To determine the antiangiogenic efficacy of IFNβ-DTPA-dextran,
rabbits were treated with saline (n = 9, 4 weeks), free
IFNβ (single dose, 7.5 MIU/kg; n = 5, 4 weeks), or
IFNβ-DTPA-dextran with 0.75 (n = 8, 4 weeks) and 7.5
(n = 10, 2 weeks) MIU/kg of IFNβ. Each substance,
beginning 3 weeks after implantation of the gelatin microspheres, was
administered intravenously twice weekly. Fluorescein angiography was
repeated weekly. To evaluate the treatments’ effects, all angiographic
images taken 7 to 9 minutes after injection to document the degree of
late fluorescein leakage were converted to digital images, and the area
of fluorescein leakage was quantified in a masked fashion by computer
(Image 1.52; NIH Image is provided in the public domain by the National
Institutes of Health, Bethesda, MD and is available at
http://rsb.info.nih.gov/nih-image/). To prevent variability during
image processing, the density of the choroidal background on the images
from the same eye was harmonized without changing the contrast. Each
measurement was scored as follows: 0, no or faint fluorescein leakage
(less than choroidal background in density; 1, mild leakage (as low as choroidal background in density); 2, focal intense leakage (20%
or less than the area with microspheres); 3, intense leakage of
moderate size (20%–50%); and 4, intense leakage of large size (50%
or more).