verifying add in progressive lens.

**Win C** · 10-07-2009, 01:05 AM

I recently prescribed a few high minus progressive lens (-6.00DS and above). When I tried to verify the add by (measuring the back surface), the reading did no show the required add.

take this Rx for example -7.50DS add +2.50.
using the lensmeter, (measure through back surface) it shows the reading power to be -5.50 meaning add is only +2.00. however when I measure the reading area through the front surface of the lens, the reading is -5.00DS.

however, when I verify plus power progressive lens, i do get the add power by measuring it the normal way, ie through the back surface of the lens.

Can someone enlighten me on this?

Thanks.

**HarryChiling** · 10-07-2009, 08:11 AM

...................

**gemstone** · 10-07-2009, 03:35 PM

Originally Posted by Win C

I recently prescribed a few high minus progressive lens (-6.00DS and above). When I tried to verify the add by (measuring the back surface), the reading did no show the required add.

take this Rx for example -7.50DS add +2.50.
using the lensmeter, (measure through back surface) it shows the reading power to be -5.50 meaning add is only +2.00. however when I measure the reading area through the front surface of the lens, the reading is -5.00DS.

however, when I verify plus power progressive lens, i do get the add power by measuring it the normal way, ie through the back surface of the lens.

Can someone enlighten me on this?

Thanks.

Just hold it up in the light and read it off the lens. It should be engraved on the temple side directly under the alignment spot. :bbg:

**Win C** · 10-07-2009, 11:27 PM

Originally Posted by gemstone

Just hold it up in the light and read it off the lens. It should be engraved on the temple side directly under the alignment spot. :bbg:

I dont usually rely on that as sometimes the full add might have been cut off due to the fitting height being too low.

**Win C** · 10-07-2009, 11:34 PM

Originally Posted by HarryChiling

It's the thickness of the lens, the normal way to measure an add is to compare the front vrtex powers.

If that's the case, I guess it only applies to high prescription lenses.

How about back surface progressive where the prescription is ground at the back surface? does it make any difference whether it's back or front surface progressive?

**gemstone** · 10-08-2009, 12:37 PM

Originally Posted by Win C

I dont usually rely on that as sometimes the full add might have been cut off due to the fitting height being too low.

If you have a prism dial on your lensmeter use it to recenter the target for proper readings. Fit them according to manufacturer's minimum hights as well.

**OCP** · 10-09-2009, 02:55 AM

Originally Posted by Win C

I dont usually rely on that as sometimes the full add might have been cut off due to the fitting height being too low.

High index mineral progressive you can´t measure your self, but I agree with gemstone that the only correct way to do this is by reading the engraved mark.

Mike

**varmint** · 10-09-2009, 09:27 AM

Originally Posted by Win C

I dont usually rely on that as sometimes the full add might have been cut off due to the fitting height being too low.

If you use the proper centering chart for the individual progressive, would that not show you if the add has been cut off?

**HarryChiling** · 10-09-2009, 10:41 AM

...............

**Darryl Meister** · 10-09-2009, 10:59 PM

the next logical question would be how about a Definity with split adds and I honestly don't have a good response, although I would likely say that the surface with the highest degree of change would be the surface to measure

The manufacturer would need to specify the method of addition power measurement in this case as well as any compensated addition power value.