EyeWorld Asia-Pacific March 2016 Issue

38 EWAP Cataract/IOL March 2016 by Maxine Lipner EyeWorld Senior Contributing Writer When the bowtie is askew 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 astigmatism. Low levels of irregular astigmatism are quite common because of dry eye, which can lead to variable irregular astigmatism, and also because of anterior basement 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, SD. “It will burn you a bit if you’re trying to do refractive cataract surgery but you’re not thinking about irregular 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 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 practitioner 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 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 cataract 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 astigmatism in most of these cases. “In general, in the patients with irregular 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 cornea 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 irregularity.” This can result in unpredictable outcomes, Dr. Yeu explained. In some cases, however, she has had excellent success with the off-label 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 consider 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 presentation 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 two different keratometric values seen on biometry and topography. “I have seen great success utilizing the toric lens in my post-PK, post- RK, post-LASIK patients, where all of those three things have lined up,” Dr. Yeu said. This can boost the patient’s acuity postoperatively. With a standard lens implant, if the just slightly irregular astigmatism or grossly irregular astigmatism, Dr. Yeu noted. “When you see any kind of irregular astigmatism in cataract surgery patients, it is often due to ocular surface disease, whether it be Salzmann nodular dystrophy, epithelial basement 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 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 keratometric 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 measurements,” 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 measuring the refraction. “This creates a new