Astigmatism. How much is really out there? Does it need to be treated? What is the best way to measure it? Is it stable? Does the axis matter? Does age of the patient matter? What about posterior corneal astigmatism?
These (and many others) are all questions that are important when considering the impact of astigmatism on vision and visual outcomes postprocedure. For refractive corneal and refractive cataract, surgeons' management of astigmatism is extremely important when it comes to delivering outcomes. When I approach patients with astigmatism, my first step is to make sure that the ocular surface is optimized aggressively. I don't hesitate to delay surgical interventions to make sure that the patient understands the importance of ocular surface/dry-eye management and the effect of an irregular ocular surface on the accuracy of preoperative measurements, consistency of measurement, as well as effect on postoperative outcomes. Next, I look for repeatability of measurements (magnitude and axis) across several diagnostic modalities. Last, I make a therapeutic plan with the patient and discuss options, including expectations and pro and cons of each option.
In this installment of Viewpoints, I discuss a paper from Valluru and colleagues, in which the authors retrospectively characterize astigmatism in the United States, comparing two cohorts of participants of the 1971-1975 and 1999-2008 National Health and Nutrition Examination Survey (NHANES). The main outcome of interest was the presence of clinically significant astigmatism; this was defined as ≥ 1.0 D, which has been generally accepted as causing visual impairment. Overall, the paper reported an overall increase in the prevalence of astigmatism from the 1970s to the 2000s, with an overall decrease in with-the-rule (WTR) astigmatism and an increase in against-the-rule (ATR) astigmatism.
Several aspects of this study were interesting to me. First, the authors reported a significant increase in the prevalence of astigmatism, from 14% in the 1970s to 24% in the 2000s. Part of this could be due to testing protocols. In the early cohort, astigmatism was determined by retinoscopy, whereas in the 2000s, astigmatism was determined by automated refraction systems. What the study did not include was any topographic data. To me, as a refractive corneal/cataract surgeon, this is a big drawback of the findings. In order to treat astigmatism (in cataract surgery), it is important to quantify the amount and regularity of corneal astigmatism, which is best done with either topography or tomography. Nonetheless, the increasing prevalence of astigmatism in the interval between the 1970s and 2000s is important as we look to improve visual outcomes with surgical procedures.
The other aspect of the study I found interesting is that the regression analysis of the cohort showed that myopic participants had eight times the odds of having astigmatism as nonmyopic participants. I can't say that I have noticed this trend in my own clinic, but I will certainly be paying more attention to see if this trend holds.
The last interesting point that I want to highlight is that the 2000s cohort had significantly more ATR astigmatism than did the 1970s cohort, which was noted to be more in male, White, and nonmyopic participants. We know that ATR astigmatism increases with age and often can be more visually impactful that WTR astigmatism. Overall, this paper was an interesting read and helped me better understand the correlation of astigmatism to various factors that may play a role in how we treat astigmatism in our practices
Sumit (Sam) Garg, MD, is the vice chair of clinical ophthalmology and an associate professor in the Department of Ophthalmology at the Gavin Herbert Eye Institute, University of California, Irvine. He specializes in corneal and cataract surgery as well as laser refractive surgery.
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Cite this: Sumit (Sam) Garg. Characterizing Astigmatism - Medscape - Jul 19, 2022.