Base Curve (Help Chris!)

**April_01** · 08-21-2004, 05:32 PM

Hi everyone! I have been working with a patient with a prescription of
o.d:-5.50-1.50X035
o.s:-5.00-1.00X150 1D BU prism
+2.50 Add ou

Pt purchased lenses only and last prescription was aprox. the same. However, when pt received the new lenses, she could not see out of distance clearly. The prescription checked out okay on the lensometer,Pd was correct(Monocular PD's were 31.5/32.0)and same as last pair, we put her in same progressive, lens type and index with same seg placement of 25.(Pt is in Hi index 1.6 Plastic Adaptar). I then took her to dr. who checked refraction and it was the same as he had prescribed. He seemed to think it was all in the pt's head and told me to add paniscopic tilt. Which I did and seemed to helpa little but pt called back after a few days saying it is still not better. So I remembed reading about the base curves of lenses and checked them. Her first pair was 3 in both and her new ones were 2.25 in both. Since this was the only thing different, I told pt we would reorder wtih a different base curve of lens. With her prescription would this be the reason of her altered vision in distance only? Should I check base curve on all prescriptions or just certain cases?

**JRS** · 08-21-2004, 08:32 PM

Adaptar is only made (1.6) in either a 2 base (2.07 tbc) or a 4 base (4.04 tbc) - no 3 base.

**April_01** · 08-22-2004, 10:52 AM

Thanks for the advice! When I checked on the old lenses using the lens clock, the black numbers said three on old pr and 2.25 on new. The lab invoice said Base Curve 2.25? Am I looking at the wrong numbers or probably using the lens clock wrong?

**shanbaum** · 08-22-2004, 11:13 AM

Originally Posted by April_01

Thanks for the advice! When I checked on the old lenses using the lens clock, the black numbers said three on old pr and 2.25 on new. The lab invoice said Base Curve 2.25? Am I looking at the wrong numbers or probably using the lens clock wrong?

If they're really both 1.6 Adaptars (which the engraving should enable you to verify), chances are, the lenses in the old pair are a little bent - which is not unusual, especially in the case of thin or minus lenses in metal frames.

The front curve can be a little tough to measure on a progressive in any case - you have to be sure you're measuring them in exactly the same place (preferably, in the center of the distance portion).

**April_01** · 08-22-2004, 12:55 PM

Thank you for your advise! I didn't realise they could be bent. I did identify the lenses as The HI index adaptar and is the same lens used as last time. If the lens is warped and pt can see better with that one, did the pt just adapt or is this were the pt sees better? What would you rec. doing? Increase wrap/pan tilt,ordering as 4 BC,etc? I am not sure what else to do. Thank you in advance.

**Clive Noble** · 08-22-2004, 02:34 PM

If what you're saying is correct, then there is only one factor that's different between the old lenses and the new lenses........ The Rx!!!!!

What was the previous Rx?

Is the doctor the sort of person who "doesn't make mistakes" ?

Let us know

**shanbaum** · 08-22-2004, 06:46 PM

Originally Posted by April_01

Thank you for your advise! I didn't realise they could be bent. I did identify the lenses as The HI index adaptar and is the same lens used as last time. If the lens is warped and pt can see better with that one, did the pt just adapt or is this were the pt sees better? What would you rec. doing? Increase wrap/pan tilt,ordering as 4 BC,etc? I am not sure what else to do. Thank you in advance.

Base curve would not be at the top of my troubleshooting list. If tilt or wrap is the issue, that suggests that the frame has been mangled a bit in the process of refitting with new lenses. How likely is that? You saw it before and after...

Did you check for abberation in the vicinity of the Layout Reference Point (the Fitting Cross)?

As Clive asked - just how different is this new Rx?

**April_01** · 08-22-2004, 06:57 PM

The frame is about four years old we made lenses only for it in 2002 with no problems. It looks in really good condition(considering how old it is) and has average paniscopic tilt and good face wrap. The dr. is really good at working with prescriptions if all adjustments necessary have been made with no success. He did check the refrection after the first time she had a problem and everything was still the same. He thinks it is just the pt and said to just remake lenses. I would have to look at the chart againg to know exactly, but I believe the prescription was only about a quarter of a diopter different in the sphere in ou.

**April_01** · 08-22-2004, 07:03 PM

Shanbaum,
What do you mean by an abberation at the fitting cross? Prism difference or are we talking about the actual sphere and cyl lines not being in focus?

**Robert Martellaro** · 08-23-2004, 12:43 PM

April,

The abberation is called a "wave". Hold the lens in front of one eye and move it up, down, and then sideways when looking at a distance object with straight lines like a display case. You might see unexpected movement or blur at the spot of the wave, somewhat like a ripple on a disturbed surface of water.

Robert

**Texas Ranger** · 08-23-2004, 03:51 PM

April 01, you would be surprised how many folks have a problem with "about a quarter shere ou"...

**Jacqui** · 08-23-2004, 03:55 PM

I get to do lots of remakes because of 0.25 changes.

**April_01** · 08-24-2004, 07:20 PM

Oh, Thanks for the advise guys! I will talk to dr about all of these options. :)

**Chris Ryser** · 08-25-2004, 08:16 PM

[QUOTE+April01]

and has average paniscopic tilt and good face wrap.

[QUOTE]

Would the expression mean the frame was rounded to instead of straight?

If that is the case you could create some discomfort. When the exam was done for the RX the phoropter used or the trial frame would have been in a straight line and no wrap. Ay a power of around -5.00 you would get a difference in power and maybe even some distortion. The RX might be totally perfect but the patient feels a difference.

**April_01** · 08-25-2004, 08:27 PM

Thanks Chris!!! I was wondering when I'd hear from you. The frame did curve for the face wrap because I was told that all progressive wearers should have good face wrap to give them a wider viewing area. However, I am starting to think that is not the case. Buy the way, when measuring a base curve with the lens clock, if the lens is aspheric will you get an accurate reading? Also, I was told that all progressives have an aspheric quality to them. Do you know if this is true?

**Chris Ryser** · 08-26-2004, 02:56 AM

Originally Posted by April_01

..................... when measuring a base curve with the lens clock, if the lens is aspheric will you get an accurate reading?

Of course you get an accurate reading at the pint where you hold it, if you hold it straight.
However your progressive lense are full of irregular curves and you will get only a decent reafing in the middle of the distance area. The reading part is most of the time to small compared to the distance of the pins of a lens clock to get an accurate reading.