slab off

**slackware** · 10-10-2007, 09:50 PM

let me see if i got this, and see if i am right o.d. -6.00 o.s. +2.00 VI 8 prism diopters b.d. o.d. slab o.d. 8 prism diopters b.u. am i right or no?

**HarryChiling** · 10-10-2007, 10:40 PM

I am guessin 10mm to NRP, in which case yes.

**slackware** · 10-10-2007, 10:42 PM

so if the reading levels are the same, you can just do the dioptric difference right?

**HarryChiling** · 10-10-2007, 11:04 PM

Originally Posted by slackware

so if the reading levels are the same, you can just do the dioptric difference right?

The prismatic difference. Just so happens you chose a DRP to NRP of 10mm given the same Rx with a scenario of a 5mm DRP to NRP:

OD -6.00 Sph
OS +2.00 Sph

OD_prism = -6.00 * 0.5cm = -3.00
OS_prism = +2.00 * 0.5cm = 1.00

Dioptirc difference is still 8, but the prismatic difference is 4.

**braheem24** · 10-11-2007, 09:41 AM

...And whatever you do, dont make them. :D

**tmorse** · 10-20-2007, 02:44 PM

Originally Posted by slackware

let me see if i got this, and see if i am right o.d. -6.00 o.s. +2.00 VI 8 prism diopters b.d. o.d. slab o.d. 8 prism diopters b.u. am i right or no?

YES, VI is 8.0^... but leave out the bd as VI itself has no base direction.;)

**Angel of Grace** · 11-20-2007, 08:47 AM

I always send my work to an out lab to calculate slab off prism. As an Optician you must recognize when it is needed and leave the rest up to the labbies that are good at slabbing off. I always remember BUMM which is base up most minus eye or the opposite if you'd like as BDMP which is base down most plus. Text books tell us at around 1.50 at RL we should consider slab off. I'll generally explain to my pt the difference between the two eyes and we'll usually try it w/o slab off up to about 2.50D of difference. When I go to dispense the glasses the pt will tell you if they have diplopia and then at least you've forwarned them and then we just remake the lenses and charge the pt the difference. Why should a pt pay for slab off if it isn't necessary?? Many will tolerate the imbalance much greater than textbook recommendations. Hope this helps. :cheers:

**chip anderson** · 11-20-2007, 10:22 AM

Just a little moderation, not a contradiction on "when it isn't necessary".
Some patients will see fine without slab off but will experience fatique, or headache or diploplia after prolonged use. You won't see this in the office but the patient will see this as he becomes fatiqued. I know that I have a slight squint myself that is only appearent after I have been up many hours. But on those nights that I have to work into the wee hours of the morning, or have insomnia and find myself watching TV in the wee hours. I start seeing double. With the TV I see one on the left slightly elevated and slightly outward from the other. The more I stay up after this the worse it is.
Now having said this I agree with your statement about "why should they pay for unnecessary slab~off?"

Chip

**Caree** · 11-20-2007, 04:32 PM

I prefer the cosmetics of a molded slab on the + side since I never liked to grind them in my lab rat days. Molded slabs are on the opposite eye so when the other cataract is removed you only have to redo 1 lens. I will go to a 3 imbalance to see if they can tolerate it and found most people can,or they are suppressing like we monoculars do.

**tmorse** · 11-20-2007, 06:29 PM

Originally Posted by chip anderson

Just a little moderation, not a contradiction on "when it isn't necessary".
Some patients will see fine without slab off but will experience fatique, or headache or diploplia after prolonged use. You won't see this in the office but the patient will see this as he becomes fatiqued.
Chip

I have to agree.
Or the patient will self-adjust his frame front to remove the diplopia and walk around with slanted eyeglasses. Or as Chip stated...simply suppress an eye.
As I mentioned on an earlier thred, SLABS-PLUS of Florida refer to themselves as 'Slab Off Specialists', and they offer Slab-0ff as low as 0.50^. Some Optician or Doctor is asute enough to sometimes recognize a patient need for thsi low amount, even if many texts do suggest a minimum of 1.0^ or 1.5^ imbalance at reading level before Slab-off is indicated.

I would hazard a guess that Reverse Slab-Off starts at 1.5^ BD for 'inventory cost' reasons only. It would be interesting to see a study done on this issue.:cheers: