originated in aerospace and engineering and is aggressively promoted in volume optical retail, particularly in the US. It is indeed impact-resistant and inherently UV-blocking, but its Abbe value of 30 is the lowest of all common lens materials — meaning it produces more chromatic aberration (colour fringing) than any alternative.
For patients with strong prescriptions or those sensitive to peripheral optical quality, this can cause asthenopia (visual fatigue). Polycarbonate remains the right choice when very high impact resistance is a genuine priority — such as for children, sport, or safety-critical prescriptions.
1.60 Mid-Index — The Overlooked Sweet Spot Best Value
Mid-index 1.60 is often overlooked in conversations about high-index lenses — patients tend to jump from 1.50 to 1.67. Yet 1.60 delivers approximately 20–25% thinning compared to CR-39, with an Abbe value of 36–42 that is significantly better than polycarbonate and acceptable for most wearers.
It accepts all major coatings and photochromic systems well, and it is available for both single-vision and varifocal lenses across Essilor's range. For prescriptions in the ±2.50D to ±4.50D zone, it often represents the best balance of thinning, optical quality, and cost.
1.67 High-Index — The Recommended Premium Step Most Recommended
1.67 high-index is the workhorse of premium thinning and the material we most commonly recommend for prescriptions above ±4.00D. It is approximately 30–35% thinner than CR-39 for the same prescription — a difference that is visible, meaningful, and consistently appreciated by patients who have previously worn standard lenses.
The Abbe value of 32 is lower than CR-39 but within the same range as 1.74 — it does not get worse as you go from 1.67 to 1.74. Anti-reflection coating is strongly recommended (Fresnel reflections from uncoated high-index lenses are visible at this level). Essilor Stylis 1.67 with Crizal coating is the standard recommendation here.
1.74 Ultra-High-Index — Maximum Thinning, Maximum Caveats High Rx Only
Ultra-high-index 1.74 delivers the maximum commercial thinning available — approximately 40–45% thinner than CR-39 at the same prescription. It is genuinely transformative for patients with very high prescriptions (above ±7.00D or ±8.00D) who have previously struggled with thick, heavy lenses.
However, it is also the most fragile of common materials, is denser (1.47 g/cm³ — meaning very thin lenses may not be much lighter than slightly thicker 1.67), and for prescriptions in the ±5.00D to ±7.00D range, the additional thinning over 1.67 is often only 0.5–1.0mm — barely perceptible. AR coating is not optional at this index.
Not suitable for rimless or drill-mount frames — the material is too brittle and will crack. Full-rim frames only.
Section 05
Aspheric Design — Beyond the Index Number
Changing the refractive index thins a lens by reducing the curvature needed. Aspheric design goes further — it changes the shape of the surface itself to reduce peripheral distortion and improve aesthetics.
Spherical lens
A spherical lens has a surface that is a section of a perfect sphere — uniform curvature across the entire lens. This works well at the optical centre but produces increasing distortion and aberration towards the edges.
For plus lenses, spherical designs create the classic "coke bottle" or "magnifying glass" appearance — thick central dome, magnified eye appearance.
Aspheric lens
An aspheric lens has a surface that gradually flattens from the centre to the periphery. This corrects the aberration profile across the full lens, producing sharper peripheral vision and a flatter, thinner lens profile.
For plus lenses: significantly reduced central dome, less eye magnification. For minus lenses: thinner edge, less minification. Most quality high-index lenses are aspheric by design — Essilor's 1.67 and 1.74 ranges are aspheric as standard.
Atoric design extends asphericity to astigmatic prescriptions — correcting aberration in both principal meridians, not just the sphere. This is particularly valuable for high cylinder prescriptions and is standard in Essilor's premium lens designs. For complex prescriptions, ask specifically about atoric design.
Section 06
Frame Choice — The Biggest Factor Nobody Mentions
Lens thickness grows with the square of the lens diameter. Moving from a 54mm frame to a 46mm frame on a –6.00D prescription can save more thickness than upgrading from 1.50 to 1.74 — at no extra cost.
Frame size recommendations by prescription
These are general guidelines — your dispensing optician will calculate exact blank requirements for your specific prescription and chosen frame.
| Prescription (Sphere) | Recommended Max Lens Width | Notes |
|---|---|---|
| 0 to ±2.00D | Any size | Frame choice driven by style; index makes little difference |
| ±2.00D to ±4.00D | ≤52mm | Benefits from mid-index; frame size critical |
| ±4.00D to ±6.00D | ≤50mm ideal | High-index and smaller frame work together for best result |
| Above ±6.00D | ≤48mm strongly advised | Smallest appropriate frame; high-index essential |
Frames that work well for thinner lenses
Frames that add thickness
Section 07
Coatings — Why AR is Non-Optional on High-Index
The higher the refractive index, the more light is reflected from the lens surface. Without anti-reflection coating, high-index lenses create visible ghost images and lose optical clarity.
| Material | Index | Reflectance (per surface) | Total (both surfaces) | Visible Effect Without AR |
|---|---|---|---|---|
| CR-39 | 1.50 | ~4.0% | ~8.0% | Minor ghost reflections |
| Mid-Index | 1.60 | ~5.3% | ~10.6% | Noticeable reflections |
| High-Index | 1.67 | ~5.9% | ~11.8% | Significant — AR strongly recommended |
| Ultra-High-Index | 1.74 | ~6.5% | ~13.0% | Substantial — AR is essential |
A 1.74 lens without AR coating reflects approximately 13% of incoming light — creating visible ghosting and making the eyes difficult to see through the lens. This is not a cosmetic preference; it is a functional necessity at high indices.
Essilor Crizal — the coating range we use
Crizal Forte UV
AR + UV back-surface protection + smudge/hydrophobic resistance. Our recommended standard for high-index lenses.
Crizal Prevencia
Blue-violet light filtering + full AR. Recommended for patients with significant digital screen exposure.
Crizal Drive
Optimised for night driving — reduces oncoming headlight reflections. Popular with high-index wearers who drive frequently.
Section 08
Is the Upgrade Worth It? An Honest Guide
We don't upsell upgrades that don't make a visible difference. Here is our honest assessment of each step up the index ladder.
Section 09
Common Questions
Questions we answer regularly about lens thickness and materials.
Will high-index lenses change my prescription?
Is 1.74 always the best choice?
Can I get thin lenses in rimless frames?
Are polycarbonate lenses the thinnest and safest?
Why does my optician always ask about my frame size when we're talking about lenses?
Expert Advice at Every Prescription
Whether your prescription is mild or very strong, we'll guide you to the right material and frame combination — and we'll only recommend an upgrade when it genuinely makes a visible difference.