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Progressive Lenses—Presio Power—Achieving Visual Acuity and Eye Adaptability

1. Eyeglasses, essential for the modern age

Portrait of Cardinal Don Fernando Nino de Guevara.
© The Granger Collection, New York /PPS

There are various theories about the origin of eyeglasses, but it is believed that they first appeared in Italy around 1280. The lens of the first eyeglass was fitted into a frame with a handle that was held like a magnifying glass. Eyeglasses that were worn on the ears, like those we have today, appeared about 300 years later. In 1596, spectacles with strings attached (a Spanish-Italian style) were worn by hanging the strings over the ears, as can be seen in the “Portrait of Cardinal Don Fernando Nino de Guevara.”

In those days, spectacles were so expensive that only scholars, philosophers and other members of the elite could afford them. It was not until the dawn of contemporary society a few centuries later that eyeglasses became an indispensable tool.

Eyeglasses are an essential tool in our daily lives.

When glasses first became widespread, they were made of glass. Nowadays, however, 95 percent of lenses in Japan are made of plastic. This is because wearers prefer thinner, lighter lenses. Over the past few years, the design and manufacturing technology of plastic lenses have rapidly improved. Complicated free-form surfacing can only be achieved with plastics.

2. Conventional progressive lenses

There are basically two types of lenses for eyeglasses: single vision lenses for both near-sighted and far-sighted people, and bifocal or progressive lenses for people who have more difficulty seeing things close up. Single vision lenses have a fixed focal length, while progressive lenses are designed with a gradual strengthening of vision from the top of the lens to the bottom so that there is smooth viewing over the distant to close-up range. Nikon achieves this Addition Power* by using precise technology to fabricate a smooth transition from a flat, shallow curve to a deeply hewn curve in plastic.

  • *Addition Power
    Since a progressive lens incorporates far vision, intermediate vision and near vision in a single lens, vision changes gradually, becoming progressively stronger from the upper part of the lens to the lower part. The ideal design enables far-sighted vision through the upper area, intermediate vision through the center area, and near-sighted vision through the lower area of the lens. Also, since the required strength in vision for near-sightedness tends to increase with age, as the level of addition power advances, there is a correspondingly greater change in the range of vision.

Curves change continuously from the upper area where the curvature for far-sighted vision is low, to the lower area where the curvature for near-sighted vision is higher.
Structure of the progressive surface

The design of conventional progressive lenses needed to prioritize either visual acuity or eye adaptability. A feature of Nikon lenses until now had been its prioritization on visual acuity; users liked the lenses because they could see well with them. This boosted Nikon's notoriety as a specialized manufacturer of optical equipment. The structure of these lenses thoroughly eliminated distortion and blurriness of the image when the eye was viewing distant or close-up subjects. The structure of lenses that prioritized eye adaptability, however, dispersed distortion and blurriness over the entire lens, and some users liked the fact that their eyes could adapt to the lenses despite the reduction in visual acuity. Neither type of lens is superior to the other, as both have strengths and shortcomings; some customers like one type, while others prefer the other. The basic issue in lens design is thus where to place the aberrations that cause distortion and blurriness. Should they be concentrated around the periphery or spread over the entire lens? Design technology until now suffered from the difficult challenge of balancing the contradictory elements of visual acuity and eye adaptability in one lens.

3. Balancing visual acuity and eye adaptability in a single lens

Presio Power is a next-generation progressive lens that has been engineered with advanced optical technology to balance visual acuity and eye adaptability. To achieve ideal viewing comfort, an innovative design approach has been used for the Presio Power lens. One aspect of this design focuses on the outer surface of the lens where addition power is produced. By expanding the field of view at the center of the lens near the pupil, there is less stress on the eyes and the wearer experiences natural comfort from the moment the glasses are put on.

Field of view comparison using a conventional progressive lens and the Presio Power
Presio Power has a broader field of view at the center area near the pupil, allowing the eyes to adapt more easily.

The second aspect of the design is to use an aberration filter that creates an ideal focal point for the light beam that passes through the lens. This filtering effect is achieved by deliberately producing a distorted surface inside the lens. For instance, if there is a distorted surface in the horizontal direction on the outer surface of the lens, which is the progressive surface, by deliberately producing a distorted surface in the vertical direction inside the lens, it is possible to create an ideal focal point free of distortion.

In the third aspect, a reverse-progressive surface that is directly opposite the progressive surface is placed inside the lens. It is impossible to completely eliminate all aberrations in a single lens. With Presio Power, however, the placement of a reverse-progressive surface inside the lens solves the fundamental problem of strong distortion and blurriness that occur in the lower part of the lens.

The interior of the Presio Power lens consists of a clear aberration filter and a power aberration filter.
Two aberration filters inside the lens

With Presio Power, it is possible to accept orders for custom-made lenses and design each lens individually. With progressive lenses, the number of conceivable patterns can be as high as one billion as the lenses incorporate both far-sighted vision and near-sighted vision, as well the specific conditions of aging eyes depending on the individual. To produce an ideal set of lenses for each individual customer, Nikon utilizes a high-speed calculation system known as the Nikon Optical Design Engine. The Nikon Optical Design Engine can quickly simulate and design a combination that is ideally suited for each individual's pair of eyes. The Nikon Optical Design Engine is a highly accurate simulation program that has been repeatedly monitored and verified up to a billion patterns. This precision program makes it possible to provide customers with lenses that are optimized for their eyes.

It has been said that no two people have the same eyes. Presio Power has achieved the balance between visual acuity and eye adaptability, which was previously very difficult. We will continue to research and develop optical lenses to attain the best solution for our customers.

Posted September 2009