Rx +2.75 -.50 x88
+1.50 -.50 x70 +2.50 add If the lenses were done in a 5.50 bc, why do they clock at 7? These are dress adidas fo4 some wrap, grooved rimless. Pt is having trouble adjusting to od rx and dr believes it is bc. I've had them remade 2x . Still clock at 7. Lenses appear nice and thin, look good. I know this is a lab tech question and am confident you can explain this to me. Thank you, Thank you, Thank you !!!!!
If the frame is an extreme wrap, then the lens were made with a 7.00 base curve. Most likely the patient is having a problem with the wrap and not necessarily the base curve. Also has there been a big change in the RX from their previous one? Patient is only having problems with the right eye.
What did the lab that made them say when you asked them?Originally Posted by witty optician
Lab says it was run on a 5.50 . The frame does not have extreme wrap at all. I've fit many of these with no problem. Od rx did change about +.50, but pt is seeing 20/15 when we refracted him. Lab has no explanation.
Check your clock for accuracy. Check the lenses for warpage (remove the lenses from the frame). Ask the lab manager for the lens manufacturer's true curve, although it's unlikely that the nominal curve and true curve would be this different.
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.
Have them remade with the flatter base curve and reduce right sphere power by .25 or at least .12 IMO.
What is the degree of wrap, and does the Rx need to be compensated to adjust for it?
Diane
Anything worth doing is worth doing well.
Simple question, but as a follow-up to Robert's...Where are you clocking the lens? Preferably along the 180 above the fitting cross. (As opposed to at 90 degrees) if these are conventional PAL's, if a totally FF design, then anywhere on the convex should give you an accurate reading (assuming your clock is accurate).
Also, check for excessive thickness, particularly from the old lenses (Check center thickness). A thicker lens will induce more plus.
This. Wrapping more than 10-15 degrees in a PAL could be a problemo.
Consider the neanderthal approach: bend the frame to take out some of that face-form.
Any notable panto or vertex changes as well from previous pair (assuming previous pair exists of course?)
Did you clock the lenses while they were inside the frame or did you remove the lenses from the frame, then clock 'em. If the lenses are poly they will flex and a frame can and will induce warpage on lenses.
lenses clock the same in or out of frame. Dr backed off a .25 in od so I'll see if that helps. However, ya'll still haven't answered my question. Can't anyone tell me why if the lab sheet says it was run on a 5.50 BC, it's clocking at a 7 ?
They've mostly answered it. Either
A) It is indeed a 5.50 base and
1) Your clock isn't accurate
2) You are clocking it in the wrong spot
B) The lab sheet is wrong, and it's not really a 5.50 base. The lab can probably give you better details about it, or maybe send it back and have the clock to verify?
I've only seen large differences between the nominal curve (the curve on the box) and the true curve the other way around. For example, the box will say 6.00 base and the true curve is a 4.86. That's how many Seiko and Shore blanks are.
You need to sort that out with the lab manager or owner. Don't take "no explanation" as an answer. There's a software glitch, inventory error, substituting, referenced to a different index instead of 1.53, etc.
Good luck.
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.
My "gut" instincts are telling me it's not a base curve problem at all. Trial lens a -.25 in front of the Right eye and see if the patient can see better. If that doesn't help, try taking out some positive face form as drk has already indicated. Good luck.
What type of lenses where used for this job? If your lab outsourced, an alias lens may have been used to create invoice and list lens type. So it is possible that it was processed on a 7 base while default my have called for 550 based on OS power
We specify every order to match the frame and have no issues with Base Curve because we do not use it as an excuse for failure.
If bc was a real issue we would not be able to do that. We also do not specify anything but the bc while not utilizing the rest of the information that can be entered because we find it can create excessive compensation and this keeps it to minimum.
We use 95% trivex so it cannot be an abbe value issue; must be an rx or fitting issue assuming you are using an IOT lens. I can only speak of what we use and we have amazing success with IOT and do not believe in bc issues.
I am ready to be flamed and that is fine. Time to really address the problem and not use BC as the issue.
FYI,
If you cannot figure out the BC with 100% certainty are you really qualified to solve this issue? I think that your lack of experience may be part of the issue and it might be time to get some local knowledge about the basics of optics.
Anisometropia.
Take the +0.50 back out or give him base down prism in the higher plus.
It seems IOT, whose lenses I know you adore, would disagree with you about the importance of BC:We specify every order to match the frame and have no issues with Base Curve because we do not use it as an excuse for failure.
If bc was a real issue we would not be able to do that. We also do not specify anything but the bc while not utilizing the rest of the information that can be entered because we find it can create excessive compensation and this keeps it to minimum.
We use 95% trivex so it cannot be an abbe value issue; must be an rx or fitting issue assuming you are using an IOT lens. I can only speak of what we use and we have amazing success with IOT and do not believe in bc issues.
I am ready to be flamed and that is fine. Time to really address the problem and not use BC as the issue.
FYI,
If you cannot figure out the BC with 100% certainty are you really qualified to solve this issue? I think that your lack of experience may be part of the issue and it might be time to get some local knowledge about the basics of optics.
http://www.feaind.com/info/art_science_camber.pdf
Relax and take a deep breath. No need to get too upset with the optician, we are all learning here. I happen to agree with you and braheem24(not the prism though). Besides the optometrist can't figure it out either.
Oh but Craig..........you started out with "99% of the time its not the BC."
That left over 1% can really kick your a** because you have spent so much time ignoring it. When the light comes on that it is the BC one can feel rather sheepish.
The stronger the Rx the more attention I pay to BC's. Back when we had a lot of Aphakic eyes to deal with BC was a HUGE deal, combined with vertex distance, (when was the last time anyone out there used a distometer? Seen or even heard of one.) Been a long time since I have taken any test, it may be on there.
How about previous Rx and lens material? assuming there was a previous pair. How did the previous pair fit the patient. Was there a lot of wrap in it.
A bit more history could help here.
The OP is troubleshooting their lab, not their client, specifically, why they're receiving a significantly different BC than what was ordered.
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.
It all comes down to a compromise and most times the curves are in the normal range, but to ignore the frame curve is not a good decision that most folks totally ignore. We don't try to put a high plus in a flat bc frame- they curves should no less than 2D from each other.
I agree with everything that I read and it is a good clear explanation of what they do.
I am relaxed knowing the folks who do what I do on a daily basis cannot figure out a base cure. If you do not know what the BC is than how can you figure out the rest of it?
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