Future Reflections Fall 1989, Vol. 8 No. 3
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By Michael X. Repka, M.D., Assistant Professor, Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine
Editor's Note: I want to thank Johns Hopkins for introducing me to Dr. Michael Repka, and Dr. Repka for submitting this highly informative article on a very timely subject. It is also our good fortune that Dr. Repka has expressed an interest in submitting additional articles to Future Reflections. If there is a particular medical topic you would like to suggest to Dr. Repka, please write to: Barbara Cheadle, Editor, Future Reflections, 1800 Johnson Street, Baltimore, MD 21230. Topics should, of course, be related in some way to eye diseases and conditions of the eye.
Retinopathy of prematurity or ROP affects an estimated 2,100 infants each year in the United States. These children may lose vision entirely, or be left partially sighted.
ROP, formerly known as retrolental fibroplasia or RLF, was first observed in the early 1940's. At its initial appearance it was often confused with an ocular tumor. At that time ROP was recognized only in the most advanced form in which the eye was very damaged. Research during the 1940's and early 50's led to the discovery that oxygen caused ROP. By restricting the use of oxygen, retinopathy of prematurity virtually ceased to occur by the mid-1950's. The patients affected by retinopathy of prematurity during the 1940's and 1950's were older and bigger than the patients who are developing retinopathy of prematurity today.
During the 1960's, 70's, and 80's, medicine's ability to support low birth weight babies has improved. This has produced a dramatically increased survival rate for infants with birth weights less than one kilogram (2 pounds, 3 ounces). For example, in 1950 only 8% of babies born with this birth weight survived. By 1980 the figure had reached 35%, and by 1990 the figure is likely to be 70% for many neonatal intensive care units. This improved survival rate has been paralleled by a dramatic increase in the number of children with retinopathy of prematurity. Retinopathy of prematurity most frequently affects the eyes of infants with birth weights less than 1,250 grams (2 pounds, 12 ounces), especially those infants with multiple medical problems. The cause of retinopathy of prematurity no longer appears to be simply excessive oxygen. Vitamin A and E deficiencies have been implicated. Low oxygen and high carbon dioxide blood levels, high acid concentration in the blood, low bilirubin, and other metabolic factors appear to play a role in the development of this disease. This has led to investigation of multiple therapies to reduce the incidence of the disease. Many hypotheses of causation still include oxygen as the ultimate cause of damage.
In the premature newborn, retinal blood vessels do yet not extend throughout the retina. The growing tips of these bloodvessels are responsive to changes in the body. These vessels respond to insult by exuberant growth, which is called proliferative disease. About 5% of small infants (1,250 grams) will develop a significant amount of proliferation. Once these abnormal blood vessels are present, they may completely disappear, or less commonly, proliferate further leading to scarring of the retina, and in some cases retinal detachment. If this proliferative change could be stopped, the scarring manifestations of the disease would not occur. Early trials of laser treatment in Japan and laser or freezing (cryotherapy) treatments in the United States showed promise for stopping the disease. Multiple small studies done since that time seemed to confirm that the proliferative changes could be completely aborted or caused to regress if a portion of the retina could be treated. Because of the relative ease of performing freezing treatments, babies today are treated with cryotherapy.
Cryotherapy involves a series of approximately 35 freezing applications to the outside portion of the retina, an area not used for vision. The treatment is done with local anesthesia. Drops are used for a few days postoperatively. The National Trial of Cryotherapy for Retinopathy of Prematurity, sponsored by the National Institutes of Health, evaluated the effect of cryotherapy when applied to patients most at risk for the scarring changes of retinopathy of prematurity. Only one eye of each patient was treated because there was concern about the short-term and long-term complications of this treatment, including loss of the eye. Of the untreated eyes, 43% of eyes had an unfavorable outcome. Such patients would not ever develop good central vision. On the other hand, for the treated eyes, only 22% developed an unfavorable visual outcome. There are therefore three important lessons from this study. 1) Only 5% of all babies born at risk for retinopathy of prematurity will develop the disease severely enough to warrant the application of cryotherapy. 2) Of those patients, one of five will still develop the scarring changes of retinopathy of prematurity. 3) Cryotherapy does not eliminate the chance of poor vision, hut only reduces its frequency.
Cryotherapy is not the final solution for this disease. Research must continue into exploring other ways to try and prevent the proliferative retinal changes from occurring. Some promising avenues of research include the extension of freezing treatments to less involved patients and earlier treatment in an attempt to further reduce the number of children who will have visual loss from retinopathy of prematurity. Research into metabolic and vitamin abnormalities continue.
Once retinal detachment or scarring has developed there are technical difficulties in treating the retina. Though extensive vitreous and retinal surgery has been successful in some cases, there is rarely restoration of functional vision for these treated eyes. Currently being initiated is a multi-center investigation into the early management of retinopathy of prematurity that has been complicated by a retinal detachment. Results from the study will take years to accumulate.
LONG TERM PROBLEMS
Premature children who develop mild or advanced forms of retinopathy of prematurity are at increased risk for multiple ophthalmologic problems. These include strabismus or squint; amblyopia (lazy eye); and high levels of refractive error (need for glasses), particularly nearsightedness. The long-term complications include retinal detachments occurring in infancy and young adulthood, as well as narrow angle glaucoma, a type of glaucoma rarely seen in young patients without retinopathy of prematurity in their background. Consequently, all patients, even those with markedly diminished vision, should continue to be monitored by an ophthalmologist for these ocular problems.
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