| Sutures, like the ones used here in conjunction with trabeculectomy, are sometimes necessary in ophthalmic surgery; suture removal timing may also be important, as in certain instances after cataract surgery Source: Tony Wells, M.D.
Ophthalmologists are well aware that incision location and length can impact astigmatism after cataract surgery. New research suggests corneal tunnel length may also be an important factor that affects astigmatism. “With accompanying individualized analysis, adequate incisional tunnel length and correct suture removal timing according to the preoperative axis of astigmatism may improve surgical results,” according to study co-author Man Soo Kim, M.D., Ph.D., department of ophthalmology, The Catholic University of Korea, Seoul St. Mary Hospital, Seoul, South Korea. The study was published in the December 2009 issue of the Korean Journal of Ophthalmology. Of course, Dr. Kim’s study involved sutured incisions at a time when many surgeons are opting to perform unsutured clear corneal incisions. Still, Dr. Kim’s in-depth analysis provides an interesting glimpse into managing astigmatism in a different way at a time when patients are demanding optimized visual results from their cataract surgeries.
Formulas for astigmatism-correcting success?
Dr. Kim analyzed 130 eyes that underwent cataract surgery. Pre-op astigmatism was divided into groups I, II, III, and IV, based on the differences between the axis of pre-op astigmatism (flattest axis) and the incision axis (105 degrees). Specifically, in group I, 0≤ absolute value of the difference ≤ 15 degrees; in group II, 15< absolute value of the difference ≤ 45 degrees; in group III, 45< absolute value of the difference ≤ 75 degrees; and in group IV, 75< absolute value of the difference ≤ 105 degrees.
It was then important to isolate the study of astigmatism only. “In order to evaluate the factors which only affected the magnitude of the astigmatism and not the axis, we excluded data which showed an axis shift (45< [the absolute value of (postoperative astigmatic axis – preoperative astigmatic axis)] ≤ 135 degrees, or 45< [the absolute value of (post-suture removal astigmatic axis – postoperative astigmatic axis)] ≤ 135 degrees),” Dr. Kim noted. “The group without axis shift was named GroupWAS. We analyzed the factors which affected postoperative astigmatism and post-suture removal astigmatism in each groupWAS (group IWAS, IIWAS, IIIWAS, and IVWAS).”
Via these intricate mathematical calculations, the study yielded some interesting insights. First, the magnitude of pre-op astigmatism impacted the magnitude of post-op astigmatism in groups IWAS, IIWAS, and IIIWAS. “This indicates that incisions other than those in the steepest meridian (group IVWAS) have little modulating effect on astigmatism in patients who have a large preexisting astigmatism,” Dr. Kim concluded. Further, post-op astigmatism impacted post-suture removal astigmatism in certain instances. “For the post-suture removal astigmatisms in Groups IWAS and IVWAS, the magnitudes of the postoperative astigmatism affected the magnitude of the post-suture removal astigmatism,” Dr. Kim noted. However, the magnitude of pre-op astigmatism had no impact on the magnitude of post-suture removal astigmatism in this study. Concerning tunnel length, in group IWAS, an increase in tunnel length was linked to an increase in the absolute value of post-op astigmatism. On the other hand, in group IIIWAS and group IVWAS, an increase in corneal tunnel length was associated with a reduction in post-op astigmatism.
“There was also a reduction in the absolute value of post-suture removal astigmatism associated with a later suture removal time,” Dr. Kim noted. The same was found in group IIWAS and group IVWAS.
“Based on the results of our study, we recommend a short corneal tunnel and a late suture removal in patients with group IWAS characteristics, a late suture removal in group IIWAS-like patients, a long corneal tunnel in group IIIWAS-like patients, and a long corneal tunnel and an early suture removal in patients with group IVWAS characteristics,” Dr. Kim concluded. “The prevalence of post-suture removal axis shift was increased in the longer tunnel group, in the low magnitude of postoperative astigmatism group, and in the earlier suture removal group.”
William Trattler, M.D., cornea specialist, Center for Excellence in Eye Care, Miami, cautioned that using sutures during cataract surgery is not standard. Dr. Kim’s analysis is also complex and may have limited clinical value, Dr. Trattler said. “This requires vector analysis,” Dr. Trattler said. “Researchers split up the groups into four different groups based on pre- and post-op astigmatism axis. It’s interesting but complicated. You need to look at what each of the groups consist of and understand the different recommendations.” Further, he said, most sutures used in cataract surgeries are not planned. They are more frequently unplanned, such as when vitreous loss occurs. “At that point you have already made the corneal tunnel,” Dr. Trattler said. There are some instances when sutures are needed and incision type can be planned, Dr. Trattler said. Surgeons implanting the Crystalens (Bausch & Lomb, Rochester, N.Y.) are suturing the wounds since incision size is larger, he said. So if Dr. Kim’s analysis is accurate, results could be applicable and potentially helpful for these patients.
Editors’ note: Dr. Kim has no financial interests related to this study. Dr. Trattler has no financial interests related to his comments.
Kim: 82-2-2258-6197, firstname.lastname@example.org
Trattler: 305-598-2020, email@example.com