TOKAI will think and suggest together with the retail shops, to find the best solution for various inquiries, needs, and wants, to obtain the satisfaction of each user.
Within the various kinds requests for multifocal lenses such as progressive addition lenses and bifocal lenses, there are users whom insist in wanting to see the near vision in a wider vision field.
The “Franklin Lens” is one of the solutions for these kinds of requests. This type of lens is a type of executive lens (Ex type lenses) in more general.
This is a type of lens in which four pieces of lenses in total are made and combined into a single pair of lenses. All of the four lenses are single vision lenses, 2 for the far vision for both the R and L eyes, the other 2 made for the near vision of both the R and L eyes. Each of these lenses are then cut in half to be fit and fixed into a single pair of frame.
Here below is the picture of the actual lenses. You can recognize the line in where the four lenses are combined.
The Franklin Lens is suitable for such users that…
- have a different astigmatic power and/or axis for the near vision and far vision.
- have the needs to see the near vision field wider than from the progressive addition lenses or standard bifocal lenses.
- have too big of a difference in the power needed for far vision and near vision. (Difficult to manufacture with progressive lenses and standard bifocal lenses.)
※※ Attention ※※
- Please select (recommend) a metal rim frame when prescribing for the Franklin Lens. Due to that the lenses are combined by fitting it into the frame a stiff rim is needed to combine the lenses firmly.
- Please understand the lens type which can be selected for the Franklin Lens is limited. Due to that the front curve of the lens for the far vision and the near vision is match for a beautiful and firm combination of the lens. The lenses which can be used is limited.
- The Franklin Lens cannot be manufactured for tinted lenses such as for sunglasses. Due to that each of 4 lenses are manufacture separately, the colors will not 100% match when the lenses are combined.
- Please do not use the Franklin Lens for intense activities and sports. Due to that the lenses are combined without any adhesives to maintain a clear view, it is fine for using in a everyday life, although the lenses may fall out when it is used intensively used.
Most often, eyewear users with strong myopia have the needs for “a thinner lens”. The thickness of the lens edge becomes very thick when lenses are made, especially for users with strong myopia. When the edge of the lens becomes thick the edge will stick out from the frame causing the looks of the glasses to worsen.
In addition to this problem of the looks of the glasses, when the myopia is too strong, it can even become hard to find a lens that can be made for the user.
To answer to these inquiries for a thin lens, even for a strong myopia, TOKAI has a processing method to manufacture the edge of the lens thin as possible.
This processing method is called the “Smooth line Process”.
In this process method, first a lens is made in the standard method, than handcrafted to sharpen the edge, using many different types of tools. There are cases in which even the tool must be made by hand to proceed in the sharpening of the lens.
The visual of the lens improves by shading off the border of the part in which the lens is sharpened and the part where the power is on the lens meets.
The smooth line processing is suitable for such user that…
- have the needs for a strong power for strong myopia, and wants to make the visual as good as possible.
- have once gave up on making a glass due to that the required power was too strong and the lens edge becomes too thick.
Examples made with the “Smooth line Process”
These are examples actually made by TOKAI in the past.
These are high power lenses that can not be made in the standard production, but TOKAI will try to answer to these request by recommending the most proper solution for the user, together with the user.
※※ Attention ※※
- The example shown is a mineral lens. Rimlon frames and rimless frames cannot be used for the mineral lens.
- The range of the area on the lens with dioptric power will be limited according to each prescription.
In the standard range of up to +15.00D at TOKAI, the lenses used to treat hypermetropia are called the “positive meniscus lens” which has a convex surface on the front and a concave surface on the back.
The lens which TOKAI suggested was,
- a plastic biconvex lens which has a convex surface on both the front and the back. (the first time producing for the plastic lens)
- using the 1.76 material plastic lens material which is the world’s thinnest index material.
- to use a aspheric surface on the back surface to reduce the aberration.
The reason why we did not suggest the meniscus lens is,
- due to that to make the lens in the prescription power necessary, there was a need to specifically make a material, causing the lens to become very expensive.
- due to that the lens will become thick and bad looking, since the front base curve estimated needed was strong.
- due to that the heavy lens will become a stress not only to that it looks bad.
In this specific case we decided to make the biconvex lens to make the lens thin and light as possible. We thought that since the wearer was a child, the weight of the face, and how it looks will effect strongly to the stress.
How to produce the biconvex lens.
- We remade our calculation programs to calculate aspects for the biconvex lens, such as its thickness.
- We rebuild the processing data within the our machines so that the newly calculated lens could to be finished as what has been calculated and designed.
- The back surface of the lens was surfaced into a convex surface using the newly programed generator. (surfacing machine)
- The convex surface surfaced on the back side was polished, using the newly programed polishing machine.
The Biconvex Lens is suitable for such users that…
- wants to make the lens thin as possible, even with strong hypermetropia.
- patients with strong hypermetropia whom gave up on making a pair of glasses, due to that the needed power was out of the production range of the manufacturers asked.
※※ Attention ※※
- The biconvex lens can be made in mineral materials as well, although for mineral lenses, it is not suitable for rim-less frames, and rimlone frames.
- The area with the prescribed power on the lens will be limited according to the prescribed power.
- The peripheral areas of the lens will have strong aberrations.