Why can't I buy glass lenses?

I am a teacher of optometry related courses. Try to explain your problem.

The optical indexes of resin (plastic) lens include the wear resistance close to that of glass lens, which is low in manufacturing cost and better in environmental protection.

Advantages and disadvantages of glass and resin

1. resin lens

Resin is a polymer compound, which softens when heated and has plasticity. Resin lens is a kind of lens which is chemically synthesized from resin and polished. Resin lenses have obvious advantages, and the lenses made of resin are light in weight and more comfortable to wear; Resin lens has strong impact resistance, is not fragile and is safer; In addition, resin lenses have good light transmittance, can be easily reprocessed to meet special needs, and are cheap, so they have become the mainstream of lenses in the market.

Disadvantages of resin lenses:

The surface wear resistance and chemical corrosion resistance of resin lens are worse than that of glass, and the surface is easy to scratch, and the water absorption is greater than that of glass. These shortcomings can be improved by coating. Fatal disadvantages are high thermal expansion coefficient, poor thermal conductivity, low softening temperature and easy deformation, which affect optical properties. You can adjust the alignment of the title by positioning.

2. Glass lens

Advantages of glass lenses:

Glass lens is a lens made of optical glass, which has slightly higher definition and higher refractive index than resin lens. The highest refractive index commonly used in lenses is 1.9. And the surface hardness of glass lens is higher, which is more scratch-resistant and wear-resistant than other lenses.

Disadvantages of glass lenses:

Glass lenses are heavy due to material reasons, which affects the wearing comfort to some extent. In addition, glass lenses are fragile, especially with the improvement of production technology and technology of resin lenses, the use of glass lenses has become less and less in recent years.

So both have advantages and disadvantages. It can only be said that it is important to choose the one that suits you best according to your own needs.

Experience of lens grinding workshop

When the resin sheet is broken, there are almost no fragments and splashes.

Another most important reason is processing: resin sheets can be easily made into full-frame glasses, half-frame glasses, rimless glasses and other styles of glasses.

Glass sheets are only suitable for full-frame glasses. Other styles of glass are very, very easily damaged even when processed.

Personal experience

At present, glass lenses are at two extremes, the cheap ones are very cheap, the expensive ones are very expensive, you dare not buy them, and the expensive ones don't want to pay. Glass lenses are now sold in the market, either in old stock (cheap) or customized separately (expensive).

Advantages and disadvantages of resin and glass lenses, the advantages of resin are suitable for the mainstream market, and the advantages outweigh the disadvantages, so glass lenses are gradually eliminated, and almost several well-known brands in China have not made glass lenses.

However, no matter what lens you choose, you should pay attention to correcting bad eye habits, mostly outdoors, supplementing eye nutrition every day, and insisting on correction, the eye degree will be more stable or improved!