ROP Classification and Findings
The International Classification of ROP (ICROP) provides a widely accepted vocabulary describing the clinical features of ROP.
The original ICROP statement characterized ROP based on the location of retinal involvement by zone, stage (severity of retinopathy at the vascular/avascular junction), the extent of retinal involvement by clock-hour, and the presence or absence of dilated and tortuous posterior pole vessels (plus disease). Although pace of disease over time (or tempo, as suggested by the term “rush disease” for what is now known as aggressive posterior ROP, discussed further below) is an important feature of ROP, it is not included in the ICROP classification. The ICROP was later expanded in 1987 and 2005.
Location of Retinopathy: The retina is divided into three concentric circles or zones centered on the optic disc (Figure 1). The zones define the area of retina covered by physiologic retinal vascularization The lower the zone, the more severe the disease.
- Zone I: the posterior pole, consisting of a circle whose radius is twice the distance from the optic disc to the macula.
- Zone II: a doughnut-shaped area of retina that extends from the edge of zone I to a position tangential to the nasal ora serrata and around an area near the temporal anatomic equator.
- Zone III: the outermost residual crescent of retina anterior to zone II.
Extent of Retinopathy: The extent of disease is recorded as 12 clock-hours, with each clock-hour representing a 30° sector.
Severity of the Retinopathy: The severity of ROP is described in stages, which often progress sequentially. Stages 1 and 2 represent early ROP. Stage 3 is the vascular phase characterized by neovascularization extending from the ridge into the vitreous. Stages 4 and 5 ROP represent the cicatricial phases of ROP whereby contraction of fibrovascular proliferation results in retinal detachment.
The Committee for the Classification of Retinopathy of Prematurity. An international classification of retinopathy of prematurity. Arch Ophthal 1984;102:1130-1134.
International Committee for the Classification of Retinopathy of Prematurity. An international classification of retinopathy of prematurity, II: The classification of retinal detachment. Arch Ophthalmol 1987;105:906- 912.
International Committee for the Classification of Retinopathy of Prematurity. The International Classification of Retinopathy of Prematurity Revisited. Arch Ophthalmol 2005;123:991-999.