7x28 poly BD slab in bifocal segment only?

[braheem24]

7x28 poly BD slab in bifocal segment only

Am I losing my mind or is this not available? Patient is wearing it.

[CCGREEN]

braheem

Is that slab line on the back side of the lens? If so a lab should be able to put it anywhere you want it.

[thep]

That should not be a problem AT all!

[braheem24]

Here's my dilemma

7x28 poly
+0.00-0.50x44 Slab 3BD
-0.25-0.75x72 2BU OS (or 2BD od or splittable if needed)
3.00

I'm under the assumption it is a reverse slab and that is only available pre-gound in the front of the lens.

X-cel does not make it and neither does younger, our outside lab says they cant do a reverse slab.

[thep]

Do you know why they are asking for a "slab"? It must be a muscular issue, not imbalance. If you can get more information, we could put our pencil to the paper and possibly solve the acuity issue. You can PM me or call John tomorrow, but the whole picture is needed. Solutions don't always come in a box. We would love to try and help.

[Wes]

Here's my dilemma

7x28 poly
+0.00-0.50x44 Slab 3BD
-0.25-0.75x72 2BU OS (or 2BD od or splittable if needed)
3.00

I'm under the assumption it is a reverse slab and that is only available pre-gound in the front of the lens.

X-cel does not make it and neither does younger, our outside lab says they cant do a reverse slab.

Base up slab is ground on the back. Base down slab is reverse slab, and is molded on the front, as you say. You're not losing your mind there. And like thep says, that's sure not an imbalance issue. What's the patient wearing now, and have you tried troubleshooting this with a press on fresnel prism?

[Wes]

Also, while I'm not a poly hater, poly isn't so great for prism jobs. 3 diopters is where I start looking at other materials. If this is for protection, can you do Trivex?

[mshimp]

I agree with everybody that is saying "why the slab". However you could grind it this way. OD 2.0 BD Over entire lens surface. OS 3.0 Slab off BU. Bring slab line just to the bifocal. This puts the amount of prism in the distance and in the reading the rx calls for. Is this a test question?

[Wes]

Is this a test question?

Doubtful, as Braheem is an experienced independent/owner. This has muscle issue all over it, so I wouldn't deviate from the DR's recommendation. Besides, reverse slab (which is called for) is not difficult, as you only need to find a supplier for the molded blank.

[mshimp]

. Besides, reverse slab (which is called for) is not difficult, as you only need to find a supplier for the molded blank.

Didn't call for a reverse slab off and the Doc said you could put the 2.0 BD distance in the right eye. reread the post # 4
Also reverse slab off not available in this product.

Your welcome Braheem24. I had to really think to figure this one out. I was just kidding about the test question.

[Wes]

Didn't call for a reverse slab off and the Doc said you could put the 2.0 BD distance in the right eye. reread the post # 4
Also reverse slab off not available in this product.

Your welcome Braheem24. I had to really think to figure this one out. I was just kidding about the test question.

Normal slab is ground base up. Reverse slab is a molded blank and is base down. post #4 reads as follows:

+0.00-0.50x44 Slab 3BD
-0.25-0.75x72 2BU OS (or 2BD od or splittable if needed)

Therefore, it is calling for a reverse slab.

Normally, the point of putting BU slab on the most minus lens is to negate the excessive BD prism that higher minus lens creates, and the reason to put BU slab on the least plus lens is to yoke the excessive BU prism the higher plus lens creates. you can only grind BU slab on the back of a lens. BD slab is molded on the front of a lens, and is used in an opposite manner that standard slab is used.

The 2 BD OS is on the overall lens. The 2 BD OS is the same as 2 BU OD overall, or 1 BD OS, 1 BU OD (split prism) and that would work, because again, the slab requested is reverse slab, on the front of the lens, base down.

Good point about availability. Hmm

[braheem24]

It's a muscle issue patient needs 2D prism distance and 5D when reading. The patient is currently wearing a slab OD, he was referred to me because no one else wanted to try slabbing the bifocal segment only. My only issue is, this is a backup pair and I don't want to switch his slab to the opposite eye.

Last case scenario, I'll suck it up and ask him where he purchased his old pair and ask them what lab they used, but it would be nice to give the patient a little confidence in our abilities.

[Robert Martellaro]

Here's my dilemma

7x28 poly
+0.00-0.50x44 Slab 3BD
-0.25-0.75x72 2BU OS (or 2BD od or splittable if needed)
3.00

I'm under the assumption it is a reverse slab and that is only available pre-gound in the front of the lens.

X-cel does not make it and neither does younger, our outside lab says they cant do a reverse slab.

If the Rx is OS distance 2∆ BU, OS near 5∆ BU, then make it the way mshimp recommended.

But the presence of a slab line on the existing right lens indicates BU on the back, unless Younger made a reverse slab trifocal, but I sure don't remember one.

http://www.youngeroptics.com/default...e-939d9278861b

That might mean that it's a neutralizing prism, that is, a 2∆ or 3∆ BU slab in the OD, for an Rx that might be OS distance 2∆ BU, with zero or OS 1∆ BD at near. That would be due to a difference between the distance phoria and near phoria, which can vary in degree, and sometimes direction.

What does the Rx say? The doc might be misinterpreting the habitual prism, throwing you a curve ball. Or they don't know we can't make a flat top trifocal BD Slab. Very strange.

Considering the above, I would contact the doctor to confirm their intentions.

[mshimp]

I'm very aware of what reverse slab offs are. I've processed them before. If this patient came into our retail office I would of neutralized the glasses , verified the material, slab direction and amount of prism, consulted with their Doctor to make sure, like Robert said, that he is not misinterpreting habitual prism, and confirm what the doc is trying to accomplish with patients near and far phorias. The rx does state 3.0 slab base down. Which would have to be a reverse slab. Many doctors don't understand a reverse slab versus a conventional slab. They just want to accomplish correcting the vision. I don't look at an rx like this and say it has to be a reverse slab. My gut feeling is the doc is wrong in his interpretation or a reverse 7/28 trifocal was made at sometime(most likely in cr-39). I don't recall one.

[braheem24]

Patient is wearing it.

My only issue is, this is a backup pair and I don't want to switch his slab to the opposite eye.

Thank you all for the help, Glad to know I haven't lost my mind quiet yet.