Which phase of retinopathy of prematurity is characterized by proliferation of retinal vessels in response to markedly elevated VEGF and erythropoietin?

• A. Phase 2
• B. Phase 1
• C. Phase 3
• D. Phase 4

Answer: (A)

The key idea is the proliferative response driven by retinal hypoxia. In this stage of retinopathy of prematurity, the immature retina becomes relatively hypoxic after the initial period of vessels failing to grow or regressing (vaso-obliteration). In response to low oxygen, the retina upregulates pro-angiogenic factors, notably vascular endothelial growth factor and erythropoietin, which stimulate new vessel growth. This neovascular proliferation tends to extend into the vitreous and can form fibrovascular membranes, setting the stage for potential traction and retinal detachment if not managed.

Phases following this proliferative period involve more advanced structural changes, such as more extensive fibrovascular proliferation and detachment, which are not characterized primarily by the VEGF/EPO-driven neovascular surge described here. So the phase described—proliferation of retinal vessels in response to markedly elevated VEGF and erythropoietin—fits the proliferative phase.