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Freeze Treatment Reduces Blindness in Premature Infants

March 29, 1988

Briefly freezing a portion of the eye’s surface can protect many premature infants against blindness from retinopathy of prematurity (ROP), a disease that causes visual loss in 2,600 infants in the United States annually. In a National Eye Institute-supported multicenter clinical trial, cryotherapy (freeze treatment) reduced the risk of severe visual loss by one-half in 172 babies with advanced ROP.

These findings, announced today by investigators at 23 medical centers participating in the Cryotherapy for Retinopathy of Prematurity (CRYO-ROP) Study, will be reported in the April issue of the Archives of Ophthalmology and the May issue of Pediatrics.

However, the study’s Data and Safety Monitoring Committee, which determined the safety and efficacy of the treatment, believed physicians who provide care for premature infants should be informed of these findings. Therefore, a “clinical alert” was mailed to 2,300 pediatric ophthalmologists, retinal specialists, neonatologists, and directors of neonatal intensive care centers in the United States on Feb. 12 conveying this message and recommending referral of potential patients to one of the studies participating clinics until a scientific paper presenting the study findings in detail could be prepared and published.

ROP, formerly called retrolental fibroplasia, is a potentially blinding disorder of very low birth-weight infants. It affects the developing blood vessels of the retina, the light-sensing tissue at the back of the eye, causing them to grow and branch excessively, leading to bleeding, scarring, or retinal detachment.

Cryotherapy applied to the sclera (white of the eye) near the front freezes the area of the eye without blood vessels and may stop the abnormal vessels from growing so excessively. It creates a ring of scar tissue and slows or stops the growth of these vessels, halting the progression of ROP. Retinal scarring from cryotherapy may cause some loss of the infant’s peripheral (side) vision, but does not affect the central part of the retina (the macula), responsible for the vision that will be needed for reading, writing and other everyday tasks.

Study investigators examined 3862 premature infants whose low birth weight put them at risk for ROP. In many of these infants, mild to moderate ROP developed and spontaneously subsided, leaving them without distortion of the critical central part of the retina. However, 291 infants developed severe ROP and, after the informed consent of their parents was obtained, were entered into the cryotherapy study. The preliminary results concern 172 of these infants.

All the premature infants enrolled in the CRYO-ROP Study were at least 28 days old, weighed less than 2.76 pounds at birth, had no other major eye or systemic abnormalities, and had ROP that had reached a threshold level of severity (“Stage 3 with plus’ disease” according to the International Classification of retinopathy of Prematurity) in at least on eye. Infants who had developed the threshold level of disease in only one eye were randomly assigned to receive cryotherapy in that eye or no eye treatment. If the second eye of the untreated babies developed threshold level ROP, then that eye was treated. For babies with threshold level ROP in both eyes at the time they entered the study, one eye was randomly assigned to cryotherapy, and in the other eye the disease process was monitored to determine its natural course. Therefore, all infants with two eyes eligible for treatment had the opportunity to receive cryotherapy in one eye.

Medical evaluation of all the babies in the CRYO-ROP study will continue and analyses of data on the long-term effects of cryotherapy for ROP will continue to be assessed over the next several years. Both short- and long-term evaluations of the treatment will provide valuable information about the natural course of ROP as well as about the visual prognosis of low birth-weight premature infants.

In assessing the impact of the CRYO-ROP results, Earl A. Palmer, M.D., study chairman and associate professor of ophthalmology and pediatrics, Oregon Health Sciences University, School of Medicine, said, “The findings from this study should greatly improve physicians’ ability to preserve the sight of small premature infants. To take full advantage of this capability, however, will require a new partnership among neonatologists, ophthalmologists and hospital neonatal care staff.”

Commenting on the significance of information announced from the CRYO-ROP study, Carl Kupfer, M.D., NEI director, said, “The National Eye Institute is pleased to have sponsored this very important study that provides physicians with new information that will help prevent blindness in our youngest children. This is yet another example of the importance of evaluating promising new therapies for progressive blinding eye diseases in a careful manner through well-designed clinical trials.”


Trans-scleral cryotherapy has been used to treat infants with ROP in the United States and other countries since 1972. However, the CRYO-ROP Study is the first multicenter randomized controlled clinical trial to evaluate scientifically the possible benefits and risks of this treatment.

The study’s findings represent the first significant advance in the treatment of ROP. An ROP epidemic occurred in the 1940s and early1950s when hospital nurseries began using excessively high levels of oxygen in incubators to save the lives of premature infants. In 1954, scientists with National Institutes of Health support conducted one of the first multicenter randomized controlled clinical trials in U.S.history to investigate the risks and benefits of oxygen therapy. The results of that study influenced the way oxygen has been used in the care of premature infant to the present day.

However, as advances in neonatal care in the 1970s and 1980s enabled the survival of very low birth-weight babies (those under 3.3 pounds), a second ROP epidemic has developed despite superb technology that regulates oxygen levels carefully. About the same number of infants lose their vision from ROP today as were blinded by the disease at the height of the epidemic in the 1940s and 1950s. While the causes of ROPare still not fully understood, cryotherapy now offers an opportunity to improve the visual prospects of many premature infants who develop ROP.

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  • Multicenter Trial of Cryotherapy for Retinopathy of Prematurity: Preliminary Results. Cryotherapy for Retinopathy of Prematurity Cooperative Group. Pediatrics. 1988 May. PubMed Pediatrics
  • Multicenter Trial of Cryotherapy for Retinopathy of Prematurity: Preliminary Results. Cryotherapy for Retinopathy of Prematurity Cooperative Group. Arch Ophthalmol. 1988 Apr. PubMed Arch Ophthalmol