I Need good technical answers for this!!

[Ryan]

Its been awhile since I have encountered this. Pt. has an RX of :

-5.75 +1.00 x 010
-6.00 +2.00 x 175

She is in a 1.67 index with Alize coating, and having trouble with chromatic abberation. Sees fine in center, moves eyes down, gets blurry, moves eyes side to side, get blurry. She seems very sensitive to the abberation.

Question, what is the abbe value of the lense she is in now? Would she be better off in a 1.60? Is the abbe value in a 1.60 that much better than a 1.67?

Her old pair (2-3) years old, has no problems with chromatic abberation. It is hard to tell what she is in, probably a mid index lens. So, help me out and give me a refresher course in abbe value. Get technical, I can handle it, I think. :idea:

PS. I have already checked the O.C height, (good) and the base curves from old pair to new (looks good as well.)

Don't you just love optics!!!!!!!

[Ryan]

Also, glass lenses are NOT an option. So you oldtimers don't even mention it as an option for me. Thanks. :hammer:

[Chris Ryser]

Also, glass lenses are NOT an option. So you oldtimers don't even mention it as an option for me. Thanks.

As an old timer.............I learned , when there was nothing else than glass lenses...............that you could get so called meniscus lenses or you could get coreccted curve lenses, like at the time a ZEISS Punktal, or an AO Tyllier lens, both of them in crown glass.

Or you you get a high index lens in flint glass. This was a flatter lens, therefore thinner and you could not make corrected curves with that material. Every time we switched a miopic Rx like your to flint we invited trouble and similar complaints as you have stated.

When plastic lenses came out, the most successful was CR39 because it had refractive values very close to crown glass and therefore became the real popular lens material. All the older materials loke a plexiglass hadhigher indexes like the old flint lens.

These types of materials are resurfacing again on the market to make thinner lenses. The also have the flatter curves again which are not always appreciated by people like you. Distortion when looking lateral and up and down.

Go back to what you had before and you will be happy again. Your optician vewry often tries to push the more expenxive lenses. Myopes should not be switched to other materials as the perception change is often not tolerated

[EyeWearGuy]

You might try measuring the back surface curve of the lenses - it is difficult to get an accurate base curve on an aspheric lens.

[mullo]

The Abbe value of 1.6 is approx 42, while 1.67 is approx 32.......hence the possible chromatic aberration. As eyewearguy said, measure the ocular/back curves to check for differences.......these may require matching to the old curves as much as possible and adjusting the base curve to obtain Rx. And as Chris said......"Myopes should not be switched to other materials as the perception change is often not tolerated". Very true......How long has she had the new glasses?

[Andrew Weiss]

The key to your dilemma, I think, lies in your comment that the patient's previous glasses were probably mid-index.

Off-axis distortion is a significant issue in 1.66-1.67 lenses, moreso as the Rx gets stronger. This results from the combination of the flatter base-curve and the inherent properties of the material. Putting a/r on helps some but it doesn't get rid of the underlying issues. Even aspheric design can help only so much to correct from the distortion resulting from the flatter base.

I've learned the hard way to take a conservative approach on these issues. :hammer: I used to think I was always doing the patient a favor by putting them in a thinner, more cosmetically-appealing material. Some of them worked out, and with others there were problems. If a person is used to CR39 or a mid-index lens like Spectralite, I am now more hesitant to move them into a higher-index material. Back when Rodenstock made their single-vision mid-index lenses, I used them alot in these situations. Now I've gone back to Spectralite. It isn't as thin as the Rodenstock lenses were, but it works.

[Darryl Meister]

So, help me out and give me a refresher course in abbe value.

Understanding Chromatic Aberration

Best regards,
Darryl

[Ryan]

Fantastic link Darryl. Just Great.

[drk]

Now I've gone back to Spectralite. It isn't as thin as the Rodenstock lenses were, but it works.

I think the above is good advice to you.

Let's face it, there are two theoretical kinds of people that define a continuum: the "vision" people and the "cosmetics" people.

You have a "vision" person, there. So, eschew the cosmetics, and go with optics.

For the picky, Spectralite is difficult to beat. It's just a nice material/aspheric design.

(Maybe Trivex will rival it in a case like this, and maybe you have more choices to go spherical or aspheric, and it's drillable.)

[Chris Ryser]

It's drillable.

Everything is drillable, if you have done your home work and know what you are doing.

[drk]

Everything is drillable, if you have done your home work and know what you are doing.

I have learned that, Chris, thanks to you and others.

I'm talking "practicality". Many optical labs would just rather not drill anything but MR-10, poly, or trivex, whether they're right or wrong.

[jediron1]

drk
I have learned that, Chris, thanks to you and others.

I'm talking "practicality". Many optical labs would just rather not drill anything but MR-10, poly, or trivex, whether they're right or wrong.[/QUOTE]


I might not have been in the business quite as long as Chris but when I first started in 1973, DRILLING GLASS was the norm. My boss would order a Shurmount at 10:00 am and wanted it by 3:00 pm, it helped that he owned his own lab and 9x out of ten he had those glasses, now sure you say well it was the boss but remember it was still glass and as Chris said:
"As an old timer.............I learned , when there was nothing else than glass"
the labs don't want to drill anything else is because they know of nothing else.
Re-read what Chris said he started in glass, I would bet Chris could drill glass
with the same if not better results then todays normal lab gets with your above. just my 2 cents

[Aarlan]

Of course you "can" drill any material you choose, but some materials simply won't withstand the everyday abuse that others can. I had a professor from the Virgin Islands come in with a broken lens in his drill mounts. It was the SECOND TIME it had happened. Just because you can doesn't mean it is a good idea...AND watch out for the duty to warn folks...they may have an aneurism if they hear you talking about glass drill mounts.

AA

[Robert Martellaro]

Sees fine in center, moves eyes down, gets blurry, moves eyes side to side, get blurry. She seems very sensitive to the abberation.

Ryan,

That sounds like the OC is too high and/or too much panto. You said you checked the OCs but it might be worth another look. They should be 1mm below the pupil for every two degrees of panto. This can be checked by drawing a horizontal line through the OCs and observe its positron when the client's head is tilted back until the lens is perpendicular to the floor. With a straight ahead gaze the line should bisect the pupil. Lenses should be no more than 15mm away from the eyes, 12mm to 14mm would ideal.

Regards

[drk]

This can be checked by drawing a horizontal line through the OCs and observe its positron when the client's head is tilted back until the lens is perpendicular to the floor. With a straight ahead gaze the line should bisect the pupil.

That's an idea I've never heard of...I may just use that!

[Spexvet]

This can be checked by drawing a horizontal line through the OCs and observe its positron when the client's head is tilted back until the lens is perpendicular to the floor. With a straight ahead gaze the line should bisect the pupil.
Regards

I never thought of checking it that way.
Wow! I can retire my protractor!
But will I have to bring my level to work?;)

[Chris Ryser]

Of course you "can" drill any material you choose, but some materials simply won't withstand the everyday abuse that others can. AA

What material would not withstand any abuse??????????????????????

Glass

We used to get an average of one customer a day with one or 2 broken lenses during the times of rimless glass frames.

This was additional income to the business replacing these lenses. During those times customers were instructed how to take care of their glasses and they were also warned that if they did not follow instructions they would be back having to pay for replacing the lenses. Warranties applied only on originally defective frames or mistakes in the RX .

[Chris Ryser]

That's an idea I've never heard of...I may just use that!

As nobody mentioned it I would put your attention to the fact that you should properly adjust the frame before taking these measurements.

In case of a metal frame the lab might bend the frame or nose pads while mounting lenses.

At least you can re-adjust it the way you had taken the measurements and it will fit right and the centers will be where you wanted them.

[Laurie]

Chris is right...

The frame should be adjusted for panto and face form to begin with.

As well as drawing a horizontal line, you can have the patient tilt their head up, until the eyewire (future lenses) are orthoscopic (perpendicular to the floor and ceiling), and then spot their pupil. Then, measure the number of millimeters the spot is below the datum line, and order a single vision OC height. (for the optical geeks, this corrects for Martin's Rule of Tilt: for every 2 degrees of panto, in effect, the OC will be raised by 1mm, and should be compensated for)...


And, I would switch to TRIVEX for sure...light weight, super ABBE value (42-44, depending on manufacturer).

: )

Laurie

[Robert Martellaro]

That's an idea I've never heard of...I may just use that!

drk,

I read about it here at Optiboard. Thanks to the original poster for sharing.

As nobody mentioned it I would put your attention to the fact that you should properly adjust the frame before taking these measurements.

Chris,

Pre-adjusting is crucial that's for sure. The frame maunfactuers rarely have enough panto out of the box. My guess is they do this so that the frame won't rest on the cheek right off the display. Sells better that way.

Regards