3.0 Blank Selection for Digital Surfacing
Since a back-surface digital surface job has the power of the lens, including the corridor, ground onto the back surface of the lens, the lens selected from inventory is a SV-style lens, or donor blank. (Other digital offerings retain the progressive design on the front, and calculate an atoric curve for the back to minimize distortion).
The remaining blank selection discussion does NOT apply to certain designs such as Essilor full-service designs, as these vendors determine the blanks to use. Note that it is the lab’s responsibility to ensure they have the proper lenses set up in the Rx-Universe inventory system for use with vendors such as Essilor..
When using blanks that are pre-marked, they should be treated similar to a polarized lens, and NOT cribbed, to avoid removing the reference marks needed for finish blocking. These reference marks are used to ensure proper location of the horizontal (again, similar to polarized lenses).
Whatever lenses are used for digital surfacing jobs, an alias needs to be set up to tell Rx-Universe which lenses to use for the particular digital lens style. For example, to use a regular, semi-finished lens blank when lens style CUST14 is entered for a job, an alias item similar to the following should be set up:
Some digital surface vendors provide special SV-style blanks for this purpose, which have markings already embedded into the lens to facilitate finish blocking. Those blanks from Epson-Seiko, for example, are loaded into the Rx-Universe inventory system with all technical information, including OPC codes, using the lens style FFSF (digital surface semi- finished), to differentiate them from regular SV lenses. Other vendors provide SV blanks which are used only for digital – Essilor lenses can be found using code SVD (for SV Digital), while Zeiss pucks use the lens style PUCK. If a digital vendor has specific requirements about which donor blanks must be used for specific designs, they will make this information available to the lab; it is the lab's responsibility to ensure the alias is set up correctly in Rx-Universe.
The base curve selected for a back-side digital progressive is different than that selected for a traditional progressive design; this is because the add power is ground on the back of the lens instead of on the front. The suggested base curve charts from lens vendors for digital jobs are based on add power in addition to sphere and/or cylinder powers. When Rx-Universe determines optimal base curve for a digital job, it takes the add power into account when looking up the chart. When entering a base curve chart for a digital design, the add power should be added to the sphere power (in the chart), and the curves entered using the combined sphere + add for the sphere column (in the case of Epson-Seiko charts), or the add power should be substituted for the cylinder power (as in the case of Shamir base curve charts).
Note that the chart number used for a digital job is determined by the chart number of the digital lens style, NOT the chart number of the SV donor blank used.
It is possible to set the alias up so that OMICS can select the best design to use based on the seg height of the job. For example, take a digital design available in 3 corridor lengths, with different minimum seg heights, as follows:
| Design | Min Seg Height |
|---|---|
| DIG18 | 18 |
| DIG14 | 14 |
| DIG11 | 11 |
The lens style setup for each lens must have the minimum seg height set, and the “Min SegHt Action” option must be set to “Y”:
Then set up the alias file to start at style DIG11, aliasing to DIG14, DIG14 aliasing to DIG18, and DIG18 aliasing to SV.
When entering an order, always enter with lens style DIG11 – Rx-Universe will then check the seg height, automatically switching the design to DIG14 or DIG18 if necessary, and will select the SV lens from inventory to process the job.
If the digital design is one for which the DS calculator can provide the allowable/preferred base curve range, Rx-Universe can use that method instead of using charts to select the base curve. This is set up on the lens style using the checkbox called “Use BRS to get BC from DS”:
When this lens style is used, Rx-Universe will request the base curve to use from the DS calculator by creating a BRS file in the outgoing folder, and will display a message “REQUESTING BASE CURVE FROM DIGITAL PROCESSOR” during blank selection while it does this. If it does not receive a response back from the processor, or no blanks are available with the base curve selected, the appropriate message will be given.