EyeWorld India March 2019 Issue

8 EWAP FEATURE • September March 2019 Ophthalmologists share their preferred approaches to measuring astigmatism “I n preparation for cataract surgery, we owe it to our patients (and to ourselves) to be as accurate as possible when making measurements that will determine their ultimate IOL power and axis,” said Kendall Donaldson, MD, medical director, Bascom Palmer Eye Institute, Plantation, Florida. Thus, the measurement of astigmatism is an essential component of the preoperative evaluation of cataract patients. Preeya Gupta, MD, Duke Eye Center, Durham, North Carolina, agreed. “Managing astigmatism is an important part of cataract surgery, especially for patients who have high visual needs, meaning they want to see well without glasses,” she said. “If you’re not assessing astigmatism preoperatively, you’re not going to be able to provide your patients with the highest refractive outcomes.” Vance Thompson, MD, Vance Thompson Vision, Sioux Falls, South Dakota, called astigmatism “the most common refractive error.” While the goal is to treat the astigmatism intraoperatively, he noted that surgical healing variables and some of the limitations to current measurements mean it is not unusual for patients to need enhancement postoperatively. In these cases, measuring astigmatism preop serves to reduce the extent to which the refractive outcomes need to be fine-tuned later on, in order to, as Dr. Thompson likes to say, “take the football in for a touchdown.” EyeWorld reached out to Dr. Donaldson, Dr. Gupta, and Dr. Thompson, as well as Tal Raviv, MD, founder and medical director, Eye Center of New York, to discuss their preferred approaches to measuring astigmatism. Series of measurements Beginning with an optical biometer such as the IOLMaster (Carl Zeiss Meditec, Jena, Germany) or LENSTAR (Haag- Streit, Koniz, Switzerland), Dr. Donaldson recommends a series of measurements that includes topography and tomography before refractive cataract surgery in order to “help meet modern day high patient expectations for outcomes after cataract surgery,” she said. Dr. Donaldson evaluates the typical manifest refraction, their current glasses prescription, and measurements made using the IOLMaster, Pentacam (Oculus, Wetzlar, Germany), and Galilei (Ziemer, Port, Switzerland). Topography is also a routine part of Dr. Gupta’s preoperative evaluation. “We do a topography on everyone,” she said. “The purpose of topography is to look at the pattern of astigmatism. We want to make sure that it is regular astigmatism as opposed to irregular astigmatism.” Astigmatism, she said, may have a variety of causes, ranging from dry eye disease, surface features such as pterygium, Salzmann’s nodules, and anterior basement membrane dystrophy, to corneal ectasia, keratoconus, and pellucid marginal degeneration. Treatment in these cases should manage the root cause. Dr. Thompson reiterated the importance of topography as a routine part of preop evaluation. “I don’t think anyone should go into surgery without a corneal topography,” he said. Conditions such as undiagnosed keratoconus and anterior basement membrane dystrophy affect the quality and reproducibility of the astigmatism measurement, he said. Dr. Thompson noted that topography reduces the uncertainty of irregular measurements taken by an inexperienced technician who may have the patient stare too long, allowing the tear film to break up before acquiring measurements. “A topography that looks beautiful eliminates all those variables,” he said. Moreover, “if the topographic astigmatism agrees with the keratometry, I know I’m going into surgery with accurate numbers.” Once the astigmatism has been The true measure of astigmatism by Chiles Aedam R. Samaniego EyeWorld Asia-Pacific Senior Staff Writer AT A GLANCE • Astigmatism is best evaluated through a series of measurements using multiple devices, including topography to identify whether the astigmatism is regular or irregular. • The ocular surface is an important consideration, and ensuring an undisrupted tear film is essential to making accurate measurements. • In the future, surgeons hope to be able to make better, more direct measurements of both the anterior and posterior corneal surface astigmatism for true measurement of total corneal astigmatism. Source: Tal Raviv, MD This color LED topography illustrates classic against-the-rule astigmatism in a 70-year-old cataract patient. The anterior cornea measures 0.63 D, but accounting for the posterior corneal astigmatism, the total cornea measures 0.84 D, making this a toric IOL candidate.