The rationale for cryotherapy with a prophylactic scleral buckle for Zone I threshold retinopathy of prematurity.

Our current surgical protocol for Zone I threshold retinopathy of prematurity (ROP) has evolved over 15 years and is rationalized by increasing knowledge of two pathologic processes of ROP: 1) angiogenic stimulation of spindle cells (clinically invisible) near the vitreal surface of the avascular retina; and 2) tractional forces of myofibroblasts [clinically visible as extraretinal fibrovascular proliferation (EFP)] in the vitreous overlying the vascular retina. These two pathologic processes occur concomitantly with normal anterior ocular growth with a constant optic disc-macular distance. Our current surgical protocol for Zone I threshold ROP, involves complex surgeries to achieve success defined as a macula which always remains anatomically attached, but which may be distorted or ectopic. This protocol requires cryotherapy in at least two sessions. The first is to the avascular retina to destroy spindle cells. The second is to the EFP to destroy myofibroblasts and to the shunt to eliminate the site of origin of myofibroblasts. The protocol also requires the concomitant placement of a prophylactic scleral buckle to allow formation of a new complete ora serrata while remnant myofibroblasts contract and while anterior ocular growth continues.