Glaucoma Watch prev next

Jan 30 2007

Optic Nerve Head Measurements with the HRT III

posted by: Bud O'Leary, OD

African-American and Hispanic populations have been found to be at greater risk for developing glaucoma. Research suggests that racial differences in the configurations of the optic nerve head exist and these differences may indicate a population specific greater risk of glaucoma.

Optic nerve disc size, cup volumes, cup to disc ratios, RNFL and rim volume have all been shown to vary between races. Appreciation of these differences is now being addressed by Heidelberg Engineering in the latest model tomograph, HRTIII.

The original database for derivation of HRT II stereometric parameters consisted of 743 Caucasian eyes. The database consisted of 349 normal eyes, 192 with early glaucoma, 97 with moderate glaucoma and 105 with advanced glaucoma.

The new HRT III database has been expanded and differentiated to include 200+ eyes of African-Americans and 100+ eyes of persons of Indian (Southeast Asian) origin. Further additions of Hispanic and Asian populations are in process.

The new HRT III software utilizes selectable databases to derive ethnic specific stereometric parameters for analysis. The HRT III Report specifies ethnicity and will select normative databases for comparison and recommendation. The attachment below identifies these new abilities (Interpreting the New v.3.0 OU Report).

In a recent article by Joseph Zelefsky, M.D., et al, in the Journal of Glaucoma, V. 15 (6), pp 548-551, the authors pose an interesting observation regarding this racially derived normative database. This prospective pilot study sought to determine if the databases enhanced HRT ability to discriminate normal from glaucomatous optic nerves.

124 African-American and 96 Caucasian subjects were enrolled. Regression analysis using the HRT II database yielded sensitivity of 50.0% with a specificity of 98.6% in African-Americans and sensitivity of 71.9% with specificity of 95.3% in Caucasians.

Regression analysis using the HRT III software before adjustment for ethnicity yielded sensitivity of 71.2% with specificity of 86.1% in African-Americans and sensitivity of 81.3 % with specificity of 93.8% in Caucasians.

Regression analysis using the HRT III software after adjustment for ethnicity demonstrated sensitivity of 65.4% and specificity of 90.3% for the African-American population.

The study shows that the HRT III database increases sensitivity but decreases specificity for African-Americans and increases only sensitivity in Caucasians for predicting glaucoma.

The authors offer that the decreased specificity may be due to the constitution of the database. The database was collected from an African-American population from a single location, Alabama, USA. The study population was collected from the New York City area, and was more likely to contain an increased level of heterogeneity and ethnic diversity within the African-American population.

The authors conclude that race-specific databases may need to be derived from multiple sources reflecting the diversity of populations within a racial classification.