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 Resource Guide
Retinopathy of Prematurity (ROP)

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The information provided in this Resource Guide was developed by the National Eye Institute to help patients and their families search for general information about early treatment for retinopathy of prematurity study (ETROP). An eye care professional who has examined the patient's eyes and is familiar with his or her medical history is the best person to answer specific questions.

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Other Names

retrolental fibroplasia

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What is retinopathy of prematurity?

Retinopathy of prematurity (ROP) is a potentially blinding eye disorder that primarily affects premature infants weighing about 2¾ pounds (1250 grams) or less that are born before 31 weeks of gestation (A full-term pregnancy has a gestation of 38–42 weeks). The smaller a baby is at birth, the more likely that baby is to develop ROP. This disorder—which usually develops in both eyes—is one of the most common causes of visual loss in childhood and can lead to lifelong vision impairment and blindness. ROP was first diagnosed in 1942.

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How many infants have ROP?

Today, with advances in neonatal care, smaller and more premature infants are being saved. These infants are at a much higher risk for ROP. Not all babies who are premature develop ROP. There are approximately 3.9 million infants born in the U.S. each year; of those, about 28,000 weigh 2¾ pounds or less. About 14,000–16,000 of these infants are affected by some degree of ROP. The disease improves and leaves no permanent damage in milder cases of ROP. About 90 percent of all infants with ROP are in the milder category and do not need treatment. However, infants with more severe disease can develop impaired vision or even blindness. About 1,100–1,500 infants annually develop ROP that is severe enough to require medical treatment. About 400–600 infants each year in the US become legally blind from ROP.

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What causes ROP?

ROP occurs when abnormal blood vessels grow and spread throughout the retina, the tissue that lines the back of the eye. These abnormal blood vessels are fragile and can leak, scarring the retina and pulling it out of position. This causes a retinal detachment. Retinal detachment is the main cause of visual impairment and blindness in ROP.

Several complex factors may be responsible for the development of ROP. The eye starts to develop at about 16 weeks of pregnancy, when the blood vessels of the retina begin to form at the optic nerve in the back of the eye. The blood vessels grow gradually toward the edges of the developing retina, supplying oxygen and nutrients. During the last 12 weeks of a pregnancy, the eye develops rapidly. When a baby is born full-term, the retinal blood vessel growth is mostly complete (The retina usually finishes growing a few weeks to a month after birth). But if a baby is born prematurely, before these blood vessels have reached the edges of the retina, normal vessel growth may stop. The edges of the retina—the periphery—may not get enough oxygen and nutrients.

Scientists believe that the periphery of the retina then sends out signals to other areas of the retina for nourishment. As a result, new abnormal vessels begin to grow. These new blood vessels are fragile and weak and can bleed, leading to retinal scarring. When these scars shrink, they pull on the retina, causing it to detach from the back of the eye.

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Are there different stages of ROP?

Yes. ROP is classified in five stages, ranging from mild (stage I) to severe (stage V):

Stage I — Mildly abnormal blood vessel growth. Many children who develop stage I improve with no treatment and eventually develop normal vision. The disease resolves on its own without further progression.

Stage II — Moderately abnormal blood vessel growth. Many children who develop stage II improve with no treatment and eventually develop normal vision. The disease resolves on its own without further progression.

Stage III — Severely abnormal blood vessel growth. The abnormal blood vessels grow toward the center of the eye instead of following their normal growth pattern along the surface of the retina. Some infants who develop stage III improve with no treatment and eventually develop normal vision. However, when infants have a certain degree of Stage III and "plus disease" develops, treatment is considered. "Plus disease" means that the blood vessels of the retina have become enlarged and twisted, indicating a worsening of the disease. Treatment at this point has a good chance of preventing retinal detachment.

Stage IV — Partially detached retina. Traction from the scar produced by bleeding, abnormal vessels pulls the retina away from the wall of the eye.

Stage V — Completely detached retina and the end stage of the disease. If the eye is left alone at this stage, the baby can have severe visual impairment and even blindness.

Most babies who develop ROP have stages I or II. However, in a small number of babies, ROP worsens, sometimes very rapidly. Untreated ROP threatens to destroy vision.

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How is ROP treated?

The most effective proven treatments for ROP are laser therapy or cryotherapy. Laser therapy "burns away" the periphery of the retina, which has no normal blood vessels. With cryotherapy, physicians use an instrument that generates freezing temperatures to briefly touch spots on the surface of the eye that overlie the periphery of the retina. Both laser treatment and cryotherapy destroy the peripheral areas of the retina, slowing or reversing the abnormal growth of blood vessels. Unfortunately, the treatments also destroy some side vision. This is done to save the most important part of our sight—the sharp, central vision we need for "straight ahead" activities such as reading, sewing, and driving.

Both laser treatments and cryotherapy are performed only on infants with advanced ROP, particularly stage III with "plus disease." Both treatments are considered invasive surgeries on the eye, and doctors don't know the long-term side effects of each.

In the later stages of ROP, other treatment options include:

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What happens if treatment does not work?

While ROP treatment decreases the chances for vision loss, it does not always prevent it. Not all babies respond to ROP treatment, and the disease may get worse. If treatment for ROP does not work, a retinal detachment may develop. Often, only part of the retina detaches (stage IV). When this happens, no further treatments may be needed, since a partial detachment may remain the same or go away without treatment. However, in some instances, physicians may recommend treatment to try to prevent further advancement of the retinal detachment (stage V). If the center of the retina or the entire retina detaches, central vision is threatened, and surgery may be recommended to reattach the retina.

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Are there other risk factors for ROP?

In addition to birth weight and how early a baby is born, other factors contributing to the risk of ROP include anemia, blood transfusions, respiratory distress, breathing difficulties, and the overall health of the infant.

An ROP epidemic occurred in the 1940s and early 1950s when hospital nurseries began using excessively high levels of oxygen in incubators to save the lives of premature infants. During this time, ROP was the leading cause of blindness in children in the US. In 1954, scientists funded by the National Institutes of Health determined that the relatively high levels of oxygen routinely given to premature infants at that time were an important risk factor, and that reducing the level of oxygen given to premature babies reduced the incidence of ROP. With newer technology and methods to monitor the oxygen levels of infants, oxygen use as a risk factor has diminished in importance.

Although it had been suggested as a factor in the development of ROP, researchers supported by the National Eye Institute determined that lighting levels in hospital nurseries has no effect on the development of ROP.

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Can ROP cause other complications?

Yes. Infants with ROP are considered to be at higher risk for developing certain eye problems later in life, such as retinal detachment, myopia (nearsightedness), strabismus (crossed eyes), amblyopia (lazy eye), and glaucoma. In many cases, these eye problems can be treated or controlled.

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NEI-Supported Research

The NEI-supported clinical studies on ROP include:

The Cryotherapy for Retinopathy of Prematurity (CRYO-ROP)-Outcome Study of Cryotherapy for Retinopathy of Prematurity Study examined the safety and effectiveness of cryotherapy (freezing treatment) of the peripheral retina in reducing the risk of blindness in certain low birth-weight infants with ROP. Follow-up results confirm that applying a freezing treatment to the eyes of premature babies with ROP helps save their sight. The follow-up results also give researchers more information about how well the babies can see in the years after cryotherapy. Read more about the CRYO-ROP study.

The Effects of Light Reduction on Retinopathy of Prematurity (Light-ROP) Study evaluated the effect of ambient light reduction on the incidence of ROP. The study determined that light reduction has no effect on the development of a potentially blinding eye disorder in low birthweight infants. The study determined that light reduction in hospital nurseries has no effect on the development of ROP. Read more about the Light-ROP study.

The Supplemental Therapeutic Oxygen for Prethreshold Retinopathy of Prematurity (the STOP-ROP) Multicenter Trial tested the efficacy, safety, and costs of providing supplemental oxygen in moderately severe retinopathy of prematurity (prethreshold ROP). Results showed that modest supplemental oxygen given to premature infants with moderate cases of ROP may not significantly improve ROP, but definitely does not make it worse. Read more about the STOP-ROP study.

The Early Treatment for Retinopathy of Prematurity Study (ETROP) is designed to determine whether earlier treatment in carefully selected cases of ROP will result in an overall better visual outcome than treatment at the conventional disease threshold point used in the CRYO-ROP study. Read more about the ETROP study.

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Other Resources

The following organizations may be able to provide additional information on retinopathy of prematurity:

American Association for Pediatric Ophthalmology and Strabismus
P.O. Box 193832
San Francisco, CA 94119-3832
(415) 561-8505
Dedicated to ensuring quality medical and surgical eye care of children and adults with strabismus. Provides information on common eye problems including strabismus, amblyopia, retinopathy of prematurity, conjunctivitis, and learning disabilities. Offers a website tool to help people find pediatic ophthalmologists in their local areas.

Association for Retinopathy of Prematurity and Related Diseases (ROPARD)
P.O. Box 250425
Franklin, MI 48025
Dedicated to eliminating the problems of low vision and blindness in children caused by premature birth and retinal disease, by funding clinical research to understand, treat, and prevent retinopathy of prematurity (ROP) and related retinal diseases. Funds innovative work on the development of new low vision devices, teaching techniques and services for children who are visually impaired and their families.

National Eye Institute (NEI)
31 Center Drive MSC 2510
Bethesda, MD 20892-2510
(301) 496-5248
Conducts and supports research on eye diseases and vision disorders. Offers free publications for the general public and patients.

For additional information, you may also wish to contact a local library.

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Medical Literature

Below is a sample of the citations available through MEDLINE/PubMed, a service of the National Library of Medicine. MEDLINE/PubMed provides access to over 11 million medical literature citations from 1966 to the present and includes links to many sites providing full text articles and other related resources. You can conduct your own free literature search by accessing MEDLINE through the Internet at You can also get assistance with a literature search at a local library.

To obtain copies of any of the articles listed below, contact a local community, university, or medical library. If the library you visit does not have a copy of a desired article, you may usually obtain it through an inter-library loan.

Please keep in mind that articles in the medical literature are usually written in technical language. We encourage you to share any articles you order with a health care professional who can help you understand them.

Retinopathy of prematurity. Stout AU, Stout JT. Casey Eye Institute, 3375 Southwest Terwilliger, Portland, OR 97201, USA. Pediatr Clin North Am 50(1):77–87, vi, 2003.
Retinopathy of prematurity (ROP) is a relatively new condition. Only in the last 60 years have children survived who were born prematurely enough to have a significantly immature retinal vasculature. This article describes the classification and physiology of ROP, the interventions now available, and possible future therapies.

Implications of the natural course of retinopathy of prematurity. Palmer EA. Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239-4197, USA. Pediatrics 111(4 Pt 1):885–6, 2003. (Commentary)
Laser therapy has become the preferred treatment modality for ROP in the United States and many other countries. Because this is effective in improving vision outcomes of severely affected cases, there is a natural eagerness to treat threatening ROP earlier than was done in the Multicenter Trial of Cryotherapy and Outcome Study of Retinopathy of Prematurity (CRYO-ROP). Many formerly debatable cases are now being treated. The optimal indications for this treatment are undergoing professional discussion and formal study.

Ophthalmological problems of the premature infant. Repka MX. Department of Ophthalmology, Department of Pediatrics, Johns Hopkins University, Baltimore, Maryland 21287-9028, USA. Ment Retard Dev Disabil Res Rev 8(4):249–57, 2002.
Preterm infants are more likely than term infants to have significant abnormalities of all parts of the visual system leading to reduced vision. The most common problem is retinopathy of prematurity (ROP). The frequency and severity of this disorder is inversely related to gestational age. Damage ranges from minor to catastrophic. Preterm infants also have higher rates of amblyopia, strabismus, refractive error, and cortical visual impairment. The later problem is largely associated with neonatal brain injury. Years later, these children may develop glaucoma and retinal detachments.

Retinopathy of prematurity. Good WV, Gendron RL. Smith Kettlewell Eye Research Institute, San Francisco, California, USA. Ophthalmol Clin North Am 14(3):513–9, 2001.
The majority of cases of ROP regress spontaneously, but better treatment methods are needed to prevent retinal detachment and other effects of ROP such as myopia. In the future, molecular mechanisms may be exploited to treat ROP.

The management of retinopathy of prematurity. Reynolds JD. State University of New York at Buffalo, Children's Hospital, 14222, USA. Paediatr Drugs. 3(4):263–72, 2001.
Retinopathy of prematurity (ROP) is a major problem in both highly developed countries and countries with emerging technology. The incidence of ROP has been stable over the last 2 decades despite improvements in neonatology. Threshold ROP occurs in about 5% of premature infants in the US with birthweights <1.25kg. Despite improvements in neonatology, ROP, potentially leading to blindness, continues to be a common problem associated with prematurity. Future management success must concentrate on discovering new modes of treatment, especially prevention.

The National Eye Institute (NEI) conducts and supports research that leads to sight-saving treatments and plays a key role in reducing visual impairment and blindness. The NEI is part of the National Institutes of Health (NIH), an agency of the U.S. Department of Health and Human Services.

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This page was last modified in April 2005

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