Help! Can someone help me with the definition of a dynamic power shift?

[HCMB]

:hammer:I know that computer/occupational lenses use power shifts, but how do you determine what power shift is the best? I know that the power shifts are actually minus powers (unlike a progressive add), but gee whiz, I am confused!!! Please help me understand the lenses, I have the hardest time ordering them from the laboratory, and getting it right! Any help is greatly appreciated! HCMB

[Refractingoptician.com]

One way is to call the lab and give them the normal bifocal RX and tell them you want a "brand x" computer lens , then they will do the rest .

Personally though , you should get out the resource materials and read up on the subject until you fully understand it and have it reasoned out correctly.

Think about a trifocal and how it works . Think about the net effect you are trying to produce . You are trying to produce a focus point at a certain distance . So if you know the distances and Rx involved then you can use formula to solve the problem .

[Refractingoptician.com]

Please explain your reasoning to me that is leading you to think that the power shifts are minus powers .

Consider this bifocal RX :

R +2.50 Add +2.00
L +3.00 Add +2.00

Now if you were making this patient Flat Top 28 computer glasses , then what RX would you order ?

Answer : take the add power and divide it in half and then add that number to the distance sphere power ( +2.00 divided by 2 = +1.00 ) Now subtract that same +1.00 from the original add power and that resultant figure is the new add power to use.

so we order : R +3.50 Add +1.00
L +4.00 Add +1.00

Consider this Rx :

R -4.00 Add +3.25
L -6.00 Add +3.25
What is the FT 28 computer Rx ?
+3.25 divided by 2 = +1.62 . This is not an even number so we either round up or down . So lets use +1.75 .

so for the right eye we add +1.75 to the -4.00 and we get -2.25
so for the left eye we add +1.75 to the -6.00 and we get -4.25
the add was +3..25 but we used +1.75 of it . SO the remainder is +3.25 - 1.75= +1.50 . Therefore the new add to order is the differnce of +1.50

so the Rx to order from the lab for a Flat Top 28 computer glass is :

R -2.25 Add +1.50
L - 4.25 Add +1.50

Now if you consider the normal distance RX in both cases you will notice that the "power shift " was not "minus" it was a plus power shift in both cases relative to the distance power .

Case (1) distance was R +2.50 and it became +3.50 for computer use

Case (2) distance was R -4.00 and it became -2.25 for computer use

These are plus power shifts.

Looking at the add powers you might that we added minus power but you are looking at the concept wrong .

Wether we are reading through a normal bifocal or a computer bifocal , we are still going to need the same Rx to do it ... so there was NO power shift in the reading .... look atthe results .

R +2.50 Add +2.00 .... so reading Rx is +4.50
(+2.50 plus +2.00 = +4.50 )

computer rx

R +3.50 Add +1.00 ... so reading Rx is +4.50
(+3.50 plus +1.00 )

there was NO CHange to the net reading Rx

THink in terms of what rx is required to make Flat Top computer glasses and make sure your progressive computer glasses will yeild that result .

Also keep in mind that each person is an individual and may require more customization of the RX

[HCMB]

Gary,

Thank you so much for your through explaination. To answer your first question: It is my understanding that the D.P.S. is the amount of power subtracted from the total reading rx, hence the gradual reduction of power from near to intermediate. I will spend more time on selecting my computer lenses, as many of them provide different choices in D.P.S., & I will take your advise & read up on fitting requirements for the most widely used. I just get alot of "call backs" from the lab. Geez, I feel like I just answered my own question! Thanks again, H. :idea:

[MTAMERIUS]

From A Lab Owners Point Of View. I Would Recommend That You Give The Lab The Distance And Near Rx. If You Allow The Lab To Calculate The Lens Power It Will Produce The Manufacturers Intended Results. Each Lens Has It's Own Unique Design That Will Work If You Allow The Lab To Use The Specifications From The Manufacturer.

Many Of The Larger Labs Have Very Sofisticated Software That Will Take Into Account The Base Curve, Material, Fitting Height And Rx To Come Up With The Correct Rx For Your Computer Lenses.

Good Luck!

[Refractingoptician.com]

I agree with the lab owners point of view, and method of ordering because it creates the least amount of confusion to the non-technical , order desk clerk, and the inexperienced optician, which is why I suggested that method in my first response .

[HCMB]

MT & Gary,

Thank you for your responses. I asked my lab to help me out. Our lab requires the total near Rx, and depending on the manufacture, the distance or near monocular p.d.. They then ask for the power shift, and instruct us to put that information in the "add" area of the order form. If I submit the order over the internet, I must repeat my requested power shift in the "special instructions" area. They want us to convert all computer lenses ourselves, except the Gradal RD, which they will do. My lab rep dropped off a nifty customized "Computer Lens Reference/Fitting Guide" to help with the 6 different manufactures & lens designs they recommend. Now THAT was huge! Loads of info at my finger tips! (From just one call!)
Thanks for the suggestions and of course, being there.
H.

[Bobie]

I recommended DP - 0.80D or - 1.00D for Occupation PALs ( OPALs ).

To learn more about OPALs : Near OPALs - http://www.apcthai.com/forum/forum_topics.asp?FID=13 (http://www.apcthai.com/forum/forum_topics.asp?FID=13)

Computer OPALs : http://www.apcthai.com/forum/forum_topics.asp?FID=10