View Full Version : How does it work ?

17th Aug 2011, 11:51
Remember those far-off days, those of us who wear spectacles, when a visit to the optician meant drops in eyes, wearing a heavy frame into which he or she popped lenses and said is this better ?...or this ? and just as you thought your mind was made up, ...or this ? and then more drops to expand the lens (cornea ?) so he or she could peer into your very soul....and after waiting hours for your eyes to clear up and get the focus back, you went home with a splitting headache (or I did, anyway).

Well, I went for a check-up yesterday as She Who Must Be Obeyed decreed I should before buying new spectacles.

First you peer into one machine where there's a tiny picture of a red house on a green field with a brown road. The machine umms and errs and the focus changes, then the other eye - and the machine spits out a printout with a complete prescription for the corrective lens in each eye. Then the next machine which blows a puff of air against each lens and spits out ANOTHER print out of intra-occular pressure. These two machines take - what ? - about 90 seconds to do their work.

Then - I suppose just to make sure, or to justify the bill, or to maintain a link with the past, the old metal frame is placed on one's head - but with the corrective lenses in it which the first machine specified - and he says "can you read that" and I say "yes" because it's always right first time.

Now I can understand the second machine testing the resilience of the front of the eye because when a puff of air is shot at it obviously tests the internal pressure. But how does the first machine work ? I assume some beam is focussed into the eye and it susses out lack of roundness, etc. Or is it reflected back distorted from the retina and the machine calulates what must be done to correct it ? Anyone know ?

Smart stuff, anyway.

BTW, everyone over 60 should get their retinas looked at for signs of degeneration, because once AMD has started it can be stopped but the damage already done can't be put right.

17th Aug 2011, 12:37
From my time working in opticians (a fair few years ago now). we had both of those machines and I used to operate them both.

The auto-refractor (with the house in the distance going blurry), basically uses the same technique the optician uses to test the eyes of unresponsive patients (have you ever wondered how they work out the prescription of a 1 year old, or a disabled, mute patient?).

This is done by using different lenses and a light to effectively test how strong your lens is and what refraction is need to focus an image on the retina. The exact science I'm unsure of, but that's what I picked up from my time there.

The justification of the fee (given your time with the optician), is that a) they are ultimately responsible for your prescription once you walk out of the door and it's their signature on the script, and b) those machines can get it royally wrong if the patient doesn't look where they're supposed to at the right time.

Hope that helps a little. :ok:

Oh, and a quick google, gave me the following: Eye Refraction - Eye Refraction Tests (http://vision.about.com/od/eyeexamination1/a/Eye_Refraction.htm)

17th Aug 2011, 12:47
So you did it till you went blind then OFSO? :}

Me too - I now have a L 1.13 / R 1.19 diodopter thingy rating.
The optiquack worked it out in 40 secs flat using a red circle
and green cross machine, and never even used the lens box.

And he didn't need to ask me how I often I played with me
todger either.

17th Aug 2011, 13:53
Now there's timely!

For years I had ummed and aahed about getting the laser thingy done to sort out the short sightedness but, the warning from the doc was that it might screw the pilot's licence. Eventually they said it was OK and then followed a few more years of umms and ahhs (didn't like the thought of someone mucking about with the Mk 1 eyeball). Eventually, I made the decision. There was window of opportunity. I had the spare cash. I made enquiries.

The upper age limit is 60 they said!! Merde with a capital F says I. But there may be other solutions they said...come along for a chat.

So, to cut a long story short. I had the last of 2 cataract operations last Tuesday (don't ask - it probably would require to be done in the future and it short circuits the coverage with private health).

I now have better than 20/20 vision. The operations were an absolute doddle and it's like I've got a new life having worn specs/lenses since age 10. And it cost me bugger all. :ok:

Now why does pprune substitute a @ in place of an a when writing l a s e r??

17th Aug 2011, 14:12
Hmm. Reach 60 in April. How long does the [email protected] thing last? Specs are costing me about 300 quid every 2 or 3 years.

sisemen: it's to stop the adbots from advertising coherent light thingies that might be pointed at aircraft.

17th Aug 2011, 14:20
How long does it last ?

Strangely enough at 68 my eyes haven't changed in the past 9 years. I've plateaued-out. I don't need specs to read and never have but past 50cms everything is out of focus, and been like that since I was eight years old.

The euphoria about laser correction should be kept in limits. Since the reason why most older people need glasses is that the eyeball loses it's resiliance and can no longer change shape to focus, NOTHING is going to change the fact that you will need glasses at some time.

I contemplated having it done but than went through the list of everything that's landed up against my spectacle lenses in the past.

Bits of hot metal from an angle grinder (tiny particles still embedded in my current lenses), molten solder from using an 'iron to desolder tags, various chemicals, and the like.....and decided to keep wearing spectacles.

When I was younger it was not unusal for me glasses to go hurling across the room from one or another young ladies back-handers, after I made a saucy suggestion of some sort of naughtiness we might indulge in together, but as I got older (and they did) acquiesence was far more common. Nowadays I don't make such suggestions, and if I did they'd only laugh and say "isn't he sweet" and bring my slippers and Powers Gold Label.

17th Aug 2011, 14:40
I'm 69 and don't yet need specs for distance viewing.
but had ćo buy some cheapies for reading. Strength 2.0.

17th Aug 2011, 14:47
Yeah, it's funny that. I'm now having to get used to tears when I do onions and get into smoke.

Still have to use specs for reading.

tony draper
17th Aug 2011, 15:09
I only need my glasses for seeing.:rolleyes:

17th Aug 2011, 15:18
Worked with top Opthalmologists for over 20yrs. Not had corrective surgery myself having it offered for free, and the majority of consultants I know wear glasses.
Not saying it is dangerous nor 100% effective, but even now things do and can go wrong.
When you reach about 40 - 45 that is when the eye muscles start to "slacken off" and the need for reading glasses is seen. The eye should stabilise around 55, but mine at 57 still are changing. I had thicker lenses when I was younger but you progressively go more hyperopic as you age resulting in thinner lenses.
So if you had the op done when young you would still need glasses as you hit 40-45. They are now saying you can have it done twice however that is dependent on the original type of op. The latest technique is flap and zap, where the cornea is peeled back and the lens reshaped. A newer method of replacing the lens with a corrected one is starting to catch on but obviously is a lot more expensive.
When choosing a clinic please check up on the surgeons qualifications and experience on doing the procedure.
You only have one set of eyes and eyesight is a precious gift:ok:

tony draper
17th Aug 2011, 15:26
Hmmm, wonder if they will ever try a eyeball transplant?:confused:

18th Aug 2011, 01:34
that it uses the same programme as auto focus on a digital camera. The 'picture' is seen by a small camera looking into you retina,and the lines the computor sees are adjusted electronically until they are crisp and straight. The numbers need in the correction are translated into a lense correction factor and the lense made. Clever stuff.:ok:

18th Aug 2011, 06:18
Hmmm, wonder if they will ever try a eyeball transplant?

I'd certainly like to try seeing life through your eyes Drapes! :E

18th Aug 2011, 08:44
I'd certainly like to try seeing life through your eyes Drapes!

For me, only one of his would suffice :uhoh:.

18th Aug 2011, 10:01
I doubt if Drapes would give any anyway :E.

tony draper
18th Aug 2011, 10:14
One thinks one's eyes could be described as 'Jaded' :rolleyes:

18th Aug 2011, 10:30
Hmmm, wonder if they will ever try a eyeball transplant

Not until they've perfected replicating that piece of string that they use to tie each eyeball to the back of your head.

To see life through Drapes' eyes :eek::eek: What has been seen cannot be unseen.

18th Aug 2011, 10:32
I am not going to blink. I am not going to blink. I am not going to blink.


Buggah! Blinked.

The bright young things in my opticians use the puffer. The senior partner is old school and uses the eye drops and spring balance gadget. Everytime I go he explains the difference between short sighted and long sighted but it hasn't sunk in yet. :confused:

They've got that whizzy box of tricks which takes picures of your retina and then displays them on a PC in 3D. It can also do ray tracing and show you where your lenses will focus and the effects of various strength prescriptions. Fascinating stuff. :ok:

tony draper
18th Aug 2011, 10:37
As optical instruments they leave a lot to be desired though,the image they produce is back to front upside down bilateraly transposed seriously chromatically abberated suffering gross pincusion distortion,they need pounds of gooey computer prossessing and billions of neurons to make any sense of their output,still one would hate to be without em.

18th Aug 2011, 14:42
One has read in several American Defective Stories that the last thing one sees remains emprinted upon one's retina, and that printing this off a victim's eyes has resulted in the murderer being captured. I find this hard to believe, somehow.

tony draper
18th Aug 2011, 14:51
Think that image retaining stuff was called visual purple or summat,load of old bollix:rolleyes: