ObjectiveTo investigate the fundus fluorescein angiography (FFA) characteristics of spontaneous regression in retinopathy of prematurity (ROP) and the range of retinal vascularization. MethodsA clinical retrospective study. A total of 82 eyes of 41 infants with ROP, who underwent FFA from January 2019 to December 2021 in Department of Ophthalmology of Xijing Hospital after completion of ROP regression, were included. There were 25 males (50 eyes) and 16 females (32 eyes). ROP was diagnosed in Zone Ⅱ in 44 eyes, with 38 eyes in stage 2 and 6 eyes in stage 3, and in zone Ⅲ in 38 eyes of stage 2. All patients underwent FFA examination under general anesthesia, at postmenstrual age of 70.70±12.25 weeks, after the natural regression of ROP was completed. Focus on the retinal vascular development, as well as choroid circulation and macular abnormalities, and compare and observe the differences between zone Ⅱ and Ⅲ after spontaneous regression. The extent of retinal vascularization was determined by the ratio between the distance of the center of the disc to the border of the vascularized zone (DB) and the center of the disc to the fovea distance (DF). The width of avascular area, recorded as the distance from the ora serrata to the vascular termination, was counted by disc diameters (DD). The measurement data between zone Ⅱ and zone Ⅲ ROP were compared by the independent sample t-test, and the count data were compared by χ2 test or Fisher exact probability test. ResultsThe linear choroidal pattern was present in 9 eyes (21.95%, 9/41), and the tortuous arteries in the posterior retina were detected in 32 eyes (39.02%, 32/82). It was noted that increased branching of vessels presented in 45 eyes (54.88%, 45/82), straight shape of vessels shown in 27 eyes (32.93%, 27/82), circumferential vessels arisen in 45 eyes (54.88%, 45/82), arteriovenous shunt appeared in 18 eyes (21.95%, 18/82), and capillary bed lost in 46 eyes (56.10%, 46/82) in areas from initial ridge to vascular termini. Punctate or linear dye leakage was observed in 23 eyes (28.05%, 23/82) during the late phase of FFA. Macular abnormalities, such as the absence of foveal avascular zone and hypoperfusion, were observed in 28 eyes (34.15%, 28/82), of which the macular ectopia presented in 1 eye. The mean DB/DF ratio of all the 82 eyes on the temporal side was 4.63±0.29 and 3.77±0.23 in the nasal. The mean avascular area on the temporal retina was 1.74±1.00 DD. Compared with ROP in zone Ⅲ, increased branching of vessels and dye leakage were more common (χ2=9.303, 10.774; P=0.002, 0.001), the extent of temporal retinal vascularization was smaller (t=－2.285, P=0.026), and the avascular area of the retina was more significant (t=5.491, P＜0.001) in zone Ⅱ ROP. ConclusionsEven after completion of spontaneous regression in ROP, incomplete retinal vascularization and vascular abnormalities may exist permanently in FFA, including those such as the tortuous arteries in the posterior retina, increased branching and straight shape of vessels, circumferential vessels, capillary bed lost and macular abnormality. Further appropriate follow-up is needed for long-term safety.