Why are we ripped off to have perscription lenses made thinner ???? - HotUKDeals
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Why are we ripped off to have perscription lenses made thinner ????

dapunk Avatar
7y, 10m agoPosted 7 years, 10 months ago
Why does it cost so much, I recently had to play £60 to make lenses thinner and this was the starting price ???? It went up again another £60 for another thinner option and again even further £80 for an even thinner option again.

I asked why it cost so much and was given some garbled response "because of the complex compounds they use" but I since found out one online retailer state there is not much price difference between stand lenses and thin lenses. If so why even offer standard lenses ,would you want heavy glasses as an options ?

I think its about things should start changing here because we are clearly being ripped off by some consortium price fixing.

So does anybody know the process to why the price costs so much for thin lenses, and why the progressively creeps up the thinner they go ??
dapunk Avatar
7y, 10m agoPosted 7 years, 10 months ago
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Comments/page:
#1
All the frames are thin now or rimless, but these look no good if your -5 and your lense look like milk bottles !

Also notice how they try and sell glasses that look like your looking through a keyhole with not much area.

D.
#2
Can't see your arguement!




I need new thinnner glasses :)
#3
And this why I finally got my eyes "cured" by laser surgery. Just got sick and tired off spending hundreds each year on contact lenses and glasses.
#4
I've just picked this off Wikipedia, doesn't explain costs but explains the differences.

Refractive index
In the UK and the US, the refractive index is generally specified with respect to the yellow He-d Fraunhofer line, commonly abbreviated as nd. Lens materials are classified by their refractive index, as follows:

Normal index - 1.48 ≤ nd < 1.54
Mid-index - 1.54 ≤ nd < 1.60
High-index - 1.60 ≤ nd < 1.74
Very high index - 1.74 ≤ nd
This is a general classification. Indexes of nd values that are ≥ 1.60 can be, often for marketing purposes, referred to as high-index. Likewise, Trivex and other borderline normal/mid-index materials, may be referred to as mid-index.


[edit] Advantages of higher indexes
Thinner, lighter lenses See Below
Convergent lenses (to correct hyperopia) of the same refractive power have a thinner center thickness when made from higher index.
In highly myopic cases high index can minimize edge thickness. This reduces light entering into the edge of the lens, reducing an additional source of internal reflections. This also makes the lenses more cosmetically appealing.
Since the lenses are made thinner, less material is used, making them lighter

[edit] Disadvantages of increased indices
Lower Abbe number meaning, amongst other things, increased chromatic aberration.
Poorer light transmission and increased backside and inner-surface reflections (see Fresnel reflection equation) increasing importance of anti-reflective coating.
Manufacturing defects have more impact on optical quality[citation needed].
Theoretically, off-axis optical quality degrades (oblique astigmatic error). In practice this degradation should not be perceptible - current frame styles are much smaller than they would have to be for these aberrations to be noticeable to the patient, the aberration occurring some distance away from the optical centre of the lens (off-axis).

Reducing lens thickness
Note that the greatest cosmetic improvement on lens thickness (and weight) is had from choosing a frame which holds physically small lenses. The curves on the front and back of a lens are ideally formed with the specific radius of a sphere. This radius is set by the lens designer based on the prescription and cosmetic consideration. Selecting a smaller lens will mean less of this sphere surface is represented by the lens surface, meaning the lens will have a thinner edge (hyperopia) or center (myopia).

Index can improve the lens thinness, but at a point no more improvement will be realized. For example, if an index and lens size is selected with center to edge thickness difference of 1mm then changing index can only improve thickness by a fraction of this. This is also true with aspheric design lenses.

The lens minimum thickness can also be varied. The FDA ball drop test sets the minimum thickness of materials. Glass or CR-39 requires 2.0mm, but some newer materials only require 1.5mm or even 1.0mm minimum thickness.


[edit] Weight
Material density typically increases as lens thickness is reduced by increasing index. There is also a minimum lens thickness required to support the lens shape. These factors results in a thinner lens which is not lighter than the original. There are lens materials with lower density at higher index which can result in a truly lighter lens. These materials can be found a material property table. Reducing frame lens size will give the most noticeable improvement in weight for a given material.

The full article can be read here

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