Retinopathy of prematurity, or ROP, happens when abnormal blood vessels start developing at the back of the eye of a premature baby.

Blood vessels that feed the retina finish forming just before a full-term baby is born.

"In a premature baby, these blood vessels have not finished forming and continue to do so after the baby is born. Most of the time, they will form normally, but if smaller, abnormal vessels start developing, the condition is called ROP," said Dr Cheryl Ngo, a consultant at the Eye Surgery Centre in the National University Hospital (NUH).

She said the incidence and severity of ROP rise with the degree of prematurity at birth, low gestational age and low birth weight.

If left untreated, the abnormal vessels can lead to bleeding and scarring in the retina.

They may also cause retinal detachment, where the retina separates or moves from its normal position in the eye, leading to poor vision or even blindness.

"It is important for the doctor to check the baby's eyes for any abnormal vessels. If these vessels are treated in time, it may help stop retinal detachment," Dr Ngo said.

The type of treatment depends on the baby's eye condition. The baby may need laser treatment, freezing treatment, injections in the eye or surgery to repair retinal detachment.

Dr Ngo said her centre screens premature babies for ROP every week.

"There have only been three cases requiring treatment in NUH over the past two years," she said.