Intermediate Distance Correction

[msawyer]

I have a need for precice focus at a distance at around 26 inches (approximately .67 meters). This should translate to 1.5 diopters add? In reality this appears to be a bit much. I want to retain as much distance vision as possible and still achieve clean focus at .67 meters. Can someone assist in the correct amount of add to achieve focus at this distance. It seems at an add of +1.0 seems to be about right.

Thanks for your help,
Marc

[Chris Ryser]

Can someone assist in the correct amount of add to achieve focus at this distance. It seems at an add of +1.0 seems to be about right.

Thanks for your help,
Marc

Your + 1.00 could be right but it could also be off...........unless you are going to keeo you head in a clamp so you can not move it forward or backward and then you would be off.

[chip anderson]

You need to know amoung other things, how old is the patient? What is the add for 14~18". Concider if the pt. is only 40~42ys old he many need no help whatsoever for .6 meter.

Chip

[HarryChiling]

The power of the add isn't just soe formula, you do have to figure into it the accomadative reserve the amount of accomadation the patient still has left the idea of the add power isn't to replace their ability to accomadate it's to give it soem help. So the 0.67m would easily be determined as 1/0.67 = 1.50, but depending on how old the patient may be you are not going to want to giev them the whole 1.50.

[Judy Canty]

Consumer in disguise?

[MarcE]

Yes.

An engineer?

[Judy Canty]

Probably.

[HarryChiling]

Consumer in disguise?

And to think I gave an answer, I feel used and dirty now. :shiner:

[msawyer]

The power of the add isn't just soe formula, you do have to figure into it the accomadative reserve the amount of accomadation the patient still has left the idea of the add power isn't to replace their ability to accomadate it's to give it soem help. So the 0.67m would easily be determined as 1/0.67 = 1.50, but depending on how old the patient may be you are not going to want to giev them the whole 1.50.

Thanks Harry, sorry if you feel proselytized. Sounds like +1.50 will work for certain, but ingnoring residual accomadation would unnessesarily compromise distance vision which is a secondary goal. A lesser add utilizing some of the residal would yeild better results on both goals. Patient has +2.0 Add now for reading. When it comes down to it probably will come to an empirical evaluation.

M

[HarryChiling]

Thanks Harry, sorry if you feel proselytized. Sounds like +1.50 will work for certain, but ingnoring residual accomadation would unnessesarily compromise distance vision which is a secondary goal. A lesser add utilizing some of the residal would yeild better results on both goals. Patient has +2.0 Add now for reading. When it comes down to it probably will come to an empirical evaluation.

M

Nah, if you were a consumer you asked a better question than some opticians I know. :cheers:

[drk]

There's a bigger question, here.

How do you determine an add to prescribe?

Several methods:
1.) Mathematical formula
2.) Functional evaluation
3.) Customary

Sure, if the patient wants to USE NO accommodation, or has no accommodation TO USE, go mathematical. The inverse of the working distance. Most people sit at arm's length, so figure +1.25.

Functional evaluation is better. Have the patient look at a computer screen, get behind it with your retinoscope, measure the lag in accommodation, and prescribe. That's the basis of the Prio Vi$ion Te$ting $y$tem. Or, use a near-point rod with a target with a hole in the middle to scope through. You'll probably get about +0.75--+1.50.

Which leads me to method #3. How about a straight +1.00 add for most everyone? You can add or subtract a 1/4 diopter if you think a +1.00 is going to kill them.

Too imprecise for you? Consider that, as a computer user myself, I like to sit all hunched over when I read about Luxottica taking over Essilor on Optiboard, due to the tension of not being vertically integrated with them...that tends to reduce my working distance so I'd need that +1.25.

But when I laugh over one of Fezz's jokes, I throw myself back in the Staples Office Chair, increasing my working distance and necessitating a +0.75 add.

So you never can know....

What I like (seriously) is a NVF lens for everyone. That way, a little head angle will cover all eventualities. You gotta go NVF for computer, and all the archaic SVNO formulae above fall away into the ash heap of history.

I'm going to plug Darryl Zeiss Vision's Sola Access lens. It's cheap as salt for the salt pan and the design isn't too ambitious (ergo it works). Just do it.:bbg:

[chip anderson]

If de patient has a +2.00 add. Use +1.00 for intermediate. If the patient has a +2.00 add he should have been fitted with a trifocal! Or a progressive! Where are your basic skills?

Chip

[AdmiralKnight]

That's pretty harsh. You know how people are. "I don't want bifocals." With a +2.00 add they're probably early 40's and don't think they're old enough to need bifocals. Just because you KNOW they'll get better vision out of a tri or a PAL, doesn't mean they'll want to go that route. It's then your job to find the second best option for them. It's not fair to question someone's skills without knowing the entire story.

[chip anderson]

Admiral:
I don't know what the texts say in Cannada, or what sort of certification tests you get. But everyone course I have taken (a whole lot) every text I have read, every lecture I have listened to (at least by an author of repute) has taught: "When the add is +2.00 or above a trifocal (or progressive) is required." They also went on explain that the prescriber need not or would not specifiy this because your basic optician should have sense enough to do this as a matter of course.
Now I do admit that we all have your basic retiree that says:" I don't work anymore and I'd rather have a trifocal."
But from the decription this is not the case with this patient and he obviously needs help at intermediate if another pair of glasses was being concidered for this distance.

Now why do I sound so "Harsh?" Because we are seeing entirely too many "opticians" as well as "reputed" course givers that don't seem to know the basics anymore. Only how to sell the latest high tech most expensive product.

Chip