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Follow-up results from a study of premature babies with apotentially blinding condition confirm that a freezing treatmentapplied to their eyes helps save their sight. The follow-up resultsalso give researchers more information about how well the babies cansee in the years after cryotherapy, the freezing treatment.
“We have good evidence that this treatment significantlyreduces the number of infants who are blinded by retinopathy ofprematurity,” said study chairman Earl A. Palmer, M.D., of OregonHealth Sciences University. “However, some patients may have anincreased chance of having less-than-perfect vision after cryotherapy,”he added.
The latest findings are from a 5 1/2-year follow-up study of 291infants who had cryotherapy for the condition, called retinopathy ofprematurity (ROP), between January 1986 and January 1988. The infantswere in the multicenter trial of Cryotherapy for Retinopathy ofPrematurity (CRYO-ROP), which was sponsored by the National EyeInstitute of the National Institutes of Health (NIH). Results of thefollow-up study were published today in the April issue of the Archivesof Ophthalmology.
Current estimated figures for the United States show that more than4,000 premature babies weighing 3.3 pounds or less develop eye damageor vision loss from ROP each year. If cryotherapy were not available,750 of the babies with the severe form of the disease would becomelegally blind each year, according to researchers’ predictions. Withwidespread use of cryotherapy, a smaller number of babies, 400, becomeblind from the disease annually, researchers estimate. The CRYO-ROPstudy involved higher-risk babies who weighed only 2.75 pounds or lessat birth and had the severe form of the disease.
ROP occurs when, for unknown reasons, blood vessels that feed partsof the retina grow in excess and become misshapen after birth. Theretina is the light-sensing nerve tissue that lines the back of theeye and is crucial for normal vision. The abnormal blood vessels causebleeding and scarring that can make the retina peel away from the backof the eye.
Doctors performing cryotherapy use a cryoprobe—a hollowinstrument filled with refrigerant—to stop the growth of theabnormal blood vessels. They touch spots on the surface of the eyewith the probe, which reaches freezing temperatures. The surface ofthe eye is not permanently harmed, but the freezing temperaturedestroys the outer edge of the retina, stopping the growth of theabnormal blood vessels.
While some babies become blind from ROP, others achieve adequate orbetter vision if left untreated. In the years after CRYO-ROP,researchers evaluated the babies’ eyes that had been treated withcryotherapy and those that had not been treated to compare theirvision and structure.
For the first several years, some of the children could not read astandard eye chart because they could not recognize letters orcooperate. Researchers used other methods to test the children’svision until they were almost 6 years old.
For the 5 1/2-year follow-up study, researchers were able to test 75percent of the children using the standard eye chart. Vision of 20/40or better was considered to be in the normal range, and children withvision of 20/200, the legal definition of blindness, or worse wereconsidered blind. The study shows that 62 percent of the infants’ eyesthat were not treated with cryotherapy became blind, whereas 47percent of treated eyes became blind. This difference is statisticallysignificant.
The findings also suggest that cryotherapy might be associated withless-than-perfect vision. Twenty percent of untreated eyes now havevision of 20/40 or better, while
13 percent of treated eyes have vision in that range. Thisdifference is not statistically significant; in addition, 25 percentof the children could not be tested at the 5 1/2-year follow-up. Atthe next follow-up, researchers will include the children whom theypreviously could not test.
Because cryotherapy was shown to be so effective in preventingblindness, the National Eye Institute sent a nationwide clinical alertto physicians who care for premature infants when the study’s initialresults became available in 1988. Since then, the treatment has becomewidely used.
“These results clearly favor cryotherapy for more severe casesof ROP, but we may want to be cautious about treating less severe ROP,”said Carl Kupfer, M.D., director of the National Eye Institute. “Ifthe milder form of this disease is left untreated, most of thechildren will have healthy eyes and good vision later on. Cryotherapymight worsen their visual acuity without providing any benefit,”he added.
The researchers are preparing to perform another follow-up study ofthe children, who are now almost 10 years old. At that time, more ofthe children will have the skills required to take the standard eyechart test, and their visual systems will be more developed.Researchers will be able to investigate further the preliminarysuggestion that cryotherapy, while effective in preventing blindness,might be associated with an increased chance of less-than-perfectvision.
The 5 1/2-year follow-up examination also showed that cryotherapywas associated with benefits other than blindness prevention in ROP.Children’s eyes that had been treated had fewer of the abnormalities,such as cataract, often seen in severe cases of the condition. Manydoctors now use lasers instead of cryoprobes to stop ROP progression.Controversy exists over whether eyes treated with lasers are morelikely to develop cataract than are eyes treated with cryoprobes.
In another NIH-supported study, researchers estimated thatappropriate screening and treatment of ROP in premature infants wouldsave society between $38 million and $65 million a year in specialeducation, disability, and other costs, and in lost productivity.
The National Eye Institute is the Federal government’s lead agencyfor vision research, and supports more than 80 percent of such researchconducted in the United States.
Cryotherapy For Retinopathy of Prematurity (CRYO-ROP)
Frederick J. Elsas, M.D.
Alabama Ophthalmology Associates, P.C.
1000 - 19th Street South
Birmingham, Alabama 35205
Telephone: (205) 930-0700
District of Columbia
William S. Gilbert, M.D.
David Plotsky, M.D.
Michael T. Trese, M.D.
Edward G. Buckley, M.D.
Duke University Eye Center
Durham, North Carolina 27710
Telephone: (919) 684-6084
Gary L. Rogers, M.D.
Kenneth P. Cheng, M.D.
Wichard A. Van Heuven, M.D.
Ocular Pathology Center
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- Multicenter Trial of Cryotherapy for Retinopathy of Prematurity. Snellen Visual Acuity and Structural Outcome 5 1/2 Years After Randomization. Cryotherapy for Retinopathy of Prematurity Cooperative Group. Arch Ophthalmol. 1996 Apr. PubMed