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When performing a limbal relaxing incision, is it preferable to use a single-depth nomogram or an adjustable-depth nomogram?
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Start simple and grow your results
For beginning surgeons, start with fixed-depth limbal relaxing incisions.
 Uday Devgan |
Limbal relaxing incisions (LRIs) are actually peripheral corneal incisions, and much like the radial keratotomy incisions of years past, they are effective but often variable in their effect. The most accurate results from LRIs that I have seen are from the Nichamin age and pachymetry adjusted nomogram, which customizes the depth and length of the LRIs based on the patient age and the peripheral corneal pachymetry measurements. But this is also the most complex. For a surgeon who is just starting to use LRIs, the goal is typically the reduction of astigmatism and not necessarily the elimination of astigmatism. If my LRI reduces the astigmatism, the patient will be happy. If, however, my LRI is too aggressive and I overcorrect the astigmatism, I will induce astigmatism at an axis 90º away from the original, so this patient may end up unhappy.
Some studies, such as the work of Kevin Miller, MD, have shown that a simple LRI nomogram at a fixed depth can work well, and that changing the depth from 500 µm to 600 µm may have little effect. When watching an experienced surgeon perform LRIs, you will notice that both science and art, and the position, length and placement of the incisions are varied based on the individual patient and the other surgical incisions. If you are just starting to use LRIs, choose a simple, fixed-depth nomogram initially. And then once you start tracking your results, you will likely add more art to the equation by adjusting the parameters, including the depth.
Uday Devgan, MD, FACS, is the OSN SuperSite Section Editor.
Does the added effort pay off?
One of the compromises you have to make as a surgeon is to determine what your level of comfort is in chasing the depth. We all know that with any corneal incision or refractive surgery, the true effectiveness of the technique is going to depend on the percent thickness of the cornea you are going into. If you can be accurate about determining the corneal thickness and you are going to chase it to 90% corneal thickness, then you are more likely to produce a more powerful and more predictable result.
 William J. Lahners |
However, as a high-volume cataract surgeon, you have to decide whether it makes sense to be doing peripheral ultrasonic corneal thickness pachymetry measurements intraoperatively, measuring the radius of the treatment, and using an adjustable diamond keratome, a special microscope that is calibrated to confirm your depth, and a nomogram that counts either clock hours or degrees. If you want to chase a lot of variables and make yourself very busy, then better results could be achieved with an LRI nomogram that is depth sensitive, age sensitive and optical zone radius sensitive.
I see the question in terms of the law of diminishing returns. We can achieve a very elegant correction in the majority of our patients with a quick and simple LRI nomogram. In order to refine it any further, it would require a lot of extra work, a lot of extra equipment and a lot of time commitment. That is something that we have not found to be productive. Our practice is going to do 5,000 IOLs this year. For us to be productive, it does not make sense for us to spend as much time on the LRI measurement.
William J. Lahners, MD, FACS, is an assistant clinical professor of ophthalmology at the University of South Florida, Tampa, and the medical director of Center For Sight.