Optician's Companion
Yamout Optical Center
Lens Thickness Estimator
Quick professional estimator (single-vision). Use for counselling, frame selection, and index recommendation.
How the estimator works (simplified) +
Uses effective diameter + sag approximation. Final thickness depends on design, base curve, edge polish, and lab minimums.
Decentration per eye ≈ ((A + DBL) − PD) / 2
Effective diameter ≈ A + 2×decentration
Sag (approx) increases with power and diameter, and decreases with higher index.
Quick Rules
Smaller + rounder = thinner edge Core optics +
For minus lenses, thickness increases with distance from the optical center. Round/oval shapes keep the edge closer to the pupil and reduce corner thickness.
PD matching reduces thickness +
PD mismatch forces decentration. More decentration = larger effective diameter = thicker edges for minus lenses.
Rimless rule (no 1.50 / 1.56) +
Rimless: use 1.60 (MR-8), 1.67 (MR-10), or Trivex. Avoid 1.50/1.56 (cracks at drill holes).
Aspheric rule (OC height) +
Most 1.67 / 1.74 are aspheric. You must measure OC height (even SV) or the patient may report blur/“weird sides”.
- Adjust frame to final fit first.
- Mark pupil center on demo lens.
- Measure height from bottom to pupil mark.
- Order with that exact height.
Abbe value (clarity vs thinness) +
High Abbe = crisper peripheral vision. Low Abbe = more color fringing off-axis.
Common counseling: upgrading from 1.50 to 1.67 may look thinner but can feel “colored” on the sides (normal physics).
Example Case: −4.00 Sphere (Reference)
Input Parameters (example): Sphere: −4.00 | Frame Width: 50mm | PD: 62mm (Assuming bridge 18mm and CT ~1.5–2.0mm depending on material)
| Index | Material | Est. Edge Thickness | Weight/Profile | Result Analysis |
|---|---|---|---|---|
| 1.50 | CR-39 Plastic | ~5.1 mm | Standard | Too thick Lens will protrude significantly. |
| 1.56 | Mid-Index | ~4.3 mm | ~15% thinner | Okay Budget option, optics lower quality. |
| 1.60 | MR-8 High Index | ~3.9 mm | ~20% thinner | Excellent Great balance of optics and thickness. |
| 1.61 | High Index | ~3.8 mm | ~22% thinner | Excellent Very similar to 1.60. |
| 1.67 | Ultra High Index | ~3.4 mm | ~30% thinner | Very thin Best aesthetic for this power. |
| 1.74 | Super High Index | ~3.0 mm | ~40% thinner | Overkill Expensive; diminishing returns at −4.00. |
Summary recommendation for −4.00+
Full rim (acetate/plastic): Use 1.60 or 1.56. Rim hides thickness; no need to overspend on 1.67.
Thin metal / semi-rimless: Use 1.60 (MR-8) or 1.67 (cosmetics + groove resistance).
Rimless (drill mount): ONLY 1.60 (MR-8), 1.67 (MR-10), or Trivex. Avoid 1.50/1.56.
Comprehensive Index Guide & Usage Rules
Technical breakdown: recommended power ranges and frame compatibility.
1.50 Index (Standard CR-39)+
The info: Excellent optical clarity (high Abbe) but thickest/heaviest.
Recommended power: 0.00 to ±2.00
- ✅ Full rim: Yes
- ❌ Semi-rimless: No (chips)
- ❌ Rimless: No (cracks)
1.56 Index (Mid-Index)+
The info: Budget “thin” lens. Thinner than 1.50 but lower clarity and more brittle.
Recommended power: −2.00 to −4.00
- ✅ Full rim: Yes
- ⚠️ Semi-rimless: Caution (chipping)
- ❌ Rimless: Never
1.60 Index (MR-8) – The “Sweet Spot”+
The info: Strong resin (MR-8). Great clarity and durability; natural UV blocking.
Recommended power: −3.00 to −6.00
- ✅ Full rim: Yes
- ✅ Semi-rimless: Best choice
- ✅ Rimless: Best choice
1.61 Index (Marketing / Blend dependent)+
The info: Sometimes interchangeable with 1.60 in marketing; verify lab resin if rimless.
Recommended power: −4.00 to −6.00
- ✅ Full rim: Yes
- ⚠️ Rimless/semi-rimless: Check with lab
1.67 Index (MR-10) – Ultra High Index+
The info: Significantly thinner; softer surface, needs quality hard + AR coating.
Recommended power: −5.00 to −8.00 (also ok at −4.00 if maximum thin look needed)
- ✅ Full rim: Yes
- ✅ Semi-rimless: Yes
- ✅ Rimless: Yes (MR-10 preferred)
1.74 Index – Super High Index+
The info: Thinnest/flattened plastic lens; more chromatic aberration and higher cost.
Recommended power: −8.00 and above
- ✅ Full rim: Best use
- ❌ Rimless: Generally not recommended (stress cracks over time)
Trivex (Index 1.53) – The missing material+
Why use it: lightest, impact-resistant, and high optics (Abbe ~45).
Best for: kids, safety, and rimless/drill mounts (especially under ±3.00).
Abbe Value: Clarity vs Thinness
| Material | Index | Abbe (approx) | Clinical Note |
|---|---|---|---|
| CR-39 | 1.50 | 58 | Best optics, thickest |
| Trivex | 1.53 | 45 | Great optics + very light |
| Mid-Index | 1.56 | 36 | Budget, more aberration |
| Polycarbonate | 1.59 | 30 | Impact-resistant, lowest optics |
| MR-8 | 1.60 | 41 | Best balance |
| MR-10 | 1.67 | 32 | Thin, more color fringing |
| 1.74 resin | 1.74 | 33 | Thinnest, still low Abbe |
The Golden Rule: Rounder + Smaller = Thinner
For minus lenses, thickness rises as you move away from the center. Corners create the “thick zone”.
1.50 Index – best / avoid shapes+
Best Small round, oval, soft panto. Thick acetate rims hide edges.
Avoid Aviator, large square/rectangle, rimless/semi-rimless.
1.56 Index – best / avoid shapes+
Best Oval, soft rectangle, rounded square (full rim support).
Avoid Rimless + sharp geometric corners (chipping/cracking risk).
1.60 (MR-8) & 1.61 – versatile shapes+
Best Works with rimless, semi-rimless, and geometric designs.
Caution Oversized aviators still show thickness at bottom-outer edge with −4.00.
1.67 – fashion shapes advantage+
Best Cat-eye, butterfly, large square: reduces bulky pointed corners.
Note Rimless okay (MR-10 preferred), but 1.60 is structurally tougher.
1.74 – when to use / avoid+
Best Smaller flatter frames, modern rectangles (lower wrap).
Avoid Wrap/sport frames (distortion) and generally avoid rimless (stress cracks).
Corner test (quick visual)+
- Round/Oval: edge equal distance everywhere (ideal for 1.50/1.56).
- Rectangle: thicker at 3 & 9 o’clock (use 1.60).
- Aviator: thickest at 4 & 8 o’clock (must use 1.60 or 1.67).
Consultation Guide: Find the Patient’s “Pain Point”
Ask these questions to match coating or filter to lifestyle.
Phase 1: Visual comfort (AR & blue light)+
- Night driving glare? → Premium AR / HMC (reduce halos & starbursts).
- Screen time 4+ hours? → Blue-control coating.
- Screen time 8+ hours? → Stronger wellness filter (e.g., yellow/amber comfort option).
- Harsh office lights? → Mild photophobia: consider wellness filter or light tint + AR.
Phase 2: Durability & maintenance (hard + hydrophobic)+
- Scratches easily? → Reinforced hard coat (and consider 1.60 vs poly in some cases).
- Smudges/fingerprints? → Super hydrophobic/oleophobic top coat.
- Fogging (mask, kitchen, humidity)? → Anti-fog coating/treatment.
Phase 3: Outdoors (photochromic + UV + polarized)+
- Hate switching glasses/sunglasses? → Photochromic (driving users may need a “car-reactive” option).
- Water/road glare? → Polarized lenses + backside AR for best comfort.
Cheat sheet: complaint → product+
| Patient complaint | Recommended treatment |
|---|---|
| “I hate night driving glare.” | Premium AR / HMC |
| “My eyes feel tired after work.” | Blue-control coating |
| “I clean them 10× a day.” | Hydrophobic/oleophobic |
| “They scratch immediately.” | Ultra hard coat + correct material choice |
| “Fluorescent lights bother me.” | Wellness filter / light tint + AR |
| “One pair inside & outside.” | Photochromic |
| “They fog when I cook.” | Anti-fog |
Benefit script: “Based on what you told me, I recommend a [Index] lens with [Coating]. It solves your [glare / fatigue / scratches] so your investment lasts longer.”
Lens Geometry: Spheric vs Aspheric vs Double Aspheric
Spheric (standard) vs Aspheric (flatter)+
Spheric: like a basketball slice. Common in 1.50 and many 1.60. Off-axis distortion increases with higher powers.
Aspheric: flattens toward edges. Common in 1.67 and 1.74. Benefits: thinner/flatter, less eye magnification/minification.
Critical rule: Aspheric needs accurate centration (especially OC height). Guessing “50/50” can cause blur/aberration.
Bi-Aspheric (double aspheric)+
Both front and back surfaces are optimized. Best for high prescriptions (typically −6.00 and above) when you want the best balance of thinness and optics.
Frame Mechanics: Base Curve & Pantoscopic Tilt
Base curve mismatch (why patients hate “new glasses”)+
If old glasses were steeper (e.g., BC 4) and new are flatter (BC 2), the patient may feel distortion even with correct power.
Wrap trap: forcing flat high-index lenses into curved sport frames can cause frame splay, lens popping, and optical distortion.
Pantoscopic tilt (progressives & aspheric)+
Typical target is ~8–12°. Too flat can reduce progressive performance and increase swim/blur.
Expanded Professional Dispensing Protocol
1) Material selection matrix (Go / No-Go)+
| Sphere range | Recommended index | Frame restriction | Why |
|---|---|---|---|
| Plano to ±2.00 | 1.50 | Full rim only | Best optics; lowest cost |
| ±2.25 to ±4.00 | 1.60 (MR-8) | Any (best rimless) | Strongest + clear |
| ±2.25 to ±4.00 | 1.56 | Full rim only | Budget, brittle |
| ±4.25 to ±6.00 | 1.67 | Full/semi-rim | Cosmetic necessity |
| ±6.25+ | 1.74 | Small full rim | Max thinness; avoid rimless |
Rimless rule: Never 1.50/1.56. Use 1.60 (MR-8), 1.67 (MR-10), or Trivex.
2) Design & centration (OC height rule)+
The error: many measure PD but guess vertical OC height for SV lenses.
Aspheric consequence: blur / chromatic aberration if OC height is not aligned.
Protocol: fit frame → mark pupil → measure height → order with exact height.
3) Progressive suitability check+
- Lens height < 28mm: danger zone → short corridor, warn about side distortion.
- 30–34mm: safe for standard corridor.
- 35mm+: excellent comfort and intermediate width.
- Fitting height < 14mm: stop (reading zone cut off).
Vertex Distance – The Keyhole Physics
The keyhole effect (simple explanation)+
Closer lens = wider usable field. If the frame sits too far away, blur zones move inward and the clear corridor feels narrower (“keyhole”).
Eyelash blink test (10–12mm target)+
Goldilocks ideal: lashes sweep just behind the lens (about 10–12mm vertex).
- Too close (lash crash): grease streaks; coating damage risk → increase tilt / adjust pads.
- Too far (tunnel): finger fits between cheek and lens → narrow corridor → adjust closer.
Critical timing: do vertex adjustments before marking progressive heights (avoid parallax error).
High Rx effective power warning+
- High minus: power becomes weaker as lens moves away → patient pushes glasses up.
- High plus: power becomes stronger as lens moves away → magnification + dizziness complaints.
Bench summary: adjust pads/temples to lock stable vertex and then re-check heights/centrations.
