Primer on Retinopathy of Prematurity

The World Health Organisation (WHO) estimates that over 15 million babies are born prematurely (generally agreed to be at less than 37 weeks) every year. This equates to 1.5 times the population of Belgium.

Premature babies are at an increased risk of complications due to the non-optimal gestation period afforded them. If blood vessels in the retina fail to develop fully, babies can be born with retinopathy of prematurity (ROP).

The retina is responsible for taking light that enters the eye and converting it into signals for the brain to interpret. They are supplied with blood through an extensive network of blood vessels that start to develop 16 weeks into pregnancy. Normally, it takes the full term (40 weeks) for the blood vessels to fully develop.

If this process is interrupted, it can leave the retina short of the blood vessels it requires to function properly. In order to make up for this deficiency, it may stimulate new blood vessels to grow. However, these are often weak and can lead to scarring and damaging of the retina. Severe ROP can also lead to retinal detachment.

In the UK, babies born under 32 weeks or at a weight of under 3lbs will be screened for potential ROP. Eye examinations will continue until the risk of needing treatment has passed.

Retinopathy of prematurity can be described in 5 stages:

• In stage 1, the new blood vessels have not started to grow and the mark between where blood vessels are present and not is flat. Usually recovery without treatment is possible at this stage.
• At stage 2, the mark between the two regions has become raised, but still no new blood vessels have begun to grow. It is still possible to recover without treatment at this stage but regular checkups to monitor the condition are recommended.
• Stage 3 is normally characterised by the growth of new vessels. These vessels are weak and can lead to scarring which may cause sight problems. Treatment is normally required at this stage.
• The new vessels that grew have begun to shrink and cause scarring in stage 4. This may start to pull the retina away from the back of the eye.
• During stage 5 the retina has fully detached and this would lead to permanent sight loss.

Treatment for retinopathy of prematurity most often involves the removal of the fragile new blood vessels that grow. This can be done with laser treatment, eye injections or cryotherapy.

If retinal detachment has begun, the patient may require surgery to help hold the retina to the back of the eye. Unfortunately, this needs to be done early during stage 4. If the condition has progressed to stage 5, it is unlikely that useful vision can be salvaged.