The spherical design type was the only type of single vision lens available in 1980.
At the time, glass lenses were generally recommended to users who wanted a thinner lens.
The mainstream plastic material at the time in question featured a refractive index of 1.50, and was quite thick compared to glass.
While glass lenses can be made thinner, but are heavy and fragile, plastic lenses, although thick, were extremely light and could be worn for prolonged periods of time without discomfort. SEIKO firmly believed that the age of plastic was about to dawn and started work at an early stage on the design and development of raw materials with the aim of realizing a thin, lightweight plastic lens.
In collaboration with a major chemicals manufacturer, SEIKO developed a plastic material for spectacle lenses with a refractive index of 1.60. This was an independently developed material called "HiLoad" and was the thinnest plastic material available at the time.
"HiLoad (MX)" was the first product to be launched using this material.
The product featured the spherical design that was the norm at the time.
Because of the rounded shape, the front surface of strong lenses protruded even though plastic was used as the constituent material, resulting in an unattractive appearance.
SEIKO believed that realization of a lightweight, thin lens using plastic as the raw material required not only new materials, but also a new surface design.
The result was the aspheric design.
If only an aspheric design could be achieved, it would be possible to flatten the lens shape with no loss of optical performance. In the belief that the fusion of the world's thinnest material with this aspheric design should make it possible to produce a lightweight, thin lens that would meet spectacle user requirements, SEIKO renewed its efforts to achieve the desired result.
To achieve a thin aspheric design using plastic material, firstly, a prototype lens with an aspheric design and a low base curve (high degree of flatness) was produced. Monitoring was performed to verify aspects of vision.
However, in many cases, users accustomed to the spherical lenses of the time reported peripheral blurring when they tried the aspheric lens and, as a result, it was realized that it would be quite a long time before the ideal aspheric surface degree could be derived.
After a process of trial and error, the ideal setting for achievement of both thinness and optical performance was completed in 1988.
"Super MX" was launched in 1989 and proved to be a spectacular hit, winning high acclaim, needless to say for its visual performance, but also for its unprecedented lightness and thinness.
At the present time, "Super Lucius," the successor to "Super MX" is commercially available.
In addition, "Prestige" with a refractive index of 1.74 and "Super Sovereign" with a refractive index of 1.67, both making use of even thinner material, are also available, realizing a lineup of 3 types of aspheric design single vision lens.
The launch of this aspheric design lens represented the world's first milestone achievement of a minus power lens. While, up to this point, the choice for users needing powerful lenses was limited to heavy glass lenses, the range of choice was now expanded to include thin, lightweight lenses.
The appearance of this product represented a turning point in the changeover to plastic materials and opened the portal to the age of the aspheric design lens.
Nowadays, more than 95% of spectacle lenses are made of plastic.