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Retinopathy of Prematurity Research

Retinopathy of prematurity (ROP) is an eye disease that causes abnormal blood vessels to grow in a baby’s retina (light-sensitive layer of tissue at the back of the eye). It happens in babies who are premature (born early) — or who weigh less than 3 pounds at birth. Some babies with ROP develop retinal detachment, which can cause vision loss.

Clinical studies funded by NEI provide doctors, patients, and caregivers with the information they need to make informed health care decisions. And the results of these studies help to direct future research on preventing vision loss from ROP.

Putting decades of eye health research into context

Scientific research is cumulative, with new breakthroughs advancing the field and changing the landscape. And given NEI’s long history of research, results that were groundbreaking decades ago may be less directly relevant today. The studies showcased here represent landmarks in eye health research that laid the groundwork the treatments, diagnostic tools, and prevention options that exist today.


In 1986, researchers started the NEI-funded Cryotherapy for Retinopathy of Prematurity (CRYO-ROP, NCT00000133) Trial to measure the effectiveness of cryotherapy (freeze treatment) to prevent vision loss in babies with ROP. The trial recruited 279 babies with stage 3 ROP. Some babies with stage 3 ROP get better on their own, but some need treatment to prevent vision loss. The babies were randomly assigned to receive either cryotherapy or no treatment.

The CRYO-ROP Trial showed that cryotherapy could prevent vision loss in babies with ROP — without risking their ability to see in the future. It established cryotherapy as a safe and effective treatment for ROP at the time. The trial also highlighted the need for long-term follow-up, since researchers didn’t see the full picture of eye health outcomes until they collected findings 10 and 15 years after the trial began.


In 1994, researchers started the NEI-funded Supplemental Therapeutic Oxygen for Prethreshold Retinopathy of Prematurity (STOP-ROP, NCT01203436) Trial to find out what effect, if any, supplemental oxygen therapy had on how ROP progressed in premature babies. The trial recruited 649 premature babies with moderate ROP and oxygen saturation below 94% and randomly assigned them to 1 of 2 groups:

  • The treatment group got supplemental oxygen for at least 2 weeks
  • The control group didn’t get supplemental oxygen

The STOP-ROP Trial showed that supplemental oxygen doesn’t cause moderate ROP to progress to severe ROP — so there’s no need to restrict use of oxygen therapy if babies with moderate ROP need it. This finding helped doctors and parents make more informed decisions about oxygen therapy for premature babies.

Light-ROP Trial

In 1995, researchers started the Effects of Light Reduction on Retinopathy of Prematurity (Light-ROP, NCT00000156) Trial to measure the effects of reduced light exposure in babies with ROP. This NEI-funded trial recruited 409 premature babies at high risk for ROP and randomly assigned them to 1 of 2 groups:

  • The treatment group wore goggles to reduce light exposure for 4 weeks after birth or until 31 weeks after conception
  • The control group was exposed to typical hospital nursery lighting

The Light-ROP Trial was the first randomized controlled trial with a large enough sample size to provide strong evidence that light exposure doesn’t significantly raise ROP risk. Because of these results, researchers were able to move forward and look into other risk factors for ROP.


In 2001, researchers started the NEI-funded Early Treatment for Retinopathy of Prematurity (ETROP, NCT00027222) Trial to measure the effects of early treatment in premature babies at high risk of a severe type of ROP (Type 1). The trial recruited 401 premature babies with ROP who were at high risk of developing a severe form of the disease and then randomly assigned them to 1 of 2 groups:

  • A group that received treatment for ROP earlier than the current standard of care
  • A group that received treatment based on the current standard of care

The ETROP Trial monitored the babies for 6 years and showed that babies with severe ROP who were treated early had a lower risk of legal blindness than those who received treatment at the standard time. This trial also showed that babies with a less-severe type of ROP (Type 2) didn’t have better vision outcomes after early treatment — helping doctors make informed decisions about when to prescribe early treatment for babies with ROP.

e-ROP Trial

In 2011, researchers started the NEI-funded Telemedicine Approaches to Evaluating Acute-phase ROP (e-ROP, NCT01264276) Trial to measure the effectiveness of telemedicine as a screening tool for babies at risk for ROP. The trial recruited 1,257 premature babies. It evaluated if staff at a remote image reading center could use photos of babies’ eyes to identify babies with suspected ROP as accurately as ophthalmologists examining babies in person.

The e-ROP Trial was the first large study to test if trained medical staff who aren’t doctors could use a telemedicine approach to screen for ROP. The trial’s telemedicine approach performed almost as well as onsite ophthalmologists at identifying ROP in premature babies. And the added convenience and expanded access to screening helped identify babies with advanced ROP earlier.

Last updated: July 14, 2023