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Freeze Treatment Reduces Blindness in Premature Infants

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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 infantsin the United States annually. In a National Eye Institute-supportedmulticenter clinical trial, cryotherapy (freeze treatment) reduced therisk of severe visual loss by one-half in 172 babies with advancedROP.

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, believedphysicians who provide care for premature infants should be informedof these findings. Therefore, a “clinical alert” was mailedto 2,300 pediatric ophthalmologists, retinal specialists,neonatologists, and directors of neonatal intensive care centers inthe United States on Feb. 12, conveying this message and recommendingreferral of potential patients to one of the study’sparticipating clinics until a scientific paper presenting the study’sfindings in detail could be prepared and published.

ROP, formerly called retrolental fibroplasia, is a potentiallyblinding disorder of very low birth-weight infants. It affects thedeveloping blood vessels of the retina, the light-sensing tissue atthe 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 frontfreezes the area of the eye without blood vessels and may stop theabnormal vessels from growing so excessively. It creates a ring ofscar tissue and slows or stops the growth of these vessels, haltingthe progression of ROP. Retinal scarring from cryotherapy may causessome loss of the infant’s peripheral (side) vision, but does notaffect the central part of the retina (the macula), responsible forvision that will be needed for reading, writing and other everydaytasks.

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 ofRetinopathy of Prematurity) in at least on eye. Infants who had developed the threshold level of disease in only one eye were randomlyassigned to receive cryotherapy in that eye or no eye treatment. Ifthe second eye of the untreated babies developed threshold level ROP,then that eye was treated. For babies with threshold level ROP in botheyes at the time they entered the study, one eye was randomly assignedto cryotherapy, and in the other eye the disease process was monitoredto determine its natural course. Therefore, all infants with two eyeseligible for treatment had the opportunity to receive cryotherapy inone 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. Bothshort- 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 andpediatrics, 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, willrequire a new partnership among neonatologists, ophthalmologists andhospital neonatal care staff.”

Commenting on the significance of information announced from theCRYO-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 yetanother example of the importance of evaluating promising newtherapies for progressive blinding eye diseases in a careful mannerthrough well-designed clinical trials.”


Trans-scleral cryotherapy has been used to treat infants with ROP inthe United States and other countries since 1972. However, theCRYO-ROP Study is the first multicenter randomized controlled clinicaltrial to evaluate scientifically the possible benefits and risks ofthis treatment.

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

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

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

March 1988