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Editors Selection IGR 7-3
Population Genetics: Glaucoma in Africans versus Europeans
Comment by Leon Herndon on:
26214 African Descent and Glaucoma Evaluation Study (ADAGES): II. Ancestry differences in optic disc, retinal nerve fiber layer, and macular structure in healthy subjects, Girkin CA; Sample PA; Liebmann JM et al., Archives of Ophthalmology, 2010; 128: 541-550
Girkin et al. (544), from the ADAGES Group, had the objective to define differences in optic disc, retinal nerve fiber layer, and macular structure between healthy participants of African (AD) and European descent (ED) using quantitative imaging techniques in the African Descent and Glaucoma Evaluation Study (ADAGES). These measures were obtained with confocal scanning laser ophthalmoscopy using Heidelberg retina tomography (HRT) and optical coherence tomography (OCT) and subjects were without ocular disease.
The AD participants had significantly greater optic disc area on HRT (2.06 mm 2; P < .001) and OCT (2.47 mm2; P < .001) and a deeper HRT cup depth than the ED group (P < .001). Retinal nerve fiber layer thickness was greater in the AD group except within the temporal region, where it was significantly thinner. Central macular thickness and volume were less in the AD group. This study also found the AD group to have a thinner central cornea thickness (CCT) than the ED group, but no difference in intraocular pressure (IOP).
Several studies confirm the observation that mean CCT in black patients is lower than mean CCT in white patients. This may help to explain why blacks are four to five times more likely than whites to be diagnosed as having glaucoma.1 In the Ocular Hypertension Treatment Study, when race is entered into a multivariate analysis, it is no longer a statistically significant predictor of progression to glaucoma; CCT and vertical cup-disc ratio remain significant predictors, however.2
The Baltimore Eye Survey (BES) showed that the average IOP among black and white subjects in the general population was similar.3 In both races, the screening IOP was higher in glaucomatous eyes than in eyes in the general population. Untreated black subjects with POAG had lower IOP than untreated white subjects in the BES, which would suggest that the optic nerve in black subjects has increased susceptibility to glaucomatous optic nerve damage. This finding of a deeper optic cup among the AD group in the current study may imply that black individuals have a thinner lamina cribrosa which would biomechanically underlie this increased susceptibility.
References
- Tielsch JM, Sommer A, Katz L, et al. Racial variations in the prevalence of primary open-angle glaucoma: the Baltimore Eye Survey. JAMA. 1991;266:369-374.
- 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;120:714-720.
- Sommer A, Tielsch JM, Katz J, et al. Relationship between intraocular pressure and primary open-angle glaucoma among white and black Americans: the Baltimore Eye Survey. Arch Ophthalmol. 1991;109:1090-1095.
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