Plus disease: this term refers to other ocular findings indicative of vascular activity. The most widely recognized feature of plus disease is posterior pole retinal venous dilation and arteriolar tortuosity (Figure 3A depicts 4-quadrant plus disease). The dilated and tortuous posterior pole vessels (Figures 3A-3C) develop as peripheral retinal vessels increase in caliber as a consequence of shunting in the periphery through ridge tissue. Additional features of plus disease include iris vascular engorgement in response to medication (rigid pupil) and vitreous haze (evident in Figure 3B). A prominent tunica vasculosa lentis (Figure 4) is also commonly noted in profoundly premature infants.
In the CRYO-ROP Study, plus disease was defined as significant dilation and tortuosity in all 4 vascular arcade quadrants.In subsequent studies (STOP-ROP and ETROP, see “ROP Clinical Trials”), and current practice, the diagnosis of plus disease is made if sufficient vascular dilation and tortuosity are present in at least 2 quadrants of the eye.