"Balance" on a Rx

[m0002a]

This thread was originally asking what "Balance" meant. My point was to address the issue of safety for the existing good eye..no more no less. Apparently you have a lot of NASCAR drivers at your shop m0002a. Vrrrooommm
Your point of peripheral quality vision is duly noted.

Staying alive on the road is all about defensive driving (seeing the other crazy drivers). No matter how good of a driver you are, the crazies will get you if you are not very careful.

[fjpod]

The odds of a patient being seriously injured or killed in a auto accident due to poor peripheral vision common with polycarb with a strong Rx, is much higher than the odds of losing one’s sight due to shattering of a non-polycarb lens. In other words, when driving a vehicle, good vision is "safer" than worrying about impact resistance of tensile strength of a lens. The importance of getting the best optics for someone with only one good eye cannot be overemphasized.

I would agree that it is extremely important to have good optics and good correction in a monocular patient.

But on the issue of poly causing bad enough peripheral vision to be a causative factor in auto accidents is, IMHO. a stretch. Peripheral vision is often referred to as 20/200 vision, so it is commonly considered that if your central VA is corrected to at least 20/200, then your peripheral vision in that eye is the same as it would be if you were corrected to 20/20. Now I know it's hard to really believe this because if we blurred our vision to test this, the blur of our central VA would be so uncomfortable as to make us feel like we're blind. But if you did this in a controlled laboratory setting, you would find it to be true. Poly does create some chromatic aberration when you view through an off axis point. but it has little, if any, impact on peripheral vision.

Distorted peripheral vision is much more a function of high lens power and lens form. But even here, unless we are talking about an Rx of over +/- 8, with a poorly fitting frame, the person's peripheral vision will be virtually normal with any material because they will make perceptual adaptations to the changes (distortions) in their visual field...and they will still have peripheral vision outside of the view through the lens. Vertex distance, base, curve, face form etc., have a lot to do with minimizing this type of distortion.

Now, does poly reduce the quality of central acuity? It's certainly not something you can pick up on an acuity chart, but I wonder if it degrades contrast sensitivity function, or critical flicker fusion frequency which play an important role in visual comfort. Anybody got more information?

[k12311997]

Another great reason to write balance: Avoid a costly PAL in front of a non-seeing eye; just use SV.

I always give monocular pts that option but have had several return and pay the difference for the progressive because they could see the cosmetic difference.

[Chris Ryser]

I always give monocular pts that option but have had several return and pay the difference for the progressive because they could see the cosmetic difference.

If you would use a spherical lens of about the same power as the good lens there is nobody that will see a cosmetic difference.

[k12311997]

If you would use a spherical lens of about the same power as the good lens there is nobody that will see a cosmetic difference.

my patients dissagree, they could see a difference.

[Andrew Weiss]

The docs I worked for in Massachusetts, to a person, all required poly or Trivex with all functionally-monocular patients. They were concerned about liability -- theirs and ours (the opticians). None of our patients had any problem with it that I recall. I was clear about which Rxs I thought would not be adequately served by poly and put those patients in to Trivex. Sometimes I'd adjust the Trivex price to the poly price to give them a break.

Also some years back I filled a "balance" Rx and had the patient complain that his vision was no good. I went back to the Dr's refraction and refilled the "balance" lens with the Rx the doc had found gave him minimal vision (I seem to remember 20/200-), oblique-axis cyl and all. Sure enough, the guy said the glasses were much better!! Was this all between the ears? Maybe, but I suspect he had gotten used to a certain minimal level of vision with that eye and when it wasn't there he noticed it. I wonder how many other patients there are out there who are like that.

[Dave Nelson]

Andrew, we do run into that situation quite often, so when someone presents with an rx that calls for a balance lens, we often do a little quizzing and assessment based on counting fingers, and often just match the exisiting prescription in the balance eye.
As to the issue of what lens to use for the monocular patient, we usually recommend poly, even if its plano, but will supply any impact resistant lens they want, as long as they understand the issue. Liability issues do not extend to twisting someone's arm to make them wear what you think they should have, but making sure you inform them of the options, and the risks.

[m0002a]

The docs I worked for in Massachusetts, to a person, all required poly or Trivex with all functionally-monocular patients. They were concerned about liability -- theirs and ours (the opticians). None of our patients had any problem with it that I recall. I was clear about which Rxs I thought would not be adequately served by poly and put those patients in to Trivex. Sometimes I'd adjust the Trivex price to the poly price to give them a break.

As someone who has worn lenses for over 50 years, and has been amblyopic (20/200 in bad eye), I can tell you my experience.

To the best of my recollection, polycarb has been recommended to me since it became available (my early lenses were glass). But in cases when I insisted on not getting polycarb/Trivex, no one refused to sell me a lens. They all warned me, which is the extent of their responsibilities, but they sold me whatever I wanted.

I would bet that if a patient pushed back on the docs you worked for in Massachusetts, that they would not refuse a purchase, so long as the patient was warned. Relatively few patients are sophisticated enough to challenge an ECP on anything, much less lens material, so it may have never happened in your case.

[m0002a]

But on the issue of poly causing bad enough peripheral vision to be a causative factor in auto accidents is, IMHO. a stretch.

Given that there are about 39,000 fatalities and over 2 million injuries every year in the US caused by vehicular accidents, I don't think it is a stretch to assume that very small percentage could be caused by poor peripheral vision in polycarbs. How about just 10 deaths and about 100 injuries?

My personal views are skewed by my experience driving home after purchasing a new pair of polycarb progressives. That was one of the more reckless things I have ever done in my life, and was probably worse than if I had been drinking heavily. Yes, I am a strong hyperope, but don’t forget that hyperopia is quite common for persons with amblyopia such as myself.

How many adults would you estimate have lost their sight in at least one eye or have been killed by not wearing polycarb/Trivex? I would like to see some factual data on that.