In ROP stage II, what happens at the demarcation margin?

In stage II of Retinopathy of Prematurity (ROP), a ridge is formed, which is a key characteristic of this stage. This ridge represents a significant change in the retinal tissue as the abnormal blood vessels and the accompanying edema create a structural alteration at the boundary of the avascular retina. The ridge forms as a result of the proliferation of the retinal neuroepithelial cells and the pulling of the vitreous body. This elevated demarcation line is important in understanding the progression of ROP, as its presence signifies that the condition is worsening but has not yet reached the more severe stages.

In contrast, at this stage, while new vessels may be present, they typically have not yet invaded the vitreous humor, and a visible demarcation line marks the transition area between normal and affected retina. Therefore, the focus is on the ridge's formation above the retinal plane, which is a critical factor for monitoring the progress of the disease.