With the advent of improved neonatal intensive care techniques, the mortality for medically fragile infants has drastically decreased. For instance, the mortality for children with birth weights of 1000g to 1500g fell from 50% in the 1960s to below 10% in the 1980s.
However, with the improvement of neonatal care, there has also been an increase in the prevalence of various disabilities such as respiratory distress syndrome and bronchopulmonary dysplasia. If either of these has been diagnosed in a baby, one should also suspect the presence of retinopathy of prematurity (ROP).
“Today we are seeing many more infants with ROP than before, and this is likely to continue as neonates of very low birth weight are routinely kept alive,” says Inge Loubser, an optometrist of Mellins i-Style. Infants born to mothers that are substance abusers during their pregnancy are at increased risk of prematurity and therefore more likely to develop ROP.
What is retinopathy?
ROP is a retinal vascular disease and is associated with supplemental oxygenation. As a result, it leads to a reduction in the frequency and degree of supplemental oxygenation given to premature newborns. This decreased the incidence of ROP but led to increased illness and mortality.
Recent studies estimate that up to 40% of infants with birth weights in the range of 1kg to 1.5kg and up to 50-80% of newborns that weigh less than one kilogram may develop some degree of ROP. However, only a small percentage of these infants will experience significant vision loss.
“The onset of ROP is likely to begin 32 to 42 weeks from the time of conception.”
The cause of ROP is thought to be due to the effects of high oxygen levels affecting immature retinal vascular tissue. The retina is the light-sensitive layer of tissue that lines the back of your eye. There is an initial vasoconstriction (constriction of blood vessels) of retinal vessels caused by increased oxygen levels in the blood due to supplemental oxygenation.
This constriction leads to obstruction of the vessels if the arterial oxygen levels remain high enough. When this eventually returns to a more normal oxygen level, there is a rapid increase of vascular endothelium (the cells that line the inside of our blood vessels). This leads to new blood vessels forming and the typical clinical appearance of ROP.
The degree of prematurity and the size of the newborn are probably more important factors in the cause and effect of ROP than is the level of supplemental oxygenation. We can, however, expect to see more ROP in the future as these tiny infants are kept alive.
Diagnosing ROP
It is often difficult to perform an adequate examination on a tiny, crying infant. Eye drops are used to dilate the newborn’s pupil (the ‘window’ into the eye) and an indirect ophthalmoscope, which has a special lens that sends a bright light into the eye, is used to enable the doctor to examine the fundus (the interior lining of the eyeball).
The onset of ROP is likely to begin 32 to 42 weeks from the time of conception and should, therefore, be examined shortly after this time by a paediatric ophthalmologist. It is necessary to monitor infants at risk of ROP for six months or longer after birth.
Infants who have ROP tend to be moderately to severely near-sighted and have a high incidence of amblyopia (lazy eye or impaired vision without an obvious defect), strabismus (abnormal alignment of the eye), cataracts (lens in the eye that becomes opaque), glaucoma (high eye pressure), nystagmus (rapid involuntary movements of the eye) and corneal problems.
Vitamin E therapy was suggested as a means of preventing the risk for the development of ROP based on the ability of vitamin E to neutralise oxygen free radicals that may cause cell damage to the developing retinal blood vessels. Premature infants typically have reduced levels of vitamin E, but there are significant risks of toxicity to vitamin E in premature infants, so this issue has not yet been concluded.
A promising treatment for ROP is cryotherapy where extreme cold is used during surgery to destroy the peripheral areas of the retina. This slows or reverses the abnormal growth of blood vessels. Unfortunately, this treatment can also destroy some side vision.
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