Optician's Utility for thickness & diameter calculation

We, the optician’s are always having troubles to explain to customers about different types of lens indexes. There are some displays which can show to the patient about various thickness according to different index selection. Most of the time it will work fine. But as you know, thickness will vary according to the diameter too. And most of us need to have a diameter chart in hand to check the diameter.

Here, I am giving you a small excel file which will help you to fine out the minimum required diameter...

This excel sheet has three sections, and the third section will help you to find the diameter with simple steps

The first section will help you to find the thickness of a lens according to its index and diameter.

And the second section will help you to have an idea to compare the thickness difference between CR-39 and other index (it will show in percentage)

Click here to download the file.

click the above link and got to the menu file>download

Let me have your feedback and suggestions… 

All about MR Series...(MR-8, MR-7, MR-10, MR-174)

"Mitsui Chemicals is a Japanese Chemicals company. The company mainly deals in performance materials, petro and basic chemicals and functional polymeric materials."

What is MR Lenses: (MR-8, MR-7, MR-10, MR-174)

    Excellent optical materials with high refractive index, high Abbe number, low specific gravity and high impact resistance are provided by polymerizing monomers of MR™ Series. MR™ Series is especially suitable for ophthalmic lenses and is known as the first thiourethane based high index lens material. MR™ Series offers a variety of products to provide the best solution for optical lens users.

R.I. 1.60： MR-8™

The best balanced high index lens material with the largest share of the R.I. 1.60 lens material market. MR-8™ is suited to any strength ophthalmic lens and is a new standard in ophthalmic lens material.

R.I. 1.67： MR-7™ & MR-10™

Global standard R.I.1.67 lens material. Great materials for thinner lenses with strong impact resistance. Material Characteristics MR-7™   : Better color tintability MR-10™ : Higher heat distortion temperature

R.I. 1.74： MR-174™

Ultra high index lens material for ultra thin lenses. Strong prescription lens wearers are now free from thick and heavy lenses.

MR™ Series is a brand name of the raw material for optical lenses.
MR™ Series based lenses are available from most leading lens manufacturers.

Comparison of physical properties of lenses made with MR™ Series vs. other optical materials

	MR™ Series				Other
	MR-8™	MR-7™	MR-10™	MR-174™	Poly carbonate	Aclyric (RI:1.60)	Middle Index	ADC (CR-39® RAV7®)	Crown Glass
Refractive Index (ne)	1.60	1.67	1.67	1.74	1.59	1.60	1.55	1.50	1.52
Abbe Number (νe)	41	31	31	32	28-30	32	34-36	58	59
Heat Distortion Temp. (ºC)	118	85	100	78	142-148	88-89	-	84	>450
Tintability	Good	Excellent	Good	OK	None	Good	Good	Good	None
Impact Resistance	Good	Good	Good	OK	Good	OK	OK	OK	Poor
Static Load Resistance	Good	Good	Good	OK	Good	Poor	Poor	Good	Good

MR Series Features:

• High refractive index for thinner and lighter lenses.

MR™ Series offers 3 different refractive index products (R.I. 1.60, 1.67, 1.74).
With higher index materials, it is possible to achieve thinner lenses with the same strength.

• Superb optical quality for wearer comfort

• Both high refractive index and high Abbe number provide optical performance similar to glass lenses.
• Glass mold-casted MR™ Series shows minimal stress-strain.

High Abbe number material like MR-8™ minimizes prism effect (Chromatic aberration) of lenses and provides comfortable view to all wearers.

High Abbe Number Material

Low Abbe Number Material

MR™ Series resin is uniformly polymerized in a glass mold. Compared to the injection molded Polycarbonate lens, MR™ Series lens shows minimal stress strain and offers stress free clear vision.

Stress Strain Observation
(Crossed Nichol method using the polarizing film and white light source)

• Mechanical strength to protect wearers from accidental injury. 

High impact and static load resistance helps promote wearer eye safety. (Pass US-FDA drop ball test standards) Good tensile strength for fashionable rimless frames. Good processability for precisely designed progressive lenses (Advantage of thiourethane materials) .

• High impact resistance of MR-8™ helps protect wearers form accidental injury.

FDA Drop Ball Test

MR-8™ shows good impact resistance

US-FDA (Food and Drug Administration) Sec. 801.410
“Use of impact-resistant lenses in eyeglasses and sunglasses”

Static Loading Test

Quasi-static loading type test for minimum robustness

MR-8™ shows good static load resistance

 

• MR-8™ lens shows good tensile strength.
• MR-8™ is widely recognized as the best material for rimless frames.

Tensile Test

Tensile test results

MR-8™ lens broke at 72kg tensile force
(All other material lenses broke at smaller forces)

Lens deformation

MR-8™ lens showed no deformation of drilled hole
(60kgf Tensile Force)

 

• MR-8™ is adequate for the long time usage of rimless glasses.

“ Butterfly Test ”for Rimless Frames

Endurance test under cyclic load for spectacle frames

JIS B7283 Specification; Broke at 20,000 strokes

• Durability during long time usage under severe conditions

• Good weatherability provides minimal change in lens color after years of usage.
• Good compatibility with coating materials.

Weatherbility Test

Accelerated test to observe lens color change after long-term usage.

QUV Test: 0.50W/m², 50ºC, 100hrs

MR-8™ shows only minor color change after exposure to strong UV light.
Wearers can enjoy clearer lenses after long-term usage.

 

Heat Resistance Test

Evaluation of cracks in coating after high temperature conditions.

Test condition: 90ºC, 15 min.

Test condition: 80ºC, 15 min.

Good heat resistance and coating compatibility of MR-8™ prevent coating cracks under servere conditions.

 

Cross-cut Adhesion Test

1) Cut a coating layer in a reticular pattern.
2) Apply tape over the pattern and then remove it.

MR-8™ showed very good compatibility with coating materials.
Lens wearers can enjoy unchanged high performance lens coating after long-term usage.

How the MR lenses are produced?

1. Preparation of MR™ Series

Mix MR™ monomer (component) A & B with additives, then degas the MR™ monomer mixture.

2. Filling

Fill molds with the MR™ monomer mixture.

3. Polymerization

Place the filled molds into ovens, where they undergo a heat-cycle, turning the MR™ monomer mixture into a MR™ lens.

4. Grinding / Polishing

Grind and polish the surface of the MR™ lens to create a curvature for required strength.

5. Tinting

Tint the surface of the MR™ lens.

6. Coating

Hard Coating Anti Reflection Coating

Coat the surface of the MR™ lens to protect from scratches, reflection etc.

7. Final Inspection

Inspect the coated lens.

"MR-8 is the best in hi-index lenses"

credit: wikipedia, mitsuichem.com

Story of Polycarbonate Lenses !

"Polycarbonate lens offered 100% protection from the harmful UV rays and were up to 10 times more impact resistant glass or plastic lenses that made polycarbonate lenses an instant hit. They were first developed in the 1970's for use in space related programs like visors on space suites and shuttle wind shields. In 1983, polycarbonate lenses were formally introduced to the marketplace by Gentex Corporation in response to the demand for light weight, durable and impact resistant lens."

|| Polycarbonates got their name because they are polymers containing carbonate groups (-O-(C=O)-O-) ||

 Polycarbonate is a type of tough and versatile plastic that is used mainly for the manufacture for various things from bulletproof windows to compact discs (CDs). These days, polycarbonate is also used for making lenses that are light weight and almost damage proof. Though there are different eyeglass lenses types, when it comes to eye safety, polycarbonate lenses are considered the best option. These lenses can be used for eyeglasses, sports eye wear and sunglasses etc. Clear polycarbonate is used in the manufacture of eyeglasses, since it is transparent, durable and has a high infraction index. Polycarbonate lenses are the first plastic high index lens having one of the highest index ratings (1.586). They are thinner and more durable than other conventional and glass lenses and are used as prescription glasses for vision correction of even very high numbers.

 Polycarbonate lenses are also used for making sunglasses that make the use of filters to block the harmful UV rays of the sun. These lenses are also polarized to block glare and are also perfect for sports wear since they are high impact resistant. Polycarbonate lenses are an excellent choice for making children's glasses and safety glasses since they are resistant to scratches as compared to the standard plastic lenses.

Advantages of polycarbonate lenses

• Greater protection: Polycarbonate lenses in your glasses protect your vision by holding up to rough play or sports practice. With high impact resistance, polycarbonate lenses provide greater protection against eye damage and vision loss from broken or shattered lenses.
  
• Lighter weight: Polycarbonate material is lighter than standard plastic or glass, which is highly suitable for people with strong prescriptions. As well as being lighter, polycarbonate lenses are thinner than standard plastic or glass, which contributes to the lighter weight.
  
• Scratch-resistant: Although no lens is scratch proof, polycarbonate lenses come with a scratch-resistant coating to keep them clear as long as possible, even when worn by children. Experts believe that a polycarbonate lens is significantly more shatter-resistant than glass or regular plastic lenses.
  
• UV protection: Polycarbonate lenses also offer inherent ultraviolet protection. About 99 percent of potentially damaging UV rays are filtered out by these lenses, whether the rays come from sunlight, fluorescent lights or a computer screen.
  
• Safety: Currently, the lenses and frames made from polycarbonate materials provide the highest level of impact protection. When glass or plastic lenses break, they do not break into harmless granules, but can break into sharp shards that can enter your eye and destroy your vision. That is why polycarbonate is far and away the safest of all the lenses made.
  

Drawbacks of polycarbonate lenses

• One of the very few weaknesses or drawbacks of polycarbonate lenses is that they are not as good optically as high index or plastic lenses.
  
• People in prescriptions with higher powers sometimes have trouble seeing out the edges of the lenses -- your clear field of vision is not as wide as with glass or plastic lenses. Similarly, you should also remember that polycarbonate lenses bend light differently. As your vision is corrected by light passing through a prescription lens and focusing an image on your retina, polycarbonate bends light to a greater degree than glass or plastic lenses of equal thickness.
  Therefore, if you previously wore a glass or plastic lens, there may be an adjustment period needed to adapt to polycarbonate lenses.
  
• Certain lens coatings may reduce the impact effectiveness of polycarbonate and some lens tints may be difficult or impossible to apply.
  
• Polycarbonate lenses will not shatter, they are more prone to scratching than other materials if not protected with scratch-resistant coating.
  
• Polycarbonate lenses are harder to make, they require more time to manufacture.

Physical Properties - (from Wikipedia)

Density (ρ)	1.20–1.22 g/cm3
Abbe number (V)	34.0
Refractive index (n)	1.584–1.586
Flammability	V0-V2
Limiting oxygen index	25–27%
Water absorption –Equilibrium(ASTM)	0.16–0.35%
Water absorption – over 24 hours	0.1%
Radiation resistance	Fair
Ultraviolet (1-380nm) resistance	Fair

External Link for polycarbonate lens

Lens Material Reference Chart

All optical measurements are based upon US standards (Helium d line). Actual values may vary depending upon individual lens supplier and product type.

Material	Refractive Index	Abbe Value	Specific Gravity	UVB / UVA Protection
CR-39® Hard Resin	1.499	58	1.32	100% / 90%
Next Gen Transitions®	1.497	58	1.27	100% / 100%
Polycarbonate	1.586	30	1.20	100% / 100%
Trivex™	1.527	44	1.11	100% / 100%
SOLA Spectralite®	1.537	47	1.21	100% / 98%
Essilor Ormex®	1.558	37	1.23	100% / 100%
SOLA Finalite™	1.600	42	1.22	100% / 100%
MR-6 1.6 Plastic	1.595	36	1.34	100% / 100%
MR-8 1.6 Plastic	1.592	41	1.30	100% / 100%
MR-7 1.67 Plastic	1.658	32	1.35	100% / 100%
MR-10 1.67 Plastic	1.661	32	1.37	100% / 100%
Hoya EYRY	1.700	36	1.41	100% / 100%
MR-174 1.74 Plastic	1.732	33	1.47	100% / 100%
Crown Glass	1.523	59	2.54	79% / 20%
PhotoGray Extra®	1.523	57	2.41	100% / 97%
Clear 16 Glass™	1.601	40	2.63	100% / 62%
1.6 Glass	1.601	40	2.62	100% / 61%
1.7 Glass	1.701	30	2.93	100% / 76%
1.8 Glass	1.805	25	3.37	100% / 81%
1.9 Lantal Glass	1.886	31	4.02	100% / 76%

Click here for detailed reference : Material Property Table