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Clinical and Epidemiologic Research: Hiroshi Sasaki, Yutaka Kawakami, Masaji Ono, Fridbert Jonasson, Ying Bo Shui, Hong-Ming Cheng, Luba Robman, Cathy McCarty, Sek Jin Chew, and Kazuyuki Sasaki Localization of Cortical Cataract in Subjects of Diverse Races and Latitude Invest. Ophthalmol. Vis. Sci. 2003; 44: 4210-4214 [Abstract] [Full text] [PDF]

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Localization of Cortical Cataract in Subjects of Diverse Races and Latitude

Tien Yin Wong   (16 January 2004)

Author Response: Localization of Cortical Cataract in Subjects of Diverse Races and Latitude

Hiroshi Sasaki, Yutaka Kawakami, Masaji Ono, Fridbert Jonasson, Ying Bo Shui, Hong-Ming Cheng, Luba Robman, Cathy McCarty, Kazuyuki Sasaki   (16 January 2004)

Localization of Cortical Cataract in Subjects of Diverse Races and Latitude 16 January 2004
Tien Yin Wong Send letter to journal: Re: Localization of Cortical Cataract in Subjects of Diverse Races and Latitude ophwty{at}nus.edu.sg Tien Yin Wong	I read with interest the article by Sasaki and colleagues1 pertaining to the location of cortical cataract in people living in Iceland, Melbourne, and Singapore. I would like to draw the attention of the authors to two important limitations that should be addressed. First, of the three populations examined, only the Iceland study could be considered population-based. The Melbourne subjects were based on participants from a clinical trial, while the Singapore subjects were based on volunteers to an eye screening examination. The possibility of selection biases from such non-random samples is substantial. Moreover, comparison of cataract prevalence between population- and non-population-based samples is problematic. For example, if persons with inferior cortical cataract were more likely to have visual impairment, then the self-selected sample from Singapore could be expected to have a higher prevalence of inferior cortical cataract than the population-based sample from Iceland. Second, the statistical analysis did not take into account factors that might have influenced the occurrence of cortical cataract. Of particular concern was the fact that age-standardization of cataract rates between the three populations was not performed. Thus, it is unclear if age, clearly the most important risk factor for cataract, was a possible confounder in the results presented. In addition, the authors should control for other possible risk factors of cortical cataract. For example, a recent study indicated that diabetes and lower body mass index were risk factors for cortical cataract in Chinese Singaporeans.2 While Sasaki's data suggest a possible exposure to sunlight as a risk factor for cortical cataract, these limitations need to be discussed and acknowledged. Tien Yin Wong Centre for Eye Research Australia University of Melbourne Australia References 1. Sasaki H, Kawakami Y, Ono M, et al. Localization of cortical cataract in subjects of diverse races and latitude. Invest Ophthalmol Vis Sci. 2003;44:4210-4214. 2. Foster PJ, Wong TY, Johnson GJ, Seah SKL. Risk factors for nuclear, cortical and posterior subcapsular cataract in Chinese: The Tanjong Pagar Survey. Brit J Ophthalmol. 2003;87:1112-1120.
Author Response: Localization of Cortical Cataract in Subjects of Diverse Races and Latitude 16 January 2004
Hiroshi Sasaki , Yutaka Kawakami, Masaji Ono, Fridbert Jonasson, Ying Bo Shui, Hong-Ming Cheng, Luba Robman, Cathy McCarty, Kazuyuki Sasaki Send letter to journal: Re: Author Response: Localization of Cortical Cataract in Subjects of Diverse Races and Latitude sasaki-h{at}k5.dion.ne.jp Hiroshi Sasaki, et al.	In the E-Letter to the Editor from Dr. Wong, the author suggests that there might be limitations regarding our study due to the different selection procedures employed in sampling the three different populations under examination and that these limitations should be addressed and acknowledged. To some extent, these limitations have been acknowledged and addressed in the article (p. 4210-11) and should perhaps have been further discussed with regard to possible bias. We have reported prevalence, risk factors and compared populations in previous studies.1-5 The aim of the present study, however, was somewhat different, namely to compare localization of the earliest onset of cortical lens opacification using the populations of Melbourne, Reykjavík and Singapore. The present study only included right eyes of individuals from the 3 populations where pupils could be dilated to 7 mm or larger and had an area of cortical opacity less than 20% determined from Scheimpflug and retroilluminated photographs. We argue that for the particular purpose of our study our selection procedure would not have produced undue bias regarding the results. It is important to keep in mind that the aim of our study was not to compare different types and grades of lens opacification in different populations but rather to compare the distribution and localization of early cortical lens opacification. Dr. Wong suggests that individuals with inferior cortical cataracts, more likely to have visual impairment, might be over-represented in the Singaporean sample which includes volunteers. Figures 1 and 2 of our article show that the prevalence of central cortical opacity within the pupillary area of <3 mm diameter (3 central concentric circles, Fig. 1), the most likely cortical area to be involved in visual impairment,6 was similar for all 3 populations. This suggests that the volunteer participants from Singapore were no more likely to have had visual impairment due to cortical lens opacification of grade I than were the samples from Melbourne or Reykjavík. We apologize if this was not stated clearly enough in the figures and text. Regarding the author's comment on age as a possible confounding variable: we acknowledge that age is the most important risk factor for both nuclear and cortical lens opacification generally speaking. We also acknowledge that age probably has some effect on the onset and the prevalence of cortical lens opacification grade I as suggested in previous publications. The Singaporeans in our sample developed cortical lens opacification at an earlier age than did the Icelanders. This is stated in our article. However, there is no evidence in the literature to suggest that age plays any role regarding the localization of early cortical lens opacification. In the Letter to the Editor it was suggested that we should have controlled for possible risk factors of cortical cataract. This has been the topic of some of our previous studies.1,3 And as far as we are aware, contrary to the suggestion, there are no indications that diabetes or lower body mass index affects the localization of grade I cortical lens opacification, which was the focus of our study. Nevertheless, we agree with the author of the E-Letter that further investigation is needed to clarify the correlations between several possible risk factors and the localization, morphology and the process of progression of cortical lens opacification. Hiroshi Sasaki1 Yutaka Kawakami1 Masaji Ono2 Fridbert Jonasson3 Ying Bo Shui1,4 Hong-Ming Cheng5 Luba Robman6 Cathy McCarty6,7 Kazuyuki Sasaki1 1Dept. of Ophthalmology, Kanazawa Medical University, Ishikawa, Japan 2National Institute for Environmental Studies, Tsukuba, Japan 3Dept. of Ophthalmology, University of Iceland, Reykjavík, Iceland 4Dept. of Ophthalmology and Visual Science, Washington University Medical School, St. Louis, Missouri 5The Schepens Retina Associates Foundation, Boston, Massachusetts 6Centre for Eye Research Australia, University of Melbourne, Melbourne, Australia 7Marshfield Medical Research Foundation, Marshfield Clinic, Marshfield, Wisconsin References 1. Sasaki H, Jonasson F, Kojima M, et al. Reykjavik Eye Study – Prevalence of lens opacification. Ophthalmologica. 2000;214:412-420. 2. Katoh N, Jonasson F, Sasaki H, et al. Cortical lens opacification in Iceland, risk factor analysis – Reykjavik Eye Study. Acta Ophthalmol Scand. 2001;79:154-159. 3. Arnarsson A, Jonasson F, Sasaki H, et al. Risk factors for nuclear lens opacification: Reykjavik Eye Study. Dev Ophthalmol. Basel, Karger 2002;35:12-20 in Hochvin O, Kojima M, Takahashi N, Sliney DH (eds.) Progress in lens and cataract research. 4. Sasaki H, Shui YB, Kojima M, et al. Characteristics of cataracts in the Chinese Singaporean. J Epidemiol. 2001;11:16-23. 5. Robman LD, Tikellis G, Garrett SK, et al. Baseline ophthalmic findings in the Vitamin E Cataract and Age-related Maculopathy (VECAT) Study. Aust NZ J Ophthalmol. 1999;27:410-416. 6. Thylefors B, Chylack LT Jr, Konyama K, et al. A simplified cataract grading system. Ophthalmic Epidemiol. 2002;9:83-95.