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Eye test (1 Viewer)

Binastro

Well-known member
Yesterday's eye test went well as my eyes were rested.

One eye remains the same as a year ago.

The other needs a change of 2.5 degrees in the axis for astigmatism.
An extra 0.25 dioptre of power.
0.75 dipotre of prism correction, whereas last year there was no prism correction.

I asked if the lab works to these standards.

The optometrist said most labs don't.
They say the normal 2 degree tolerance takes care of small changes.

However, the boss of one lab is more flexible.
My optometrist says 'I have a crazy astronomer who consistently sees small differences and wants prescriptions made to accurate corrections'.

So it is possible to get high accuracy lenses, but most labs don't work to these standards.

There are no significant cataracts and the eyes are fine otherwise.
However, the small 'bubble' I see could not be detected.
It is about 0.3mm in size.
He says that he needs a high power microscope to see these problems in the lens, and one was not to hand.

Although this 'bubble' appears right and above centre, it is actually in the opposite direction in the lens of the eye, as the image we see is inverted.
 
David,

Perhaps Lars (looksharp65) will chime in on this.
I would have thought that 0,25 dioptres here or there (the smallest tolerance) would make much more difference than small changes in the axis angle.
Most tests for far vision are made at about 4 m. That is 0,25 dioptres. I asked both my eye docter and my optician if they added this to the prescription. Both said not, and that 4 m was to all intents and purposes infinity!

John
 
As far as I know U.SA doctors use 20 ft. for infinity 4 m. would be about 13ft. I have had my Dr. take me out and show me that the prescription was ok for longer distance, I had some trouble with his prescriptions at distance in the past . I am 66 yrs. old so that might be some of it.;) The thing I think about is that they use mirrors but the distance to the mirror you are looking at is closer than 20ft.
 
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As far as I know U.SA doctors use 20 ft. for infinity 4 m. would be about 13ft. I have had my Dr. take me out and show me that the prescription was ok for longer distance, I had some trouble with his prescriptions at distance in the past . I am 66 yrs. old so that might be some of it.;) The thing I think about is that they use mirrors but the distance to the mirror you are looking at is closer than 20ft.

I'm 66, too, and believe that any eye doc who thinks 20 feet is "infinity" needs to have his license pulled—they don't think on an astronomical scale. Even the US Navy—working with optical engineers and ophthalmologists—settled on 1 NAUTICAL mile, or 6,000 feet. Sometimes what is taught in school has little relevance in the real world. Also, even at our age, 2 full millimeters of accommodation is to be expected. So, a deviation of .25 diopters (8 times smaller) should be inconsequential. :cat:

Bill
 
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Ted so if we are the computer and there is a window that we can look out it is a good idea to look out the window every so often for a least 20 seconds looking at green objects. I can do that , we have lots of trees etc.. I have done this lots of times. I wonder if I should start drinking beer that comes in green bottles?;) BTW another thanks for the links Pileatus!
 
Ted so if we are the computer and there is a window that we can look out it is a good idea to look out the window every so often for a least 20 seconds looking at green objects. I can do that, we have lots of trees etc.. I have done this lots of times. I wonder if I should start drinking beer that comes in green bottles?;) BTW another thanks for the links Pileatus!

Hi, John, Ted, and Mooreorles:

It should be remembered that it was an EXPERT, a DOCTOR, an OPTOMETRIST who told a customer of mine she should always focus her right eye first because she was “right eye dominant.” Regardless of the medical science, this advice was wrong because the vast majority of CF binoculars focus LEFT SIDE FIRST and no amount of medical training has been able to change thinking in the consumer optics industry—thank goodness.

I would be the first to admit the Navy’s tolerance for collimation was unrealistically stringent for a non-wartime situation and I only used it on quality binos capable of holding it. My everyday standard for middle of the road instruments was Dr. Johnson’s (Imperial College of Science and Technology, London) observation, which was much tighter than anyone other than Superman could detect.

I have no doubt that—IN A PERFECT WORLD—“infinity” need not be 6,000 feet to 6,000 light-years. At 6,000 light-years there’s a good chance birds would be oxygen starved. But, should there not be a universal target? Were it not so, our threads would be filled with nitnoids complaining their binocular was collimated for 200 feet when it should have really been collimated for 199.7119643 feet.

In addition, let’s say the bino is collimated at (medically popular) 20 feet for a fellow with a 72mm IPD. What happens to collimation when the IPD is dropped to 54mm for a son or daughter?

That’s the kind of thing that is ALMOST NEVER thought of by those who live in an academic or medical world. But as Aristotle was prone to say: “Reality bites!”

Numerous tests have repeatedly shown that dioptric accommodation ranges from as much as 14 diopters for a 10-year old to as little as 2 diopters for a person in their 60s. Thus, I have a difficult time understanding why a .25 diopter difference would cause the slightest problem for a person of any age without the problem being related to a number of physiological problems, such as weakness or hardening of the ciliary muscles, or some degree of synaptic blockage (http://jpet.aspetjournals.org/content/140/1/19). :cat:

Just a thought,

Bill
 
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Doctors have 10 minutes to see patients, opticians 20 or maybe 30 minutes.
This is not enough time for a comprehensive eye test.
So they do what they are taught and use 6 metres or 20 ft and say it is infinity.

My eye tests usually take 90 minutes, but the recent one 75 minutes as my eyes were very relaxed.

6 metres or 20ft is not infinity.

My astro glasses are computed at 37 metres.
I observe a wall at this distance in good light. There are fine details in the bricks and mortar.

The astro glasses are clearly different to my distance glasses computed for 6 metres or 20 ft.

My accommodation is about 0.5 dioptres, although more than one dioptre first thing in the morning with rested eyes.

I clearly see more and better stars with the astro glasses rather than my distance glasses.
The fact that I can accommodate 0.25 dioptres is to me tiring. Why should I?

The boss of the optical lab makes the lenses accurately, although there must be some slight variation from my prescription.

Incidentally, my optometrist used his 1/8th dioptre lens with me till two years ago, as I could repeatedly see the difference.
He wrote the prescription to 0.125 dioptres.

P.S.
There is a difference in focus for ones eyes at night compared to daytime, but the astro glasses computed for 37 metres seem to work well, at least in light polluted skies.
 
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I can attest, from spending a fair amount of time on the water, that some individuals have much better vision than others. In some cases a profesional fisherman's ability to see birds or fish better than the average charter client is down to familiarity with what he is looking at, but there is no doubt in my mind that some folks simply have better visual acuity than others. When observing a bird in flight side by side with my brother, both of us using glasses made to prescriptions drawn up by the same optician and therefore made using similar tests and measures, I need to go to binoculars earlier. There is no doubt in my mind that some individuals are more capable of (for want of a better expression) "stacking BBs" than others.
 
Doctors have 10 minutes to see patients, opticians 20 or maybe 30 minutes.
This is not enough time for a comprehensive eye test.
So they do what they are taught and use 6 metres or 20 ft and say it is infinity.

My eye tests usually take 90 minutes, but the recent one 75 minutes as my eyes were very relaxed.

6 metres or 20ft is not infinity.

My astro glasses are computed at 37 metres.
I observe a wall at this distance in good light. There are fine details in the bricks and mortar.

The astro glasses are clearly different to my distance glasses computed for 6 metres or 20 ft.

My accommodation is about 0.5 dioptres, although more than one dioptre first thing in the morning with rested eyes.

I clearly see more and better stars with the astro glasses rather than my distance glasses.
The fact that I can accommodate 0.25 dioptres is to me tiring. Why should I?

The boss of the optical lab makes the lenses accurately, although there must be some slight variation from my prescription.

Incidentally, my optometrist used his 1/8th dioptre lens with me till two years ago, as I could repeatedly see the difference.
He wrote the prescription to 0.125 dioptres.

P.S.
There is a difference in focus for ones eyes at night compared to daytime, but the astro glasses computed for 37 metres seem to work well, at least in light polluted skies.

Nicely put, David. :t:
 
The four navy divers, including a doctor, who spent about a week in darkness, with occasional torch light, had to protect their eyes when they emerged from the Thai cave.

The children who spent more than a fortnight in almost complete darkness would need to take extra care.
Hopefully they were introduced to dim torch light for an hour or so before they emerged.

I have noticed strong negative effects after maybe 5 hours sleep, if exposing my eyes to bright sunshine.
I completely avoid that where I can.

I have not read research papers as to the effects of sunlight on long term dark adapted eyes, but have seen reports of blindness in extreme cases.
 
I can attest, from spending a fair amount of time on the water, that some individuals have much better vision than others. In some cases a profesional fisherman's ability to see birds or fish better than the average charter client is down to familiarity with what he is looking at, but there is no doubt in my mind that some folks simply have better visual acuity than others. When observing a bird in flight side by side with my brother, both of us using glasses made to prescriptions drawn up by the same optician and therefore made using similar tests and measures, I need to go to binoculars earlier. There is no doubt in my mind that some individuals are more capable of (for want of a better expression) "stacking BBs" than others.
Or sometimes it's just what people can pick-out.

Near as my partner and I can tell, I have better vision overall. I can see far away better, and with readers, up close better.

Yet she often spots camouflaged birds (like great herons or rails amongst the reeds) at a distance before I do. She admits they are often blurry and when she points them out I can see them quite clearly once I find them.

So some of it is the optical nature of sharpness and vision, and some of it may just be how the brain "sees" the image presented to it by the eye. She is the artsier of the two of us, and I suspect that plays a part (creative visual thinking).
 
That is the difference between observational skills and acuity of vision.

When a person has both of these to a high order then unusual observations can be made.

I wouldn't have a clue with regards to birdwatching, as it is not a specialist subject for me.

There was an interesting interview with Prof. Jocelyn? Bell, discoverer of pulsars, 1970s?

At a public observatory in the U.S.A. a woman viewed the Crab nebula.
She said that the main star was flashing.
The professional astronomer, said no, that is scintillation.

She said 'I hold a pilot's licence and I know scintillation, that star is flashing'.
This was in the 1950s.

Had she been believed, pulsars would have been discovered 20 years earlier, again by a woman.

The star flashes 30 times a second, something most can't see.
But the pilot could see it.
 
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As far as I know U.SA doctors use 20 ft. for infinity 4 m. would be about 13ft. I have had my Dr. take me out and show me that the prescription was ok for longer distance, I had some trouble with his prescriptions at distance in the past . I am 66 yrs. old so that might be some of it.;) The thing I think about is that they use mirrors but the distance to the mirror you are looking at is closer than 20ft.

You aren't looking at the surface of the mirror, you are looking "into" the mirror at the reflected image which appears as far behind the mirror as the object is in front of it.

(I think)
 
That is the difference between observational skills and acuity of vision.

When a person has both of these to a high order then unusual observations can be made.

I wouldn't have a clue with regards to birdwatching, as it is not a specialist subject for me.

There was an interesting interview with Prof. Jocelyn? Bell, discoverer of pulsars, 1970s?

At a public observatory in the U.S.A. a woman viewed the Crab nebula.
She said that the main star was flashing.
The professional astronomer, said no, that is scintillation.

She said 'I hold a pilot's licence and I know scintillation, that star is flashing'.
This was in the 1950s.

Had she been believed, pulsars would have been discovered 20 years earlier, again by a woman.

The star flashes 30 times a second, something most can't see.
But the pilot could see it.

This topic falls under the rubric of Critical Flicker Fusion (CFF),which varies between individuals. It's effected by several factors summarized in the main article. I've attached Fig. 6 showing the average relationship with illumination. So, for dark adapted situations average CFF is about 30 Hz, with half the population above and half below. I'm not sure if gender is a factor, but I doubt that pilot experience has much to do with it.

Ed
 

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Thanks Ed.

The pilot part is that she knew and understood scintillation and was able to state that the star was flashing.
She was a good observer, and probably had good sight also.
I suppose the professional astronomer regretted not believing her and pursuing this further, as he may have got a Nobel prize, which Bell didn't receive as her professors got it.

I am disturbed by T.V. flashing with my side vision, at least on old T.Vs, which may be 50 times a second?
In addition I clearly see the kitchen neon tube flashing, again with side vision. I think the U.K. is 50 Herz but the U.S. 60 Herz?
I don't really see this with direct central vision, but I'll check.
So I think that side vision and central vision detect flashing differently.

I find it amazing how much detail birdwatchers see in fine detail of birds.
Observational skills take time and care.
 
The Crab Pulsar is the central star of maybe visual magnitude 16.5, which is very faint.
The public observatory seems to be the University of Chicago telescope, possibly the Yerkes 40 inch refractor.
It may be possible to see down to magnitude 20 with this.

So the reference above may not really be applicable to this faint star.
The source used in the reference above was 0.2 degrees across, probably larger than the star in the telescope, although the Yerkes refractor has massive CA, which probably would not affect a faint star much.
I think the difference in focus between red and blue light is about 5 inches.
I don't think that many people can see the central star flashing.
The star flashes 30.2 times a second.

The astronomer who disregarded the pilot's observation was Elliot Moore, even though the pilot protested that this was not scintillation.
The pilot's observation was made in the late 1950s and Bell's first pulsar was discovered in 1967.
I think that nowadays she would have shared the Nobel prize, but attitudes were different then.
Anyway, the Nobel prize committee has questionable methods.
 
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Thanks Ed.

The pilot part is that she knew and understood scintillation and was able to state that the star was flashing.
She was a good observer, and probably had good sight also.
I suppose the professional astronomer regretted not believing her and pursuing this further, as he may have got a Nobel prize, which Bell didn't receive as her professors got it.

I am disturbed by T.V. flashing with my side vision, at least on old T.Vs, which may be 50 times a second?
In addition I clearly see the kitchen neon tube flashing, again with side vision. I think the U.K. is 50 Herz but the U.S. 60 Herz?
I don't really see this with direct central vision, but I'll check.
So I think that side vision and central vision detect flashing differently.

I find it amazing how much detail birdwatchers see in fine detail of birds.
Observational skills take time and care.

Hi David,

Yes, all that. CFF varies under different circumstances including the size of the retinal stimulus, where it's positioned on the retina, the nature of the oscillation, and so forth. No two individuals are exactly the same, nor are their CFF's invariant. In the end, we're talking about averages.

Ed
 
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