Over ten years have passed since SEIKO developed the world's first aspheric single vision lens (with an aspheric back surface and spherical front surface) in 1998, breathing new life into the plastic lens market.
At the time, development of thin plastic lens materials had come to a halt.
In response to calls from spectacle users for a lens that was even a little thinner, SEIKO started work on the development of what was to become the world's first double-sided aspheric single vision lens.
As the name implies, the double-sided aspheric single vision lens features aspheric design on the front and back surfaces, making it possible to realize a flatter lens with a low base curve.
Although normally, the lower the base curve, the poorer the optical performance (degraded vision), perfect optimization of the aspheric design of both the front and back surfaces made possible by Double-sided Aspheric design enables realization of a greater degree of thinness with no degradation of vision.
As a result, it has become possible to optimize astigmatic strength, an achievement previously difficult to realize with single-sided aspheric design.
Design began with the application of production technology, design technology and assessment technology for the back-surface progressive lens that was launched in 1997.
Although, thanks to this development know-how, design proceeded relatively smoothly, the establishment of the necessary production technology took quite a long time since SEIKO was pursuing the realization of a lens shape never before seen in the world.
Because the lens was a fixed-focus type, mass-production was required.
To realize mass-production, glass moulds had to be created into which melted plastic would be injected.
The glass moulds for this product had to be formed with an aspheric surface corresponding with the back surface of the lens.
Because, up to this point in time, the spherical shape was the norm, it was inevitable that independent development had to be undertaken. The process of developing a glass mould for the double-sided aspheric lens involved a seemingly endless number of prototypes and work on production of a glass mould that would provide the optical performance required by the design continued day and night.
Finally, "SSV AZ," the world's first double-sided aspheric single vision lens, made its debut in 1998.
At the present time, this series features a lineup of three products: "SPG AZ" with a refractive index of 1.74, "SSV AZ" with a refractive index of 1.67 and "SLU AZ" with a refractive index of 1.60.
A double-sided aspheric single vision lens that realizes both thinness and optical performance (ease of vision), the two eternal themes of plastic lenses.
This achievement has engraved the name "SEIKO" on the history of plastic lenses and tells of Seiko's untiring, passionate pursuit of technological development.