Follow-up results from a study of premature babies with a potentially blinding condition confirm that a freezing treatment applied to their eyes 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, the freezing treatment.
“We have good evidence that this treatment significantly reduces the number of infants who are blinded by retinopathy of prematurity,” said study chairman Earl A. Palmer, M.D., of OregonHealth Sciences University. “However, some patients may have an increased 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 291 infants who had cryotherapy for the condition, called retinopathy of prematurity (ROP), between January 1986 and January 1988. The infants were in the multi-center trial of Cryotherapy for Retinopathy of Prematurity (CRYO-ROP), which was sponsored by the National EyeInstitute of the National Institutes of Health (NIH). Results of the follow-up study were published today in the April issue of the Archives of Ophthalmology.
Current estimated figures for the United States show that more than 4,000 premature babies weighing 3.3 pounds or less develop eye damage or vision loss from ROP each year. If cryotherapy were not available,750 of the babies with the severe form of the disease would become legally blind each year, according to researchers’ predictions. With widespread use of cryotherapy, a smaller number of babies, 400, become blind from the disease annually, researchers estimate. The CRYO-ROP study involved higher-risk babies who weighed only 2.75 pounds or less at birth and had the severe form of the disease.
ROP occurs when, for unknown reasons, blood vessels that feed parts of the retina grow in excess and become misshapen after birth. The retina is the light-sensing nerve tissue that lines the back of the eye and is crucial for normal vision. The abnormal blood vessels cause bleeding and scarring that can make the retina peel away from the back of the eye.
Doctors performing cryotherapy use a cryoprobe—a hollow instrument filled with refrigerant—to stop the growth of the abnormal blood vessels. They touch spots on the surface of the eye with the probe, which reaches freezing temperatures. The surface of the eye is not permanently harmed, but the freezing temperature destroys the outer edge of the retina, stopping the growth of the abnormal blood vessels.
While some babies become blind from ROP, others achieve adequate or better vision if left untreated. In the years after CRYO-ROP, researchers evaluated the babies’ eyes that had been treated with cryotherapy and those that had not been treated to compare their vision and structure.
For the first several years, some of the children could not read a standard eye chart because they could not recognize letters or cooperate. Researchers used other methods to test the children’s vision 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 with vision of 20/200, the legal definition of blindness, or worse were considered blind. The study shows that 62 percent of the infants’ eyes that were not treated with cryotherapy became blind, whereas 47percent of treated eyes became blind. This difference is statistically significant.
The findings also suggest that cryotherapy might be associated with less-than-perfect vision. Twenty percent of untreated eyes now have vision of 20/40 or better, while
13 percent of treated eyes have vision in that range. This difference is not statistically significant; in addition, 25 percent of the children could not be tested at the 5 1/2-year follow-up. At the next follow-up, researchers will include the children whom they previously could not test.
Because cryotherapy was shown to be so effective in preventing blindness, the National Eye Institute sent a nationwide clinical alert to physicians who care for premature infants when the study’s initial results became available in 1988. Since then, the treatment has become widely used.
“These results clearly favor cryotherapy for more severe cases of ROP, but we may want to be cautious about treating less severe ROP,”said Carl Kupfer, M.D., director of the National Eye Institute. “If the milder form of this disease is left untreated, most of the children will have healthy eyes and good vision later on. Cryotherapy might worsen their visual acuity without providing any benefit,”he added.
The researchers are preparing to perform another follow-up study of the children, who are now almost 10 years old. At that time, more of the children will have the skills required to take the standard eye chart test, and their visual systems will be more developed.Researchers will be able to investigate further the preliminary suggestion 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 cryotherapy was 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. Many doctors now use lasers instead of cryoprobes to stop ROP progression.Controversy exists over whether eyes treated with lasers are more likely to develop cataract than are eyes treated with cryoprobes.
In another NIH-supported study, researchers estimated that appropriate screening and treatment of ROP in premature infants would save society between $38 million and $65 million a year in special education, disability, and other costs, and in lost productivity.
The National Eye Institute is the Federal government’s lead agency for vision research, and supports more than 80 percent of such research conducted in the United States.
Cryotherapy For Retinopathy of Prematurity (CRYO-ROP) Participants List
- Alabama
- Frederick J. Elsas, M.D.
Alabama Ophthalmology Associates, P.C.
1000 - 19th Street South
Birmingham, Alabama 35205
Telephone: (205) 930-0700 - California
- Alan M. Roth, M.D.
Department of Ophthalmology
University of California at Davis Medical Center
1603 Alhambra Boulevard
Sacramento, California 95816
Telephone: (916) 734-6078 - District of Columbia
- William S. Gilbert, M.D.
Childrens Hospital National Medical Center
Retina Group of Washington
5454 Wisconsin Avenue, Suite 1540
Chevy Chase, Maryland 20815
Telephone: (301) 656-8100 - David Plotsky, M.D.
650 Pennsylvania Avenue, S.E.
Suite 270
Washington, D.C. 20003
Telephone: (202) 544-1900 - Florida
- R. Michael Siatkowski, M.D.
Bascom Palmer Eye Institute
University of Miami School of Medicine
900 N.W. 17th Street
P.O. Box 016880
Miami, Florida 33136
Telephone: (305) 326-6019 - Illinois
- Marilyn T. Miller, M.D.
University of Illinois Eye and Ear Infirmary
1855 West Taylor Street, Room 1.44
Chicago, Illinois 60612
Telephone: (312) 996-7445 - Indiana
- Forrest D. Ellis, M.D.
Department of Ophthalmology
Indiana University School of Medicine
702 Rotary Circle
Indianapolis, Indiana 46202
Telephone: (317) 274-1214 - Kentucky
- Charles C. Barr, M.D.
Kentucky Lions Eye Research Institute
University of Louisville
301 East Muhammad Ali Boulevard
Louisville, Kentucky 40292
Telephone: (502) 852-5470 - Louisiana
- Robert A. Gordon, M.D.
Department of Ophthalmology
Tulane University
School of Medicine
1430 Tulane Avenue
New Orleans, Louisiana 70112
Telephone: (504) 588-5804 - Maryland
- Michael X. Repka, M.D.
Wilmer Ophthalmological Institute
The Johns Hopkins Medical Institutions
Wilmer Building, Room B1-35
600 North Wolfe Street
Baltimore, Maryland 21287-9009
Telephone: (410) 955-8314 - Michigan
- John D. Baker, M.D.
2355 Monroe Boulevard
Dearborn, Michigan 48124
Telephone: (313) 561-1777 - Michael T. Trese, M.D.
Associated Retinal Consultants, P.C.
3535 West Thirteen Mile Road, Room 632
Royal Oak, Michigan 48073
Telephone: (313) 288-2280 - Minnesota
- C. Gail Summers, M.D.
Department of Ophthalmology
University of Minnesota
Phillips-Wangensteen Bldg., 9-240
Box 493, 420 Delaware Street, S.E.
Minneapolis, Minnesota 55455-0591
Telephone: (612) 625-4400 - New York
- Dale L. Phelps, M.D.
Box 651, Neonatology
University of Rochester SOM
601 Elmwood Avenue
Rochester, New York 14642
Telephone: (716) 275-5884 - North Carolina
- Edward G. Buckley, M.D.
Duke University Eye Center
Box 3802
Durham, North Carolina 27710
Telephone: (919) 684-6084 - Ohio
- Miles J. Burke, M.D.
Department of Ophthalmology
Childrens Hospital Medical Center
Pavilion 2-80
3333 Burnet Avenue
Cincinnati, Ohio 45229-3039
Telephone: (513) 559-4751 - Gary L. Rogers, M.D.
Don L. Bremer, M.D.
Columbus Childrens Hospital
(Office Address) 555 South 18th Street
Columbus, Ohio 43205
Telephone: (614) 224-6222 - Oregon
- Earl A. Palmer, M.D.
Oregon Health Sciences University
Casey Eye Institute
3375 S.W. Terwilliger Boulevard
Portland, Oregon 97201-4197
Telephone: (503) 494-5945 - Pennsylvania
- Graham E. Quinn, M.D.
David B. Schaffer, M.D.
Children’s Hospital of Philadelphia
Division of Pediatric Ophthalmology
One Children’s Center
Philadelphia, Pennsylvania 19104
Telephone: (215) 590-2791 - Kenneth P. Cheng, M.D.
Pediatric Ophthalmology & Strabismus
3518 Fifth Avenue
Pittsburgh, Pennsylvania 15213-3387
Telephone: (412) 682-6300 - South Carolina
- Richard A. Saunders, M.D.
Storm Eye Institute
Medical University of South Carolina
171 Ashley Avenue
Charleston, South Carolina 29425-2236
Telephone: (803) 792-2761 - Tennessee
- Stephen S. Feman, M.D.
Department of Ophthalmology
Vanderbilt University Medical Center
8000 Medical Center East
Nashville, Tennessee 37232-8808
Telephone: (615) 936-2020 - Texas
- Rand Spencer, M.D.
7150 Greenville Ave., Suite 400
Dallas, Texas 75231
Telephone: (214) 821-4540 - Wichard A. Van Heuven, M.D.
Department of Ophthalmology
University of Texas Health Science Center
7703 Floyd Curl Drive
San Antonio, Texas 78284-6230
Telephone: (210) 567-8400 - Utah
- Robert O. Hoffman, M.D.
Department of Ophthalmology
John Moran Eye Center
50 North Medical Drive
Salt Lake City, Utah 84132
Telephone: (801) 581-4955
Resource Centers
- Chairman’s Office
- Earl A. Palmer, M.D.
Casey Eye Institute
3375 S.W. Terwilliger Boulevard
Portland, Oregon 97201-4197
Telephone: (503) 494-5945 - Coordinating Center
- Robert J. Hardy, Ph.D.
School of Public Health
University of Texas Health Science Center
Coordinating Center for Clinical Trials
1200 Herman Pressler Street, Suite 801
Houston, Texas 77030
Telephone: (713) 792-4495 - Ocular Pathology Center
- David J. Wilson, M.D.
Casey Eye Institute
3375 S.W. Terwilliger Boulevard
Portland, Oregon 97201-4197
Telephone: (503) 494-7881 - Vision Center
- Velma Dobson, Ph.D.
University of Arizona, SOM
Dept. of Ophthalmology
1801 North Campbell
Tucson, AZ 85719-3758
Telephone: (520) 321-3677
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Citations
- 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