Hi. I'm Dr. Shtein. I'm a cornea specialist at the University of Michigan Kellogg Eye Center, and we're going to be talking today about astigmatism management in cataract surgery. So we'll start off by defining astigmatism. Which is just the variation in curvature of the refractive elements of the eye that prevent light rays from focusing to a single point on the retina. And there are various types og astigmatism. There can be astigmatism that comes from the corneal itself, the irregularities in the corneal that leave to the light being focused in different parts on the retina. Astigmatism can also come from the lens itself. So, if the lens is off kilter you can get the extreme form of astigmatism. Smaller amounts of lens irregularities can also lead to astigmatism. There can be regular astigmatism, where you have symmetric astigmatism, or irregular and asymmetric astigmatism. Astigmatism can be with the rule meaning that the steep axis is at the 90 degree axis. Or against the rule where steepness is at the 180 degree axis. Regardless of what type of astigmatism the general corrections that we use are either glasses, which work best for regular astigmatism. Or contact lenses. Either soft or rigid gas permeable that will work for both regular or irregular astigmatism. Especially rigid gas permeable lenses, which work best for irregularities of the cornea. And really the point of this talk is how do we correct astigmatism with cataract surgery? So, the easiest form is when we're talking about lenticular astigmatism, we simply remove the lens, which is what you're doing with cataract surgery. Anyways, the more complexities occur when we're talking about corneal astigmatism, where there's a number of different potential ways to correct astigmatism and we'll go into these in greater detail. So the first thing that you can do to affect corneal astigmatism is just to change your wound construction. A transverse incision will flatten the central cornea. And also steepen the cornea to perpendicular axis. You have minimal overall spherial effect, but you do have an effect of the astigmatism. Now, in modern cataract surgery, the incisions that we do, tend to induce minimal astigmatism. But, you can alter the way that you make your incision to cause more changes to the corneal curvature. Making a larger incision will lead to more flattening. Making your incision more central, also, can lead to more flattening. And making a shorter tunnel. So, a shorter incision into the eye itself, can lead to more flattening. And you can make these alterations as needed, on a patient per patient basis. Astigmatic keratotomy is another procedure that can be added on with cataract surgery to affect astigmatism. So astigmatic keratotomy are arcuate or tangential corneal incisions that are made in the mid-periphery of the cornea. They're vertical incisions that are meant to be rather deep within the cornea. The technique for performing astigmatic keratotomy requires marking the patient while sitting up so that you have a good measure of where the axis of the eye is. You mark both the central pupil and the optical zone with a specialized AK marker. And, then you can use an interoperative keratometer to help adjust as you go. This procedure can be performed either concurrently with surgery or after the cataract surgery. Astigmatic keratotomy is usually guided by a nomogram. The nomogram will vary on a number of different variables. One is the patient age. The location of the astigmatism, the number of incisions that you're aiming to do. The length of the arc, and the depth of the cut. All these variables will alter the amount of astigmatism that is corrected. Although astigmatic keratotomy has been performed for many years, there are several disadvantages to the procedure. It can induce irregular astigmatism. Some patients will get refractive fluctuations after this procedure. Some patients also complain of either glare or light sensitivity, discomfort or foreign bodies sensation. And there's some degree of unpredictability even with nomograms. Usually surgeons who perform this repeatedly have a better sense of predictability in their hands. Limbal relaxing incisions are another surgical intervention that can be used to help correct corneal astigmatism. They're similar to AK cuts but their arcuate peripheral corneal incisions they're just inside of the limbus, so not in the mid-periphery of the cornea. Performing these requires a careful pre-operative examination of the peripheral cornea to make sure you know what you're getting into. The surgical technique is otherwise very similar to Astigmatic Keratotomy, and there are similar nomograms that can be used. The advantages as compared to AK are less irregularity, faster healing, less refractive fluctuations, less of the other side effects including glare and light sensitivity, discomfort, and foreign body sensation. But these can be somewhat unpredictable. Somewhat more predictable would be performing corneal refractive surgery, or either LASEK or advanced surface ablation procedures such as LASEK or PRK can be used after cataract surgery to treat specific amounts of corneal astigmatism particular to each patient. One potential advantage of this, is if there is any residual spherical shift after the cataract surgery, it can also be corrected with these refractive surgeries. Of course, there are the attendant risks of performing corneal refractive surgery, as well as the costs associated, and these all need to be discussed with the patient, prior to proceeding. And, finally, we can actually treat corneal astigmatism with the lenses that we implant into the eye at the time of cataract surgery. In general, planning got a Toric intraocular lens that corrects the corneal astigmatism requires an astigmatically neutral cataract surgery. Or at least good knowledge of how much astigmatism you induce with your cataract surgery. It's very important to have accurate surgical alignment of the axis of the lens at the time of surgery. And to maintain that access even after surgery. There can be post operative rotation of these lenses. And even as little as a ten degree rotation. Could lead to a one third loss of effect of the astigmatism correction of these toric lenses. There are currently two different companies that have FDA approved toric intraocular lenses in the United States. One is the Staar lens and the other is the Alcon lens. Both of these lenses have the specifications listed here. And can be used for patients with certain amounts of astigmatism, to correct them at the time of surgery. In summary, there are a number of different ways to treat both corneal and lenticular astigmatism at the time of cataract surgery. It just requires a thorough discussion with the patient and a thorough evaluation of the patient to see what works best for both the surgeon and the patient in each particular situation.
