title: Computer-assisted measurement of retinal vessel diameters in the Beaver Dam Eye Study: methodology, correlation between eyes, and effect of refractive errors.
abstract: OBJECTIVE
  Narrowed retinal arterioles may independently predict cardiovascular disease. We describe a computer-assisted method to measure retinal vessel diameters from digitized fundus photographs in a large population, and examine the correlation of retinal vessel diameters between eyes and whether refractive errors affect these measurements.
  
  
  METHODS
  Population-based, cross-sectional study in Beaver Dam, Wisconsin (n = 4926; age, 43-84 years).
  
  
  METHODS
  Retinal photographs were digitized, and all arterioles and venules located in an area 0.5 to 1 disc diameter from the optic disc were measured with the aid of computer software.
  
  
  METHODS
  Summary of retinal arteriolar and venular diameters, and the ratio of their diameters (arteriole:venule ratio [AVR]).
  
  
  RESULTS
  Correlation between right and left eyes was substantial for retinal arteriolar diameters (Pearson correlation coefficient, rho = 0.71) and venular diameters (rho = 0.74), and moderate for the AVR (rho = 0.49). The inverse association of higher blood pressure and smaller retinal arteriolar diameters was similar using data from either one eye or two eyes; arteriolar diameters decreased by 4.1 microm (right eyes), 4.0 microm (left eyes), and 4.0 microm (mean of both eyes) with each 10-mmHg increase in mean arterial blood pressure. A myopic refraction was associated with smaller retinal vessel diameters; arteriolar diameters decreased by 2.8 microm and venular diameters by 3.3 microm with each -1.0-diopter shift towards myopia. However, the pattern and strength of the association of blood pressure and retinal vessel diameters were not altered by variations in refractive errors.
  
  
  CONCLUSIONS
  There is good correlation of retinal vessel diameters between eyes. A myopic refraction is associated with smaller retinal vessel diameters. The association of retinal arteriolar diameters and blood pressure seems similar using data from either one eye or two eyes, and is minimally affected by refraction. These data suggest that measurement of retinal vessel diameters from one eye without regard to its refractive status may provide adequate information indicative of a person's retinal vessel caliber if information from two eyes and refraction is unavailable.
authors.affiliation: Department of Ophthalmology, University of Wisconsin, Madison, Wisconsin, USA. ophwty@nus.edu.sg
authors.forename: Tien Yin
authors.initials: TY
authors.lastname: Wong
authors.forename: Michael D
authors.initials: MD
authors.lastname: Knudtson
authors.forename: Ronald
authors.initials: R
authors.lastname: Klein
authors.forename: Barbara E K
authors.initials: BE
authors.lastname: Klein
authors.forename: Stacy M
authors.initials: SM
authors.lastname: Meuer
authors.forename: Larry D
authors.initials: LD
authors.lastname: Hubbard
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D001160:Arterioles / Q000503:physiopathology; D001794:Blood Pressure / Q000502:physiology; D003430:Cross-Sectional Studies; D005260:Female; D005654:Fundus Oculi; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010781:Photography; D012030:Refractive Errors / Q000503:physiopathology*; D012171:Retinal Vessels / Q000503:physiopathology*; D014699:Venules / Q000503:physiopathology; D014922:Wisconsin