Dr. David Goldman interviews Prof. Donald T. H. Tan, Director of the
Singapore National Eye Centre. Prof. Tan offers his insight on the
design and use of the Tan EndoGlide, a new medical device designed for
DSEK / DSAEK surgery which allows surgeons to insert endothelial tissue
while minimizing iatrogenic damage. Prof. Tan offers surgical pearls
and discusses the benefits of the device.
Dr. David Goldman Interview with Dr. Donald Tan
Dr. David Goldman: Hi, I'm Dr. David Goldman, speaking today with Dr. Donald Tan, the medical director of Singapore National Eye Center. Thank you so much for joining us today.
Dr. Donald Tan: It's a pleasure.
Dr. David Goldman: I'd like to speak to you today about a device you've invented, the Tan EndoGlide. We all know DSEK's a very popular surgery now in the United States and throughout the world. What were some of the motivations and things that you discovered that motivated you to develop this device?
Dr. Donald Tan: Well, I think the DSEK is a fantastic new procedure for corneal transplantation, but one of the major challenges today is still to reduce the endothelial cell loss which comes with the procedure. After all, you're inserting a 8.75 or a nine millimeter donor through a--anywhere from a four to five millimeter incision.
And the studies which have now been published quite clearly show that you're getting endothelial cell loss rates at about six to 12 months in the region of anywhere from 28 to 35 percent. And so, the main motivation initially for us was to develop a device for donor insertion which would considerably enhance the ability for us to preserve the endothelium.
Dr. David Goldman: Right.
And in this device, the tissue is actually loaded into a cartridge, which is then delivered into the anterior chamber?
Dr. Donald Tan: Yes.
Our second objective--you know, the classic technique of donor insertion now is a folding technique with forceps. And to fold the donor and insert it is less of an issue technically, but one of the major problems is to unfold the donor, and there is a certain loss of control. So, a major aspect--a second objective was to make a device which is easy to use, predictable and in which you actually get better control of the donor and the anterior chamber.
Dr. David Goldman: And to maintain the anterior chamber, do you need to use an artificial device to maintain the anterior chamber with this device?
Dr. Donald Tan: Most of my DSEK patients are in Asian eyes, and the Asian eye generally is smaller, has a shallow anterior chamber, and also high vitreous pressure. So, when we perform DSEK in these eyes, we usually need an AC maintainer; having said that, the EndoGlide is now being used without an anterior chamber maintainer.
Dr. David Goldman: Now, is it placed through a scleral tunnel incision or through a clear cornea?
Dr. Donald Tan: Well, I tend to prefer a scleral incision because there certainly is less astigmatism, and so that's my current choice--.
Dr. David Goldman: --Um-hmm--.
Dr. Donald Tan: --The EndoGlide was designed for scleral insertion, but it could easily be for limbal or corneal insertion as well--.
Dr. David Goldman: --Sure.
And I've noticed on the device there's a lip to the cartridge. What--?
Dr. Donald Tan: --Um-hmm--.
Dr. David Goldman: --Is the function of that lip?
Dr. Donald Tan: Well, that was an important concept. When you open a wound, and either you don't have an AC maintainer or you have an AC maintainer with positive pressure, when you open that wound you may get iris prolapse, and that's very common in high vitreous pressure eyes--.
Dr. David Goldman: --Um-hmm--.
Dr. Donald Tan: --The idea came from our previous technique with--the sheets glide technique, in which we inserted an anterior chamber IOL sheets glide, and that was really to prevent iris prolapse and to stabilize the eye and to prevent contact with a--either a phakic lens or an AC IOL which may be in place.
Dr. David Goldman: Um-hmm.
Dr. Donald Tan: So, that glide has a very important role because it allows you to insert the inserter right through the wound, and you don't have any problem of iris popping out, and it's just a very useful technique to ensure that.
Dr. David Goldman: Sure.
What about--are there any concerns with flipping of the donor optical?
Dr. Donald Tan: Well, you know, that's been one of the major concerns with donor folding and unfolding. This technique, which is essentially a pull-through technique because what you're using is you're using intraocular forceps introduced from the nasal side, and that holds the donor and pulls it in. Now, as long as you hold onto that donor, you have complete control.
One of the advantages over some of the other techniques--you know, most of the techniques, they focus on putting the donor in, but then managing control of that donor in the anterior chamber, whether you're unfolding it or uncoiling it, is difficult unless you're holding onto the tissue.
Dr. David Goldman: Um-hmm.
Dr. Donald Tan: So, one of the--what we always try and tell surgeons who use EndoGlide is that once you pull the donor tissue in, you can take out the EndoGlide, you can put in air, you can do whatever you like; don't let go. As long as you don't let go, you have complete control of the donor.
Dr. David Goldman: In that case, are you marking the stroma anymore or--?
Dr. Donald Tan: --Well, we used to because we thought that there might be some difficulty in seeing the edge of the donor once we insert it through the wound--.
Dr. David Goldman: --Um-hmm--.
Dr. Donald Tan: --Through a very cloudy cornea. But, in fact, it is very visible because the device is clear plastic--.
Dr. David Goldman: --Um-hmm--.
Dr. Donald Tan: --And so, we've had no difficulty.
So, we started off with marking the stroma, but we've done away with that completely.
Dr. David Goldman: And what sort of studies have you done regarding endothelial cell loss comparing this now to traditional forcep folding?
Dr. Donald Tan: Well, you know, we've published previously that with the--looking at vital dye staining in human eye-bank eyes, and also scanning electronic microscopy, you may get anywhere from about 30 percent cell loss with the folding technique--.
Dr. David Goldman: --Um-hmm--.
Dr. Donald Tan: --With non-appositional forceps. Our sheets glide technique showed about a nine to 10 percent cell loss using vital dye staining, and our preliminary studies with the EndoGlide shows about five to 7 percent loss--.
Dr. David Goldman: --Um-hmm--.
Dr. Donald Tan: --In the laboratory.
Dr. David Goldman: And how have the patients--I understand you've done 20 patients now--.
Dr. Donald Tan: --Um-hmm--.
Dr. David Goldman: --With this device. How have they done so far?
Dr. Donald Tan: Well, we're very pleased at our initial results. Now, these are the first 20, right from the--from a prototype designed for the first few cases.
And firstly, we've had no primary graft failures, no dislocation. Most importantly are the endothelial cell counts. So, we are looking at an endothelial cell loss at three months of about 15 percent and at six months about 19 percent. Now, this is far lower than any other published study so far that I'm aware of.
So, the primary objective of the EndoGlide, which was deliver a safer and more endothelial-friendly treatment for DSEK, I think--we're hoping that that's been achieved now.
Dr. David Goldman: Absolutely.
Well, I know we're all looking forward to using it here in the United States. Thank you so much for joining us today.
Dr. Donald Tan: You're very welcome.