Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a potentially blinding eye disorder that primarily affects premature infants weighing about 2¾ pounds (1250 grams) or less that are born before 31 weeks of gestation (A full-term pregnancy has a gestation of 38–42 weeks). The smaller a baby is at birth, the more likely that baby is to develop ROP. This disorder—which usually develops in both eyes—is one of the most common causes of visual loss in childhood and can lead to lifelong vision impairment and blindness. ROP was first diagnosed in 1942.

ROP is a problem that affects the tissue at the back of the eye called the retina. The retina senses light and sends signals to the brain so you can see. With ROP, unwanted blood vessels grow on the baby’s retina. These blood vessels can cause serious eye and vision problems later. When ROP is severe, it can cause the retina to pull away or detach from the wall of the eye and possibly cause blindness.

 Most ROP resolves without causing damage to the retina. If ROP does not go away, however, it needs to be treated. Otherwise, the child can have severe vision loss, or even go blind

Today, with advances in neonatal care, smaller and more premature infants are being saved. These infants are at a much higher risk for ROP. However, not all babies who are premature develop ROP. Amongst those who develop ROP, about 90 percent are in the milder category and do not need treatment. In many cases, the disease improves and leaves no permanent damage in milder cases of ROP. However, infants with more severe disease can develop impaired vision or even blindness.

Causes of ROP:

Doctors do not know for sure what causes ROP. Blood vessels in the eyes normally finish developing a few weeks before birth. An infant who is born early is exposed to many different things. Medicine, oxygen, bright lights, or temperature changes might affect how an eye’s blood vessels develop.

ROP occurs when abnormal blood vessels grow and spread throughout the retina, the tissue that lines the back of the eye. These abnormal blood vessels are fragile and can leak, scarring the retina and pulling it out of position. This causes a retinal detachment. Retinal detachment is the main cause of visual impairment and blindness in ROP.

Several complex factors may be responsible for the development of ROP. The eye starts to develop at about 16 weeks of pregnancy, when the blood vessels of the retina begin to form at the optic nerve in the back of the eye. The blood vessels grow gradually toward the edges of the developing retina, supplying oxygen and nutrients. During the last 12 weeks of a pregnancy, the eye develops rapidly. When a baby is born full-term, the retinal blood vessel growth is mostly complete (The retina usually finishes growing a few weeks to a month after birth). But if a baby is born prematurely, before these blood vessels have reached the edges of the retina, normal vessel growth may stop. The edges of the retina – the periphery – may not get enough oxygen and nutrients.

Scientists believe that the periphery of the retina then sends out signals to other areas of the retina for nourishment. As a result, new abnormal vessels begin to grow. These new blood vessels are fragile and weak and can bleed, leading to retinal scarring. When these scars shrink, they pull on the retina, causing it to detach from the back of the eye.

Risk Factors to cause ROP:

Premature babies are the number-one risk group for retinopathy of prematurity. In general, the smaller and more premature the infant, the more likely he or she is to develop ROP, and the more likely to need treatment.

Babies considered most at risk for ROP have:

• a gestational age of 30 weeks or less, compared with 38 to 42 weeks for a full-term infant (“gestational age” means the amount of time since the baby was conceived)
• a birth weight of 1,500 grams (3.3 pounds) or less, which is 2,000 grams (about 4.4 pounds) less than for a typical full-term infant

Other possible risk factors for ROP include:

• anaemia
• infection
• transfusions
• breathing difficulties
• heart disease
• ethnicity (ROP occurs slightly more often in Caucasian children)

ROP has also been linked to supplemental oxygen, something often given to preemies. But excessive oxygen levels are largely a thing of the past, thanks to modern-day improvements in monitoring systems.

 

Factors determining the severity of ROP

Birth weight and gestational age are the most important risk factors for development of severe ROP. Other factors that are associated with the presence of ROP include anaemia, poor weight gain, blood transfusion, respiratory distress, breathing difficulties and the overall health of the infant. There is active research into the correlation of levels of growth factors in the blood and ROP. Close monitoring has decreased the impact of oxygen use as a risk factor for development of ROP. Light levels do not affect severity of ROP.

Different Stages of ROP

ROP is classified in five stages, ranging from mild (stage I) to severe (stage V):

Stage I — Mildly abnormal blood vessel growth. Many children who develop stage I improve with no treatment and eventually develop normal vision. The disease resolves on its own without further progression.

Stage II — Moderately abnormal blood vessel growth. Many children who develop stage II improve with no treatment and eventually develop normal vision. The disease resolves on its own without further progression.

Stage III — Severely abnormal blood vessel growth. The abnormal blood vessels grow toward the centre of the eye instead of following their normal growth pattern along the surface of the retina. Some infants who develop stage III improve with no treatment and eventually develop normal vision. However, when infants have a certain degree of Stage III and “plus disease” develops, treatment is considered. “Plus disease” means that the blood vessels of the retina have become enlarged and twisted, indicating a worsening of the disease. Treatment at this point has a good chance of preventing retinal detachment.

Stage IV — Partially detached retina. Traction from the scar produced by bleeding, abnormal vessels pulls the retina away from the wall of the eye.

Stage V — Completely detached retina and the end stage of the disease. If the eye is left alone at this stage, the baby can have severe visual impairment and even blindness.

Most babies who develop ROP have stages I or II. However, in a small number of babies, ROP worsens, sometimes very rapidly. Untreated ROP threatens to destroy vision.

Another way to understand your child’s condition, it helps to know the three most common ways doctors describe ROP: by zone, by stage and by the presence or absence of “plus disease.”

• The zone indicates where the disease is located. Zone 1 is a small area at the heart of the retina (surrounding the central visual area, including the optic nerve); Zone 2 covers the middle of the retina; and Zone 3 runs along the retina’s outer edge. The lower the zone number, the more serious the ROP.
• The stage describes how far the disease has progressed. Stage 1 has mildly abnormal vessel growth, while Stage 5 is “end stage” — the abnormal growth and scarring are so severe that the retina detaches.
• Plus disease means that the blood vessels themselves are abnormally twisted and enlarged. A finding of plus disease or its warning signs (known as pre-plus disease) is a serious one, and has become very important in helping doctors decide when treatment is needed.

Signs and symptoms

Many of the signs of retinopathy of prematurity happen deep inside the eye, which means you won’t be able to see them just by looking at your child. Only an ophthalmologist who is trained to recognize and treat ROP can spot these signs, using special instruments to examine your child’s retina.

The Indian Academy of Paediatrics has set ROP screening guidelines for all new-born intensive care units, and the vast majority of infants with ROP are identified through those exams.

An infant with severe ROP might develop visible complications, such as nystagmus (abnormal eye movements) and leukocoria (white pupils). However, these are also general signs of vision trouble—if your child has any of these, you should see an ophthalmologist right away.

Diagnosis of ROP:

Ophthalmologists who are skilled in the evaluation of infant eyes make the diagnosis of ROP. They examine the eyes after the pupils are dilated with drops. There is active research which is evaluating the effectiveness of digital photography for diagnosing ROP. Infants less than 1500 grams and with a gestational age less than 31 weeks undergo eye examinations to monitor for ROP.

Treatment of ROP

At first, an ophthalmologist may monitor ROP to see if it goes away on its own. If abnormal blood vessels continue to grow, the infant’s eyes must be treated. Once it is determined that treatment is necessary, the ophthalmologist may treat ROP in one or more of the following ways:

• Laser treatment
• Freezing treatment (cryotherapy)
• Medication eye injections

1.      Laser Ablation: The most effective proven treatments for ROP are laser therapy or cryotherapy. Laser therapy “burns away” the periphery of the retina, which has no normal blood vessels.

2.      Cryotherapy: With cryotherapy, physicians use an instrument that generates freezing temperatures to briefly touch spots on the surface of the eye that overlie the periphery of the retina.

Both laser treatment and cryotherapy destroy the peripheral areas of the retina, slowing or reversing the abnormal growth of blood vessels. Unfortunately, the treatments also destroy some side vision. This is done to save the most important part of our sight – the sharp, central vision we need for “straight ahead” activities such as reading, sewing, and driving.

Both laser treatments and cryotherapy are performed only on infants with advanced ROP, particularly stage III with “plus disease.” Both treatments are considered invasive surgeries on the eye, and doctors don’t know the long-term side effects of each.

3.      Medical Treatment for ROP: The second method of treatment involves an injection of medication into the eye.  These medications may be used as an alternative to, or in addition to, laser treatment.  This is a newer treatment and while results have been encouraging, further research is being done to help determine long term side effects and rate of ROP recurrence.

In the later stages of ROP, other treatment options include:

• Scleral buckle. This involves placing a silicone band around the eye and tightening it. This keeps the vitreous gel from pulling on the scar tissue and allows the retina to flatten back down onto the wall of the eye. Infants who have had a sclera buckle need to have the band removed months or years later, since the eye continues to grow; otherwise they will become near-sighted. Sclera buckles are usually performed on infants with stage IV or V.
• Vitrectomy. Vitrectomy involves removing the vitreous and replacing it with a saline solution. After the vitreous 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. Vitrectomy is performed only at stage V.

The outcome of laser or medical treatment for ROP is usually favourable with the disappearance of abnormal blood vessels and resolution of plus disease. Despite accurate diagnosis and timely laser treatment, the ROP sometimes continues to worsen and the retina pulls away from the back of the eye. Eyes with retinal detachment caused by ROP generally have a poor visual prognosis. Retinal detachment can be treated with vitrectomy and/or scleral buckling procedure. Despite optimal treatment, some eyes with ROP progress to permanent and severe vision loss.

Eye exams recommended after discharge from the hospital

If a hospital stay isn’t necessary, you can take your child home about an hour after the procedure. Follow-up care for ROP surgery includes giving your child eye drops (to prevent infection) for at least a week.

To make sure the eyes heal properly and that ROP hasn’t returned, the ophthalmologist will schedule follow-up eye exams. These are usually every 1–2 weeks. For scleral buckling, the ophthalmologist must examine the buckle every 6 months to account for a child’s growing eye.

The goal of ROP surgery is to stop the progression of the disease and prevent blindness. ROP surgery has a good success rate, but not all babies respond to treatment. Up to 25% of babies who have ROP surgery might still lose some or all vision.

With all types of ROP surgery, a degree of peripheral (side) vision will be lost. And even if the ROP stops progressing, vision still can be affected. Because some vision loss and complications can happen, any child who has had ROP surgery should have regular, yearly eye exams well into adulthood.

It is VERY IMPORTANT to have eye exams after discharge from the hospital since ROP may not be resolved before discharge. Also, even with successful treatment of ROP, prematurity may lead to other vision abnormalities. Prematurity is a risk factor for the development of amblyopia (lazy eye), eye misalignment (strabismus), the need for glasses (even at a young age), and cortical visual impairment. Therefore, every premature infant needs the long-term attention of an ophthalmologist.

What happens if treatment does not work?

While ROP treatment decreases the chances for vision loss, it does not always prevent it. Not all babies respond to ROP treatment, and the disease may get worse. If treatment for ROP does not work, a retinal detachment may develop. Often, only part of the retina detaches (stage IV). When this happens, no further treatments may be needed, since a partial detachment may remain the same or go away without treatment. However, in some instances, physicians may recommend treatment to try to prevent further advancement of the retinal detachment (stage V). If the centre of the retina or the entire retina detaches, central vision is threatened, and surgery may be recommended to reattach the retina.