Pediatric Eye Diseases
Beyond clinical services, scientists at the Casey Eye Institute are involved in several clinical studies related specifically to pediatric ophthalmology, funded by the National Eye Institute of the NIH.
Retinopathy of Prematurity (ROP)
Retinopathy of Prematurity is a disease that frequently affects the eyes of premature infants. When a baby is born prematurely, the blood vessels in the retinas (inner lining of the back wall of the eyeball) have not finished developing. Physicians are still not sure of all the reasons why, but in some premature babies, these blood vessels do not continue to grow as they should. This abnormal blood vessel growth is called Retinopathy of Prematurity (or "ROP" for short). ROP is more likely to occur in the very smallest babies who have the most complications. Signs are usually apparent before infants leave the Newborn Intensive Care Unit. ROP can cause blindness, but is uncommon.
If ROP does develop, one of three different things can happen:
- In the majority of premature babies with ROP, the blood vessels that did not grow correctly will heal completely before the baby is one year old.
- In some infants, the blood vessels that are not growing correctly will leave scarring in the retina when they heal. These babies may have to wear glasses because they are nearsighted (myopic). They may also develop lazy eye (amblyopia) or a wandering eye (strabismus). Medical care can usually correct these two problems if the child is seen by an eye physician (M.D. or D.O.) at an early age. It is important that an ophthalmologist continue to examine the baby's eyes regularly, to be sure that the child reaches school age with the best possible vision. Sometimes, the partially healed ROP leaves worse scarring in the retina that might cause eye problems that cannot be fixed by glasses or even by surgery. To control the damage as much as possible, these children need medical eye care regularly for the rest of their life.
- When scarring in the eye from ROP is the worst, the blood vessels in the retina keep on growing incorrectly and form into a large amount of scar tissue, which can shrink and pull the retina loose from the inside of the eye. This is called retinal detachment. Retinal detachment usually means that the baby will not be able to see well or it might even mean that the baby will become blind. Fortunately, this happens only to a very small number of eyes with ROP (about 4.5%).
What Can Be Done about Severe Retinopathy of Prematurity?
Until the late 1980s, there was no proven treatment to keep severe retinopathy of prematurity from getting worse. Now we know that cryotherapy or laser therapy can help in many cases. These therapies are surgical procedures often used to help various eye problems in older children and adults. Every surgery has risks and drawbacks, so this surgery is not recommended unless the ROP becomes severe.
On the average, treatment will reduce the chances of blindness by about 24 percent.
What Are Cryotherapy and Laser Therapy?
These treatments are used to kill certain tissues.
Cryotherapy involves holding a cold probe repeatedly on the surface of the eye to freeze through the outside wall of the eyeball into the retina (the inside lining of the eyeball). The cold temperature destroys a part of the retina where the blood vessels have not grown.
Laser treatment is done with a bright laser light beam aimed through the eye's pupil by the surgeon. Hundreds of small laser treatment spots are placed to burn off some of the retina where the blood vessels have not grown.
Cryotherapy has been proven safe and effective; laser therapy is believed to have similar effects. In certain cases one treatment may be more easily administered than the other.
How Does this Type of Surgery Help the Vision?
In order to save the important central vision used for reading and seeing details, the part of the retina that gives the farthest peripheral (side) vision is destroyed. Destroying this part of the retina slows the progression of ROP, and helps stop ROP before too much scar tissue is formed. This scar tissue can cause permanent vision problems, including blindness for some babies.
The entire part of the retina without blood vessels must be treated. Usually one cryotherapy or laser therapy session is enough to do this. If a second operation is needed, it is usually done within 14 days of the first treatment.
Treatment - What Happens?
Preparing the baby for surgery takes 30-60 minutes and the operation itself takes about 60 minutes. Some babies undergo treatment with general anesthesia so that they sleep quietly. Others may do well remaining awake, with only a local anesthetic to prevent pain. In some cases a compromise is used so that the baby is treated while under sedation, and local anesthesia is administered. The baby may receive anesthesia intravenously, or by an injection into the tissues surrounding the eye, or by breathing gas. Sometimes the treatment is done in an operating room. As with many kinds of operations or treatments, the premature baby may need help to breathe during the treatment. The doctors may decide to place him or her on a mechanical respirator with a tube in the windpipe. This may also help control movement and make it safer to give pain medication.
The thin transparent tissue that covers the white of the eyeball is called the conjunctiva. For some infants having cryotherapy, the doctor needs to make several small cuts (incisions) in the conjunctiva. Doctors do this for almost all eye surgical procedures. There is a possibility of infection whenever an incision is made, so antibiotics would be put on the treated eye(s) for several days following surgery. Laser surgery has the advantage that an incision is not needed.
Are There Any Risks to the Baby?
Generally, the risks of this treatment are small and no more than the risks of any kind of surgery on a premature baby. The primary risk comes if a respirator is needed, as it might take time for the baby to breathe without it again, especially if there have been problems getting off a respirator in the past. There are also possible hazards to the trachea (wind pipe) from having the tube placed there, as with any premature baby on a respirator. Complications from general anesthesia for other surgical conditions have occasionally resulted in death, but it is very unlikely that death would occur as a result of treatment for ROP. In a national study of very premature babies, no deaths occurred among 265 babies who had cryotherapy, with about a quarter of them under general anesthesia.
Are There Risks to the Eye Itself?
The tissues around the eyeball may be very swollen for about five days after treatment. The discomfort the baby feels from the treatment does not seem to seriously affect a baby's overall health.
Complications involving the eye itself are possible. For example, minor bleeding inside the eye occurs 22 percent of the time. Bleeding can occur from retinopathy of prematurity even if a baby doesn't have cryotherapy or laser therapy, but it is sometimes brought on during these procedures. The blood eventually clears up on its own.
Pressure on the eyeball during the treatment can briefly stop circulation of blood to the optic nerve. This happens in less than one percent of the treated eyes and seldom damages vision.
Eyes treated exclusively with the laser are usually less red and puffy than after cryotherapy, and treatment may be faster and more thorough. However, laser treatment has a greater risk of producing a cataract (cloudy lens of the eye), which is a very serious complication that might require further surgery. Also, laser treatment is newer and has not been studied as scientifically as cryotherapy has. We think the overall risks of the two treatments balance out to be about the same.
Cryotherapy and laser therapy destroy the part of the retina normally used for far peripheral vision (vision to the side). This means that the peripheral vision in the treated eye will be several degrees less than normal. However, this is considered a reasonable trade because vision in the "line of sight," used for reading and detailed sight, is more likely to stay good. School-age children who have had this treatment are not aware of any difference in their peripheral vision.
There could also be long-term risks to an eye that receives cryotherapy or laser therapy. So far a group of children who received cryotherapy have been watched for ten years and doctors have not found that the treatment has caused any serious eye problems. But cryotherapy or laser therapy might change the way an eye grows or could affect it during adulthood, in ways we don't know yet.
Which Babies Should Receive Cryotherapy or Laser Therapy?
Doctors closely examine a baby before any decisions are made to perform surgery. The more severe the ROP, the more urgently treatment is recommended. Occasionally, the value of cryotherapy or laser therapy is uncertain and the treatment will be done on only one eye. Then both eyes as well as the baby's general health are monitored. If the doctors and parents think it is needed, the ophthalmologist can do cryotherapy or laser therapy on the other eye later. Often, the ROP worsens so fast that surgery should be done on both eyes right away.
OHSU's pediatric ophthalmologists are also studying amblyopia (lazy eye), the most common cause of monocular visual impairment in both children and young adults. Existing treatment involves patching or blurring the vision in the "good" eye with daily drops of atropine. Current research is designed to determine which treatment is most effective.