EyeWorld Asia-Pacific December 2020 Issue

CATARACT 34 EWAP DECEMBER 2020 Mohan Rajan, MD Chairman and Medical Director Chennai, Tamilnadu, India Rajan Eye Care Hospital, No. 5, Vidyodaya Second Street, T. Nagar, Chennai 600 017 drmohanrajan@gmail.com ASIA-PACIFIC PERSPECTIVES W e read the article by Susan MacDonald and Robin Vann with great interest and like to congratulate the authors for a wonderful write-up highlighting the importance of MSICS and different methods to control astigmatism. These include making an incision on the steep axis, using the Maloney astigmatism keratometer, reducing the size of the incision with the help of miLOOP. We would like to mention a few additional points and simple steps to control preoperative astigmatism. We all know that placing an incision in the steep axis produces a flattening along the meridian of the incision. The astigmatism induced is greatest with a traditional incision made concentric to the limbus, intermediate with a straight incision, and least with a frown shaped configuration. The authors have quoted that they found no significant association between white-to-white diameter of the cornea and surgically induced astigmatism. However, we would like to highlight that the incision size used by the authors was 2.2 mm, which is supposed to be astigmatically neutral. Burgansky et al. have shown an increase in astigmatism with an increase in incision size, the mean surgically induced astigmatism was 0.6±0.3 D for a 6-mm incision, 0.75±0.67 D for 6.5 mm incision and 1.36±0.77 D for a 7-mm incision. Thus, based on the preoperative astigmatism readings, the surgeon can modify the site, size, and type of incision to provide the best outcomes. Radial sutures produce local tissue compression, thus resulting in peripheral flattening and central steepening along the meridian of incision and flattening 90˚ away. Over the follow-up of 2 years, suture materials such as Mersilene showed superior preservation of structural integrity over nylon. Astigmatic keratotomy has also been described to reduce the preexisting astigmatism of up to 2 D. Transverse incisions placed between 5- to 6-mm zones have been shown to have greatest efficacy. Some of the other techniques described include scleral and flap recession or resection. One can operate along the flat meridian and resect tissue, or can operate along the steep meridian and recess or advance the scleral flap. Studies prove recession to be more effective, resulting in a mean corneal change of 2.1 D of astigmatism in comparison to 0.5 D in resection till 2 years of follow-up. Toric intraocular lens implantation is another way to correct preexisting astigmatism. Different lenses can control up to 4 D of astigmatism, with an acceptable limit for misalignment of up to 10˚. We believe that with in-depth understanding of ways to control astigmatism and adapting to newer modifications such as the use of miLOOP for performing MSICS can ensure good outcomes even in places with low resource settings. Editors’ note: Dr. Rajan declared no conflicting interests. In this study, incisions were kept to 2.2 mm. However, in cases where they are slightly larger, astigmatism may be a factor. Dr. Vann cited a previous study 2 that suggested that white-to-white diameter of the cornea did influence the surgically induced astigmatism. “In the study, they were doing their incisions superotemporally or superonasally, making 3-mm incisions,” he said. “They were operating closer to the visual axis and they were using a larger incision.” Many think that incisions under 2.5 mm tend to be relatively neutral in terms of overall impact on the cornea, Dr. Vann continued, adding that with this in mind it can be helpful to keep incisions as small as possible. Dr. Vann said he’s now using an intraoperative aberrometer to help address astigmatism. “Typically, we’ll bring the pressure up to physiologic, so that it’s a normal 15–20 mmHg, then we’ll take a reading of the aphakic refraction so it can tell us what the astigmatism is,” Dr. Vann said. This also takes into account the posterior cornea and the impact of the main incision that might otherwise limit success. In Dr. MacDonald’s view, all cataract surgeons, even in developed countries, should be comfortable with small incision cataract surgery. There will likely be a time when the best choice for patient safety and quality may be small incision cataract surgery, Dr. MacDonald said. “If you don’t have confidence in that skillset, you are more likely to say, ‘I can phaco everything,’” she said, adding that the small incision technique can avoid damage to the cornea in complex cases. To learn MSICS properly, Dr. MacDonald recommended taking a course. “It’s great to learn pearls from other surgeons who are experts in the field,” she said. Going forward, a new technology is being developed by Carl Zeiss Meditec that will remove the nucleus without any phaco energy, which Dr. MacDonald thinks will help as well. “I think using technology that is being developed will allow us to bring small incision surgery to all who need it without fear of damaging the nucleus,” Dr. MacDonald concluded. EWAP References 1. Zhang W, et al. Influence of corneal diameter on surgically induced astigmatism in small-incision cataract surgery. Can J Ophthalmol. 2019;54:556–559. 2. Theodoulidou S, et al. Corneal diameter as a factor influencing corneal astigmatism after cataract surgery. Cornea. 2016;35:132–136. Editors’ note: Dr. MacDonald is Associate Clinical Professor, Tufts University School of Medicine, Boston, Massachusetts, and has interests with Carl Zeiss Meditec and Perfect Lens. Dr. Vann is Associate Professor of Ophthalmology, Duke University, Durham, North Carolina, and has interests with Alcon.