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Liang Xu, MD; Haitao Zhang, MD; Ya Xing Wang, MD; Jost B. Jonas, MD

Arch Ophthalmol. 2008;126(3):435-436.

Central corneal thickness (CCT) has been described to be a predictor for the development of primary open-angle glaucoma and the progression of glaucomatous visual field defects in the Ocular Hypertension Treatment Study¹ and other investigations.^2-3 Correspondingly, a previous investigation by Herndon and colleagues³ found that CCT was the most consistent predictor of the degree of glaucomatous damage in their hospital-based cross-sectional study. However, CCT also influences applanation tonometry, so it has remained unclear whether the reported findings are due to the dependence of intraocular pressure measurements on CCT and a corresponding selection artifact of patients or whether a thin cornea may predispose the eye to a higher glaucoma susceptibility. Since optic disc hemorrhages can indicate progression of glaucomatous optic neuropathy and because most of the previous investigations were hospital-based studies with a possible referral bias, it was the purpose of our population-based study to assess whether CCT influences the development of disc hemorrhages.

Methods
The Beijing Eye Study is a population-based cohort study in northern China.⁴ The medical ethics committee of the Beijing Tongren Hospital approved the study protocol and all of the participants gave informed consent according to the Declaration of Helsinki. Of 5324 individuals aged 40 years or older residing in the study area, 4439 individuals (2505 women) participated in the eye examination (response rate, 83.4%) in the year 2001 as described in detail previously.⁴ In 2006, the same population was invited for a reexamination, with 3251 subjects participating (response rate, 73.3%). All of the participants underwent a standardized ophthalmic examination including CCT measurement by slitlamp optical coherence tomography. Only 1 randomly selected eye was taken for statistical analysis. Glaucoma was defined by the appearance of the optic nerve head as described recently (Table).⁴

View this table: [in this window] [in a new window] [as a PowerPoint slide]   Table. Criteria for the Definition of Glaucoma in the Beijing Eye Studya

Results
Of the 3251 subjects, CCT measurements were available for 3100 subjects (95.4%); 32 of them (1.0%) showed an optic disc hemorrhage. The CCT was slightly greater in the hemorrhagic group (mean [SD] CCT, 569.5 [33.8] µm) than in the nonhemorrhagic group (mean [SD] CCT, 556.0 [33.0] µm) (P = .03; after application of the Bonferroni method to correct for performing multiple statistical analyses, P = .06) (Figure). Including glaucomatous eyes (n = 77) only, the CCT did not vary significantly between the hemorrhagic group (n = 5 eyes [6%]; mean [SD] CCT, 571.8 [36.1] µm) and the nonhemorrhagic group (n = 72 eyes [94%]; mean [SD] CCT, 549.3 [31.4] µm) (P = .24), with the hemorrhagic group having slightly thicker corneas than the nonhemorrhagic group.

View larger version (18K): [in this window] [in a new window] [as a PowerPoint slide]   Figure. Box plots showing the distribution of central corneal thickness in subjects with and without optic disc hemorrhages in the Beijing Eye Study. Open circles indicate outliers. The box contains 50% of the data; the line in the box represents the median.

Comment
The findings point against a thin cornea as an associated factor for disc hemorrhages in glaucoma.^5-6 Because disc hemorrhages are usually associated with glaucoma progression, the results do not support a thin cornea to be a pathogenic risk factor for glaucoma progression.

AUTHOR INFORMATION
Correspondence: Dr Jonas, Universitäts-Augenklinik, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany (jost.jonas{at}augen.ma.uni-heidelberg.de).

Financial Disclosure: None reported.

Funding/Support: This work was supported by grant 7071003 from the Beijing Natural Science Foundation.

REFERENCES
1. Gordon MO, Beiser JA, Brandt JD; et al. The Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma. Arch Ophthalmol. 2002;120(6):714-720. FREE FULL TEXT 2. Medeiros FA, Sample PA, Weinreb RN. Corneal thickness measurements and frequency doubling technology perimetry abnormalities in ocular hypertensive eyes. Ophthalmology. 2003;110(10):1903-1908. FULL TEXT | ISI | PUBMED 3. Herndon LW, Weizer JS, Stinnett SS. Central corneal thickness as a risk factor for advanced glaucoma damage. Arch Ophthalmol. 2004;122(1):17-21. FREE FULL TEXT 4. Xu L, Wang Y, Wang S, Wang Y, Jonas JB. High myopia and glaucoma susceptibility: the Beijing Eye Study. Ophthalmology. 2007;114(2):216-220. FULL TEXT | ISI | PUBMED 5. Leske MC, Heijl A, Hussein M, Bengtsson B, Hyman L, Komaroff E, Early Manifest Glaucoma Trial Group. Factors for glaucoma progression and the effect of treatment: the Early Manifest Glaucoma Trial. Arch Ophthalmol. 2003;121(1):48-56. FREE FULL TEXT 6. Chauhan BC, Hutchison DM, LeBlanc RP, Artes PH, Nicolela MT. Central corneal thickness and progression of the visual field and optic disc in glaucoma. Br J Ophthalmol. 2005;89(8):1008-1012. FREE FULL TEXT

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