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Glasses

Making your money go further
GeoffF100
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Glasses

#392760

Postby GeoffF100 » March 5th, 2021, 2:39 pm

I have just had an eye test. The young lady at Specsavers persistently claimed that 0.25 diopters reversion back to a previous value would make a huge difference. My experience was that it did not. My distance glasses are fine. I could, however, do with a pair of computer glasses. The add on power needed for computer glasses (over distance glasses) in diopters is one divided by the distance from the screen in metres. The young lady did not seem to get that. I left in frustration, but her suggested (a weak word given her attitude) value of 1.75 diopters is about right. If I return to order a pair, I will be no doubt faced with claims that expensive extra super thin lenses will make a huge difference. Let us look at the numbers.

https://www.quora.com/What-is-the-relat ... -of-a-lens

power = 1 / focal_length = (refractive_index - 1) / radius_of_curvature

(power is in diopters, and focal_length and radius_of_curvature are in metres.)

Specsavers does not say what the refractive indices of its lenses are, but I found this for Superdrug:

https://opticians.superdrug.com/which-lens-thickness

Bronze Standard 1.5 index CR39
Gold 1.6 index
Gold+ 1.67 index
Platinum 1.74 index

Let R = radius of curvature, r = radius of the lens and x = the thickness of a single curved surface lens that is infinitely thin at the centre.

For a concave lens (I am short sighted), Pythagoras's Theorem gives:

(R - x)^2 + r^2 = R^2

R - x = sqrt(R^2 - r^2)

x = R - sqrt(R^2 - r^2)

My computer glasses would need a power of -6 diopters. Plugging the numbers into a spreadsheet gives:

Bronze     1.5     3.2 mm
Gold 1.6 2.7 mm
Gold+ 1.67 2.4 mm
Platinum 1.74 2.2 mm

That is 1 mm difference in thickness between the cheapest and the most expensive lens. I also have some astigmatism, which would add the the thickness of the lenses (and the centre of the lens would not be infinitely thin either). Nonetheless, the improvement given by the expensive lenses would not be much to shout about.

GeoffF100
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Re: Glasses

#392805

Postby GeoffF100 » March 5th, 2021, 3:59 pm

I should have mentioned that the radius of the lenses of my glasses is 2.3 cm, i.e. 0.023 m.

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Re: Glasses

#392817

Postby bungeejumper » March 5th, 2021, 4:32 pm

GeoffF100 wrote:That is 1 mm difference in thickness between the cheapest and the most expensive lens. I also have some astigmatism, which would add the the thickness of the lenses (and the centre of the lens would not be infinitely thin either). Nonetheless, the improvement given by the expensive lenses would not be much to shout about.

I'll leave the mathematics to those who know more about these things than I do, but the whole business of gold/silver/platinum/any old iron just smells too much like a load of overblown hype to me. And the same goes for all those expensive lens coatings. I don't doubt that there are some genuine advantages to getting the fancier options, but the average visit to the opticians is a bit like going into a car showroom and getting the full up-sell treatment when all you really want is the comfortable model with not too many gizmos.

The last time I went to SpecSavers I didn't end up buying anything at all, because the young lady had annoyed me so much with the hard sell that I went off in a huff and bought my reading specs from Glasses Direct instead. Same branded frames, thinned lenses, about a third of the price. The only real snag with mail order is that you do have to know your own pupillary distance (the exact distance between the centres of your eyes), and the chances are that your optometrist keeps that information fiercely private as his/her own personal ticket to making a sale.

There was, however, another reason why I didn't stick around for the sales pitch at SpecSavers. I might have been close to my 70th birthday, but any optometrist who sits me down and repeatedly calls me sweetie is going to get a pair of carbon fibre nose ends right where she least expects it. :evil:

BJ

PhaseThree

Re: Glasses

#392822

Postby PhaseThree » March 5th, 2021, 4:34 pm

I always get the prescription then order from elsewhere - Selectspecs have always done well for me and are currently selling their cheapest glasses at £6 a pair for basic lenses or £15 with thin lenses. Cheap enough to experiment,

https://www.selectspecs.com/cheap-glasses/

Note :- There are apps around to measure inter Pupil Distance or a ruler works work pretty well too.

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Re: Glasses

#392878

Postby AF62 » March 5th, 2021, 7:12 pm

GeoffF100 wrote:I will be no doubt faced with claims that expensive extra super thin lenses will make a huge difference.


If you buy glasses from Asda opticians then they include in the fixed price thinner lenses if you need them - there is a set scale so a 'normal' prescription and you get 'normal' lenses but outside that the stronger the prescription you go up from the range of normal lenses to the super thin lenses. And they include the anti-reflection coating in the price. And they include varifocals in the price.

As someone with a minus 8 prescription the last pair of glasses with super thin lenses cost me £50 from Asda. I shudder to think what they would have cost elsewhere.

Sure you can get cheaper online, but for a 'bricks and mortar' optician they cannot be beaten.

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Re: Glasses

#392890

Postby Stompa » March 5th, 2021, 7:48 pm

bungeejumper wrote:The only real snag with mail order is that you do have to know your own pupillary distance (the exact distance between the centres of your eyes), and the chances are that your optometrist keeps that information fiercely private as his/her own personal ticket to making a sale.

Quite why it's not automatically included on the prescription is beyond me, other than for the reason you've given of course. But whenever I've asked for it it's been provided without any fuss.

Interestingly, Specsavers have a tool which allows you to measure it online:

https://www.specsavers.co.uk/glasses/bu ... y-distance

I've no idea how good/bad/accurate it is.

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Re: Glasses

#392893

Postby GeoffF100 » March 5th, 2021, 7:53 pm

I tried Asda several years ago. Their -7 prescription glasses were rather thick. I am sure that they did not use thinner lenses. That was not much of a concern, but the lenses scratched badly. Asda said that they had all the coatings, but they clearly did not have an anti-scratch coating. When they got really bad, I drove back to the store. They said the lenses were just out of warranty. They offered to send them back to the manufacturer for evaluation, but I would have to pay if the manufacturer did not find fault with them. They offered me a good deal on a new pair, but they only had letter box shaped lenses, which were fashionable at the time. I looked at Asda's website earlier today. Their £45 glasses are all square and I want round. There was a good choice at £80, but there should be at that price.

I have looked into pupil distance. Glasses direct asks for a selfie with a credit card on my forehead. That does not look too hard. They have got Everly round stainless steel glasses for £20 + £10 for lenses. They should do the job.

Specsavers have got Rufus round tortoise shell round plastic glasses for £49.

Boots has got M2174 round tortoise shell round plastic glasses for £40.

I can walk to Specsavers and Boots. I had my latest eye test at Specsavers, but I have used Boots in the past, so they should still have my records. I gave up on Boots when they did a very bad job of adjusting my glasses, and did not fix the problem properly despite repeated visits. Hopefully, the people concerned have moved on. I have not had any complaints about the glasses that I have got from Specsavers.

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Re: Glasses

#392894

Postby GeoffF100 » March 5th, 2021, 7:55 pm

The Specsavers tool is a credit card on your forehead. That seems to be the standard method for online retailers.

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Re: Glasses

#392895

Postby AF62 » March 5th, 2021, 8:01 pm

GeoffF100 wrote:I tried Asda several years ago. Their -7 prescription glasses were rather thick. I am sure that they did not use thinner lenses.


They used to have a chart on the desk which showed which lenses came with each band of prescription strength and from the snap I took at the time -

For full frame glasses -

>=+7.25 - Seek advice from the optician
+6.25 to +7.00 - Super Thin & Light (1.67 ASPH)
+4.25 to +6.00 - Extra Thin & Light (1.60 ASPH)
+3.25 to +4.00 - Anti Reflection (1.50 ASPH)
Plano to +3.00 - Anti Reflection (1.50)
Plano to -3.00 - Anti Reflection (1.50)
-3.25 to -5.00 - Extra Thin & Light (1.60)
-5.25 to -7.00 - Super Thin & Light (1.67 ASPH)
-7.25 to -9.00 - Super Thin & Light (1.70 ASPH)
>= -9.25 - Seek advice from the optician

For rimless glasses -

>=+6.25 - Seek advice from the optician
+3.25 to +7.00 - Super Thin & Light (1.60 ASPH)
Plano to +3.00 - Extra Thin & Light (1.60)
Plano to -5.00 - Extra Thin & Light (1.60)
-5.25 to -7.00 - Super Thin & Light (1.67 ASPH)
-7.25 to -8.00 - Super Thin & Light (1.70 ASPH)

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Re: Glasses

#392899

Postby Lootman » March 5th, 2021, 8:09 pm

bungeejumper wrote: the same goes for all those expensive lens coatings. I don't doubt that there are some genuine advantages to getting the fancier options, but the average visit to the opticians is a bit like going into a car showroom and getting the full up-sell treatment when all you really want is the comfortable model with not too many gizmos.

The last time I went to SpecSavers I didn't end up buying anything at all, because the young lady had annoyed me so much with the hard sell that I went off in a huff

The thinner lenses are a must for any stronger prescription, unless you like the "coke bottle" look. Plus thick lenses weigh more and modern frames are very lightweight - my last pair is made of titanium.

I am picky about the lens coatings. Anti-scratch can be worthwhile as I had one pair ruined by a scratch. And I choose non-reflective because I do not like looking at other people whose lenses are like mirrors. But I don't do the light-reactive type nor the bi/multi-focus types.

My approach is not to go to a high street place at all. I go and see a proper ophthalmologist once a year and, amongst all the tests he does, I get a prescription that I can take anywhere. He doesn't sell glasses, of course. He is not cheap but the equipment and tests he does are a marvel to behold. And when I eventually need to get my cataracts done, he teaches cataract surgery at a university teaching hospital. Some girl calling me "sweetie" in a shop next to a kebab house isn't really the same.

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Re: Glasses

#392901

Postby GeoffF100 » March 5th, 2021, 8:20 pm

It was a long time ago when I went to Asda. It think I ordered extra thin and light, but my memory may not be accurate after all this time.

Glasses Direct say they routinely do standard refractive index 1.5 up to plus or minus 6. I just make that hurdle with computer glasses. I do not believe that should be an issue, particularly with the round plastic frames. I should be able to adjust those with a hair dryer. Not expensive, but extra expense. I can probably just bend the stainless steel wire frames into shape. Cosmetics are not an issue for computer glasses that I use at home.

A 6 mile round trip walk into the city is exercising locally. I will probably do that tomorrow.

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Re: Glasses

#392986

Postby GeoffF100 » March 6th, 2021, 9:00 am

In the Asda list above ASPH stands for aspherical. Aspherical lenses are up market and may be thinner. I assumed a spherical surface in my calculations above. A big problem here is that you are told that your lenses will be "extra thin" or whatever, but you are not told what that means.

Having slept on it, I think my most sensible option is to order online. I was Pfizered over a month ago, but visiting an optician is still risky. It was necessary to have an eye test to check that all was well, but further visits are an unnecessary risk. Glasses Direct looks good. These glasses look suitable:

https://www.glassesdirect.co.uk/glasses ... trustpilot

The all up cost is about £35. Not much risk. Adjustment should be easy. I should be able to just bend them:

https://youtu.be/D-IJNlNBZZk

Pupillary distance should not be a problem. I can just email them a selfie with a bank card on my forehead:

https://www.glassesdirect.co.uk/pupillary-distance/

Stay away from the Covid!

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Re: Glasses

#393009

Postby GeoffF100 » March 6th, 2021, 10:08 am

I get an error when I add my prescription on the Glasses Direct website. It tells me that the sum of my spherical plus cylinder must be in the range -8 to +8, but it is outside that range. There is a number to ring, but that is getting complicated. I will take the risk of visiting Specsavers and Boots.

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Re: Glasses

#393013

Postby 88V8 » March 6th, 2021, 10:25 am

Twelve years ago, when my short vision began to decline, an independent made me some lift-up glasses to use in the workshop. A frame hinged to a frame, where the front frame has the lenses.
Boots were able to relense them for me three years ago but it took a lot of song & dance and they went back twice to the factory because they first sent them with the glass in both frames then in the inner frame... sigh.

I used to get good service from Kodak, then they moved away.

I really need glasses for the computer and using my phone, but I try to manage without as I find that after wearing specs my eyes seems a lot worse.

V8

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Re: Glasses

#393108

Postby Stompa » March 6th, 2021, 2:10 pm

I suspect the OP will have already discovered this, but just in case he hasn't I'd point out that there are a number of online lens thickness calculators available, for example:

http://opticampus.opti.vision/tools/thickness.php

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Re: Glasses

#393139

Postby GeoffF100 » March 6th, 2021, 4:27 pm

I do not believe that calculator. The thickness values that it gives are too small for spherical lenses.

The saga continues. Specsavers was rammed. They would not let me in without an appointment. They were busy turning customers away. I went into Boots. It was virtually deserted. They said that it would be illegal for them to make me intermediate glasses because my prescription did not have an intermediate addition. They said that I should go back to Specsavers and get my prescription amended. They also said that they would be retesting a 71 year old after on year, not two. They said that they did not have the £40 M2174 in store but could order it, so I seem to have a peg in the ground. The young lady said that they could make my glasses with standard lenses. It looks as though I will have to phone Specsavers and go back on Monday.

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Re: Glasses

#393181

Postby GeoffF100 » March 6th, 2021, 6:56 pm

I horrible thought here is that Specsavers probably does not have to provide an intermediate addition with an NHS test. If I want Boots glasses, I could pay for a £25 Boots test. There is a Vision Express opposite. Their cheapest eye test costs £50. I thought we had left these problems behind.

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Re: Glasses

#393195

Postby 88V8 » March 6th, 2021, 8:05 pm

I bet most people just go with whatever is prescribed.
Probably spend more time pondering the frames than the minutiae of the prescription.
Ignorance is bliss.

V8

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Re: Glasses

#393244

Postby GeoffF100 » March 7th, 2021, 8:07 am

I have some further pieces to the jigsaw puzzle. Specsavers is a franchise operation. The optician who tested my eyes shows as the "Ophthalmic Director" on the local branch website. I expect that he profits personally if I buy glasses from that branch.

I made it very clear that I was looking for computer glasses. At the end of the test, he said he would speak to somebody about the computer glasses. As I have said, the young lady proposed an intermediate addition of 1.75. That number was not on my prescription, and she would not discuss the basis for it. She had already annoyed me by persistently trying to sell me distance glasses. I got fed up and left.

The correct procedure appears to be for the optician to put the intermediate addition on the prescription and for the dispensing optician to use that. I expect that did not happen because the optician wanted to stop me taking the prescription elsewhere.

I expect diplomacy rather than confrontation is best here.

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Re: Glasses

#393553

Postby GeoffF100 » March 8th, 2021, 10:27 am

Just rang Specsavers. The earliest appointment for them to sell me glasses is in a week's time. I have booked a slot, but this is not good at all.


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