Overview
Near Vision lenses are designed for intermediate and near vision (not distance and near as with traditional multifocals). When a lens style is identified as a Near Vision style in Rx-Universe, that implies several things:
- Lens is dispensed with a “distance” power and an add power.
- The add power is converted to a degression based on rules specific to that lens style.
- The lens blank with the specified degression is selected.
- Power is measured at the NEAR reference point, not the distance.
- Prism, however, is measured at the PRP (in the distance or intermediate section of the lens).
- True curve of the near vision blanks is at the NEAR reference point (not distance as with a regular progressive).
- Wrap compensation CANNOT be done on a near-vision lens.
Setting Up A Near Vision Lens Style
On the lens style screen, there is a tab for “Near Vision” – checking the “Near Vision” checkbox causes the lens to be processed as a Near Vision lens in Rx-Universe:
When set up as a Near Vision lens, there must be an association set up for add powers to degressions. A Near Vision lens comes in specific “degressions”, which is the change in power from the near portion to the intermediate portion of the lens. The associations between the add power (as dispensed) and the degression, are provided by the specific lens vendor.
In the above example, for the Essilor Computer lens, the relationship between add and degression is given in the technical documentation on the lens:
In Rx-Universe, set up the maximum add (on the left) with the degression to use up to that add. The lens style screen displayed above corresponds to the degression table above.
Entering a Near Vision Rx
When entering an order into Rx-universe, enter the dispensed power and dispensed add, exactly as provided by the dispenser. For example, if the dispensed Rx is +1.00/-0.50@135, add 2.25, the Rx should be entered into Rx-Universe exactly like that:
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When Rx-Universe selects the blank to use, it will convert the Rx to Near Vision:
Near Sphere = Dispensed Sphere + Dispensed Add
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And select a blank with the add power corresponding to the required degression for the lens. In the above example, the lens selected is a 650-base ECOMP, with a degression of 2.00 (the degression stored in the add field for a near vision lens blank):
The correct degression is determined from the table on the lens style (a dispensed add of 2.25 corresponds to a degression of 2.00).
Since the true curve of the lens blank is measured at the near reference point, the back curves (tools) of the Rx are based on the Near Vision power of the lens (in this case, near sphere = 3.25, cyl = -0.50).
Entering a Near Vision Rx
The work ticket shows the near vision power (for checking), as well as the original Rx as dispensed:
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Something similar is displayed on the invoice – the Near Vision sphere power is shown as the power, along with the degression add power – the dispensed Rx is shown in the comments:
Essilor Anti-Fatigue Lens
The Essilor Anti-Fatigue Lens is a unique case of near vision lens. This lens is marketed as a SV lens, and dispensers dispense it as such. However, the lens has a “power boost” of 0.60D in the near portion – so, in effect, it is a near/intermediate type lens. In Rx-Universe, the lens is processed as a progressive with a 75-add power.
On the lens style, you can set the lens to Anti-Fatigue:
This has the following effects on lens processing:
- The lens is processed like a progressive – the add power defaults to 0.75D at Order Entry
- Add is not printed on the invoice
- Curves are calculated on distance power (not near power as with other near-vision lenses)
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