OSN Technology and Equipment Workshop presentation: M&S Technologies' Contrast Sensitivity System

Jack T. Holladay

The following excerpt is from a presentation by Jack T. Holladay, MD, MSEE, FACS, at the 2009 OSN Technology and Equipment Workshop on M&S Technologies' Contrast Sensitivity System.

Jack T. Holladay, MD, MSEE, FACS: It is a pleasure to be here this afternoon and talk to you about something that we've been working on for almost 5 years, but about 2 years ago the CEO and engineer got into a little bit of an argument, and so for 2 years it was down, and now it's back up and we've resurrected it. Some of you have seen this before, and in that time we've had some things that have changed. And primarily what that is, as you'll see, is that we've gone from monitors that are old CRTs to an LCD.

But basically, contrast sensitivity, as you know, there are two sides that we look at for vision. One side is visual acuity, which is looking at the smallest thing you can see in high contrast. And the other side of vision, which some people think is more important for things that we do today, is contrast sensitivity, which measures the threshold, the lowest contrast that you see of any object size, which turns out to be about 20/200, where we have our maximum contrast sensitivity. In other words, what contrast sensitivity measures is your ability to see a gray truck coming over the hill in the fog, which doesn't have anything to do with visual acuity. And that's what this system is talking about.

Now, some of the things that we've run into in the past that are problems with contrast sensitivity ... What we see is, when you use charts, like many of the systems that you can see on the floor today here, the problem with charts are, if it's illuminated and you do it by turning up room lights and stuff, well, then it's difficult to control the lighting in the room. It's hard to prevent that light from scattering and giving you back lighting that gives the patient a kind of glare test. And today the FDA has adopted 85 cd/m² and 3 cd/m² as the photopic and low mesopic settings that we do all of our clinical testing in.

Now, vertical linear gradings. I'll show you why there is a little bias there for with-the-rule astigmatism and horizontal coma. In other words, if you use what we call vertical gradings, some people see vertical lines better than others. And that, then, would give an advantage in the contrast sensitivity test, which is not good.

The other thing is, there is a blanking period. Our photoreceptors need to be rested for 5 to10 seconds before we actually do a test on them. And the reason is that if you leave them untested too quickly, oftentimes we'll get an after-image or a problem that reduces and makes it not as repeatable as it could be.

Response time. You can't leave an open-ended test where somebody can sit there all day and kind of look at it. We limit it to 10 seconds.

And then finally, you have to be able to detect false positives. We have people that are trigger-happy and we have people that are gun-shy. If you've got somebody that's trigger-happy, and every time you show a display, they hit a button, well, they can look like perfect. In fact, you have to have some kind of control that tests whether they really see it or not.

Joe Marino is the CEO. The booth, I believe, is 513. Is that right, Joe?

Joe Marino: 540.

Jack T. Holladay, MD, MSEE, FACS: 540. It's on the floor. You can look at the system. And what we've done is, we've addressed each of these problems. We've looked at each one of these problems in the past.

The problem with the vertical grading ... A sinusoidal bull's eye. All of a sudden it doesn't matter what your axis of astigmatism, it doesn't matter if you have coma or other directional Zernike higher-order things, because whatever happens is, you'll pick up this contrast at the meridian that's most sensitive for you. The system allows you to provide the contrast that's automated, so you don't have to do this. But when you click this particular thing, it goes through a little training for the patient and then it goes through the real test.

There is a control, a gray disk. And you can see the gray disk or the bull's eye. The point is, when you get high enough in the frequency or low enough in the contrast, it looks like a gray disk to you. So what happens is, the patient sits there, and there are two buttons. I see it, gray disk, or I don't see it, a bull's eye. And basically they hit the bull's eye or the gray disk.

Now we've gone to LCDs, which allow flat screens at the end of the room. It's calibrated in a way that also lets you do visual acuity testing, other optic types for children.

There are normative values that we have determined for photopic sensitivity curves. We also like to take the area under the curve to compare one patient to another. The mesopic contrast sensitivity curve is a little lower. This is done in 3 cd/m². And what happens is, the report that's generated for you gives you the values for the patient, gives you the area under the curve, shows you what their thresholds are for each level. And this is sensitive to 0.1 log units, or what we call 1 dB.

Now, that is three times more sensitive than any other system that's available and working today, and a study that just came out in The Journal of Cataract and Refractive Surgery that was done in Norway compared five contrast sensitivity systems. This one vertical Vernier testing, they also did it with a machine that they had that was very sensitive. But the fact is, they all came up with about 0.3 of a log unit in terms of the standard deviation. And then this is 0.1 log unit, or 1 dB, which means we'll be able to show differences between multifocal lenses.

Now companies have a dilemma. If you have something and you want to show that there's no difference between a multifocal lens and a monofocal lens, you don't want to do this test, because it will show that there is a big difference. If you want to show they are the same, then you use some of the standard tests today that are 0.33 dB, which is about 40% to 50% contrast. That's a big deal. So these will let you get good things.

The point is, this particular system allows you to use a calibrated monitor, automated it takes about 9 to 10 minutes per eye, it uses the sinusoidal bull's eye, it has a blanking period and the response time is 5 seconds. And it also has a reliability factor at the end that, of the 5 to 10 presentations throughout there that are random, it tells you how many of those they got right. Because if that guy missed all of the gray disks, then obviously it wouldn't work very well.

So, that's the new contrast sensitivity system from M&S Technologies. And I'm so glad this is available, because what it's going to now do is give us a test that really will show us differences in performance and many of these premium IOLs and other things that we have today that we're saying, "Gee! It's all the same."

The OSN Technology and Equipment Workshop is a showcase of the clinical benefits of new surgical and diagnostic equipment, surgical instruments, software, vision testing and contrast sensitivity testing systems. Step beyond the brochures, bring the products in the exhibit hall to life, and hear surgeons' clinical impressions of the newest equipment and instrumentation. This workshop will allow attendees to interact with surgeon users and manufacturers.