title: A New Method of Magnification Correction for Accurately Measuring Retinal Vessel Calibers From Fundus Photographs.
abstract: To report a semiautomated retinal vessel caliber measurement system that measures central retinal artery (vein) equivalent (CRAE [CRVE]) with individual correction for magnification errors under conditions assuming optimal focus.
  
  
  
  The focusing condition of the subject eye fundus camera optical system was individually determined by constructing an optical model of each eye applying its refractive error, corneal curvature, and axial length (AL) to Gullstrand's schematic eye, and by adjusting the position of the camera's focusing lenses using each eye's refractive error. Once the focusing condition of the entire optical system was fulfilled, magnification of the fundus images was calculated using paraxial ray tracing. Measurements of CRAE (CRVE) were performed in an annular area centered on the optic disc with magnification-corrected diameter from 1.8 to 2.7 mm. Reproducibility of the measurements of the results using the new method and comparison with those using interactive vessel analysis (IVAN) were performed in normal Japanese eyes.
  
  
  
  Intra- and interexaminer intraclass correlation coefficient (ICC) for CRAE (CRVE) measurements was greater than 0.978. CRAE (CRVE) using the new method averaged 148.9 ± 10.9 μm (225.0 ± 13.9 μm; mean ± SD, N = 99). Differences between the new method and IVAN were greater with increasing AL (P < 0.001). The new method yielded CRAE (CRVE) in good agreement with IVAN in eyes with AL of approximately 24 mm. However, the new method yielded smaller values in eyes with shorter AL and vice versa.
  
  
  
  A new accurate and reproducible method to measure CRAE (CRVE) from fundus photographs was reported.
authors.affiliation: Tajimi Iwase Eye Clinic, Tajimi, Japan.
authors.forename: Aiko
authors.initials: A
authors.lastname: Iwase
authors.affiliation: Topcon Corporation, Tokyo, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Sekine
authors.affiliation: Topcon Corporation, Tokyo, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Suehiro
authors.affiliation: Tajimi Iwase Eye Clinic, Tajimi, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Tanaka
authors.affiliation: Department of Public Health, Yamagata University Graduate School of Medical Science, Yamagata, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Kawasaki
authors.affiliation: Department of Public Health, Yamagata University Graduate School of Medical Science, Yamagata, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Kawasaki
authors.affiliation: Topcon Corporation, Tokyo, Japan.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Sinai
authors.affiliation: Kanto Central Hospital of the Mutual Aid Association of Public School Teachers, Tokyo, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Araie
mesh_terms: D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012171:Retinal Vessels / Q000033:anatomy & histology*