Required Power at Specific Distance

[D_Zab]

I have had a couple conversations with a doctor recently who wanted to begin offering his patients occupational progressives. Until recently he had been manually calculating what their intermediate power was and prescribing that modified power/add combination into a regular progressive design.

I spoke with him at length about various occupational designs and how they function and his biggest concern was not being able to accurately predict what the final power was going to be in the upper portion of the lens. Ultimately we came to a consensus but I've been thinking about it and I wanted to take a closer look for my own understanding.

What is the formula required to determine what someone's intermediate prescription would be at a specific distance?

For example, if a patient had a distance Rx of -3.00 sphere OU with a 2.00 add, what would be the necessary Rx to see up to 13ft? What about up to 7ft?

I can calculate dynamic power for various occupation designs but I wanted to play with some hypotheticals to see how they would compare in various situations. Any input is appreciated.

Just to clarify, I do not need occupational lens recommendations, I have a well established knowledge of the products that are available in this category.

Thank you ahead of time for any input.

[NCspecs]

I have had a couple conversations with a doctor recently who wanted to begin offering his patients occupational progressives. Until recently he had been manually calculating what their intermediate power was and prescribing that modified power/add combination into a regular progressive design.

I spoke with him at length about various occupational designs and how they function and his biggest concern was not being able to accurately predict what the final power was going to be in the upper portion of the lens. Ultimately we came to a consensus but I've been thinking about it and I wanted to take a closer look for my own understanding.

What is the formula required to determine what someone's intermediate prescription would be at a specific distance?

For example, if a patient had a distance Rx of -3.00 sphere OU with a 2.00 add, what would be the necessary Rx to see up to 13ft? What about up to 7ft?

I can calculate dynamic power for various occupation designs but I wanted to play with some hypotheticals to see how they would compare in various situations. Any input is appreciated.

Just to clarify, I do not need occupational lens recommendations, I have a well established knowledge of the products that are available in this category.

Thank you ahead of time for any input.

Frankly, in my office, we ask people to measure in real space, how far away their intermediate and near work is. Quite literally, we have people have a friend assist them with a tape measure. I'm not familiar with a particular formula just because I've found there to be so many different factors at play, like occupation, pt's height, habitual use, etc.

I know you didn't ask for a recommendation but I don't typically use occupational multifocals. I've been having great success with jerry-rigging a Definity with an intermediate Rx at the typical seg height which obviously transitions into the near Rx. It's been working beautifully for my IT patients.

[D_Zab]

I know you didn't ask for a recommendation but I don't typically use occupational multifocals. I've been having great success with jerry-rigging a Definity with an intermediate Rx at the typical seg height which obviously transitions into the near Rx. It's been working beautifully for my IT patients.

Do you some sort of standard digression formula for the Rx you put into the Definity and what are the approximate results (ie. the distance they can see clearly)? And then is there a reason you choose this over the occupational designs?

[shanbaum]

I think you're looking for the reciprocal of the object distance in meters - for example, an object at 3 meters exhibits a vergence of -0.33 diopters (1/3), so that much plus power is required to focus at that distance (assuming zero accommodation). As far as the range over which a lens of a particular power will be useful is concerned, that's a function of the patient's amplitude of accommodation, something that's measured during a typical exam but never (in my experience) conveyed in the Rx. You can make a guess based on the patient's age - an advanced presbyope may only have 0.5D to 1.0D of accommodation left.

[D_Zab]

I think you're looking for the reciprocal of the object distance in meters - for example, an object at 3 meters exhibits a vergence of -0.33 diopters (1/3), so that much plus power is required to focus at that distance (assuming zero accommodation). As far as the range over which a lens of a particular power will be useful is concerned, that's a function of the patient's amplitude of accommodation, something that's measured during a typical exam but never (in my experience) conveyed in the Rx. You can make a guess based on the patient's age - an advanced presbyope may only have 0.5D to 1.0D of accommodation left.

Thank you! This will give me something to work with and give me an idea of what else I can research.

[NCspecs]

Do you some sort of standard digression formula for the Rx you put into the Definity and what are the approximate results (ie. the distance they can see clearly)? And then is there a reason you choose this over the occupational designs?

I use the Definity because of the plus sign shaped corridor, the intermediate is very wide, as is the reading. I've encountered some issues with peripheral distortion with the Shamir office lens and other similar designs. The Definity has always worked in my favor- My OD and I sort of stumbled upon it togther and now it's a go-to solution in many cases.

[Robert Martellaro]

I use the Definity because of the plus sign shaped corridor, the intermediate is very wide, as is the reading. I've encountered some issues with peripheral distortion with the Shamir office lens and other similar designs. The Definity has always worked in my favor- My OD and I sort of stumbled upon it togther and now it's a go-to solution in many cases.

The intermediate isn't used if we Rx for the work distance, typically for a desktop monitor or sheet music, on the distance portion of a general purpose PAL. Consider using a PAL that has a wide and generous distance zone for the best possible acuity across the width of the monitor or monitors.

What is the formula required to determine what someone's intermediate prescription would be at a specific distance?

It will be better for you and your client if you just trial frame the client at the measured work distance.

[DanLiv]

his biggest concern was not being able to accurately predict what the final power was going to be in the upper portion of the lens.

You can predict it. Each occupational/computer/workspace has a defined percentage of add at the MRP. The doc can Rx whatever power he wants for the intermediate and your can work backwards through various models and digression powers to get the intermediate and near powers you want.

[essegn]

http://www.optiboard.com/forums/show...-just-know-it?