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

Lens Thickness Formula !

After reading my last post for the basic thickness calculator, I have received some mails were asking me for the formula to find the thickness. (In that post, the formula was hided from the users)

Here I am explaining how to find the estimated thickness of a lens before it makes. To find the thickness you need to know the power, index, diameter and the edge/ center thickness.

For plus power you have to consider the edge thickness and for the minus powers you have to consider center thickness. (usual range is 0.9mm to 2.00mm according to the index)

Formula: 

Thickness= [(1/2*Diameter)^2*Power / [2000*(Index - 1)]] + edge/center thickness

For instance, given a lens power of -3.75 D, a refractive index of 1.53, and a minimum blank size of 65 mm, with 1.50mm center thickness, then the thickness would be:

[(1/2*65)^2*3.75 / [2000*(1.53 - 1)]] + 1.50 = 5.24 mm

For the ease of use I have created an excel file, there you can enter all the input values for the result (fig. 1).

You can download this calculator from here : Download Link

Download Basic thickness Calculator!!!

Download Basic thickness Calculator!!! Just input the power, index, size and you will get the thickness in center, edge@180, lens height with graphical representation. It’s a cool excel macro.

Download link: Thickness Calculator