Good day :)
About two years back, I noticed that the local practitioners were apparently not too keen on dispensing occupational multifocals. Deciding that this would be a decent means of building up a client base, I set about calling up the labs and obtaining more information regarding occupational PALs and also occupational lens fitting in general.
The problem was, most of my lab techs were very cooperative, to the point whereby I was swamped with information and could not pick between lenses. Addition, degression, inset, variable corridors, working distance, induced prism... I'm sure most of you would know how I felt!
So I decided to cut some deals here and there, and put my theoretical knowledge of a few occupational PALs to the test: hypothetically, if a practitioner understands the design of a lens, modifying the Rx submitted to the supplier along with the fitting can convert the lens into a 'normal' PAL... which is what I did with my own prescription. Two years later, here is a current list of my converted office lenses - I hope my observations are of use to someone out there :)
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My Rx:
OD -4.00/-2.00x180 (6/6)
OS -6.25/-1.00x180 (6/6)
From here, I expected all my PALs to present with more swim on the right eye. For control purposes, all of them were ordered to produce an addition of +0.75.
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Lenses used:
Zeiss Office Lens (full Rx on top, add +0.75)
Nikon Home & Office (full Rx on top, add +0.75)
Free form desk lens (from a local lab - full Rx on top, add +0.75)
Sola Access (worn over my CL, plano on top, add +0.75)
And a pair of FT-28 with a blue coat for my music practice, which I shall describe briefly as follows.
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Results:
Zeiss Office Lens - The most noticeable swim and addition progression of all my lenses. Balanced zone width from top to bottom, can function as a general use PAL well enough until the Add reaches +1.50 (from customer feedback). No peripheral distortion above the fitting cross.
Nikon Home & Office - Feels almost like SV sideways and also vertically. Slightly narrower zones than the Zeiss. Cannot be used as a general use PAL since even with Add +0.75, above the fitting cross there is slight temporal blurriness.
Free form desk lens - I suspect this is a design modified from the old Asahi Optical, Pentax, and/or Kodak designs. Feels similar to the Nikon, but stopped using it due to sloppy lab workmanship and also the lab consistently delivering the wrong Rx (by their own admission).
Sola Access - Wanted to try out this golden oldie, and it didn't disappoint. A little hard on the distortion/swim, but fantastic width on the top/bottom. Negligible corridor width, but I've not had a single dissatisfied customer with this one. Have also used it as a 'beginner' PAL for those customers with smaller frames.
Bifocals FT-28 - I play music as a hobby, and since the music stand is on my right and off to the side about 1.5 feet away from me... suffice to say, I usually swap to bifocals if I'm in an Addition mood and it's time to practice on the trombone. Can still see the notes well enough for now, but my Add is a measly +0.75; those customers of mine who are musicians have appreciated the heads-up, and sometimes the switch to bifocals.
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Overall, what I've observed from my own wearing of these lenses and customer feedback on others is that occupational PALs tend to follow three distinct patterns:
- Balanced width from top to bottom (Nikon Home & Office, Hoya TACT/Workstyle, and arguably Sola Access though it's more an hourglass)
- Barrel design with wider middle, narrower top/bottom, mild swim at upper corners (Zeiss Office Lens, Varilux Computer, Tokai Resonas Presso)
- Inverted 'T' with distortion at the upper corners (Nikon Soltes/Online, Tokai Largo, Seiko PC, you could fit Access this way as well)
... and an occupational bifocal is whatever you make of it, haha
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So, will be continuing to fit my office lenses to a customer base which seem to appreciate them more than their PALs, for the most part! All my experimenting with lenses has been hugely entertaining, and it's also nice knowing that regardless of the manufacturer's intended design, I can usually obtain an alternate clinical outcome by modifying the Rx and fitting on the order forms
A gem of advice I got from these boards was to convert normal PALs into office lenses: had a few hiccups initially, but now it's smooth sailing, and of course, it's hard to beat the intermediate clear zone on a converted PAL. I tend to like using Nikon/Hoya/Seiko/Sola for these, since they do produce rather flat lenses for an Rx which is actually over-plussed. Just need to watch the corridor lengths and insets.
... some of the nearby shops have not been amused at eating a pair or several when a patient of mine goes by and they ordered the same lenses without being aware of the need to modify the submitted Rx and/or fitting.
Have a good day, folks!
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