Premature Babies At Risk For Eye Problems
By George Leposky
Advances in treating the smallest, least developed premature babies now allow many to survive who would have died a generation ago, but not all of these "super-preemies" will grow up to lead normal, healthy lives. A serious complication that some of them face is retinopathy of prematurity (ROP), an eye disorder formerly called retrolental fibroplasia.
According to the National Eye Institute (NEI), ROP can lead to blindness in one out of 48 infants weighing less than 2.7 pounds (1,251 grams) at birth.
What ROP Is
We are able to see because the lens inside each of our eyes focuses light energy on the retina, a layer of cells on the inner surface of the eye. The retina captures this light energy and transforms it into electrical impulses, which the optic nerve sends to the brain.
During the last few weeks before the birth of a full-term baby, blood vessels grow outward from the optic nerve into the retina. In some premature babies, something interrupts this process. Then abnormal vessels begin to grow, accompanied by fibrous scar tissue that in the worst cases forms a ring all the way around the inside of the eye.
"Fortunately, most premature infants do not develop ROP, and most infants with ROP improve spontaneously," notes ophthalmologist Scott C. Richards., M.D., of the Country Hills Eye Center in Ogden, Utah.
In other cases, however, ROP can grow progressively worse. Ultimately the scar tissue contracts, detaching the retina from the choroid, an inner layer of blood vessels underneath the retina. A partial detachment may allow fluid from inside the eye to seep behind the retina, enlarging the area of detachment and further decreasing visual acuity. Complete detachment of the retina will leave the infant blind.
The NEI says about 74 percent of the 27,000 "super-preemies" born each year survive, and six percent of them develop severe ROP. Although treatments for ROP exist, they dont help every patient. According to the NEI, about 35 percent of eyes with severe ROP are blind a year after treatment.
Researchers still arent sure what causes ROP. It is associated with premature birth - an inherently serious problem - and with a constellation of other complications associated with prematurity. These include a chronic shortage of oxygen before birth, circulatory and respiratory problems, anemia, seizures, and the use of blood transfusions and mechanical ventilation to treat premature infants. However, sorting out cause and effect from a mere association remains a challenge.
After ROP was discovered in 1941, the earliest efforts to find a cause focused on the practice of giving premature newborns high levels of supplemental oxygen. When neonatologists began administering less oxygen to their tiny patients, ROP should have gone away - but it didnt. In fact, the number of cases began to rise in the 1970s. This coincided with major advances in neonatal care that expanded the frontiers of survivability for the smallest and most premature infants, in whom ROP is most likely to develop and most likely to need treatment.
Selecting the appropriate level of supplemental oxygen a premature infant should receive involves a delicate balance. Too much oxygen increases the risk of ROP; too little can cause other complications, or death. With current technology for monitoring the oxygen level of an infants blood, that balance is being achieved today.
Another possible risk factor is the use of indomethacin, a drug similar to ibuprofen, to promote closure of the ductus arteriosus, a small fetal blood vessel bypassing the lungs. In a full-term infant, this vessel normally closes by itself soon after birth. One study found an association between indomethacin and severe ROP, but another did not.
Although the use of calf-lung surfactant to treat respiratory distress syndrome in premature infants has been associated with a decreased risk of ROP, Dr, Richards says this may be due to improvements in lung function and nutritional status "rather than a direct effect of the surfactant on the ROP process."
On the theory that bright light may cause ROP or make it worse, many newborn intensive-care units have installed dim lights or covered the babies isolettes or cribs with blankets. However, a clinical study supported by the NEI found that "a reduction in the ambient-light exposure does not alter the incidence of ROP."
Vitamin E deficiency also has been considered as a cause of ROP. Although the results of studies to explore this theory were ambiguous, they suggest that giving vitamin E to premature infants doesnt seem to hurt and may help.
Treatment of ROP
Most newborn intensive-care units now screen for ROP with an indirect ophthalmoscope, a device that provides a three-dimensional view of the retina. The procedure involves use of a local anestethic and can be stressful to the infant. "We do our initial examinations," Dr. Richards says, "at 33 weeks gestational age or six weeks after birth, whichever comes first, assuming that the infant is stable enough for the examination." If ROP is present, the procedure is repeated at intervals of a week or two until the abnormal retinal vessels disappear or until the disease progresses to the point of requiring treatment. Four treatment methods are available:
· Cryotherapy, use of a supercooled probe on the outside wall of the eye to freeze portions of the retinal surface.
· Laser photocoagulation, which is more precise than and has largely supplanted cryotherapy. It treats the retina and choroid directly without affecting the whole eye wall.
· Scleral buckle, a surgical procedure in which a silicone band tightened around the eye helps to relieve stress on a detached retina so it can reposition itself against the eye wall.
· Vitrectomy, a complex procedure involving replacement of the vitreous gel inside the eye with a saline solution, and removal of the scar tissue on the retina. Sometimes the lens also has to be removed. Reattachment of the retina to the eye wall succeeds in 25 to 50 percent of ROP victrecomy patients, but only about 25 percent of that group can see "well enough to reach out and grab an object or recognize patterns," Dr. Richards says. "The disappointing visual results of surgery underscore the need for careful screening and timely laser treatment for patients at risk for visual loss."
Infants with ROP - even a mild case that goes away by itself - are prone to complications that can cause vision loss later in life. These include:
· Glaucoma, a disease in which increased pressure inside the eye damages the optic nerve, gradually reducing visual acuity until blindness occurs.
· Amblyopia (lazy eye), dimness of vision without a detectable organic cause.
· Myopia (nearsightedness).
· Nystagmus (a rapid, involuntary shaking of the eyeball).
· Retinal detachment during adolescence and early adulthood.
· Strabismus (crossed eyes).
Thus, anyone who was treated for ROP as an infant should see an eye doctor frequently during childhood and at regular intervals throughout life. Furthermore, because careful screening for ROP is a relatively recent practice, adults who know that they were born prematurely and dont know whether they had ROP also should have regular eye exams, to detect and receive prompt treatment for any late-onset complications of ROP that may threaten their vision.
George Leposky is editor of Ampersand Communications, a news-features syndicate based in Miami, Florida.
For More Information
National Eye Institute - http://www.nei.nih.gov/neitrials_script/studydtl.asp?id=58
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