Thickness On An Order

While Rx-Universe has many options to set the default thicknesses for orders, sometimes it is necessary to specify a specific center or edge thickness for an order.

Beginning with version 6.48.00, Rx-Universe supports specific center thickness (CT) and edge thickness (ET) for any job. On the Order Entry screen, there are fields for CT and MinET both:

To illustrate, consider a sample job as follows:

The red numbers under the MinET box show the default minimum edge thickness for the lens, based on the material settings for uncuts, which are:

In the example, the lens would normally be calculated such that the ET at the thinnest edge would be 1.25mm.  In this case, the lab has specified a CT of 1.5mm, so the lens will be computed with that center thickness.

On the work ticket, the lab will be warned that the lenses will be LESS than the thickness constraints set up in Rx-Universe.  In the above case, the work ticket will show:

The CT will be the requested 1.5mm (shown in the "User Spec CT" line), but the lens will, overall, be thinner than the thickness rules that are set up. Specifically, the thinnest edge will be 0.82, which is 0.18mm thinner than the MINIMUM edge defined on the thickness screen.  The lens is also 1.34mm thinner than the Sum of Thickness constraint of 5.0mm.  As a reminder, Sum of Thickness specifies that the CT + MinET should equal the specified value, in this case, 5.0mm.  Since the CT=1.5, MinET=0.82, the Sum=2.32, which is 2.68 less than 5.00, and therefore the lens is 1.34mm thinner (remember that increasing the thickness of the lens by 0.1mm increases the Sum by 0.2, since it is the total of the CT + MinET).

Restrictions on User Center Thickness

There are some restrictions on the CT that is entered by the user.  If the CT entered will result in non-positive thicknesses at any edge point on the lens, the thickness of the lens will be increased to make the edge at least knife-edge.  If using cut-to-polish technology, this is still not recommended, because the knife-edge of the cribbed lens could cut into the soft block. 

For example, the following order:

With a CT=1.0, the ET at the crib would be negative (the blank would not even be 65mm because part of the blank would be cut off). In this case, Rx-Universe will increase the thickness of the blank enough to make the edges non-negative:

The CT of the lens has been increased to 1.9mm, which makes the thinnest edges 0 (or knife-edge).  Note that there are no specific messages printed for this situation - it is assumed that the lens must have a non-negative thickness over the lens surface.

Digital Surfacing

There are no digital calculators that support directly specifying center thickness on a plus job.  (IOT has an option, _ICTK, which is supposed to do this, but it still respects the thickness constraints imposed by minimum thickness at crib diameter, and minimum edge thickness).

To try to request the CT as close to the value requested as possible, Rx-Universe does the following when a specific CT is requested for a digital job:

1) The requested CT is sent in label MINCTR

2) The MINTHKCD label (minimum thickness at crib diameter) is suppressed for the job

3) The MINEDG is set to 0.01

Note that some digital vendors will have their own rules for thicknesses, and they may over-ride the requested thickness from Rx-Universe.

When specifying center thickness (especially on a plus lens) in Rx-Universe, and sending the job to the digital calculator, if the results are not as expected, the lab can verify what is being sent to the calculator in the LDS file.

Ensure that the MINEDG and MINCTR labels are both being sent, and that the MINEDG=0.01, and that MINCTR is sent as the requested CT.  For example, if a CT of 1.8 was requested on a digital job:

The lab can check to ensure that the correct MINEDG and MINCTR were sent in the LDS file:

In this case, the CTHICK sent back by the calculator is exactly as requested (CTHICK=1.8).

If the correct MINCTR is sent, and MINEDG=0.01 is sent, but the resulting thickness is not what the lab requested, the lab should contact the specific digital vendor to discuss.

Electronic Interfaces

Rx-Universe can receive a specified center thickness as part of an order file sent in GIF format.

CTHICK - specifies a particular center thickness

THNP - specifies the edge thickness of the thinnest point

Both can be included in an order file, and both will be respected, but THNP will be interpreted, in this case, as the desired minimum edge thickness. If the lens, when using CTHICK, has an edge thinner than THNP, then the thickness will be increased to respect BOTH requests.