BS: eyes - seeing things twice

Subject: BS: eyes - seeing things twice
From: Mo the caller
Date: 21 Mar 19 - 09:53 AM

I went to the hospital to have a couple of "probably nothing"s checked today.
Before I saw the doctor a nurse tested my sight with the usual test card (with my usual glasses on). She gave me something to hold onto my nose like specs but 1 side covered. R eye fine. When I turned it round it took a while before I could focus on even the top few lines with the L eye, all the vertical lines were 2 lines. She then hinged up a shutter over the place I'd been looking through, so that instead of a lens hole there were pin-holes. This made it all a lot clearer and I could see down to the line below the red line (the line below that sort of, R eye was a bit better on that line).
So why could I see better through pin-holes than a big hole, and what causes the double lines. Don't remember learning that in physics lessons (a very long time ago)

Subject: RE: BS: eyes - seeing things twice
From: Backwoodsman
Date: 21 Mar 19 - 10:11 AM

I have a similar problem - my specs now have to have prisms in the lenses. Without the prisms, I get a double image, with the 'ghost' image above and to the left of the 'true' image.

My optician says it's pretty common, to do with the alignment of your eyes, and I'd guess it's due to the eye-muscles beng out-of-whack.

Subject: RE: BS: eyes - seeing things twice
From: Donuel
Date: 21 Mar 19 - 10:24 AM

each pin hole acts like a lens.
The lines are a normal product of polarization

Subject: RE: BS: eyes - seeing things twice
From: Bonnie Shaljean
Date: 21 Mar 19 - 10:29 AM

It's a standard phenomenon - I experienced it too, and when I asked the doctor why, he said everybody did, and explained it similar to what's been said above.

Subject: RE: BS: eyes - seeing things twice
From: Stilly River Sage
Date: 21 Mar 19 - 11:22 AM

I had it come on rather suddenly in my 30s, and tried many times to get an answer for what seemed to me to be a sort of "double vision" the vertical line and a shadow just to one side of it.) At my most recent eye exam I asked about it again - I'm so accustomed to it and my glasses correct the problem - it seems it is the result of an astigmatism and can come on quite suddenly.

Subject: RE: BS: eyes - seeing things twice
From: Donuel
Date: 21 Mar 19 - 11:51 AM

Eye sockets might change shape and push the eyeball into astigmatism ?

My eyes were never shaped perfectly. They even have contacts designed to correct astigmatism.

Subject: RE: BS: eyes - seeing things twice
From: Donuel
Date: 21 Mar 19 - 05:08 PM

The line test determines if the eye is misshapen on the vertical and horizonal.

Subject: RE: BS: eyes - seeing things twice
From: leeneia
Date: 21 Mar 19 - 07:31 PM

As I understand it, astigmatism occurs because the cornea may not be completely smooth on the outside. "Ridges and valleys" may occur on the surface. They change with time.

I have such bad astigmatism that I have seen five crescent moons where only one ought to be. This has improved to the point where I only see three. Fortunately, my glasses take care of this.

Subject: RE: BS: eyes - seeing things twice
From: Stilly River Sage
Date: 21 Mar 19 - 07:48 PM

Not just the cornea.

"Astigmatism is a common vision problem caused by an error in the shape of the cornea. With astigmatism, the lens of the eye or the cornea, which is the front surface of the eye, has an irregular curve. This can change the way light passes, or refracts, to your retina. This causes blurry, fuzzy, or distorted vision." Source.

Subject: RE: BS: eyes - seeing things twice
From: Mo the caller
Date: 22 Mar 19 - 05:55 AM

Yes, I have noticed it before, when not wearing glasses, and thought it was due to astigmatism. The thing I didn't understand was that, although wearing glasses cures this so that I didn't see the lines when looking at the chart with both eyes, when I covered my R eye (still wearing my glasses) the whole thing became very blurred and it took a while to make it out at all, then there where double lines.
Does this mean (a) my varifocal glasses are not correcting it, and (b) my brain is ignoring what my L eye sees, usually?

Subject: RE: BS: eyes - seeing things twice
From: Jim Carroll
Date: 22 Mar 19 - 07:16 AM

Having to come to terms with gradual but inevitable hearing loss I am learning that a sense of humour is essential - the 'Liverpool Hearing Aid' has become a standard with me
I tried to put up the'Conquering Twin Peaks of Mount Everest' for this one, but it's been removed
Jim Carroll

Subject: RE: BS: eyes - seeing things twice
From: Backwoodsman
Date: 22 Mar 19 - 08:06 AM

I'm not an optician, Mo, but I'm pretty sure it's not a question of 'varifocals correcting it', Mo - it's prisms that are needed in your specs, irrespective of whether they are varifocals, bi-focal, or single-vision lenses.

Subject: RE: BS: eyes - seeing things twice
From: Mo the caller
Date: 22 Mar 19 - 12:06 PM

Well I had assumed that when I go for an eye test the lenses I am prescribed have whatever they need, prisms or what-have-you. Just mentioned varifocal because they are.

Subject: RE: BS: eyes - seeing things twice
From: Mr Red
Date: 22 Mar 19 - 02:02 PM

remember the Total Eclipse of the Sun?

The message was to shine sunlight through a pin hole on to white paper.

and early cameras were pin-hole.
Lenses use their whole width and rely on being the right shape, across their width. Pin-holes have precious little width. The eye is logarithmic in registering intensity, so with the reduced amount of light the retina gets is compensated by the retina/Optic nerve/brain. And we barely perceive a change in intensity. That's evolution for you.

The pupil changes diameter and visual acuity improves in brighter light because the pupil limits the amount of the lens used.

Subject: RE: BS: eyes - seeing things twice
From: Donuel
Date: 22 Mar 19 - 04:28 PM

Methinks even a pin hole is too much for the retina to see the sun directly. Instead you should project the pin hole image onto a sheet of white paper.

Today I took the plunge and scheduled to have cataracts and lens removed surgically one at a time.

Subject: RE: BS: eyes - seeing things twice
From: Mr Red
Date: 23 Mar 19 - 02:39 AM

well keep an eye out for the progress.

Subject: RE: BS: eyes - seeing things twice
From: BobL
Date: 23 Mar 19 - 03:31 AM

...said Harold Godwinson to his aide...

Subject: RE: BS: eyes - seeing things twice
From: Mr Red
Date: 24 Mar 19 - 03:54 AM

a arrowing experience

Subject: RE: BS: eyes - seeing things twice
From: Donuel
Date: 24 Mar 19 - 07:34 AM

manaracts

Subject: RE: BS: eyes - seeing things twice
From: Mrrzy
Date: 24 Mar 19 - 10:53 AM

I have taken to seeing squares that aren't there in my xword puzzles, and am frequently trying to think of a, say, 8-letter word when there are 7 squares. Only happens with the verticals. I SEE 2 squares, then there is only 1. Hmmm.

Subject: RE: BS: eyes - seeing things twice
From: leeneia
Date: 24 Mar 19 - 02:36 PM

Mrrzy, I think you should have that vertical double vision checked out.

Subject: RE: BS: eyes - seeing things twice
From: Mrrzy
Date: 26 Mar 19 - 03:46 PM

Can you believe I went to a neuro and forgot to ask about this...

Subject: RE: BS: eyes - seeing things twice
From: Ebbie
Date: 27 Mar 19 - 12:37 AM

I don't have astigmatism but for a few months before I had my cataracts removed, sometimes - but only sometimes- I saw two images, one above the other, on the TV. With the cataracts gone, so are they.

Subject: RE: BS: eyes - seeing things twice
From: robomatic
Date: 27 Mar 19 - 03:27 PM

I think I'm saying the same thing as Mr. Red only in a way I can understand it.

A perfect lens is a wonderful thing, but it requires calculation and grinding if it's made out of glass and good genes, good nourishment, and youth if it's made out of flesh.

But, most lenses that are not perfect are more close to ideal at their centers, where there is just a little curvature. So even if your eyes are decrepit, if there is enough light you can get a better sense of focus if you just hold some little pinholes close to your eyes. That way in the morning if I don't have my glasses, I can make a little hole out of my thumb and forefinger and make out the numbers on my bathroom scale.

That is also why in cheaper older non digital cameras you could usually get sharper images at the higher f-stops. Higher f-stops meant the light was limited around the perimeter and less well honed shape of the lens and mainly through the better shaped central part.

The principles of our eye lenses and camera lenses are the same, but the specific ways digital cameras work are not my forte. There are doubtless digital finagles known to the professionals which make digital cameras function so well so cheaply.

Subject: RE: BS: eyes - seeing things twice
From: Jos
Date: 27 Mar 19 - 04:58 PM

I thought looking through a hole made with thumb and forefinger was to trick your (long-sighted) eyes into bringing into focus the thing you want to see, by making them try to focus on something nearer, so that the thing further away comes into focus - the difficult bit is to get the distance right, but I have managed it sometimes.

Subject: RE: BS: eyes - seeing things twice
From: Donuel
Date: 28 Mar 19 - 07:08 AM

Due to a rare fluid build up, sometimes my cornea acts like a second lens and as a result I get super binocular vision in which details a half mile away are sharp. It is called of all things 'Fuch's syndrome'. However it's occurence is random by degree and timeing within minutes and has no control except to lower pressure with salt and progressive glasses.