All right, now we're here to talk about another step of cataract surgery which is wound construction. We have a brief lecture to go over that with you today. The goals of wound construction for cataract surgery. One is, of course, is to keep it watertight. Number two would be to minimize astigmatism as much as possible. And finally, once you've mastered those first two goals, you want to have it as quick and as efficient as you possibly can for surgery. In the past, when they did cataract surgery, they did the old, extracapsular cataract surgery where they used a long, tapered knife, called a von Graefe knife. That was inserted at the temporal limbus, all the way through the eye, out the nasal limbus, and then pulled superiorly, which then made a 180-degree wound. After the surgery, the patient would then hold their head still with sand bags on either side of their head, so they couldn't move their head back and forth for one week or longer to heal. This is what happens when you see your patients come in and say, boy, cataract surgery has come a long way. I remember when grandma had surgery. She had to have sand bags next to her head for a whole week. Well now, thankfully, we've progressed and progressed quite a bit. The two most common incisions we use for cataract surgery now include number one, the scleral tunnel. And number two is a clear corneal incision. I will go over both incisions in this talk. To create a scleral tunnel, initially, you make a conjunctival peritomy that's about 4 to 7 millimeters, depending on the size of the eye while you're putting it in place. Here, you can see, is the conjunctival peritomy. Once that conjunctival's taken down, you'll then use cautery to dry up the sclera to eliminate any bleeding blood vessels. Once you're finished with this cauterizing of the sclera, typically you'll use a crescent blade although other types of blades can be used for this. And you make an initial groove into the sclera approximately half the thickness which is what the schematic is showing you right there. Once you've made that initial groove, you then take the crescent blade and you put it with the butt of the blade down, so this is flat up against the sclera. And you tunnel up through the sclera until you get to clear cornea. Once you've gotten to clear cornea, oftentimes we switch to a keratome, which is the incision we're showing here. And that keratome will then mirror that image of going into the clear cornea. And then once you're at the clear cornea, you will then enter in completely into the eye. Here's a video that shows an example of what I've just discussed. >> Initially you make a conjunctival peritomy. Use Westcott scissors and forceps to make a button hole through cong down to bare sclera. And you dissect cong and enlarge your opening. Then use cautery to dry out this sclera and eliminate bleeding blood vessels. >> And you can use a crescent blade to make the initial groove, about one half the depth of sclera. Then you turn the crescent blade around and you place it heel down, toe up. To tunnel up through sclera into clear cornea. You want to be able to see your crescent blade through the sclera, but you only want to be able to barely see it. That's how you know that you're not making a flap that's too thick or too thin. And you want to tunnel all the way up into clear cornea. You don't want to enter the eye too soon because you will have iris prolapse throughout the case. You want to keep tunneling up until you're into clear cornea. And once you're there, you can use a keratome blade. You want to find your plane, and go up into clear cornea. And you head toe down, heel up, and you enter the eye with your keratome. >> So the advantage of a scleral tunnel are a number of things. One is it can minimize the astigmatism. The second thing that helpful, it's easy to to convert into an extracapsular cataract extraction if the posterior capsule is ruptured. Another point of scleral tunnels is it's easier for beginners. It's a more controlled incision. The main reason it's more controlled is when you're first operating, it's difficult take your instruments inside and out of the eye without pressing down on the posterior aspect of the incision. When you press down on the posterior aspect of the incision, you're moving fluid out of the eye and making the interior chamber flat. The most important step of the surgery where you really want to have a formed chamber is when your doing the capsulorhexis. So for beginners who aren't good at keeping the interior chamber nice and formed. Having a scleral tunnel makes a much longer tunnel and the longer tunnel allows you to keep the interior chamber more solid while your doing that capsulorhexis. It's also potentially a lower risk of endophthalmitis. You see I put a question mark on that on my slide. Because there are some studies that support scleral tunnel being lower risk for endophthalmitis. But there's also are other studies that don't say there's any difference between scleral tunnel versus a clear corneal incision. The disadvantages of making a scleral tunnel, as opposed to the clear cornea, is it does take longer to create. It's also possible that as you're tunneling, you could enter into the eye too posterior. If you entered into the eye too posterior, it could make the rest of the case very challenging. The opposite's also true. If you enter in too anterior, it can also be very challenging. Finally, taking down the conjunctiva and manipulating can cause some scarring to happen in the future. And if that did happen, and the patient eventually needed trabeculectomy or a tube shunt, it could make future glaucoma surgery more challenging. Clear cornea is the most commonly used incision now for cataract surgery. For clear corneal incision, typically you make a triplaned incision very similar to what you make when you make the scleral tunnel incision. However this triplanar incision, instead of going into the sclera and then up in the clear cornea, all three planes of this is just in the clear cornea. Different people use different instruments for that initial plane of the triplanar incision. This is an example of a guarded blade. This is a blade where you can rotate this handle here forwards or backwards to a pre-set depth, so you know exactly how deep you're making the initial groove for the incision. I actually do not use a guarded blade. I just use a keratome for all three parts of the incision. But many people use a guarded blade, versus a crescent blade, versus a keratome to make this incision. Once you've gone into the cornea with your initial groove, typically, your initial groove is right here, for example. You then take your second instrument, and then you tunnel up into the cornea in this fashion here. Typically, we use a first plane to go here. The second plane will then tunnel up in the cornea, and the third plane will then enter into the interior chamber. Again, this is mimicking the scleral tunnel incision, but the scleral tunnel incision goes halfway in here, tunnels up into the cornea, and then enters. As opposed to the clear corneal incision which goes in here, just tunnels a little bit and then enters. And as I mentioned, the final step of the clear corneal incision is enter the eye which is typically done with a keratome. The advantage of a clear corneal incision is much faster. As you can see you don't take down the conjunctiva. You don't have to do the scleral cauterization. And you don't have to tunnel nearly as long. This is used by quote unquote, advanced cataract surgeons. The vast majority of people in private practice do use clear corneal incision. Mostly for the speed and the efficiency of the surgery. It's also a small incision which can also minimize the astigmatism. In particular compared to the older fashioned extracapsular cataract surgery. Another big benefit of clear cornea it's easy to use topical anesthesia. If you use topical anesthesia for a scleral tunnel, that can be significantly more uncomfortable for the patient and typically those patients require more anesthetic than just the eye drops. And finally when you do clear corneal incisions you typically sit temporally. If you're sitting temporally, you don't have to worry about the patient's brow being in a challenging position. Scleral tunnels are typically done when you sit superiorly. If you're sitting superiorly and you had a very deep set eye, that brow can get in your way and can be challenging to get the incision where you want it to be. When you operate on the temporal clear cornea, it makes it much easier from deep set eyes. The disadvantages to clear corneal incisions is basically the opposite of the advantage for the scleral tunnel. In this case if you do have to convert into an extracapsular cataract extraction, it's more challenging. You essentially have two options. You can either close this incision and then go to a different position to start a scleral tunnel all over again. Or you could just take your small incision of clear cornea and extend it to make it larger. If you extend it to make it larger, it's much more challenging to make it watertight at the end. And it can be, induce quite a bit of astigmatism afterwards. The other issue is when you're initially doing cataract surgery, it takes you longer to do it when you're in the learning stages. The longer it takes to do the surgery, the more the cornea can get hydrated from the BBS backing up into the cornea stroma. As that cornea stroma gets hydrated, it also gets hazy and cloudy. So, if the case goes on for too long, it can make the cornea hazy and cloudy and be difficult to finish the final two steps of the case. The longer the cataract surgery takes for clear cornea also the higher risk of losing endothelial cells. I have a schematic on this coming up in just a minute. And again, I've added a question mark to this last point, but there's potentially a higher risk of endophthalmitis. But again that has yet to be beared out in the literature. Here is an example of a Phaco Time for the different types of cataract surgery. The green one we have down here is scleral tunnel, and the red is temporal clear cornea. As you can see, for a very long cataract surgery case, the amount of endothelial cell loss is much, much higher when you're doing a clear corneal versus doing a scleral tunnel. However, when you become an experienced surgeon and you're working more in down these ranges, the amount of difference is negligible. This is another reason why people often do scleral tunnels when they first start, and they're taking longer to do their cataract surgeries. That way they can save some more endothelial cells. However, once you're more experienced, it's really not that big of a difference. As far as what types of clear corneal incisions are available. One, as we've mentioned before, is the single plane incision, which is the stab. Essentially you're taking a blade and you're just going straight into the eye without doing the three planes. The negative to this is it's not a valved incision. When it's not a valved incision, it's again hard for the anterior chamber to stay tight and formed. And, therefore during the capsulorhexis the chamber can shallow and make the rest of the case more challenging. Advantage of the stab incision over the triplanar clear corneal incision is the cornea doesn't hydrate in this situation. And finally, theoretically, since it's not a valved incision, there is a possibility for a higher risk of bacteria inoculating the eye. The triplanar incision is exactly the opposite of the stab incision, as we've already discussed. No, I've discussed endophthalmitis a couple of times, briefly we'll go into a little more depth right now. But there's many studies I've done in the literature, and so far the results are inconclusive. I chose a handful of studies that had very high numbers and with these high numbers, some of them showed an inkling towards a higher risk of endophthalmitis in clear corneal incisions, otherwise did not show a statistically significant change. The majority of surgeons do use temporal clear cornea as opposed to scleral tunnel. So, I don't believe the majority of surgeons believe it is a higher risk of endophthalmitis. And, if it is a higher risk, if that is eventually bet on in the future, it is a very small amount of higher risk. When you're doing a study, and you're using over 16,000 patients. And with 16,000 patients, you still can't tell if one is significantly better than the other one. Certainly if one is better, it's by a very, very small amount. So, in real life, the vast majority as I've mentioned do use clear corneal incisions. I think this is primarily because of the efficiency of the surgery, the minimizing of the astigmatism. The ability to use topical anesthesia along with working temporally to avoid the brow and, and challenging anatomy. Scleral tunnel is very good for beginners when you're first learning how to do the surgery and can also still be used for difficult cases even when trained, experienced surgeon
