JAN 2016

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

Issue link: https://digital.eyeworld.org/i/618732

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Page 28 of 78

EW CATARACT 26 January 2016 by Maxine Lipner EyeWorld Senior Contributing Writer my post-PK, post-RK, post-LASIK patients, where all of those 3 things have lined up," Dr. Yeu said. This can boost the patient's acu- ity postoperatively. With a standard lens implant, if the patient has great- er than 3 or 4 D of astigmatism, the uncorrected visual acuity will not allow them to see well and even cor- rected will not match that attained with a toric lens. "As we know, the quality of vision above 1.5 D is just not as good when trying to spectacle correct as compared to being able to do it in an intraocular lens format," Dr. Yeu said. Dr. Berdahl cautioned that putting in a toric lens in some of these patients can do more harm than good. For example, if you think that the patient will need a specialty contact lens afterward, you do not want to use a toric lens, he said. "You can't just put a toric lens in an irregular astigmatism patient and think if it doesn't work, they'll wear a gas permeable contact lens; now that gas permeable contact lens be- comes more expensive and harder to fit because it's a toric gas permeable contact lens," Dr. Berdahl said. Overall, Dr. Yeu is very optimis- tic about the success in treating the irregular astigmatism patient these days. "I think that we're blessed to be in a stage where refractive cataract surgery has opened up all of these technology options to improve patient visual acuity," she said, add- ing that with 50% of patients sad- dled with visually significant corneal astigmatism, she is looking forward to seeing what other platforms can do in the future. EW Editors' note: Drs. Berdahl and Yeu have financial interests with Abbott Medical Optics (Abbott Park, Ill.), Alcon (Fort Worth, Texas), and Bausch + Lomb (Bridgewater, N.J.). Contact information Berdahl: john.berdahl@vancethompsonvision.com Yeu: eyeulin@gmail.com need a specialty contact lens," he said. "If we think that it's something like epithelial basement membrane dystrophy, we may do a PTK, polish the cornea, get them to a nice round surface, and do the refractive cata- ract surgery." Dr. Berdahl avoids limbal relaxing incisions or astigmatic keratotomy in anyone whose cornea is unstable because this can make the situation worse. However, if someone has mild enough irregular astigmatism, in some cases he may consider a toric lens. Dr. Yeu likewise cautions against using incisions to correct astigma- tism in most of these cases. "In general, in the patients with irregu- lar astigmatism that show a skewing of the axis that is concerning for a form fruste or a subclinical picture, I will not do a relaxing incision because any kind of astigmatic keratotomy that we do on the cor- nea can further destabilize it," she said. "I have certainly seen relaxing incisions causing an ectasia picture because the cornea itself already has some tendency toward weakness, and the relaxing incision can lead to greater instability and irregulari- ty." This can result in unpredictable outcomes, Dr. Yeu explained. In some cases, however, she has had excellent success with the off-la- bel use of a toric IOL in the right irregular astigmatism patients. Some with frank irregular astigmatism from prior refractive surgery or from keratoconus may be considered. "In those patients, you have to consid- er what the astigmatism looks like within the central 3 mms," Dr. Yeu said, adding that if the pattern in their visual axis looks fairly regular and visual acuity at the time of pre- sentation or prior to cataract surgery was very good, she may consider a toric lens. One last factor that must be considered here is whether the steep meridian of the refraction is consistent with 2 different kerato- metric values seen on biometry and topography. "I have seen great success utilizing the toric lens in or to hot spots or flat spots. Any of those can lead to an irregularly shaped astigmatism. "If the Placido disk image appears washed out or not crisp and round like a bullseye-shaped pattern, that suggests something else is going on to throw off the tear film and the epithelium," Dr. Yeu said. If the irregular astigmatism is due to something that is epithelial-based or pre-corneal tear film-based, that needs to be optimized because it can significantly throw off your ker- atometric value in preparation for cataract surgery, she said. Likewise, Dr. Berdahl finds that dryness, corneal scars, keratoconus, and epithelial basement membrane dystrophy tend to be the major causes of irregular astigmatism. "For anyone who is considering refractive cataract surgery, we get multiple sources of keratometry measure- ments," Dr. Berdahl said, adding that this usually involves biometry and topography. To determine the degree of the irregularity, Dr. Berdahl places a gas permeable contact lens over the patient's eye while measur- ing the refraction. "This creates a new artificial spherical surface above the cornea that is filled with tears," he said, adding that the tears help smooth out the lumps and bumps of the astigmatic cornea. If a patient's acuity was measured at 20/40 and after placing the gas permeable lens, it significantly improves, the practi- tioner knows that it is probably due to irregular astigmatism. But if the vision remains at 20/40 despite the placement of the gas permeable lens, then the practitioner knows it is the cataract that is the issue, Dr. Berdahl explained. Treatment options If the irregular astigmatism appears to be causing the refraction issues, Dr. Berdahl talks to the patient about this. "We explain to the patient that a refractive surgery approach probably doesn't make sense because in order to get the best vision afterward, they may Dressing irregular astigmatism patients for cataract treatment success I t's one of those things that cataract surgeons have to keep on the radar—irregular astig- matism. Low levels of irregular astigmatism are quite common because of dry eye, which can lead to variable irregular astigmatism, and also because of anterior base- ment membrane dystrophy; studies show 10% of the population has at least a bit of this and 1% has in it a meaningful way, according to John Berdahl, MD, partner, Vance Thompson Vision, Sioux Falls, S.D. "It will burn you a bit if you're try- ing to do refractive cataract surgery but you're not thinking about irreg- ular astigmatism," Dr. Berdahl said. Elizabeth Yeu, MD, partner, Virginia Eye Consultants, and assistant professor, Eastern Virginia Medical School, Norfolk, Va., agreed that this can be an all too common problem. "Irregular astigmatism is going to be anything where the bowtie may be orthogonal but is a little skewed or if the axes are skewed," Dr. Yeu said. "Irregular astigmatism in the purist sense can actually occur quite frequently. I would say upward of one-quarter to one-third of the astigmatism that I see is not the perfect bowtie shape." Assessing the problem So what can be done to improve post-cataract vision? This depends on the severity of the condition. The patient may have just slightly irregular astigmatism or grossly irregular astigmatism, Dr. Yeu noted. "When you see any kind of irregu- lar astigmatism in cataract surgery patients, it is often due to ocular sur- face disease, whether it be Salzmann nodular dystrophy, epithelial base- ment membrane dystrophy, or just dry eye disease with staining of the ocular surface," she said, adding that this can lead to missing spots on the Placido disk image of topography When the bowtie is askew

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