EyeWorld Asia-Pacific December 2012 Issue

43 EWAP GLAUCOMA December 2012 AT A GLANCE • Lens softening with the femtosecond laser hopes to restore flexibility to the crystalline lens • Liquid crystal eyeglasses change power at the press of a button • Scleral expansion bands purport to help the posterior zonules work in changing lens shape • LaserACE restores the plasticity of the sclera, increasing the efficiency of the ciliary body WANG Ningli, MD Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology and Visual Sciences Key Laboratory No. 1 Dongjiaominxiang Street, Dongcheng District, Beijing, China 100730 Tel. no. +8610-5826-9968 Fax no. +8610-5826-9930 wningli@vip.163.com G laucoma is the second leading cause of blindness worldwide. A study by Quigley estimated that the majority of individuals with OAG and ACG were in China. In recent years, there has been an influx of Asians migrating to the United States. For this reason, a study led by Joshua D. Stein contrast d glaucoma incidence and prevalence rates for Asian Americans with other races, and pinpointed the incidence and prevalence rates of different glaucoma types among Asian Americans. 2.26 million patients over the age of 40 who were enrolled in a managed-care network between 2001 and 2007 were included in this study. Incidence and prevalence The study showed that narrow-angle glaucoma (NAG) prevalence rates were higher among Asian Americans compared with each of the other races. This result is consistent with other studies for Chinese showing a tendency to have thicker irides, greater iris area and lens vault than other races. Although it was once believed that open-angle glaucoma (OAG) was rare among Chinese persons, three recent urban surveys performed by He et al., Xu et al., and Wang et al. separately reported its prevalence to be similar to that seen in persons of European descent. Joshua et al. also surprisingly found that the hazard of OAG among Asian Americans as a group is actually 50% higher than that of Non-Hispanic whites. Is this a coincidental result? The etiology of glaucoma is believed to be due to both genetic and environmental factors. Genetics plays an important role in the growth of the eye, and at the same time, changes in environmental factors continue to remodel the structure of the eye. The modern human eye has to adapt to a more close-up working environment and more education requiring close reading, resulting in a deepening of the anterior chamber, an increase in myopia, and a decrease of hyperopia. Those lead to a lower chance of developing NAG and greater chance of developing OAG. Joshua et al. mentioned that Japanese Americans had a 3- to 10-times higher incidence of normal tension glaucoma (NTG) than other Asian ethnicities. However, the study estimated this proportion based on a screening or a follow-up IOP measurement, which cannot provide precise reference data. In our study, over 90% of subjects from Handan had IOP below the cutoff of 21 mmHg after a single measurement of IOP. This result parallels a large study from Japan in which ninety-two percent of those found to have POAG had IOP <21 mmHg. So clinicians should not only have a higher index of suspicion for NTG in Japanese, but also in Chinese. Clinic examination In the clinic, performing gonioscopy is necessary not only to check the angle anatomy for narrow angles, but also to exclude some secondary glaucoma, such as pigmentary glaucoma, which myopes are more vulnerable to. In addition, the high incidence and prevalence rates of NTG imply that factors other than IOP may play a role in the pathogenesis of glaucoma. Recent studies by Ren et al. and Berdahl et al. suggested that the cerebrospinal fluid (CSF) may play an important role in the optic neuropathy of OAG. So some new method for noninvasive estimation of the ICP may apply in the clinic, and become a routine diagnosis and typing tests for glaucoma. Applying genetic research We agree with Dr. Stein that glaucoma prevalence paves the way for genetic profiling and research within glaucoma. Until now, at least 29 genetic loci for OAG have been reported, and MYOC, OPTN and WDR36 are the most identified. Recently, Kathryn et al. associated the CDKN2B-AS1 gene with NTG. Others have found that altered alleles at the COL11A1 gene may make eyes hyperopic and increase the risk of NAG. The genotype–phenotype correlations and their potential mechanism are really large areas ripe for exploration. This year, Prof. Aung Tin and I reported three new loci involved in primary angle closure glaucoma, and this paper was published in Nature Genetics. I think that with the discovery of new gene loci in OAG and NAG, the gene chip may become a routine screening test for glaucoma in the future. Editors’ note: Prof. Wang has no financial interests related to his comments. Views from Asia-Pacific Department of Ophthalmology, University of California, San Francisco, Calif., USA. For example, the scanning peripheral anterior chamber depth analyzer for angle- closure glaucoma is more prevalent in Asia, which makes sense when you consider the higher risk of this glaucoma type among Asians, he said. Although Dr. Rhee believes that glaucoma prevalence in the Asian population is now well established, he thinks this kind of study paves the way for genetic profiling within glaucoma. “In the distant future, we may be able to attribute risk to the presence or absence of certain genetic profiles,” he said. Asian countries, said Shan Lin, MD, professor of ophthalmology, Department of Ophthalmology, University of California, San Francisco, Calif., USA. For example, the scanning peripheral anterior chamber depth analyzer for angle- closure glaucoma is more prevalent in Asia, which makes sense when you consider the higher risk of this glaucoma type among Asians, he said. Although Dr. Rhee believes that glaucoma prevalence in the Asian population is now well established, he thinks this kind of study paves the way for genetic profiling within glaucoma. “In the distant future, we may be able to attribute risk to the presence or absence of certain genetic profiles,” he said. Dr. Lin agreed that genetic profiling and research is an area ripe for exploration. He also believes that a closer look at risk in Asian ethnicities that could not be covered in this study would be another future research area. Although Dr. Lin believes the ethnicity classification method used in the study is a weakness, he said it does not detract from the overall value of the study results. Dr. Stein and co-investigators are conducting research regarding whether racial disparities exist in how eyecare providers care for glaucoma patients. EWAP Editors’ note: The physicians have no financial interests related to this article. Contact information Cantor: 317-274-8485, lcantor@iupui.edu Lin: Lins@vision.ucsf.edu Rhee: 617-573-3670, douglas_rhee@meei.harvard.edu Stein: jdstein@med.umich.edu