Retinopathy of prematurity Retinopathy of prematurity plus 2018-02-19T20:17:35Z Venous dilatation and arteriolar tortuosity of the posterior retinal vessels and may later increase in severity to include iris vascular engorgement, poor pupillary dilatation (rigid pupil), and vitreous haze. This definition has been further refined in the later clinical trials in which the diagnosis of plus disease could be made if sufficient vascular dilatation and tortuosity are present in at least 2 quadrants of the eye. ROP plus