Harmonizing the classification of age-related macular degeneration in the three-continent AMD consortium.
OBJECTIVE
To describe methods to harmonize the classification of age-related macular degeneration (AMD) phenotypes across four population-based cohort studies: the Beaver Dam Eye Study (BDES), the Blue Mountains Eye Study (BMES), the Los Angeles Latino Eye Study (LALES), and the Rotterdam Study (RS).


METHODS
AMD grading protocols, definitions of categories, and grading forms from each study were compared to determine whether there were systematic differences in AMD severity definitions and lesion categorization among the three grading centers. Each center graded the same set of 60 images using their respective systems to determine presence and severity of AMD lesions. A common 5-step AMD severity scale and definitions of lesion measurement cutpoints and early and late AMD were developed from this exercise.


RESULTS
Applying this severity scale changed the age-sex adjusted prevalence of early AMD from 18.7% to 20.3% in BDES, from 4.7% to 14.4% in BMES, from 14.1% to 15.8% in LALES, and from 7.5% to 17.1% in RS. Age-sex adjusted prevalences of late AMD remained unchanged. Comparison of each center's grades of the 60 images converted to the consortium scale showed that exact agreement of AMD severity among centers varied from 61.0-81.4%, and one-step agreement varied from 84.7-98.3%.


CONCLUSIONS
Harmonization of AMD classification reduced categorical differences in phenotypic definitions across the studies, resulted in a new 5-step AMD severity scale, and enhanced similarity of AMD prevalence among the four cohorts. Despite harmonization it may still be difficult to remove systematic differences in grading, if present.
Department of Ophthalmology and Visual Sciences, University of Wisconsin School of Medicine and Public Health , Madison, Wisconsin , USA .
Ronald
R
Klein
Stacy M
SM
Meuer
Chelsea E
CE
Myers
Gabriëlle H S
GH
Buitendijk
Elena
E
Rochtchina
Farzana
F
Choudhury
Paulus T V M
PT
de Jong
Roberta
R
McKean-Cowdin
Sudha K
SK
Iyengar
Xiaoyi
X
Gao
Kristine E
KE
Lee
Johannes R
JR
Vingerling
Paul
P
Mitchell
Caroline C W
CC
Klaver
Jie Jin
JJ
Wang
Barbara E K
BE
Klein
D000368:Aged; D000369:Aged, 80 and over; D001315:Australia / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008268:Macular Degeneration / Q000145:classification* / Q000453:epidemiology / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D015995:Prevalence; D012720:Severity of Illness Index; D014481:United States / Q000453:epidemiology