Originally Posted by
Robert Martellaro
There's a lot of educated guessing and assumptions with these types of lenses, so caveat emptor.
Here's how it's done using a traditional PAL or segmented multifocal. When the appointment is made, tell the client to measure the distance from their cheek or eyeglasses to the center of the desktop monitor display, and then to the desktop. Refract that distance, typically 60cm to 70 cm, and 35cm to 45cm to the desktop. Select a PAL that has a wide clear distance zone. Corridor length does not have to be fast and/or short because of the low add power, typically +.75 to +1.25, but should be adequate for their visual needs. For example, lawyers and radiologists will have distinctly different needs at near.
The primary advantage with these 'office' type lenses is that they provide a distance window at or above the primary gaze. Unfortunately, the price we pay for that capability is a much narrower intermediate zone width (see the illustration below), not a good idea with todays 27" and bigger monitors or multiple monitor configurations.
Moreover, if the lens design does not calculate the power based on the measured work distance (to the best of my knowledge none of them do), a monitor at 55cm gets the same power as one at 80cm, and that's just not going to be optimal, or may be downright rejected, especially with absolute presbyopes.
For those who are ambulatory or are unable to adapt to the the distance blur, one might underplus the distance portion (now the intermediate).
Hope this helps,
Robert Martellaro
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