Zenni Optical - Again

On Thu, 26 Jul 2007 19:19:01 -0400, with neither quill nor qualm, snipped-for-privacy@northstate.net quickly quoth:

Give them the numbers from your last prescription, excluding the "add" numbers, which are the bifocal zooms.

- Metaphors Be With You -

I use Zini progressives. With them you can see the dash as well as down the road. Bi-focals should work as well. See if they can make "Executive" BF's. These go all the way across.

Chuck P.

Thanks Larry.

As to progressivs, I've been wearing them for years, but in some cases they don't work well for me; especially driving. I tend to hold my head high enough that the first 50 ' or so in front of the vehicle goes out of focus. My current sun glasses are a couple of perscriptions out of date, so it's time to replace them and Zenni's prices make it much less painful than most other sources.

On Thu, 26 Jul 2007 21:35:26 -0400, with neither quill nor qualm, snipped-for-privacy@northstate.net quickly quoth:

I tried progressives for two miserable weeks and nearly physically forced the opto and his office girls to put me back in bifocals. They never told me that 80% of the lens would be entirely useless to me. I lost my peripheral vision (who needs rear view mirrors or being able to see your feet going up and down stairs?) and got dizzy as hell with them. All that lens and no astigmatism correction for 90% of it. Sheesh! Never again.

It's time to bite the bullet and pay the $55 for an eye exam to get the proper pair for the -current- needs of your eyes, boy.

I've been plinkin' with grandpa's old .22 this evening and have so far missed 3 ground rat^H^H^Hsquirrels at about 50 yards, and these are new glasses. Time for a scope on the old beast. My eyes aren't what they used to be. Maybe this is the time to sight in the scope on the SKS...

- Metaphors Be With You -

You don't! You tell your optometrist, who factors your desire into the prescription he writes.

Grant

look on your scrip, usually the dv is listed first.

I have given up on bifocals.

I have one pair of distance glasses I use for driving, and one pair of general glasses I use for the computer or around the house.

When I need to focus closer, I have a selection of drug store reading glasses I got at the 99 cent store that will give be several options in focal length and magnification. I just wear the second pair in addition to the regular glasses.

As an example if I have to read a map in the car I will pop on a set of

+2.75 lenses and I can see the fine print on the map.

If I am in the shop doing a up close inspection like reading a scale with fine divisions, I will pop on a set of + 3.75

If I am in bed with a novel that I do not want to hold at arms length I will pop on a set of +1.75 that gives me a good image at 9 to 12 inches.

At a buck a shot the readers are cheap and if they get scratched or bent they are disposable.

I have had several pairs of progressives and basically love 'em. I did learn that all versions aren't equal, though. Maybe that has something to do with your problems.

First two pairs, good, me likie lots. There was a period of feeling slightly uncomfortable with distortions as you were moving (sort of like you were under water or something) but that quickly passed.

One of the big advantages... Driving - see where you are going BUT also read the gauges AND be able to see the clock or the radio dial or read a map or notes. Almost like being young again.

No drawbacks on first two pairs except a short period of getting used to the feel of walking with a slight distortion from what was normal. Long enough ago that the lenses were pretty big, as was the style.

Now -- pair three.

Went to Pearle Vision -- don't know if that was part of the problem or just coincidence. Got smaller lenses for the first time. Went progressive. When I got them, there was only a tiny area straight ahead where I had good distance vision. It was horrible. I went back and said, "why are these so differnt?" No good answer. Made them give me bifocals. Much more limiting than my earlier good progressives but way better than the limited crap progressives. Sounds very like what you described.

Pair 4.

Got my eyes checked at Pearle Vision -- no big changes, but bought my glasses in a different place. About the same size smaller lenses. Told them about my problem the last time. Tried it anyway. Result - good progressives in small lenses. Wearing them now more than a year later.

So, there are different results depending on how the lenses are made. How can you predict? Wish I knew.

If your bad experience with progressives is that you only had decent vision through a tiny area straight ahead, my thought is that you accidentally started with my 'pair 3'.

If astigmatism is one of your problems, I can't speak to that. Not something I know about directly.

Short course on vision: If you are nearsighted (myopia), without glasses you see close up well but distant objects are out of focus. The focussing powerd of your cornea + eye lens is "too powerful" for the length of your eyeball and focuses distant light in front of your retina, so you need a negative correction (- diopters) to weaken the total effect and have distant objeccts in focus.

Diopter D =3D 1/f where f is the focal length of the lens in meters - the shorter f, the larger D, the more powerful is the lens.

Reverse the first paragraph if you are "far sighted" - you see distant objects OK but can't see close up. You need more optical power so you get + diopters.

If your cornea isn't symmetric, you have astigmatism and need cylindrical correction (think of a lens shaped like a piece of plexiglas rod - it corrects in one direction only (perpendicular to the rod axis), not "all the way round like a sphere). Your correction will say "-2.75 cyl@70", the first number is the power (-2.75 diopters), the "cyl" means it is an astigmatic (not symmetric) correction, and the number following the @ means the angle of the correction - I think 0=B0 is up, 90=B0 is right, etc. Sometimes the @ sign is missing, the number following "cyl" is the direction of the correction.

FInally, as we get older we lose the power to focus close up, called "accomodation", so we need reading glasses or bifocals. These are always positive corrections, as +2.75D.

Know you know all....Joel in Florida (former teacher of optics and built machine vision systems)

On Fri, 27 Jul 2007 04:57:59 -0700, with neither quill nor qualm, xray quickly quoth:

I have 3 requirements:

1) correction for astigmatism in the entire lens area, which progressives won't do, ever, period. I wasn't warned first, which really pissed me off.

2) correction for farsightedness throughout the entire lens, which the progressives won't do, ever, period. Again, I wasn't warned and couldn't see my rear view mirror or view my feet peripherally without physically turning my head each time.

3) correction for nearsightedness

I felt that, too, but it never went away, even after two solid (and horrible) weeks of daily use.

Ayup. And they were the leading lens in the USA at the time, Varilux. May the gods bless the lines in my bifocals! I love 'em!

My eyes' view of verticals are something like this / \. It means that to correct it, the entire lens must be corrective. They tilt the polarity to make my brain see vertical things as vertical. This is something that progressive lenses, AFAIK, can never do. As my eyes moved from dead center to the left to look out my mirror, they went from 100% correction to zero correction with 2% or better distortion. Tell me I'll like these lenses, Doc. Just try. I wanted to strangle him. ;)

- Metaphors Be With You -

Greetings Joel, I am interested in optics. I bought the book from Edmunds titled "Popular Optics". It's OK but I'd like to read some other books to round out my education. Since I'm just a beginner can you recommend any other books that would be good for someone trying to teach themselves? Thank You, Eric R Snow

Modern Optical Engineering is a very good newer book, most of my experience was teaching senior optics with an emphasis on physical optics (the science of light (diffraction and interference) and it's manipulation) as opposed to geometrical optics - (how to make optical instruments), Older books are Jenkins & White "Fundamentals of Optics", and my favorite, Fowles "Introduction to Modern Optics" (Dover) - very little geometric optics but the theory is great.

A whole 'nother world is the blend of electrical engineering - signal processing theory and optics called "Fourier Optics", and the text by Goodman is a great grad level book - very neat stuff and the ultimate answer to how good is an optical system in terms of "signal fidelity"

- the 2-D versi> On Fri, 27 Jul 2007 05:55:19 -0700, " snipped-for-privacy@aol.com" >

Yeah. That sounds like an issue that would be unsolvable with progressives. Your 'underwater' sensation would have been much worse than mine and I can see why you never got used to it. Glad I'm not in that situation.

I just wanted to point out my experience with not horrible nearsightedness vs now needing a slight magnification for close up. I like the ability to see most of my viewing area clearly on the distance side, but also being able to tilt or aim my head to also easily see gauges or documents at random distances.

Two of my three fulfillments of prescriptions have been good -- better that simple single or bifocals. One sucked with horrible periferal vision. How do you tell in advance? No clue.