Classification
According to the International Classification of Retinopathy of Prematurity (1984, revised in 2005), ROP is classified in stages that are applicable to diagnosis, treatment and ocular prognosis:
Stage I: Mildly abnormal blood vessel growth; white demarcation line between vascularized and non-vascularized retina; usually gets better without any treatment and has no long-term effects.
Stage II: Moderately abnormal growth of retinal blood vessels; characterized by an elevated ridge rather than a flat demarcation line; neovascularization may be present posterior to the ridge; usually gets better without any treatment and has no long-term effects.
Stage III: Severely abnormal retinal vessel growth; protrusion of the extraretinal vessels from the ridge into the vitreous; may require treatment and has a higher risk of long-term vision problems. Infants with "plus" disease, a sign that ROP is advancing quickly, usually require treatment at this stage
Stage IV: Severely abnormal blood vessel growth and partial retinal detachment; usually requires treatment and may lead to long-term vision problems or blindness. At this stage, the retina may sometimes reattach spontaneously.
Stage V: Total retinal detachment which is funnel-shaped and may be either open or closed at the anterior and posterior ends; requires treatment and may lead to long-term vision problems or blindness.
The location of ROP is described in zones centered on the optic nerve (I-III).
The circumferential extent of the disease is based on the clock hours (1-12):
Zone I is the posterior zone of the retina, defined as the circle with a radius extending from the optic nerve to double the distance to the macula; any disease in zone I is critical and must be monitored closely.
Zone II is an annulus with the inner border defined by zone I and the outer border defined by the radius defined as the distance from the optic nerve to the nasal ora serrata; the disease may progress quickly but usually there are warning signs.
Zone III is the residual temporal crescent of the retina; the disease in this zone is usually inactive, with no ill sequelae.
"Plus" disease refers to severe tortuosity of the vessels, iris vascular engorgement, pupillary rigidity, and vitreous haze. "Pre-plus" disease is characterized by more arterial tortuosity and venous dilatation than normal but not severe enough to be classified as "plus disease". Rapidly progressing "plus" disease is sometimes referred to as Rush disease.
