The natural history of ROP and its classification

In the womb, the developing foetus is in a stable, warm, quiet, dark environment, suspended in fluid and able to move. And they are continuously supplied with the nutrients and oxygen they need via the umbilical cord. Achieving this level of stability in premature babies who have been ‘born too soon’ is a great challenge for the neonatal teams caring for premature babies.

Risk factors for ROP

The chances of a premature baby of developing retinopathy of prematurity (ROP) are increased if the baby is:

• Born extremely premature, that is born more than 8 weeks early with a gestational age of less than 32 weeks. These babies are most at risk as the more preterm the baby, the greater the risk.

• Born with a gestational age of 32-36 weeks (4 – 8 weeks premature) and they receive poor neonatal care.

• Born with a low birth weight (<1500g).

• Born with a higher birthweight but receive poor neonatal care.

• Given too much oxygen for too long. High blood oxygen levels damage the developing blood vessels in the retina.

A baby’s risk of ROP is also increased if they receive inadequate care during the first few weeks of life:

• Inadequate nutrition leading to poor weight gain.

• Infection.

• Anything that makes the baby unstable, such as pain, poor temperature control or not keeping the baby comfortable and supported in the cot or incubator.

Preventing blindness and visual impairment from ROP

Reducing the risk of ROP

To reduce the risk of ROP it is important to provide high quality care in neonatal units where:

• Staff members are adequately trained.

• There are enough staff members.

• There is adequate equipment to deliver and monitor oxygen.

• Mothers are encouraged to play a role in caring for their babies and giving them breast milk.

Identifying ROP disease and providing timely treatment

How ROP progresses – its natural history – is well understood and there are three important points to remember:

• ROP is not present at birth but starts a few weeks after birth.

• In a high proportion of babies who develop less severe stages of the disease it resolves spontaneously and no treatment is needed.

• However urgent treatment is essential once sight-threatening ROP (ST-ROP) develops.

The different stages of ROP disease were first defined in the 1984 international classification (revised in 2005). ROP is classified in four ways:

• Site – its location in the retina, which is classified into zones 1 to 3

• Severity, which is classified into 5 stages:

  • Stage 1: demarcation line between the vascular and avascular retina
  • Stage 2: raised ridge between the vascular and avascular retina
  • Stage 3: vascularised ridge
  • Stage 4a: subtotal retinal detachment – macular not detached
  • Stage 4b: subtotal retinal detachment – macular detached
  • Stage 5a: total retinal detachment – open funnel
  • Stage 5b: total retinal detachment – closed funnel

• Signs of active disease:

  • “plus” disease – retinal vessels in the posterior pole are dilated and tortuous in all 4 quadrants. The iris vessels may also be dilated, and the pupils difficult to dilate*
  • “pre-plus” diseases – the vessels are more dilated and tortuous than normal, but not enough to be called plus disease
• Aggressive posterior ROP (see next section)

*Poor pupil dilation is important, as it can make a detailed examination of the retina difficult. If the pupils fail to dilate the suspect the presence of plus disease.

The International classification of ROP is currently being updated by an international group of ROP experts, and this course will be updated once the revised version has been published.

Classifying ROP enables clinicians to predict which babies are most at risk of progression to vision-threatening disease and to intervene with appropriate treatment, in a timely manner. Reducing the risk of visual impairment and blindness from ROP in the neonatal unit requires screening – the systematic, timely examination of the eyes of all ‘at risk’ babies.

Watch the video on this step to learn more about the natural history and classification of ROP and how to screen for the disease. As you watch, consider how ROP screening is carried out in your setting or within your health system.