The Birth of 1.56 Index Lenses

1.56 index lenses are not a single product invented by a particular company, but rather a stage in the evolution of eyewear materials technology. Their emergence is closely linked to the development of plastic lenses. To understand the context of its development, we need to view it within the broader history of the evolution of optical materials for eyewear:

1. The 1986 Technological Breakthrough: Breaking the Dominance of CR-39

In the 1940s, the American Columbia Broadcasting System (CBS) laboratories developed CR-39 (refractive index 1.50), a resin material that remained the undisputed leader in the global plastic lens market for decades. However, as the nearsighted population increased, the drawback of CR-39 being "too thick" became increasingly apparent.

By 1986, two companies worldwide (primarily major American optical corporations and resin catalyst laboratories) successfully increased the refractive index to 1.56 by introducing specific functional groups into the molecular chains of acrylic or polyurethane organic resins. That year, 1.56 was officially launched as the first generation of "medium-index/high-index" plastic lenses in human history.

2. The Essence of the Material: The Classic NK-55

The early substrate material used in 1.56 lenses had a well-known codename: NK-55 (due to their Abbe number typically ranging between 35-38 and a refractive index of 1.55-1.56).

Unlike later materials such as 1.60 (MR-8 developed by Mitsui Chemicals), this material did not possess ideal toughness.

Essentially, 1.56 was a modified acrylic resin that was relatively hard and brittle. Although its impact resistance was only moderate and its edges were prone to chipping, it had one decisive advantage: its molecular synthesis was relatively simple, making it exceptionally suitable for large-scale injection molding and curing production.

3. Japan and Taiwan: The Turning Point of Technology and Market

Although the concept and the earliest products were born in Europe and the United States, the Western market soon encountered legal barriers. In 1972, the U.S. FDA implemented strict impact-resistance Drop Ball Test regulations for eyeglass lenses. The relatively brittle nature of 1.56 material made it difficult to use safely in rimless frames across Europe and America.

As a result, 1.56 technology gradually shifted to Asia:

Japanese companies such as Hoya Corporation and Nikon improved the coating technologies and optical corrections of these medium-index materials during the late 1980s, addressing issues such as chromatic dispersion (rainbow edging caused by low Abbe values) and scratch resistance.

In the 1990s, lens factories in Taiwan, China undertook a technology transfer and began leveraging cheap labor and increasingly sophisticated molding techniques to significantly reduce the production costs of 1.56 lenses.

4. Danyang, China: The "Ultimate Flourishing Ground" of 1.56

If the "birth certificate" of 1.56 lenses was written in the United States, then their true industrial coming-of-age undoubtedly took place in Danyang, Jiangsu, China.

In the early 21st century, mainland China (especially Danyang) successfully mastered and absorbed the complete manufacturing process of 1.56 resin lenses, creating a remarkable industrial cluster effect. Due to China's enormous nearsighted population and highly price-sensitive consumer market, Danyang reduced the production cost of 1.56 lenses to astonishingly low levels.

This transformed 1.56 into the genuine "people's lens," which was subsequently exported back to Southeast Asia, South Asia, and low-to-mid-end optical markets around the world.

Summary

1.56 lenses were first developed in the United States in 1986 as an upgraded replacement for CR-39. Although they did not gain widespread popularity in their home markets of Europe and the United States, they became a classic material that transformed the cost of eyeglasses for hundreds of millions of people worldwide as the supply chain in Asia evolved.