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Abstract #18967 Published in IGR 3-1
How large is the optic disc? Systematic errors in fundus cameras and topographers
Meyer T; Howland HCOphthalmic and Physiological Optics 2001; 21: 139-150
PURPOSE: To determine whether or not there are systematic differences in the areas of optic discs as measured by different machines using different measurement algorithms and whether racial or gender differences exist in optic disc area measurements. METHODS: The authors examined the results of 23 published studies on the size of normal optic discs of various patient populations. Studies differed in the type of instrument and method used to measure optic disc area, and the number, age, race and gender of subjects examined. Noticing that different machines exhibited statistically significant systematic differences in optic disc sizes of comparable populations, the authors computed a 'normalization' factor for each machine based on these mean differences. Applying this normalization factor to the results, they then re-examined the differences between racial and gender groups. RESULTS: By comparing the results of mean optic disc areas of different racial groups made with different machines, and normalizing results according to those of the Zeiss fundus camera, the authors found the normalization factors for the following machines to be, Zeiss fundus camera: 1 (by definition), Rodenstock Optic Disc Analyzer (RODA): 1.51, Topcon fundus camera: 1.04, Heidelberg Retina Tomograph (HRT): 1.15 and TopSS scanning laser ophthalmoscope: 1.29. That is, to bring the results of area measurements made with a RODA machine in line with those made with a Zeiss fundus camera, the former should be multiplied by the factor 1.51. Using the normalized results, the authors confirmed the findings of previous authors that the optic disc areas of black subjects were statistically significantly larger than those of white subjects (n-weighted mean effect = 0.556 ± 0.142 S.E., n = 5). Further, the meta-analysis of various racial populations from five studies shows that males have significantly larger discs than females (n-weighted mean effect = 0.151 ± 0.055 S.E., n = 9). CONCLUSIONS: Different machines and techniques give different results when populations of similar racial composition are measured. The authors recommend applying the above normalizing factors when comparing studies that employ different instruments.
Dr T. Meyer, Department of Neurobiology and Behavior, W-201 Mudd Hall, Cornell University, Ithaca, NY 14853, USA
Classification:
2.14 Optic disc (Part of: 2 Anatomical structures in glaucoma)