Just about any incision in the cornea will induce some astigmatic change. We have shown how to place the phaco incision on the steep axis to help reduce astigmatism. And we have demonstrated a technique using paired phaco incisions to help treat even more astigmatism. This video will review the concepts and technique of using limbal relaxing incisions (LRIs) to treat corneal astigmatism. Note that these incisions are actually inside the limbus, in the clear cornea, but the name LRI has stuck.
The corneal coupling effect means that if we flatten the cornea in one meridian then it will steepen in the meridian 90 degrees away. Note that the spherical equivalent of the refraction and the average keratometry do not change. This is because the coupling ratio is about 1: for every diopter of flattening in one meridian, there will be about the same 1 diopter of steepening in the other meridian. You do not need to change your IOL calculations if you are planning a limbal relaxing incision at the time of cataract surgery. The larger the arc length of the incision, the larger the degree of corneal flattening at that meridian.Incisions which are more central in the cornea will also cause more astigmatic flattening, however the more central the incision, the higher the risk of corneal irregularity. The smallest optical zone diameter recommended is about 8 or 9 mm.Shallow limbal relaxing incisions will have much less effect with almost no effect if the cuts are less than 50% corneal depth. The deeper cuts, such as 90% depth, will have more astigmatic effect but the risk of corneal perforation is higher.
Click below to learn from this video about Limbal Relaxing Incisions:
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Professor Uday Devgan MD is a Los Angeles Cataract Surgeon who authors CataractCoach.com to teach the best techniques of Cataract Surgery to Eye Surgeons from around the world.
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