OD: +1.50 -0.25 X 040
OS: -0.75 -0.50 X 132
1.5D prism. Which lens would you attribute the prism to?
OD: +1.50 -0.25 X 040
OS: -0.75 -0.50 X 132
1.5D prism. Which lens would you attribute the prism to?
There is information missing in this script and the script itself should tell you not only which eye or both eyes but also which direction. Contact the Doctor that wrote the Rx.
I'm neutralizing only.
You need to know the patients monocular PD. Dot the lenses accordingly and measure what you find.
This is a pair out of a donation pile I'm neutralizing for practice.
This pair has -1.50 in highest meridian in one lens and +1.50 in the other. That's why I'm wondering which lens to give the prism to.
Look at Uncle Fester's post. If the oc is located where the patient's pupil would be, there is no prism. If the oc is located anywhere else, there is prism. Put the patient's pupil location (you'll have to make one up in this theoretical situation) over the lensometer and read any resultant prism. Whether the lens is plus or minus makes no difference. If there is a meridian (in either lens) with little or no power, check the other lens first. With low powers, you can be fooled into checking the lens in an off-center location which makes the other, stronger lens seem to be reading with prism. Remember also, if you have equal base down in both eyes, that is no prism. Base in, in one eye, base out in the other? That's sloppy work, but it's still no prism, or at least effectively no prism since there is no imbalance.
I think you need to learn or refresh your memory about Prentice's Rule.Originally Posted by pseudonym
If there is no vertical prism when you put them level on the lensometer shelf you can only create a horizontal prism*. You should try to split them but like finefocus says keep them both in the same direction (.75^ in or out OU).
Sorry but I'm not ready to spoon feed the answer at least just yet.:p
* You could create vertical prism by displacing the patients pupils but I don't think you should try to go there yet.
Last edited by Uncle Fester; 09-23-2010 at 04:30 PM.
Why do you think there is any prism in the first place.
Also, this is nitpicking, -1.25 is the strong meridian (@ 42 degrees) in the OS.
What prism? I think you need to brush up on your optical "book knowledge".
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
OK, I'm trying to choke down the solids. Difficult without a spoon, but I'm working on it.
The highest power on the 90th is +1.35 in the right. It is only -0.97 in the left. I should attribute 1.5 vertical prism to the right eye.
Not possible to get the horizontal prism without pd info, so either make them up or leave it alone.
Correct.
No bashing the students! :finger:
I think pseudonym is trying to learn how a prism could be read in this pair she/he is "practicing" on.
Pseudonym really needs to tell us if the pd is 60 (30/30) what would the pd be with .75^ base in O.U. be.
At the risk everyone is typing a reply at the same time again...
Pseudonym- I suggest you need to create a simpler example.
Rx +2.00 OU PD 60 (30/30)
What would the Pd be to create 2^ base in be?
What would the vertical difference of the OC's be to create 1^up OD 1^down OS?
Or am I way off in your thinking? :)
You're not trying to calculate a slaboff, are you? Otherwise the different powers at 90 in the two eyes makes no difference; only a difference of OC height matters.
I'll tell you the answer I'm getting. I'm getting that both lenses need to be moved 10mm in.
No. If you don't mind, I don't think I want to tackle slaboff right now.
Now I'm confused again. Are you calculating decentration to create prism? If so, you're creating base in OD and base out OS. That's not right. Or are you calculating decentration to avoid creating prism? A total of 20mm decentration can't be right. A job with a frame 60 eye 20 dbl and a patient PD of 60 (an extreme example) would only produce half of that decentration.
One big problem they have is they're neutralizing only -they have no reference PD. They're from a donation. Until you know that, you can't figure prism, unless it's vertical.
DragonlensmanWV N.A.O.L.
"There is nothing patriotic about hating your government or pretending you can hate your government but love your country."
I don't think you are the one who is confused. I wasn't clear to begin with.
I've been neutralizing glasses all day. Read the powers, the axis, the pd, lens material, the seg heights, the A the B and the DBL etc.
Then I centered a pair on the right side, spotted it and read it. When I moved it across the lens table, it was no longer centered. The OC was showing 1.5 BD.
The power on the 90th is strongest in the right. Does this mean there is 1.5 D of BD prism in the left?
IMO, pseudonym.....yes. Proviso: Indeed, in this particular set, the O.C. of the right lens is absolutely at midpoint of B dimension(datum)
...
Last edited by pseudonym; 09-23-2010 at 07:55 PM. Reason: need a juice box and a nap
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Last edited by pseudonym; 09-23-2010 at 07:53 PM. Reason: bzzzt
For some reason, I can't edit my bad answer. So I'll have one more go at it and hope this is right.
Rx +2.00 OU PD 60 (30/30)
What would the Pd be to create 2^ base in be?
Both lenses are plus. You go 5mm in on both lenses to get 2^ base in. Making the pd 50 (25/25.)
What would the vertical difference of the OC's be to create 1^up OD 1^down OS?
Plus lens. You need to go 5mm up to get the 1^ up in the OD and 5mm down to get the 1^ down in the OS.
Correct! (assuming you mean 2^ in total, split 1^ in each eye)
OK, now, complicate your life a bit. How about the same prism using the Rx ---OU +4.00 -2.00 x 45 ---- or +4.00 -2.00 x 90---or +4.00 -2.00 x 180
Well, if you're up for a round of stump the noob, then I am.
For 2^BI total: Rx ---OU +4.00 -2.00 x 45 move the lens 3.3mm IN both eyes.
For 1^BU & 1^BD: Rx ---OU +4.00 -2.00 x 45, move one lens UP 3.3 and the other DOWN 3.3mm
For 2^ BI total: OU+4.00 -2.00 x 90, move the lens 5mm IN both eyes.
For 1^BU & 1^BD: move one lens 2.5 UP and the other 2.5 DOWN.
For 2^BI total: OU +4.00 -2.00 X 180, move the lens 2.5mm IN both eyes.
For 1^BU & 1^BD: move one lens 5mm UP and the other 5mm DOWN.
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