it's been a long time...

[Spexvet]

since I had to think about slab-off rules. I know that there's slab-off and reverse slab-off. Which can be done in poly FT 28, and which is base up prism and which is base down prism?

Thanks in advance,
Spexvet

[Blake]

You'd need a regular old-fashioned slab off, which is ground on theback side. A reverse slab is ground on the front. The slabis ground on the most minus or least plus Rx (reg. slab). Ibelieve it's base up.

Of course, this is coming from someone who has seen maybe threeslaboffs in his career, none of which were ground in my lab - sohopefully someone more knowledgeable will enlighten us. :bbg:

[Laurie]

Blake is correct.

Conventional Slab Off: Base Up, in the Most Minus Lens (BUMM)

Reverse Slab Off: Base Down, in the Most Plus Lens (BDMP)

: )

Laurie

[Spexvet]

Here is the situation:

poly FT-28 lenses

Rx
OD +0.25 -0.50 X 90 add +2.50
OS -0.50 -0.50 X175 add +2.50

The distance needs OS: 4D prism base down

The Near needs OS: a total 14D prism base down, or an additional 10D prism at near only (slab off)

I ordered OD: 4D prism base up, with OS: slab off 10D prism base down.

The job came in with the slab off on the back of the left lens, but it is base up, not base down prism. Is this all the lab could do, slab off base up in OS? If so, I would have expected them to call.

[drk]

There may be an availability issue with such a large degree of reverse slab off?

You may have to reverse your approach:
Add the back side slab off to the right eye, to get 10 pd BU OD (=10pd BD OS)

AND

Order the new OS with the 4 pd BD prism.

Comment: It's rare to see a vertical muscle deviation that varies on downgaze, but it happens. It's probably an acquired neurological problem.

Comment #2: Slab off confuses everyone

Comment #3: I sure hope the Dr. knows what they're doing!

[Robert Martellaro]

Spexvet,

Here are some additional ideas.

Younger's reverse slab goes up 6^. I would consider a trial run with Fresnel press on prism. I would also consider separate reading glasses for the near correction. See if Epic Labs can get you prism seg. I've seen them in and out up to twenty diopters or so, don't know if they can make it 14^ dn or 7^ up and down. Grind two separate SV lenses for far and near, cut each in half and bond them together.

[Spexvet]

There may be an availability issue with such a large degree of reverse slab off?

You may have to reverse your approach:
Add the back side slab off to the right eye, to get 10 pd BU OD (=10pd BD OS)

AND

Order the new OS with the 4 pd BD prism.

Comment: It's rare to see a vertical muscle deviation that varies on downgaze, but it happens. It's probably an acquired neurological problem.

Comment #2: Slab off confuses everyone

Comment #3: I sure hope the Dr. knows what they're doing!

During open heart surgery in mid-1990s plaque (?) lodged in his optic nerve, causing his double vision. Last Rx was OS 3 down in distance with an additional 4 down slab, which worked fine. He since has had cataract surgery, which has exacerbated the issue. Apparantly, he didn't notice how bad the double vision was at OU 20/60 or so.

Thanks for the advice.

[jofelk]

Order reverse slab in os 6^ down. Have od sufaced with as much up prismas possible, we will only slab up to 7^. You should be able to orderreverse in cr39, surface od in cr39 also. Alot of money to spend oniffy Rx !

[chip anderson]

Make a Franklin Bifocal, it's cheap, quick and works.