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Variations in Corneal Asphericity (Q Value) Between African-Americans and Whites

Fuller, Daniel G.*; Alperin, Danielle

Optometry and Vision Science: July 2013 - Volume 90 - Issue 7 - p 667–673
doi: 10.1097/OPX.0b013e318296befe
Original Articles

Purpose To search for differences in corneal asphericity on the basis of ethnicity between African-American and white populations.

Methods A prospective cohort design was used to analyze corneal asphericity (Q value) data obtained by Pentacam HR (Oculus, Wetzlar, Germany) on right eyes from African-American (n = 80) and white (n = 80). Subjects were stratified by ethnicity, age, and spherical equivalent (SE) refractive error. Q values were obtained from each quadrant (superior, nasal, inferior, and temporal) and two meridians (horizontal and vertical).

Results The mean Q values were African-Americans −0.26 ± 0.19 and whites −0.20 ± 0.12, indicating that the eyes of African-Americans were significantly more prolate (p = 0.003) than those of whites. There was a significant difference between mean Q values for ethnic groups only in the 30- to 39-year olds (p = 0.01) and there was a lack of correlation with age in both ethnic groups. Q value contrasts by gender were only significant between males (p = 0.01). There was a lack of correlation between Q value and SE for either ethnic group. Age group contrasts between ethnic groups found significant differences for those with SE greater than 0.00 D to −3.00 D (p = 0.05) and greater than 0.00 D to +3.00 D (p = 0.05). Comparison of mean Q values in opposing meridians within and across ethnic groups were significant, although neither group showed significant differences between horizontal and vertical meridians.

Conclusions Corneal asphericity as represented by mean Q value varies significantly between African-Americans and whites. The greatest differences are evident in opposing quadrants and appear to be little influenced by age, gender, or SE.



Cornea Contact Lens Service, The Eye Center, Southern College of Optometry, Memphis, Tennessee (DGF), and University Hospitals Eye Institute, Center for Anterior Segment Diseases and Surgery, Case Western Reserve University School of Medicine, Cleveland, Ohio (DA).

Daniel G. Fuller Cornea Contact Lens Service, The Eye Center, Southern College of Optometry, 1225 Madison Ave, Memphis, TN 38104; e-mail:

© 2013 American Academy of Optometry