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EW NEWS & OPINION 24 February 2017 by Liz Hillman EyeWorld Staff Writer in patients with [diabetic mellitus,] and by increases in SO2 levels 1 day before CRAO onset in patients with [hypertension] and in patients [older than 65 years]." Possible mechanisms for ambi- ent air pollution increasing risk of CRAO include hypercoagulability, vasospasm, destabilized athero- sclerotic plaques, inflammation, and disturbed cardiac autonomic system induced by air pollution, said the study's lead author Hui-Chen Cheng, MD, Department of Oph- thalmology, Taipei Veterans General Hospital. In addition to exposure to air pollution, the study authors found that an increase in temperature a couple of days prior to the event increased risk of CRAO as well. Each 1-degree C increase was associated with a 1.23 increase in likelihood of CRAO onset, Cheng et al. wrote, acknowledging that more studies are needed to validate the association between short-term change in tem- perature with CRAO risk. Limitations to the study includ- ed the relatively small sample size, possible timing lags between CRAO onset and visiting a medical facility, and defining the patient's residence with that of the local clinic or hospi- tal, not his or her actual address. "For an ophthalmologist, we may remind the public about the importance of air quality for general health and vision," Dr. Cheng said. "Air pollution is a modifiable risk factor, which means we may lower or prevent the CRAO attack via controlling the levels of air pol- lution. Altering activity patterns diabetes or hypertension and those older than 65 years," Dr. Wang said. The retrospective, popula- tion-based cohort study enrolled patients from a database with newly diagnosed CRAO between 2001 and 2013. The patient's residence was identified and associated with the nearest clinic or hospital. The researchers then obtained meteoro- logical data from stations operated by the Central Weather Bureau of Taiwan and ambient air concentra- tions from monitoring stations oper- ated by the country's environmental protection agency. These were paired to patients' "residences," which again were defined by the nearest hospital/clinic. Two hundred and sixty-six patients with CRAO during the time period were identified, but only 96 were matched with nearby monitoring stations and thus were included in the study. A case-crossover study design was used to evaluate different kinds of ambient air pollution prior to CRAO onset. "In brief, each patient's expo- sure before a case-defining event (case period) was compared with the patient's exposure during a control period, when the patient did not experience a case-defining event," Cheng et al. wrote. Overall, the researchers conclud- ed that the data showed "short-term exposure to gaseous air pollutants might be positively associated with CRAO onset, particularly in patients with cardiovascular risk. […] we found that CRAO risk was signifi- cantly impacted by increases in NO2 levels 4 to 5 days before CRAO onset term increases in the number of people visiting an ophthalmological emergency department. 4 In addition, it has been observed that retinal microvasculature may respond to short-term and long-term changes in air pollution levels. 5,6 In regions of higher air pollution, older people may have narrower arteriolar diame- ter of the retinal artery." A paper co-authored by Dr. Wang and published in the journal Ophthalmology in 2016 added to this body of research, finding a possible association between ambient air pollution and risk for developing central retinal artery occlusion (CRAO). 7 "In our study, we found that transient elevated levels of nitro- gen dioxide (NO2) or sulfur diox- ide (SO2) may increase the risk of CRAO, particularly in patients with Study suggests ambient air pollution increases risk of central retinal artery occlusion W hile the effect of air pollution on one's lungs is well known, how atmospheric pollution affects one's eyes is less considered among the general population "The most well-known impact of air pollution in ophthalmology is ocular surface disease, such as non-specific conjunctivitis, allergic conjunctivitis, and dry eye dis- ease," 1,2,3 said An-Guor Wang, MD, PhD, Department of Ophthalmolo- gy, Taipei Veterans General Hospital, Taipei, Taiwan. "The levels of air pollution are also linked to short- Air pollution linked to sight-threatening condition Research highlight the desired myopic target more accurately. My own practice has evolved. In the relatively bad old days of con- tact A-scan and earlier generation formulas, I would routinely do the myopic eye first in order to exploit that information gleaned from this first myopic eye. Now that precision has improved so much I have found the greatest challenge is ensuring a refraction close to plano for the dis- tance eye, and if this is not achieved for whatever reason then monovi- sion can be reconsidered. I currently most often perform surgery on the first emmetropic eye. This allows the patient and me to evaluate if the vision is satisfactory for distance needs before targeting myopia for the other eye. If the answer is "no," then steps can be taken to correct residual refractive error. Alternative- ly, we can throw out the monovi- sion plan entirely and plan surgery around the second eye to try to achieve emmetropia as well as possi- bly using the first eye's result. To do the opposite, doing the myopic eye first, targeting for example –1.50 and instead having a –2.50 result, does take a great leap of faith to adjust the second emmetropic eye. You could wind up in an anisometro- pia situation with the myopic side being –2.50 and the emmetropic eye instead resulting in hyperopia due to an inappropriate adjustment. In the next installment, we will explore the "hedge"—additional adjustments based upon various situations. EW Editors' note: Dr. Gossman is in private clinical practice at Eye Surgeons & Physicians, St. Cloud, Minnesota. He has no financial interests related to this article. Contact information Gossman: n1149x@gmail.com Art continued from page 23

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