Vertical Slab-Off?

[melthemadhatter]

The OD I work for presented me with this RX:

OD -0.50 -1.00 X 030 8.00 Base Out
OS -0.75 -0.50 X030 8.00 Base Out

He wants to put in vertical slab off.

How do we calculate this?
Is it even possible?


Regards, Melody

[braheem24]

Regular slab fixes vertical displacements. If I'm understanding correct your OD wants a Vertical line (Horizontal Slab).

I'm guessing your OD thinks a slab would be a better/thinner way to achieve the 8BO prism, if that is the case it's not.

You may want to ask the OD what the slab is correcting, so far there is not enough information to give you an informative answer.

[melthemadhatter]

Thanks, I shall investigate further. I will keep you posted.

[Robert Martellaro]

You may want to ask the OD what the slab is correcting, so far there is not enough information to give you an informative answer.

I'm thinking it might be for a vertical phoria on the downgaze only, but the doc has to Rx the power- there is no vertically induced prism to speak of, hence nothing to calculate. As you say, talk to the doctor to discover their intentions.

[melthemadhatter]

More information: Prism is to be slab off horizontal using PD 65.
I manually took the patients PD and got 32 OD AND 27 OS.

The intent is to thin the lenses. I will be using 1.67 with Transitions and AR.

[melthemadhatter]

He wants the prism to start at the edge of the 65 PD and go out as he does not have any peripheral vision. Hence, the horizontal slab off.

Does anyone know if Luzerne does this? How would I phrase this to the lab?

[DragonLensmanWV]

??
If he wants the prism to start temporally past his eyes, and he has no peripheral vision, what's the point? The prism would have zero effect the way he wants it, as it would not intrude on his vision, just act as a blinder.

[Wes]

Don't you mean he wants the slab to start peripherally past the forward gaze pd to thin the edges?
Also, use the highest abbe value material you can for prism jobs; 1.70 is more appropriate for this order. 1.67 is only slightly better than poly, which is the worst.

[Fezz]

Contact Michael Walach at Quest Labs!

http://www.questopticallab.com/Personnel.htm


He can do amazing things and should be able to help!

[Robert Martellaro]

The intent is to thin the lenses.

Tell the lab to thin the periphery with no regard to the optics. I know this can be done with minus powers on a freeform platform, but I doubt it can be done with eight prism diopters. It would also be somewhat risky, not knowing where to start trashing the optics exactly, considering vertex distance and patient sensitivity. Let's say very risky, but intriguing, considering the circumstances.

I will be using 1.67 with Transitions and AR.

You didn't mention VAs, but I generally wouldn't use anything more dispersive than Trivex with this much prism, if you want the best VA. My approach would be to use a small (40mm to 44mm) somewhat round zyl frame, and consider cr39 for the best VA. Some folks like to layback or roll the edges, but I think that looks bad from the front.

Hope this helps.

[Jeff Trail]

I may have been around to long.. but you could treat this the way we used to do hand facet.. you could control the location of the line to make it customized to the frame vs. PD vs. area where the patient has visual accuity ... if you have a hand stone and polish wheel I would do it inhouse where you had complete control and no confusion between second guessing with the location of the line. than after you do the hand work send the lens out for AR coating..

Jeff Trail

[chip anderson]

Has the good doctor been hanging out at one of the medical Marijuana places?

[braheem24]

8BO with pt Rx and a properly fit frame with 1.0ET nasally would be very thin with a full field, A slab is overkill.

[optical24/7]

He wants the prism to start at the edge of the 65 PD and go out as he does not have any peripheral vision. Hence, the horizontal slab off.

Does anyone know if Luzerne does this? How would I phrase this to the lab?

It sounds like the patient has homonymous hemianopia. ( I did my Master's paper on this subject). If the Dr is attempting to expand the patients field of vision, he's only going to give this patient about a 4 degree expansion (not much). There are better options than what he's attempting. PM me here or have the Dr. PM me and I'll be glad to discuss those with him.

[Jacqui]

I was wondering about hemianopia too. A 2 piece hemianoptic lens sounds more like what he needs or wants. And you're right George, 8 BO isn't going to expand the field that much

[Robert Martellaro]

The OP said there was no peripheral vision, or tunnel vision. Maybe optic nerve damage or retinitis pigmentosa. Besides, wouldn't the prism be yoked if it was homonymous hemianopia? Regardless, this person certainly has some serious vision problems. I hope this turns out well for your client.

[DragonLensmanWV]

We had a guy present us with an Rx yesterday that included 10 BO prism OU with 2 BU OS also. He said he didn't want the prism as it made his lenses too heavy. So we tell him about high index lenses, he doesn't want that - too expensive he said. Checked with the prescribing OMD who said he's a "special case" and we can leave the prism out if he wants us to. So we'll see today how he fares when he picks them up.

[RIMLESS]

Old thread but I would have two staged it. Make a basic pair and stick on some 8BO fresnel prism strips. I'd see how that went before going forward with HI Trans A/R lenses.

[Jacqui]

Old thread but I would have two staged it. Make a basic pair and stick on some 8BO fresnel prism strips. I'd see how that went before going forward with HI Trans A/R lenses.

This is what I do when fitting hemianoptic lenses.

[RIMLESS]

This is what I do when fitting hemianoptic lenses.

Guess brilliant minds think alike!!!!!!!!!!!!!!!!!!!!!