Glass indices

Degrees of thinning

Degrees of thinning are measured by refractive index. The higher the decimal number, the thinner the lens.

• 1.5    
• 1.56  
• 1.59  
• 1.6    
• 1.67  
• 1.74

Regular plastic index 1.5

This plastic is twice as light as mineral glass. It is an economical solution for uncomplicated prescriptions. It was the first type of plastic created to produce ophthalmic lenses.

It is recommended for prescriptions :

MYOPIC HYPERMETROPIC ASTIGMATIC*

PLANO at -3.00 PLANO at +3.00 -0.25 to -3.00

* Note: For astigmatism, the power must be determined taking into account the prescription of the sphere. Ex: -2.50 -2.50 x 90 gives a total of -5.00 in combined power. In this case, 1.5 would not be appropriate.

Polycarbonate index 1.59

Up to 2 times lighter than a regular plastic lens, polycarbonate lenses will make your customers forget they're wearing glasses. It's also recommended in the slimming category because it's up to 35% thinner than a regular plastic lens.

It is also extremely impact-resistant. Polycarbonate also filters out 100% of UVA and UVB rays. So your eyes are protected from harmful light rays at all times. We recommend polycarbonate for grooved frames because of its high resistance.

Its weak point is that it is a thermoplastic that reacts to heat. Exposed to intense heat or cold, plastic can expand or contract, causing anti-reflective coatings to peel off. This type of plastic also has the characteristic of having more chromatic aberrations than a regular plastic lens, which can cause visual discomfort for some patients.

It is recommended for prescriptions :

MYOPIC HYPERMETROPIC ASTIGMATIC*

-3.00 to -5.00 +2.00 to +5.00 -0.25 to -3.00

Thinned plastic index 1.6

This type of plastic is recommended for all types of wearer. It is 30% thinner than regular plastic, giving it unbeatable aesthetic properties. The quality of vision is clear and its transparency perfect. This type of plastic is recommended for grooved or drilled frames. It is also 100% UV400.

It is recommended for prescriptions :

MYOPIC HYPERMETROPIC ASTIGMATIC*

-3.00 to -5.00 +2.00 to +5.00 -0.25 to -4.00

* Note: For astigmatism, the power must be determined taking into account the prescription of the sphere. Ex: -2.50 -2.50 x 90 gives a total of -5.00 in combined power. In this case, the 1.6 would be perfect (taking into account a good choice of frame).

Thinned plastic index 1.67

This type of plastic is recommended for all types of wearer and high requirements. This very high index material gives absolute purity and transparency. This glass is very flat, very thin and very light. It is recommended for all types of mounting, including drilled and grooved. The 1.67 offers perfect vision quality and high UV protection.

It is recommended for prescriptions :

MYOPIC HYPERMETROPIC ASTIGMATIC*

-4.50 to -8.00 +3.00 to +8.00 -0.25 to -4.00

* Note: For astigmatism, the power must be determined taking into account the prescription of the sphere. Ex: -2.50 -2.50 x 90 gives a total of -5.00 in combined power. In this case, 1.67 would be an excellent choice (taking into account a good choice of frame).

The 1.67 surface is the best material for the very hypermetropic. It gives better results than 1.74 in general. There is therefore no point in recommending 1.74 to a highly hypermetropic person to improve the aesthetics of their lenses unless they have an Rx greater than +8.00. Above +8.00 The aspheric version of the 1.67 is no longer available. The 1.74 is therefore a better option, since the asphericity of the lens is necessary to achieve optimum results in the thickness of hypermetropic lenses.

Thinned plastic index 1.74

This type of lens has the highest refractive index available for plastic lenses. It is ultra flat, ultra thin and very light. It offers maximum aesthetics in terms of thickness and absolute comfort. This type of lens minimises the magnification effect on the eyes and offers high UV protection. The 1.74 can be used for all types of mounting, including drilled and grooved.

It is recommended for prescriptions :

MYOPIC HYPERMETROPIC ASTIGMATIC*

-8.00 to -12.00 +8.00 to +10.00 -0.25 to -4.00

*Note: For astigmatism, the power must be determined taking into account the prescription of the sphere. Ex: -5.50 -2.50 x 90 gives a total of -8.00 in combined power. In this case, the 1.74 would be perfect (taking into account a good choice of frame).

Please note: In the case of very hypermetropes, the 1.74 is not a better choice than the 1.67 in cases below +8.00. It is therefore better to work with the 1.67 in order to have a less expensive product and more reasonable lead times for the customer.

Mineral lenses

 These are glass lenses (silica-based) that combine high optical quality with excellent scratch and abrasion resistance. They can be more or less thin, depending on their chemical composition. However, glass can shatter if dropped on a solid surface.

As for mineral lenses, few are made from this material today.

• There are no new digital mineral products.
• The last progressive design created for the mineral dates back to the 1990s.

People often prefer plastic because it's much lighter and, above all, safer.

However, some people prefer mineral because it is less likely to scratch. So we sell it to people who work in places where they come into contact with a lot of dust, or to special trades.

We won't go into all the details of each index, since they are virtually no longer sold, but we will look at the broad outlines of the indices on offer.

Index 1.5/ can be chemically hardened for impact resistance

Index 1.6/ can be chemically hardened for impact resistance

Index 1.7/ Cannot be hardened/ Very fragile to shocks

Index 1.8/ Cannot be hardened/ Very fragile to shocks

Chemical hardening means that the lenses are specially treated to withstand any impact.

• Be careful: glass is still fragile, and simply dropping your glasses on a ceramic floor can shatter the lenses. Mineral glass is not recommended for children, as it is not impact-resistant. What's more, you can't use this material for drilled or grooved frames, as the glass would be far too fragile and could be damaged very quickly.

To conclude, what's important to understand when selecting a type of lens is that the aesthetic result of a pair of glasses depends on more than just the material.

• Even with maximum thinning, a lens can give a thick result if combined with the wrong choice of frame.
• The higher the prescription, the more important it is to centre the eyes in the frame. So you need to be very careful not to create false expectations among your customers.
• There is no miracle for people with very high hypermetropia. Despite all the thinning lenses available, there will always be a magnifying effect on the eyes. An aspheric lens will give better results, but will still result in bigger eyes (-20% magnification effect).