Retinopathy of prematurity

Retinopathy of prematurity is when the retinal blood vessels don’t develop normally in babies that are born earlier than their expected date of delivery. 

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– What is retinopathy of prematurity (ROP)?
– What causes ROP?
– How does ROP affect the eye?
– How common is ROP?
– How is ROP diagnosed?
– What is the treatment for ROP?
– How will ROP affect vision?
– Coping



What is retinopathy of prematurity (ROP)?

The retina is a delicate tissue made up of light-sensitive cells that lines the inside of the back of our eye. The retina converts light that we see into electrical signals that travel along the optic nerve to the brain. The brain interprets these signals so we can “see”. The retina is supplied with blood by a delicate network of blood vessels on its surface and by a layer of blood vessels underneath the retina.

Our retina needs a good blood supply to work properly. As a baby develops in the womb, the blood supply for the retina starts to develop around 16 weeks into pregnancy and only finishes around 40 weeks when a full-term baby is born. At full term, a baby's blood vessels are fully developed and can keep the baby's retina healthy.

If a baby is born too early then their retinal blood vessels don’t develop completely which can cause problems. Abnormal blood vessels may grow out of the retina and cause scar tissue to form, leading to detachment of the retina which can cause blindness. This damage is known as retinopathy of prematurity and if not monitored or treated at the correct time, can cause vision loss.



What causes ROP? 

The reasons why babies develop ROP are complicated, but ROP is more likely to occur in babies that:

  • are born very prematurely – particularly those born before the 28th week of pregnancy 
  • have a low birth weight of less than 1,500 grams
  • required oxygen treatment soon after they were born. 

Often premature babies need additional oxygen which is necessary for the baby's survival but this can increase the risk of developing ROP. 

Not all premature babies that need oxygen develop ROP. Paediatricians (hospital consultants that specialise in caring for children) monitor levels of oxygen a baby needs very carefully to ensure that enough oxygen is given for the baby’s survival while also taking into account the effects this may have on the baby's eye. Checks for ROP are a regular part of care for all premature babies born before 32 weeks or babies born weighing less than 1,500g (3lb).

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How does ROP affect the eye? 

ROP mainly affects the retinal blood vessels. When the retinal blood vessels haven’t developed completely, the retina isn’t receiving enough oxygen so tries to grow new vessels. However, these new blood vessels grow abnormally and are fragile, can cause scarring and damage to the retina. The most severe forms of ROP are very rare but if left untreated, can lead to retinal detachment and blindness.  

There are a few ways of describing the amount of ROP present in the eyes, which includes its location, extent and stage. 

Location

The location on the retina is divided into three zones where zone 1 is the innermost and zone 3 is the outermost. The zones are centred around the optic nerve. This is because the blood vessels tend to grow from the area where the optic nerve leaves the eye called the optic disc.

Extent

The extent of ROP is described using clock hours. This refers to how much of the retina is affected by ROP. If you imagine the retina being divided up like a clock face: if there is ROP present from the bottom round to the left hand side, this would be equivalent to three clock hours. 

Stage

Broadly speaking there are five stages of ROP. These stages describe what the ophthalmologist (hospital eye doctor) sees when they look into a baby's eyes.  

Stage 1: This is where the junction of the central part of the retina that already has blood vessels and the peripheral part of the retina where blood vessels have not yet grown is marked by a demarcation line or a flat white line. Babies with stage 1 ROP usually recover without needing any treatment.  

Stage 2: In stage 2, the demarcation line is raised and is more like a ridge. Babies with stage 2 ROP may recover without needing any treatment as well. These babies may require more regular check-ups to monitor progress.

Stage 3: Stage 3 is where new blood vessels start to grow out of the ridge. These blood vessels are very weak and they will cause vision problems if they start to scar. If there is also enlargement and tortuosity of the main normal blood vessels of the retina, this is known as “plus disease”. Stage 3 ROP with plus disease usually requires treatment.

Stage 4: In stage 4, the fragile new blood vessels that grow in stage 3 can contract (shrink) causing scarring which can pull the retina away from the back of the eye (partial retinal detachment).

Stage 5: Stage 5 is where the retina can become totally detached from the back of the eye (total retinal detachment). This would lead to permanent loss of vision.

Most babies with ROP only develop stage 1 and stage 2 with only a small number developing stage 3 and needing treatment.

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Diagram of eyes showing location and extent of retinopathy of prematurity
Illustration of the five stages of retinopathy of prematurity


How common is ROP?

In the UK, about 65 per cent of babies who have a birth weight of less than 1,251 grams will have ROP. However, the majority of these babies will have mild ROP that doesn’t require treatment. There are only around six per cent of premature babies that will have advanced ROP requiring treatment (stages 3, 4 or 5).

The incidence of ROP is on the rise as more and more babies now survive when they are born prematurely. This means that there are more babies with ROP. Treatments are now offered at an earlier stage than in the past, so the sight threatening severe forms of ROP (stage 4 and 5) are rare.



How is ROP diagnosed?

All newborn babies that weigh less than 3lbs or 1,501g or babies born at or before 32 weeks of pregnancy will have at least one eye screening examination. An ophthalmologist will perform the screening and can diagnose retinopathy of prematurity. The first eye examination is done a number of weeks after birth. The timing of this is determined using a table based on the baby’s gestational age at birth.

Eye drops will be placed into the baby's eyes to enlarge the pupil which is necessary for the ophthalmologist to view the retina inside the eye clearly. Anaesthetic drops are also used so that the baby doesn’t feel any pain.

The ophthalmologist will use a special lens and light to view the retina which often only takes a few minutes. Often the doctor will use a speculum or a clip to help keep baby’s eyelids open while looking in the eye. They may also use an indentor, which is a tiny rod, to press gently on the eyeball so that the doctor can have a thorough look inside the eye. It’s not uncommon for your baby to cry during the procedure. Some centres may use a special camera to take pictures of the retina.

This screening will happen weekly or fortnightly until the risk of developing ROP requiring treatment has passed. If a baby has some signs of ROP then these examinations will continue until your baby’s due date.

Further details on timings and frequency of ROP screening for babies can be found in “Guidelines for Screening and Treatment of Retinopathy of Prematurity” produced by the Royal College of Ophthalmologists.

Following the eye examination, the ophthalmologist will then decide whether treatment is required.

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What is the treatment for ROP?

Many babies with ROP don't need treatment as it often resolves on its own.

If new blood vessels start to grow then treatment can be used to stop them causing more damage. Some babies will need more than one treatment.Usually treatment is done using a laser machine, but in certain circumstances treatment is done by injecting a drug into the eye. Treatment for ROP can be a distressing time for both parents and baby.

A baby will need to go on a ventilator which is a breathing machine and be intubated where a breathing tube is inserted in baby’s mouth for treatment; this means that your baby will be unconscious for the whole treatment. This is to ensure they are completely still and don’t experience any pain while the treatment is happening. Your baby’s heart and breathing are carefully monitored during the treatment. The treatment can take between one and two hours to complete. Most babies stay on the breathing machine for a day or two but sometimes can take longer to come off breathing support.

The treatment uses a laser to make small burns on the retina inside the eye. This can stop the new blood vessels from developing. Although the laser helps to safeguard vision, it can affect your baby’s peripheral or side vision.

Once the treatment is finished your baby’s eye may look red and swollen. Eye drops may also be required following treatment for a week or so, but the eye will no longer be painful. The baby's eye will need to be examined in about a week's time to check if the laser treatment has worked. Sometimes, further treatment will be required.

Another possible treatment option that is sometimes required for ROP is anti-vascular endothelial growth factor (anti-VEGF). The term “anti” means “against” and “vascular” refers to blood vessels. Anti-VEGFs are drugs that stop blood vessels from forming or growing and are given by injection into the eye. In the UK this treatment is for babies who do not respond to laser treatment or who are too sick to go back on the breathing machine. It is still not known what affect anti-VEGF injections into the eye might have on blood vessel development elsewhere in a baby, in particular on brain development.

In most babies early treatment is usually successful. This means that the abnormal blood vessels stop developing and a retinal detachment doesn't occur. In some babies the treatment may stop the retina from detaching, but their vision may still be affected; they may not recover all their sight after treatment.

In a baby with stage 4 ROP, surgical treatment such as a vitrectomy may be done. A vitrectomy procedure involves removing the vitreous gel in the eye and replacing it with a clear solution. The solution then holds the detached retina against the back of the eye. Some useful vision may be preserved by this type of surgery, especially if it is done very soon after stage 4 ROP has developed. Unfortunately, surgical treatment for stage 5 ROP rarely achieves useful vision.

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How will ROP affect vision?

Vision in children develops from when they are born up until they are around seven years old. It’s not possible for doctors to know what a baby's vision is like until at least six weeks after their original due date when vision “switches on”. Even then, as vision continues to develop during childhood, it may not be possible to know what a child’s vision is like until they are much older. However, doctors will be able to give an approximate estimate of how well each child is likely to be able to see, based on the health of the eyes, and of the brain.

Vision development depends on the health of the visual nerve pathways in the brain as well as of the eyes. Premature babies can have some areas of brain injury, usually caused by bleeding into the brain soon after birth. Unfortunately, some children who were born prematurely have poor vision due to brain injury, even if their eyes have not been damaged by retinopathy of prematurity.

Babies who have stage 1 and stage 2 ROP may not have any vision problems and therefore won’t usually require regular eye exams by an ophthalmologist. Often babies in Stage 1 and 2 would then only need to have the national vision screening which begins in school age at around the ages of 4-5 years. This is a vision check to make sure vision is developing normally in children. If you have any future concerns about your child’s eyes or vision, you should speak to your GP or optometrist (optician) who would be able to refer your child to an ophthalmologist.

Babies who have stage 3 ROP may be followed up in the hospital clinic according to the centre's protocol as they may be more likely to have eye problems. Babies who have had treatment will be regularly monitored for myopia or short sightedness and whether there are any long-term effects from the laser scars which can occasionally affect vision.

It’s likely that babies who have stages 4 and 5 ROP will have significant vision loss. Although vitrectomy surgery is successful in some of these babies, many have a poor visual outcome.

Although the incidence of ROP is rising due to more premature babies surviving, our knowledge and understanding of the condition has also increased. The number of babies with ROP requiring treatment still remains very small. There have been great improvements in the screening, diagnosis and treatment of ROP which has led to better visual outcomes for these children.

Babies who are born early are at higher risk for having vision problems, which aren't caused by ROP, when they grow older. Some of these problems may include:

Myopia or short sightedness and squint can normally be corrected with glasses. Vision problems due to brain injury may be severe, and are then apparent at an early age. However, they may be mild and subtle and are then only recognised at an older age. Some of these milder problems consist of an inability to cope with a crowded visual environment (“crowding”), and reduced awareness of the lower visual field which can result in clumsiness while walking.

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Coping

It’s completely natural to be upset when your child has been diagnosed with an eye condition and it’s normal to find yourself worrying about the future. We’re here to support you every step of the way, and to answer any questions you may have – just get in touch with our Sight Loss Advice Service.

Your local authority (LA) should have at least one qualified teacher of visually impaired children (QTVI) to work with you and your child both at home and at school. QTVIs are qualified teachers who can provide support with development, play, learning and education. At an early stage, ask your local authority to put you in contact with a QTVI. They will support you and your child as soon as a vision impairment is suspected or diagnosed. If you have difficulty getting help, or need the details of the specialist teacher in your area, contact our Helpline.

Useful contacts

  • Bliss is the UK’s leading charity for babies born premature or sick.
  • LOOK, the national federation of families with visually impaired children, brings together families of children with visual impairment.
  • Guide Dogs offer a range of services and activities for children and young people, and also provide advice for parents and teachers.
  • VICTA supports children and young people who are blind or partially sighted and their families across the UK.
  • The Royal College of Ophthalmologists has guidance on ROP.

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