Unifying Concepts

International Classification of Retinopathy of Prematurity

The International Classification of Retinopathy of Prematurity (ICROP) was published in 2 parts, the first in 1984 and later expanded in 1987. It was a consensus statement of an international group of retinopathy of prematurity experts.

Retinopathy of Prematurity (ROP)
Four features are evaluated: zone, stage, extent, and presence or absence of plus disease.

Location of disease
The location of the retinopathy within the retina is defined by dividing the eye into three zones, centered on the optic nerve:

  • Zone 1, the central zone at the posterior pole of the eye, has a radius of twice the distance from the optic disc to the macula and subtending an arc of 60 degrees centered on the disc.
  • Zone 2 forms a circle outside zone 1 with a radius from the optic nerve to the nasal ora serrata.
  • Zone 3 is the remaining temporal crescent of retina.

Staging the disease
Stage 1: Demarcation line
Stage 2: Ridge
Stage 3: Ridge with extraretinal fibrovascular proliferation
Stage 4: Subtotal retinal detachment

A. Extrafoveal
B. Retinal detachment including fovea

Stage 5: Total retinal detachment

A is an open funnel.
B is a closed funnel.

Extent of disease
The extent of disease is described by dividing the retinal surface into 30º sectors, similar to the hours of a clock. As many as 12 clock hours can be affected, and the stage of retinopathy can vary among sectors.

Plus disease

Plus disease refers to dilation and tortuosity of the retinal arterioles and venules in the posterior pole of the retina as defined by a standard photograph. This indicates severe ROP, perhaps caused by excessive shunting of blood through the neovascular tissue at the ridge and often is followed by rapid progression to retinal detachment. Plus disease also may be a direct effect of excessive vascular endothelial growth factor (VEGF) acting on retinal blood vessels. Vitreous haze, engorgement of the iris vessels, and poor dilation of the pupil sometimes accompany plus disease, and often heralds rapid progression with poor prognosis.
Pre-plus disease is defined as dilation and tortuosity of the posterior pole arterioles and venules that are insufficient for the diagnosis of plus disease. It is the precursor to plus disease and in one study predicted progression to severe ROP that required treatment.

Involutional Sequelae Retinopathy of Prematurity

Peripheral Changes


  1. Failure to vascularize peripheral retina
  2. Abnormal, nondichotomous branching of retinal vessels
  3. Vascular arcades with circumferential interconnection
  4. Telangiectatic vessels


  1. Pigmentary changes
  2. Vitreoretinal interface changes
  3. Thin retina
  4. Peripheral folds
  5. Vitreous membranes with or without attachment to retina
  6. Latticelike degeneration
  7. Retinal breaks
  8. Traction /rhegmatogenous retinal detachment

Posterior Changes

  1. Vascular tortuosity
  2. Straightening of blood vessels in temporal arcade
  3. Decrease in angle of insertion of major temporal arcade


  1. Pigmentary changes
  2. Distortion and ectopia of macula
  3. Stretching and folding of retina in macular region leading to periphery
  4. Vitreoretinal interface changes
  5. Vitreous membrane
  6. Dragging of retina over disc
  7. Traction/rhegmatogenous retinal detachment



  1. International Committee for the Classification of Retinopathy of Prematurity. The International Classification of Retinopathy of Prematurity revisited. Arch Ophthalmol. 2005 Jul;123(7):991-9. [Medline]
  2. Committee for the Classification of Retinopathy of Prematurity. An International Classification of Retinopathy of Prematurity. Arch Ophthalmol. 1984;102:1130-1134.  [Medline]
  3. Committee for Classification of Late Stages ROP. An international classification of retinopathy of prematurity, II: the classification of retinal detachment. Arch Ophthalmol. 1987;105:906-912. [Medline]


Created: Jul 08, 2010

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