Retinopathy of prematurity (ROP) occurs in premature babies when abnormal blood vessels and scar tissue grow over the retina. The retina is the light detecting layer of cells at the back of the eye that allows us to see. Abnormal blood vessels and scar tissue can grow over the retina in premature babies with ROP. An ophthalmologist can detect ROP during an examination of your baby’s dilated eyes in the neonatal intensive care unit (NICU) or nursery.
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The causes of ROP are not completely understood. The retinal blood vessels in some very small, premature babies seem to develop abnormally during the therapy necessary for the infant’s survival. It was once thought that oxygen, given to almost all premature babies, was entirely responsible for all cases of ROP, but newer evidence indicates this is not true. How premature your baby is and their birthweight are factors which appear to influence ROP. For example, a baby who weighs 3 pounds at birth has about a 5% chance of developing ROP; an infant weighing less than 2 pounds has a 40% chance of developing ROP.
Not all babies who are premature will have ROP. Many of the babies who are born with ROP will improve spontaneously. However, since ROP is “responsible for more blindness among children in this country than all other causes combined” (Watson, 1997), it is important that premature babies are screened for ROP. This examination is done with an indirect ophthalmoscope which allows the doctor to get a wide-angle view of the retina. First a drop of topical anesthetic is applied to the eye to reduce the baby’s discomfort. Then the baby’s eyelids are held open with a device called a speculum and a special probe holds the eyeball still while the doctor examines it. Because this examination can be stressful to the baby, sometimes the exams are postponed until the baby’s medical condition is more stable. Usually only babies that are at high risk for ROP are screened. Those babies are usually the ones with a young gestational age and a low birth weight. Utah NICUs use 2000 grams or less as a weight guideline for screening. (Ophthalmology Associates Homepage, 1997)
Although there has been a correlation made between premies who receive high levels of oxygen and ROP, there appear to be a variety of factors that may account for development of ROP. These include, in addition to birth weight and gestational age: elevated blood carbon dioxide levels, anemia, blood transfusions, intraventricular hemorrhage, respiratory distress syndrome, chronic hypoxia in utero, multiple spells of apnea or bradycardia, mechanical ventilation, and seizures. (Ophthalmology Associates Homepage, 1997) There are some who feel that exposure to bright fluorescent lighting in hospitals contributes to the development of ROP (Prevent Blindness in Premature Babies, 1997), but to date this has not been proven and many ophthalmologists strongly disagree with this theory (Ophthalmology Associates Homepage, 1997). The current thinking is that probably it is a combination of factors, some occurring in utero and some occurring after the baby is born, that lead to this outcome.
Will ROP Affect Vision?
It is difficult to predict whether vision will be affected. In many infants, the abnormal blood vessels shrink or go away without affecting vision. In other infants with more extensive disease, bleeding and scar tissue may lead to distortion or detachment of the retina. This may result in moderate to severe loss of vision. Only a very small percentage of babies become blind. Nearsightedness (myopia) is common in children with ROP. Glasses may improve the vision of these children, unless the eye is badly damaged.
Can ROP be Prevented?
Unfortunately, clinical research has not yet found a way to prevent ROP in all babies. The sophisticated medical care provided in modern neonatal intensive care units has improved the survival chances of very small babies. Because more premature infants survive, ROP has become more common.
The blood vessels of the retina begin to develop 3 months after conception and complete their development at the time of normal birth. If an infant is born very prematurely, eye development can be disrupted. The vessels may stop growing or grow abnormally from the retina into the normally clear gel that fills the back of the eye. The vessels are fragile and can leak, causing bleeding in the eye.
Scar tissue may develop and pull the retina loose from the inner surface of the eye. In severe cases, this can result in vision loss.
In the past, routine use of excess oxygen to treat premature babies stimulated abnormal vessel growth. Currently, oxygen can be easily and accurately monitored, so this problem is rare.
Today, the risk of developing ROP depends on the degree of prematurity. Generally, the smallest and sickest premature babies have the highest risk.
Typically all babies younger than 30 weeks gestation or weighing fewer than 3 pounds at birth are screened for the condition. Certain high-risk babies who weigh 3 – 4.5 pounds or who are born after 30 weeks should also be screened.
In addition to prematurity, other risks factors may include:
*Brief stop in breathing (apnea)
*High carbon dioxide (CO2) in the blood
*Low blood acidity (pH)
*Low blood oxygen
*Slow heart rate (bradycardia)
The rate of ROP in moderately premature infants has decreased dramatically with better care in the neonatal intensive care unit. Ironically, however, this has led to high rates of survival of very premature infants who would have had little chance of survival in the past.
Since these very premature infants are at the highest risk of developing ROP, the condition may actually be becoming more common again.
Premature infants do not have symptoms. External signs develop only after disease has become severe or progressed to retianl detachmetns. Timely detection of ROP depends upon examination by an ophthalmologist experienced in the examination of premature infants.
Following pupillary dilation using eye drops, the retina is examined using a special lighted instrument (an indirect ophthalmoscope). The peripheral portions of the retina are pushed into view using scleral depression. Examination of the retina of a premature infant is performed to determine how far the retinal blood vessels have grown (the zone), and whether or not the vessels are growing flat along the wall of the eye (the stage). Retinal vascularization is judged to be complete when vessels extend to the ora serrata. The stage of ROP refers to the character of the leading edge of growing retinal blood vessels (at the vascular-avascular border). The stages of ROP disease have been defined by the International Classification of Retinopathy of Prematurity (ICROP).
Retinal examination with scleral depression is generally recommended for patients born before 30-32 weeks gestation, with birthweight 1500 grams or less, or at the discretion of the treating neonatologist. The initial examination is usually performed at 4–6 weeks of life, and then repeated every 1–3 weeks until vascularization is complete (or until disease progression mandates treatment).
In older patients the appearance of the disease is less well described but includes the residua of the ICROP stages as well as secondary retinal responses.
Most babies’ eyes with ROP do well without any treatment. In more severe cases, cryotherapy (freezing) and/or laser surgery may be used. The pen-like tip of the cryotherapy instrument, a cryoprobe, can briefly freeze side areas of the retina through the outer wall of the eye. Laser photocoagulation surgery may also be used to treat the side areas of the retina. These treatments can slow down or reverse the abnormal growth of blood vessels and scar tissue in more severe ROP. It may be necessary for your ophthalmologist to examine a baby frequently while the infant is in the NICU or nursery before a treatment can be recommended. Important factors in the decision include where ROP is located in the eye, how severe it is, and how it is progressing.
Even with treatment, there is still a definite risk of serious vision loss. The long-term effects of cryotherapy and laser surgery for ROP are not known. If severe ROP disease pulls the retina out of place, more complex surgical procedures can sometimes restore limited vision. Other ROP complications such as glaucoma and misaligned eyes may also require surgery later in life. Periodic eye examinations will be necessary as your baby grows, to ensure that the child’s vision is developing as normally as possible.
There are certain classifications of ROP that are used to describe the progression of the condition. What this classification relates to is the location and degree of retinal scarring that has occured. Chart 1 (below) shows the various stages of ROP (1-5) and what these notations mean. The zone number refers to the International Classification of Retinopahty of Prematurity (ICROP) diagram which designates three zones of the retina. Chart 2 shows the ICROP. For example, stage 3, zone 1 ROP describes ROP which is pretty severe while stage 1, zone 3 ROP describes a condition which is not as progressed. It is important to stress that not every child with ROP will progress to stage 5, and some babies with ROP may recover spontaneously from stage 1 or 2 ROP.
Chart 1 – Stages of retinopathy of prematurity (Vaughan, et al, 1995)
Stage and Clinical Findings
Stage 1 Demarcation line (line where the normal and abnormal vessels meet)
Stage 2 Intraretinal ridge (ridge that rises up from the retina as a result of the growth of the abnormal vessels)
Stage 3 Ridge with extraretinal fibrovascular proliferation (the ridge grows from the spread of the abnormal vessels and extends into the vitreous)
Stage 4 Subtotal retinal detachment (the partial detachment of the retina)
Stage 5 Total retinal detachment
Chart 2 – ICROP diagram (Ophthalmology Homepage, 1997)
Zone and Area of Retina Affected
Zone I – Area centered on the optic disc and extending from the disc to twice the distance between the disc and the macula.
Zone II - A ring, concentric to Zone I, which extends to the edge of the retina on the side of the eye toward the nose.
Zone III – The remaining crescent area of the retina toward the side and away from the nose.
Treatment for ROP depends on the stage of the condition. Stage 1 and 2 usually require nothing more than observation. (Vaughan, et al, 1995) There are a variety of ways that ROP is treated, but the most common is laser treatment. Laser photocoagulation is used to eliminate the abnormal vessels before they cause the retina to detach. Cryotherapy involves placing a very cold probe on the outside wall of the eye and freezing until an ice ball forms on the retinal surface. These treatment options are usually done with children in Stage 3 ROP. A scleral buckle involves placing a silicone band around the equator of the eye and tightening it to produce a slight indentation on the inside of the eye. This keeps the vitreous gel from pulling on the scar tissue and the retina and allows the retina to flatten back down onto the wall of the eye. Infants who have a sclera buckle done need to have the band removed months or years later since the eye continues to grow. Otherwise they will become nearsighted. Vitrectomy involves making several small incisions into the eye to remove the vitreous and replace it with a saline solution to maintain the shape and pressure of the eyeball. After the vitrous has been removed, the scar tissue on the retina can be peeled back or cut away, allowing the retina to relax and lay back down against the eye wall. Since it may take weeks for the retina to re-attach afterwards, holes or tears can occur which usually prevent the retina from re-attaching. If this happens the lens of the eye has to be removed to be able to remove the scar tissue. Sclera buckles are usually performed on children with Stage 4 and 5 ROP while vitrectomy is performed only at Stage 5. (Ophthalmology Associates Homepage, 1997)
Additionally there are some late complications from ROP which include strabismus (crossed eyes), amblyopia (lazy eye), myopia (near-sightedness), and glaucoma. (Ophthalmology Associates Homepage, 1997) Regular follow-up is needed to monitor and treat these conditions.
Depending on the stage of ROP, a child may have anywhere from near normal vision to light perception to total blindness. Many children will not progress to Stage 5. Usually children will benefit from early intervention and sensory stimulation. Adaptions such as high illumination, magnification for close work, telescopes for distance viewing, and closed-circuit television (CCTV) can be helpful to some students. (Levack, et al, 1991) Students may be braille readers.
Parents of children with ROP may wish to contact some of the following resources for information and support:
ROP Online Support Group – This support group is an attempt to provide a source of information and support for those struggling with these issues about how ROP will affect the future. You can post a message, ask a question, or answer someone else’s questions simply by sending e-mail to the group (email@example.com). Any messages posted to the group will be forwarded to you as long as you are a member.
Ophthalmology Associates of Ogden, Utah – The purpose of this website is to provide information to the internet public concerning eye diseases and their medical and surgical treatment and has a variety of subjects, with real data in an understandable format. Go to <www.konnections.com/eyedoc/index.html>.
Most premature infants with ROP recover with no lasting visual problems. Many premature infants with slight problems in retinal blood vessel growth have the vessels return to normal without treatment. Most infants with mild ROP can be expected to recover completely.
About 1 out of 10 infants with early changes will develop more severe retinal disease. Severe ROP may lead to significant vision problems or blindness. The most important factor in the outcome is early detection and treatment.
In premature newborns who need oxygen, oxygen levels are monitored carefully so that the lowest amount of oxygen necessary can be used. Oxygen levels can be indirectly monitored using a pulse oximeter, an external sensor that measures the level of oxygen in the blood going through a finger or toe.
Retinopathy is usually mild and resolves spontaneously, but the eyes need to be monitored by an ophthalmologist until blood vessel growth is mature.
For very severe retinopathy of prematurity, laser treatment is done on the outermost portions of the retina. This treatment stops the abnormal growth of blood vessels and decreases the risk of retinal detachment and loss of vision.You may click to see:->Laser Cures Retinopathy in Infants
“Prevent Blindness in Premature Babies” – The major effort of the organization is to work to eliminate the use of bright fluorescent lighting in hospital premie units. Go to <www.brailleplanet.org/pbpb.html>. You may also contact them by phone or mail at P.O. Box 44792, Madison, Wisconsin 53744-4792, (608)845-6500.