Hello All,
I've a patient with the following rx: OD -9.25 -3.00 x 180
OS -5.75 -.25 x 180. With a 10mm reading level I calculate slab off to be 4.75BU OS. Is this correct? Steps taken: Determine power in 90th meridian; dist. from OC (10mm); Prentice's Rule ; difference between the two eyes prism power, and, ta-da 4.75 BU.
Thanks!
You can check slab-off on various on-line calculators. Our very own, Darryl Meister has an excellent site with lots of calculators and tools. Check it out here:
www.opticampus.com
Here is another site for slabs:
http://www.robertsonoptical.com/slaboff.cgi
I know this is the easy way out, but it is a good resource. Also, another Optiboarder, OPTIDONN, wrote a great article for Opticourier(EyeCareProfessional). Check it out here:
http://www.opticourier.com/1webmagaz...rner/index.asp
Welcome to Optiboard. This place is great.
No add, no need for a slab off. These patient's just tilt head and read through lens center. However there is a distance in distance image size that may need to be delt with. Patient really should be fitted with contacts for this and field distortion. And for God's sake don't put him in poly. Also do not neglect to measure vertical centers.
Chip
I agree with chip, no bifocal, no slab. Assuming you did slab this, you would slab the OD, not the OS. (unless it's a reverse slab, you slab the strongest minus or weakest plus)
One last thing, once again assumung this was a bifocal, and you had 10mm from oc's, youd slab 6d (you've got -6 d difference from OD to OS in the 90)
Thank you for the replys! Where am I going wrong in my math? Add power is a +2.75. I'm figuring OD -10.75 in 90th meridian, os -5.87 soooooo 4.88 BU OS (10mm reading level).
I'm going to check out the calculator (but just have to know where I went wrong)!
:)
Power in the 90 OD -12.25 OS -6.00 Difference of 6.25. Times 10 mm equals 6.25 imbalance. Add power makes no difference. If you rx axis is 180 use the full cylinder power. Show your formula.Originally Posted by Daylilly
I hope if I am ever tested on this they give my an axis of 90 or 180. You can figure in your head.
Thanks for the note! I had - well - a senior moment - lets say :-O, and used 50% of cyl power.....
Hate to rehash an old thread but I was trying to use this calculator and wanted to make sure I understood Reading drop correctly:
http://www.robertsonoptical.com/Slab-OffCalculator.aspx
The Seg Height for the Pal is 21mm but is that also the reading drop?
PAl's are lousy lenses to use slab off on. With the add progressively increasing, you are not going to eliminate the prismatic imbalance throughout the umbilic. Tell your patient they have a condition where PAL's are not a good option and put them in a tri or bi or separate readers/distance. (unless they have had this imbalance long, then they have probably been suppressing vision in one eye already when reading).
If they're insistant on a PAL, I would use a short channel PAL and see if you can push Distance BD prism in the more plus eye in the 90 meridian. The calculate for residual imbalance. The calculation should be based on a short channel reading depth of 15 not the actual seg ht.
After reading these comments, I am even more reluctant to fill his RX.....high Anisometropic RX due to penetrating eye injury OS.
We already explained to them at length that they will most never be happy with the vision in glasses due to the eye injury, resulting anisometropia and displaced pupil.
Even after all this patient decides to purchase a new pair or progressive glasses:
RX
OD +1.75-0.50x110
OS +4.00-4.75X034 ONLY CHANGE FROM PREVIOUS RX WAS BUMPING UP HIS ADD BY 0.25 TO +2.50
So what I am gathering is Slab off would not be beneficial for a PAL patient with this RX?
There's not enough vertical imbalance (<1 D) at near for a slab-off prism. However, SVNO eyeglasses should be on the table.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Agreed
Thank you for the advice.
Your welcome.
Yup, I've never done it. Their fusional reserves were usually adequate to prevent diplopia, or they were suppressing, and/or they were better of with separates, including PALs for general purpose use and auxiliary SVROs.
But if I had to do it, I'd first measure the reading depth using the "mirror method", subtract the PAL drop (distance from the fitting point to the prism reference point, and use that value to neutralize the induced vertical imbalance at the near reference point. Placement should be about 5mm to 7mm below the bottom of the pupil.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
From a previous thread---
mirror method
Hi Mary,
I am familiar with what you are talking about...
The 'mirror method' is great for troubleshooting PALs, especially when the client has some kind of vergence issue, cyclo-dextro phoria, ect...
Here are the steps:
1. put the PAL markings on the lens.
2. place the mirror (approx. 8 inches square) in the middle of the dispensing table, flat
3. place a dot in the middle of the mirror.
4. have client look at the dot, with their eyewear/demo lenses on
5. carefully mark the demo lens on the patient, while looking in the mirror...this gives you the exact location of where they converge to read, a more subjective method....I would recommend practicing on co-workers first, it is tricky marking the lenses, kind of like a dentist, working upside down and backwards in a mirror.
It could be used to fit PALs off the mono subjective near PD, but that is a bit radical.
: )
Laurie
http://www.optiboard.com/forums/show...=mirror+method
Thanks Uncle Fester, I didn't have time to dig that up. The key here is to draw a horizontal line instead of a vertical line, drawing the line about where I expect the eye will rotate to on the downgaze, and then adjust it up or down as needed for accuracy. Pretty much how I determine the pupil heights and fitting points for PALs. Without the mirror, I would have them stand to read, or sit on the floor when they're reading in a chair, the later somewhat more realistic, but awkward.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Now that's a fitting session I want to watch! Mrs. Pickybritches sitting in a chair with Robert on the floor, sitting between her legs taking a fitting height! (Can I steal that?) " Yes Ma'am, I do need to sit right here...."
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