...but maybe a gentle breeze. Inspired from reading this board.
What's the downside to using the Tscherning ellipse's "other branch" (Ostwald? Wollaston?) for Rx sunwear?
Base curve too crazy, like +10.00?
Minus lenses a million miles thick?
Impractical to order special base curve?
I've heard tell the ill-fated "Enigma" lens used this principle.
Can we "free-form" this more easily?
Goal: Using 8-10 base wrapped sun frames for Rx jobs.
Merci.
Tough to process, even worse using FF.Originally Posted by drk
Some could be freeformed. I would need to see each individual Rx to say for sure.
Autograph Attitude is great for wraps but 8 base is the highest base and the RX's you can do in the 8 base is limited by the design.
In a 1.67 you can do up to -6.00 but only to a -0.75 cyl so your total power can't exceed -6.75. In the 1.60 it can't exceed -6.00 on the 8 base.
Some people see the glass as half empty, some as half full. I see the glass and wonder what the radius of curvature is.
I don't have it in front of me, but I'm thinking the top side of the ellipse was clocking in at something more like 18 diopters, not 10... nicht wahr?
Yes it is so. Wollaston used the steeper of the base curves (18-20) and Ostwalt used the flatter base curves.
SOLA had a lens, I do not remember the name, that had an extreme base curve. It is not around so I guess it did not do well.
The Enigma Lens/frame series. They may have been called Contour Optics as well. Mine is still in use. The drill holes have all spider-webbed and the lenses are pretty scratched. Neat idea...........but not practical.
I believe that the Sola lenses were based off of a +16.00 base curve. I forget what the power ranges/limitations were.
Thanks, guys. Oh, well.
People love wrap sunglasses.
I did get the Contour lenses by Sola way back....I sure got shocked looks by OD's and opticians...
The vision was nice...
The lenses actually looked like little fishbowls...
Hey, drk, why stop with with wrap w/sunwear?
I make *night-driving* wrap SV eyewear, with extra sauce (minus).
They LUV 'em!
Barry
Last edited by Barry Santini; 01-19-2009 at 11:19 AM.
Hey Barry when you extra sauce these folks are you checkign to see fi the Rx is now balanced? Are you compensateing the Add with a little extra sauce the other way when your adding extra sauce? I'm just not convinced that extra sauce is the right thing to be doing.
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I flipper or trial frame their DV, both at 20 feet and "down the street", especially at dusk or night.
Extra sauce (aka-minus; or even sometimes some minor cyl) *always* helps *most* people for night driving. Yes, I also check monocularly for *balance*
Why do you feel it may not, in some cases?
Your humble student,
Barry
Well I'm not sure I feel either way about the issue, I see why and understand the effects of using 20 feet as the measure, but at the same time it's a set standard and although more minus might be welcomed by myopes, the early presbyopes may experience discomfort when reading through a lens with more minus, I wear about a -4.75 sph equiv and I'm undercorrected by about -0.50 because I do a lot of close work. I actually prefer my Rx underminused. So I see it as more a peference in my case anyway, but I also understand the implications that my full correction would have on the close work I do. I guess for driving not really an issue, but even then I have to ask, "Does anyone and by anyone you know who get upset when you change scripts?".
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I'm with you, Harry.
I too am undercorrected for full DV by 0.50 for my *indoor*/general use progressives. I like them this way (+2.50 add).
Remember that I stated these were *night* driving eyewear, and therefore are generally SV DV, not progressives.
No one gets mad that I changed the Rx. The only people who get annoyed are the refractionsists when they see the client back if I *don't* tune the Rx.
Barry
How much "sauce" do you generally add...on average?
When I do this for night driving, its generally not more than -0.25D.
When I used to do this for astronomy, it could be anywhere from -0.50 to -1.25D.
It depends on a number of factors, none of which are calculated. Trial frame and flippers in the key, done at night.
FWIW
Barryu
Yes there is a thing we call pseudomyopia that seems to occur at night time. I have had several patients who complain night myopia and I found that overminussing them seems to help.
But usually they are younger folks...
Next time I will trial frame and see if that helps with presbyopic patients. Theoretically it should not...but as we know...real life situations sometimes do not fit textbooks!
"Night myopia" is often due to a number of factors, including the increase in spherical aberration that occurs with larger pupil sizes, involuntary accommodation, and the Purkinje shift in sensitivity to blue light in the presence of chromatic aberration.
There is a minor visual advantage to refracting at a finite viewing distance, such as 6 meters, at least for daytime vision. This is close to the hyperfocal distance of the human eye, or the distance associated with the limit of our depth of focus, so refracting at this distance maximizes our depth of field.
Darryl J. Meister, ABOM
I wouldn't call it false myopia. The focus effect is exactly like myopia.
Barry
I know what you mean...but that is the term being used officially...and Darryl Meister is correct in writing the source of 'pseudomyopia'.
We have a term called Pseudoexfoliation and by strict definition it is false exfoliation but there is actually foreign exfoliate stuff being excreted that blocks the trabecular meshwork thus leading to increased intraocular pressures in the eyes...
Correct me if I am wrong but the scotopic from photopic shift accounts for about 0.25 to 0.37 of the correction (510nm from 555nm) that's with nothing else factored in like spherical aberration or the minus atributed to accomadation, the total would be somewhere in the ball park of 2.00D if we were to go adding sauce to the mix. My question wasn't about the understanding it was more about the legality and where one stops at adding sauce? My guess would be that the shift is an objective measure so I can see that, but the effects from: absence of the stiles crawford effect, wider pupils, and absence of high contrast resolvable details on the effect of accomdation is going to vary upon each individual and be more subjective than anyting else.
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It is *very* subjective. You can use dioptric "flippers" to subjectively determine the degree of myopia at night.
Or, especially for astronomical uses, use this rule of thumb:
Get hold of an accurrate, well-calibrated, individual focus binocular, like a Fujinon, Nikon Marine, or Zeiss/Steiner and focus the eyepieces several times for each eye optimally (over your Rx`eyewear or CLs).
Then note the dioptric readings on each eyepiece, 60% of the shoen minus value, and add that dioptric value to your new night/astronomy glasses.
You won't belive how well you'll see!
FWIW
Barry
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