ObjectiveTo analysis the fundus characteristics of fundus fluorescein angiography (FFA) of retinopathy of prematurity (ROP). MethodsEighty-four cases (168 eyes) who were diagnosed with ROP by a binocular indirect ophthalmoscope were included in the study. Among the 84 cases, there were 2 cases (4 eyes) of stage 1 ROP, 26 cases (52 eyes) of stage 2 ROP, 40 cases (80 eyes) of stage 3 ROP, 4 cases (8 eyes) of stage 4 ROP, and 4 cases (8 eyes) of stage 5 ROP, 9 cases (18 eyes) of plus disease, 8 cases (16 eyes) of aggressive posterior ROP (APROP). All infants received FFA with RetCam Ⅱ under general anesthesia and mydriasis. The retinal vein morphology, capillary filling state, neovascularization morphology and fluorescein leakage were observed. ResultsFFA revealed increased branching, expansion and tortuous peripheral retinal capillaries, increased capillary permeability with a small amount of fluorescein leakage in stage 1 ROP. There was a clear dividing line between the vascular area and the remote avascular area. In stage 2, the peripheral branches of temporal retinal blood vessels increased, and parallel distributed like a broom. The capillary end anastomosed with each other to form a loop. The fibrous tissues at the lesion edge proliferated as a ridge, with popcorn phenomenon. In stage 3, the ridge continued broadening, and the neovascular fibrous membrane formed breakthrough internal limiting membrane, stretched into the vitreous with a lot of fluorescein leakage. The ridge and remote avascular zone demarcated clearly. In stage 4 and 5, the vessel changes had similar phenomenon with the stage 2 and 3 in undetached retina, but the vessels in the detached retina expanded with fluorescein leakage. As for plus disease, the retinal arterioles in the posterior pole were tortuous, there were a large number of non-perfusion area in the peripheral retina with hemorrhage and obscured fluorescence. The retinal vessels in posterior pole in AP-ROP were also tortuous, and the capillaries were extreme expanded, while there were very few tortuous vessels and no capillary formation in the other part of retina.At the avascular zone boundaries, there were a large group of neovascularization with fluorescein leakage. ConclusionsThe demarcation line separating the avascular from the vascularized retinal regions is formed in stage 1, 2 and 3, and the amount of fluorescein leakage gradually increase from stage 1 to stage 3 ROP. The detached retina of stage 4 and stage 5 has an unclear focal length in the FFA. The plus disease mainly has arteriolar tortuosity in the posterior pole retina. In the AP-ROP cases, both of the arterioles and venules in posterior pole of retina are tortuous and expanding with neovascularization leakage of fluorescein.