Lowering Cyl for intermediate/reading RX

[Tallboy]

I get RXs from a doctor (optometrist, old school) who lowers the cyl in his RXs for dedicated intermediate SV or NVO SV.

In my 10 years he is the only one who I've seen do this, and I have worked with many many RXs from many DRs.

Has anyone ever seen this? Why does he do it?

Here is an RX I got:
PAL:
OD -1.50 -1.75 075
OS -1.00 -2.25 095
Add: +2.00

He told the patient NOT to get a computer/office progressive (which the patient had previously expressed interest in being as he has 3 monitors at varying distances), but instead to use this RX:
SV Intermediate?:
OD +0.25 -1.50 075
OS +0.75 -2.00 095


This is not the first patient of his that I've seen these RXs from

[braheem24]

Makes sense, if you think of cyl in the same way you would sphere and prism their powers change depending on the focal length needed.

Prism for 20 feet is not the same at infinity but most people don't ever need to see infinity. Ask a boat captain and they'll tell you the prism is usually too much or not enough when sailing because they get to experience true infinity when looking at the horizon.

[optimensch]

How do these near cyl adjusted Rxs work out for you?

I do that some of the time as well and basically it works about 99% of the time and to the patient's benefit. Less expensive than office progressives and easy adaptation. Its always case by case and depends on patient's needs and previous correction.

[fjpod]

I've done it. I guess I am old school.

[Tallboy]

They almost always work out, sometimes his RXes are over plussed, but for the most part I respect this doctor very much, bot his RXes and his medical exams.

I'd say 95% of the time. I just have never seen another doctor do this. Thanks for the input guys, you both strike me as knowing your way around a phoropter so I will now start harshly judging the docs who DON'T do this with their near rxes

[drk]

A quarter cyl is here in a blink, gone in a blink. It's like doing nothing. Placebo for the doctor.

Astigmatic blur is not good, ever. Certainly not on a computer monitor.

Why would you induce astigmatic blur when you could add a simple quarter diopter of plus, if you wanted? It's stupid.

[Tallboy]

A quarter cyl is here in a blink, gone in a blink. It's like doing nothing. Placebo for the doctor.

Astigmatic blur is not good, ever. Certainly not on a computer monitor.

Why would you induce astigmatic blur when you could add a simple quarter diopter of plus, if you wanted? It's stupid.

This is what has been said to me by another doctor I work with when I asked her what she thought about his computer RXes

[Robert Martellaro]

I get RXs from a doctor (optometrist, old school) who lowers the cyl in his RXs for dedicated intermediate SV or NVO SV.

In my 10 years he is the only one who I've seen do this, and I have worked with many many RXs from many DRs.

Has anyone ever seen this? Why does he do it?

I've seen it a few times. I believe it was discussed on Optiboard, but I can't find the thread. I did find this...

http://www.opticianonline.net/near-r...d-aberrometry/

Here is an RX I got:
PAL:
OD -1.50 -1.75 075
OS -1.00 -2.25 095
Add: +2.00

He told the patient NOT to get a computer/office progressive (which the patient had previously expressed interest in being as he has 3 monitors at varying distances), but instead to use this RX:
SV Intermediate?:
OD +0.25 -1.50 075
OS +0.75 -2.00 095

If a near refraction was performed, use those cylinder and axes values. But I would red flag the add power used for the computer glasses, which works out to +1.87, essentially a 40cm work distance, which is rare for a desktop monitor. Maybe the +2.00 add for the general purpose eyeglasses is for some other distance than the standard 40cm. That needs clarification.

If there are three work stations at varying distances, find the best compromise with a bias towards the most frequently used station, and let the depth of focus do the rest. You'll probably end up with a multifocal lens to address the distance to the desktop as well as the distance to the monitors.

[drk]

Ah, yes, Robert, thank you for the refresher.

Some really old-schoolers may do a separate near refraction (including astigmatism) with the assumption that accommodation (or the effort thereof) or extraocular muscle actions can have effect on astigmatism.

(N.B. While I don't doubt this can occur in super-rare circumstances, I haven't ever been tripped up by ignoring this likelihood. So maybe it's not "stupidity" but "hyper-overcaution".)

[fjpod]

A quarter cyl is here in a blink, gone in a blink. It's like doing nothing. Placebo for the doctor.

Astigmatic blur is not good, ever. Certainly not on a computer monitor.

Why would you induce astigmatic blur when you could add a simple quarter diopter of plus, if you wanted? It's stupid.

Not so fast, there, dr K.......
many people walk around without their DV/cyl correction on, and when they sit down at the computer, any significant amount of cyl can make them uncomfortable.

also, for every diopter cyl the patient gets at near, you have to add more plus ( or less minus), which shortens the users depth of field.

People walk around all the time without their cyls on, and to give them 100% for near can often upset the apple cart. Especially if they generally use otcs. The dispensing optician may not have the benefit of knowing the patients habitual state before the new rxs were issued.

[braheem24]

Am I the only one who believe astigmatism correction at 18" is not the same as astigmatism correction at infinity?

I'm not talking about the 1/8th of a diopter of minus, I'm talking about the actual skew deviation that cyl corrects is increased the further the object.

Cylinder is nothing more then prism like every other component in an Rx.

Take a Plano-0.25 and over-refract yourself at 18", then walk outside and do the same, you'll notice at 18" its negligible at infinity however it's very noticeable.

In any eyeglass Rx, The Sphere as well as the Prism and/or PD is adjusted based on focal length required without hesitation Why would anyone believe Cylinder is a static number?

[Fred Dagg]

Not so fast, there, dr K.......
many people walk around without their DV/cyl correction on, and when they sit down at the computer, any significant amount of cyl can make them uncomfortable.

also, for every diopter cyl the patient gets at near, you have to add more plus ( or less minus), which shortens the users depth of field.

People walk around all the time without their cyls on, and to give them 100% for near can often upset the apple cart. Especially if they generally use otcs. The dispensing optician may not have the benefit of knowing the patients habitual state before the new rxs were issued.

I don't disagree with your point about reducing the cyl to aid adaptation, but this optom apparently habitually prescribes a lower cyl for sv near/int than he gives for distance or progs. Personally I would incorporate the reduced cyl into both D & N rx if I felt that an under-correction was indicated. If I wanted a different working distance for a SV pair then I would tweak the add from the prog rx instead, and leave the cyl alone.

I'm not sure myself that this fellow's prescribing foible is 100% explainable in terms of pure optics. Mind you, apparently this guy is getting good results, so good on him. He's obviously not getting things wrong. We all tend to develop prescribing habits which are perhaps not entirely textbook, but have served us well. More power to him, I reckon.

[optimensch]

I won't attempt to get into a theoretical textbook explanation here, so I will stay in the anecdotal mode.
A purely myopic astigmatic patient (say -0.50 -1.00 X 180 OU) wears glasses for driving and other mainly DV activities. This patient hits the mid 40s, even 50s and continues to read and report no near point difficulties so long as their glasses are off. The uncorrected -0.50 part of their myopia gives them pretty good intermediate vision and the uncorrected -1.50 meridian gives them pretty good reading vision. I have noticed that uncorrected astigmatism (below a certain level of course) can be much less noticeable and even mildly helpful for near vision activities - for some people, once they become presbyopic.

It is this phenomenon - which I have noticed many times over the years - which is the basis for undercorrecting the full astigmatic Rx at near point - whereby one astigmatic meridian, left undercorrected, allows for greater depth of focus and range of "clear enough" vision for near activities.

This can provide some of the benefits of a multi focal lens (like a computer progressive) at a lower cost and easier adaptation - for some of the people, some of the time. Using a slight undercorrection of astigmatism as a tool to lower the needed add power for near point (especially in a computer progressive) if you are going with a multifocal can also be helpful. At least this way we get less un natural unwanted astigmatism (based on the manufacturers design) and we use the patient's own natural astigmatism to help do some of the lifting.

This is part of the art of prescribing. Remembering that what a person sees - without their glasses on - at different distances is always an obvious comparison for them to make with how they see with their glasses. How many ODs scratch their heads when confronted with hyperopes - even +2.00 or more, who report to never wearing or needing a distance Rx , and how their progressives are just for reading? Same idea at work..

[HarryChiling]

Its called NVEE Near Vision Effectivity Error, (t/n)L1(L1+2F1)
This should be applied to both meridians of power not just the cyl. Real old school but a rule of thumb the doc is using maybe good, but might be a good idea to run the numbers.

[Robert Martellaro]

Harry,

I think that NVEE is only a concern with high plus, and their typical lens forms. However, if there is NVEE, we certainly would correct both principle meridians, just as we would compensate for the change due to effectivity when a strong lens is moved closer or further from the eye.

[HarryChiling]

Harry,

I think that NVEE is only a concern with high plus, and their typical lens forms. However, if there is NVEE, we certainly would correct both principle meridians, just as we would compensate for the change due to effectivity when a strong lens is moved closer or further from the eye.

NVEE is going to introduce more error in higher plus and both meridians as you've mentioned but all powers plus or minus are effected to some degree. The simple way of thinking about it is the change in power and form due the change in vergence entering the lens. We assume infinity for distance power lenses or zero power entering the lens when calculating power and computing form, but when L1 is equal to roughly +3 entering the lens and the vertex doesn't change significantly and the foveal distance doesn't change significantly the power must be adjusted.

Without working out numbers I can positively say that it is not correct to apply any one factor like +0.25 to the cyl but that's like saying 1.5mm inset per eye is not an accurate inset for a bifocal segment yet its commonly applied by most opticians because its a good average over the majority on the common prescription range.

[drk]

Not so fast, there, dr K.......
many people walk around without their DV/cyl correction on, and when they sit down at the computer, any significant amount of cyl can make them uncomfortable.

also, for every diopter cyl the patient gets at near, you have to add more plus ( or less minus), which shortens the users depth of field.

People walk around all the time without their cyls on, and to give them 100% for near can often upset the apple cart. Especially if they generally use otcs. The dispensing optician may not have the benefit of knowing the patients habitual state before the new rxs were issued.

Are you talking about adaptation effects to habitually undercorrected astigmats? If so, yeah, I get you.

I was referring to intentional undercorrection of fully corrected astigmats.

Mensch, you are really talking about the same thing: habitually undercorrected astigmats (at near).

I say: fix 'em up.