A severity scale for diabetic macular edema developed from ETDRS data.
OBJECTIVE
To develop a severity scale for diabetic macular edema (DME) and to assess relationships between severity and duration of DME and visual acuity (VA).


METHODS
From the Early Treatment Diabetic Retinopathy Study (ETDRS), mean baseline VA scores were tabulated for 7422 eyes cross-classified by (1) location of retinal thickening (RT) and its area within 1 disc diameter of the macular center, and (2) degree of RT at the center. Adjacent (row, column, and off-diagonal) cells with the greatest similarity in baseline VA (mean and SD) based on a Gaussian (normal) likelihood were merged. An initial eight-step scale was chosen using the Schwarz criterion (Bayesian information criterion; BIC) and was revised based on clinical judgment to nine steps. Relationships between baseline VA and other photographic and fluorescein angiographic characteristics were examined singly and in combination with the scale.


RESULTS
Modeling baseline VA as a function of the nine-step scale yielded an R(2) of 38.0%, compared with 38.4% using the full cross-classification of these variables. Addition of each of the other baseline characteristics changed the adjusted R(2) for the combination very little. Between scale levels 1A and 5B mean (SD) VA decreased from 86.8 (5.8) letters to 59.8 (13.6) letters. In a model of change in VA as a function of time spent at each DME severity level, VA loss increased progressively from 1 letter per year at level 2 to 17 letters per year at level 5B.


CONCLUSIONS
The scale facilitates documentation of the relationship of severity and duration of DME with VA.
Department of Population Health Sciences, University of Wisconsin, Madison, Wisconsin 53711-1068, USA.
Ronald E
RE
Gangnon
Matthew D
MD
Davis
Larry D
LD
Hubbard
Lloyd M
LM
Aiello
Emily Y
EY
Chew
Frederick L
FL
Ferris
Marian R
MR
Fisher
D003930:Diabetic Retinopathy / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology; D018450:Disease Progression; D005451:Fluorescein Angiography; D005500:Follow-Up Studies; D005654:Fundus Oculi; D006801:Humans; D008266:Macula Lutea / Q000473:pathology* / Q000503:physiopathology; D008269:Macular Edema / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D011379:Prognosis; D012720:Severity of Illness Index; D014787:Vision Tests / Q000379:methods; D014792:Visual Acuity / Q000502:physiology