Retinopathy of prematurity (ROP) is when the retinal blood vessels do not develop normally in babies that are born prematurely. It can cause a serious loss of vision if it isn't diagnosed and treated early. A premature baby is born before their expected date of delivery.
The retina is found at the back of the eye and is a very complex and sensitive structure that is responsible for the initial formation of the visual image. The light image is transferred by the optic nerve to the brain which allows us to see.
If a baby is born too early then their retinal blood vessels do not 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. This damage is known as retinopathy of prematurity and if not monitored or not treated at the correct time, can cause vision loss.
At the front of your eye is a clear tissue called the cornea, it allows light to enter the eye. Your cornea focuses light through your pupil which is a hole in the centre of your iris, the coloured part of your eye. Behind the iris is your lens, this also focuses the light coming through the cornea. Both the cornea and the lens focus the light coming into your eye onto an area of your retina.
Your retina is at the back of your eye and lines the inside of your eye ball. The retina is made up of a number of layers but the most important for vision is the layer made up of cells called photoreceptors. Photoreceptors are cells which are sensitive to light. When light is focused onto the retina the photoreceptors react and convert the light into electrical signals.
When light enters your eye it is focused first by the cornea and then more accurately by the lens so that it reaches the retina properly. The focussing that the cornea and lens do help to make your vision clear and sharp. When the light reaches the retina the photoreceptors react to the light reaching them by sending a small electrical charge through the optic nerve to the brain. The photoreceptors react differently to different light levels or lighting conditions and this changes the nature of the electrical signals that are sent through the optic nerve. When the parts of your brain that deal with vision receive these electrical signals, they make sense of them and this provides you with the pictures that we call sight. All this happens so quickly it is almost instant.
The reasons why babies develop ROP is complicated, but ROP is more likely to occur in babies that:
Often premature babies need additional oxygen and although it is necessary for the baby's survival, 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 may need very carefully to ensure that enough oxygen is given for the babies survival, taking into account the effects this may have on the baby's eye. ROP checks are a regular part of care for all premature babies born before 32 weeks.
ROP mainly affects the retinal blood vessels. When the development of the retinal blood vessels is incomplete, the retina is not receiving enough oxygen so tries to grow new vessels. These new vessels are fragile and cause scarring. Rarely, the most severe forms of ROP, if left untreated, can lead to retinal detachment and blindness. There are a few ways of describing the amount of ROP present which includes its location, extent and stage.
The location on the retina is divided into three zones where zone one is the innermost and zone three is the outermost. The zones are not centred around the retina but rather, 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 nerve disc.
The extent of ROP is described using clock hours. For example if there is retinopathy present from 6:00 to 9:00 then the extent of ROP is three clock hours.
Broadly speaking there are five stages of retinopathy of prematurity. These stages describe what the ophthalmologist would see when they looked into a baby's eyes.
Stage one: The peripheral or outer part of the retina has mild changes which is clearly marked by a demarcation line or a flat white line that divides the abnormal area of lack of blood supply with the normal area. Babies usually recover without any medical treatment.
Stage two: The damage is still in the periphery and considered a mild abnormality but the demarcation line is raised and is more like a ridge. Babies usually recover without any medical treatment in this stage as well.
Stage three: New blood vessels start to grow on the ridge. These blood vessels are very weak and they will cause vision problems if they start to scar. Plus disease is when blood vessel growth is severe and there is enlargement and tortuosity of these blood vessels. Stage 3 ROP with plus disease usually requires treatment with LASER.
Stage four: The fragile new blood vessels that grow in stage three can contract (shrink) causing scarring which can pull the retina away from the back of the eye (partial retinal detachment).
Stage five: The retina can become totally detached from the back of the eye (total retinal detachment). This would lead to permanent loss of vision.
Most premature babies only develop stage one and stage two of ROP with only a small number developing stage three and needing treatment.
In the UK, over 60 per cent of babies who have a birth weight of less than 1,251 grams will have ROP. However, the majority of these babies (about 94 per cent) will have mild ROP that does not require treatment. There are only around six percent of premature babies that will have advanced ROP requiring treatment.
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. However, advances in medical treatment of babies means that fewer babies are needing treatment. Treatments are now offered at an earlier stage than in the early 2000s so the sight threatening severe forms of ROP (stage four and five) are rare.
All newborn babies that weigh less than 3lbs or 1501g, or babies born at or before 32 weeks gestation, will have an eye screening examination. An eye doctor (ophthalmologist) will perform the screening and can diagnose retinopathy of prematurity.
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 does not feel any pain. The ophthalmologist will use a special lens and light during the examination which often only takes a few minutes. Following the eye examination, the ophthalmologist will then decide whether treatment is required.
This screening will happen weekly or fortnightly until about 36 weeks gestation when the risk of developing ROP requiring treatment has passed. If a baby has some signs of ROP then these examinations will continue past 40 weeks.
Many babies with ROP don't need treatment as often it resolves on its own.
If new blood vessels start to grow then LASER treatment can be used to stop them causing more damage. A baby will need to have a general anaesthetic for this treatment which means that they will be unconscious for the whole treatment to ensure they are completely still and because the treatment is painful while it is happening. The treatment uses a laser to make small burns on the retina inside the eye. This can stop the new blood vessels from developing. Once the treatment is finished the baby may have eye drops 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. Some babies may need more than one of these treatments.
Another possible treatment option that is currently being explored for ROP is anti-vascular endothelial growth factor (anti-VEGF). The term "anti" means against and "vascular" refers to blood vessels. Anti-vascular endothelial growth factor medications (anti-VEGFs) are substances that stop blood vessels from forming or growing. However, this treatment requires further research and evaluation before it can be safely used on babies and it is not clear at the moment what kinds of effects these medications may have on the rest of the baby's body.
In many 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 back after treatment.
In a baby with stage four or five 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 liquid then holds the detached retina against the back of the eye or retinal pigment epithelium from inside.
Babies who are born early are at higher risk for having vision problems, which aren't caused by ROP, when they grow older. These problems include myopia or short sightedness and squint which can often be corrected with glasses. Other possible problems such as damage to the optic nerve or visual pathway to the brain cannot be corrected and can result in permanent problems with vision. Vision in children develops from birth to age seven. The doctors will not be able to say anything about the baby's vision until at least six weeks after their original due date when vision switches on. It is often several years before a true idea of the child's visual potential is possible.
Babies who have stage one and stage two retinopathy of prematurity may not have any vision problems and therefore will not require regular eye exams by an ophthalmologist. Often babies in stage one and two would then only need to have the national vision screening which begins in school age at around the ages of four to five years. Any future concerns with their eyes or vision would require a GP referral to an ophthalmologist.
Babies who have stage three ROP may be followed up in clinic according the centre's protocol as they may be more likely to have eye problems. Babies who have been treated will be regularly monitored for short sightedness and long term effects from the LASER scars which occasionally affect vision.
In babies who have stages four and five 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 on the increase 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.
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