Prism Thinning

Owned by Tony LeBlanc
Last updated: May 10, 2016
2 min read

A lab can have a default for all progressives, whether to use prism thinning or not. Under "Setup", "System Settings", Surf1 tab:


For toric jobs, the following are the possible values for prism thinning.  For digital jobs, N means no prism thinning, and any other value tells the digital calculator to do prism thinning, if applicable for the job.  In VCA terminology, PTOK=0 tells the digital calculator not to do prism thinning, and PTOK=1 tells the digital calculator it is okay to do prism thinning if it is applicable for the job
F - our recommended setting; calculates up to 2.00D of prism to try to equalize thinning at the top and bottom of a toric lens
E - an older calculation which tries to equalize thinning using a different approach, does not limit the prism to 2.00D
Y - calculates thinning prism as 2/3 of the ADD power
G - does "F" prism thinning for executives as well as progressives
Z - does "E" prism thinning for executives as well as progressives
X - does "Y" prism thinning for executives as well as progressives

Then, the lab can set a different value for specific lens styles (designs).  In the lens style (for each different design), on the General tab, is a field "Prism Thinning":


If left blank, it will use the system default.  If set to a specific value, that will be the new default for that lens design.

Default can also be set for a Customer (some doctors or ECPs do not want any of their lenses with prism thinning).  On the Customer screen, for a particular customer, a specific value for prism thinning can be set, or the customer can be left to "default":


Finally, the prism thinning switch can be set for a particular order.  On the F12 (Optional) screen from OE:


For most labs, our recommendation is to set the system default to "F", and then set specific customers, designs, or orders to "N" if needed.

Prism Thinning on Minus Lenses and Base Up Prism

Sometimes prism thinning can be done on a low-power minus lens which will result in better cosmetic thicknesses.  Due to the optics, however, some labs will prefer not to do prism thinning on these types of jobs. 

Similarly, sometimes the "best" thinning prism for cosmetic reasons will be base-up (rather than the more common base-down).  Again, some labs will prefer not to do base-up prism thinning, while others may be fine with it.

Rx-Universe offers system-wide controls, on the "Setup", "System Settings", Surf1 tab, to control this:

 




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