OSN Technology and Equipment Workshop presentation: Reducing surgical astigmatism

Eric D. Donnenfeld, MD Eric D. Donnenfeld

The following excerpt is from a presentation by Eric Donnenfeld, MD, FACS, at the 2009 OSN Technology and Equipment Workshop on reducing surgical astigmatism.

Eric Donnenfeld, MD, FACS: What I'm here to do today is to talk about new technology for reducing surgical astigmatism. I think any of you who are practicing in ophthalmology right now know that the key to good results with refractive cataract surgery is to minimize astigmatism to the lowest level possible.

Now, that can be done through a variety of different means. We can do excimer laser ablation. You can put toric IOLs in. You can do limbal relaxing incisions. You can even do CK. But the whole key is, you need to have great results. And the key to good results is reducing cylinder. And the number one reason why I see patients come to me who are unhappy after refractive IOL surgery is that they have residual astigmatism.

I consult with a variety of different companies. I'm talking today about some Accutome products. I do not consult with them, and I have no financial interest in any of the products I'm about to show you.

Let's start with refractive legend number one, and that is, refractive IOLs will tolerate small refractive errors, and that could not be in any way true. Refractive IOL patients are incredibly sensitive to small errors. And we, as surgeons, must be willing and able to treat postrefractive surgical results.

Now, I am a big believer in limbal relaxing incisions. I think they have a very significant place. I have moved more, though, in recent history, towards using excimer laser photo ablation, which can really fine-tune results very significantly. But for patients with minimal residual cylinder, or for patients who have a lot of cylinder and you want to debulk the cylinder, I do a lot of limbal relaxing incisions. And probably 30% of my patients who are having cataract surgery today are receiving limbal relaxing incisions. They are inexpensive, easy to perform, minimal instrumentation. They can be done at the time of cataract surgery. No impact on healing. They can be repeated.

But there are some downsides. The number one downside is, they are not as nice as laser vision correction, which means sometimes I need to fine-tune with a laser. But in general, they do very well.

One of the concerns that I've had is, there are a lot of different nomograms that are out there. And sometimes these nomograms can be very difficult to understand. And for any of you who have looked at these nomograms, they can be a little bit overwhelming.

So we developed what we called "the Donnenfeld Nomogram," or "the DoNo nomogram," which is a very simple nomogram for using for patients who are having cataract surgery, and basically involves using one or two incisions according to these parameters to reduce cylinder. And it can be certainly personalized, but it's really pretty good. And then it can be fine-tuned down the line as you look at your results.

This nomogram I find very effective in my hands and very easy to teach with. And then if you want to move to a more advanced nomogram later on, please feel free. But I view limbal relaxing incisions as an art form, rather than as a science. In a paper that we presented at ASCRS this year, we showed a really pretty good effect through the use of this nomogram.

One of my concerns, though, with limbal relaxing incisions is that sometimes they are a little bit difficult to work with. One of the concerns is that when you are operating the eye, the eye is circumferential. We're using a straight diamond knife. I have found the use of a curved diamond knife with a 15° curve at the end, you get better applanation to the eye, so you approach the eye more perpendicularly with an angle diamond knife. And it makes it easier to do the limbal relaxing incisions, and you get a more reliable result. Instead of cutting the eye tangentially and getting a tangential incision, it's a more perpendicular incision, which gives a greater effect. This diamond knife was developed, again, for me by my friends at Accutome. Again, I have no financial interest.

The surgical procedure using this diamond knife is really very simple. It's a preset, 0.6-mm depth diamond knife. I use this marker, which is basically the modification of the Dell marker that has my nomogram built into it so we have 1 clock hour, 1.5 clock hours, 2 and 3 clock hours. I press fairly firmly, but I want to see a good mark on the eye.

And then I use a little — this is a little pearl — Blink Tears (Abbott Medical Optics). And it has a property of lubricating the eye very effectively, similar to Healon (AMO). So, I don't get any abrasions. I basically have limited abrasions with my diamond knife incisions very effectively. I insert the blade, and the little angulation allows a more perpendicular incision. And that's very effective at reducing cylinder in a very significant way.

Now, an intraoperative procedure done during cataract surgery. A lot of times patients may come back and they may not have the ability to go back to the operating room. And that was one of the reasons why we developed this blade, that all surgeons are not comfortable performing limbal relaxing incisions. And I think that a lot of them are comfortable. They just don't have a place to do it. So, we all have access to slit lamps in our offices. And the problem with slit lamps, again: It's hard to angle with the patient sitting up to get to the optimum exposure. And that's why I find this diamond knife very, very helpful. That 15° angulation allows me to have better access to the eye and, again, achieve a more perpendicular incision to achieve a more reliable, deeper incision to get the desired effect.

The number one reason why we don't get good results with limbal relaxing incisions is that the surgeon doesn't go deep enough. And this helps us achieve that effect. I use lidocaine gel. I can repeat the incision later on. And I just use a phoropter as my guide to decide where to center the LRI.

The next form of astigmatism is toric IOLs. And I think LRIs are terrific. I think toric IOLs are terrific as well. But the key to toric IOLs, just like in real estate, it's alignment, alignment, alignment. You have to know where you are operating. And that's one of the concerns.

A technology that I like very much is something called WaveTec. If you are off by 10°, you have reduced the effect of your IOL by approximately one-third. If you go greater than 30° off, you are actually losing ground. So, here is a device that we've been working with. Again, I have no financial interest. I do consult with them, though. That allows us to do intraoperative aberrometry. So, during the operation I can see what my residual cylinder is, and then either add some LRI or rotate the IOL and achieve the best possible result. And this has really been a wonderful new technology for improving my astigmatic results by giving me real-time intraoperative results. This will be available at ASCRS.

But the key is to be able to rotate the lens. And one of the problems in rotating the lens is that you need to take the viscoelastic out to make sure you are in the final position. So, once you take the viscoelastic out of the eye, it's sometimes a little bit difficult to adjust the IOL power or the rotation, because it's just difficult to manipulate, unless you want to do a bimanual technique. You are irrigating with one hand and using a positioning hook with the other.

So, I designed what I call "the Donnenfeld Irrigating Positioner." I named it after my good friend Ed Holland. And it's an irrigating Sinskey hook, essentially, that allows fluid to blow up the capsular bag to maintain the anterior chamber and allow easy lens manipulation. When I am doing a 360° rotation around the eye just to rotate the position, the chamber is maintained. I know exactly where my lens is going to end up. It blows open the capsular bag and allows me to maintain good, anterior chamber stability. I think this is another nice instrument that my friends at Accutome have developed with me for improving astigmatic results following cataract surgery.

Thank you very much for letting me share this with you this afternoon.

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.