As parents you may have many concerns and worries with your baby being born prematurely. In addition, you have been told that your baby needs an eye test to screen for Retinopathy of Prematurity (ROP) – a potentially blinding condition.
This information leaflet will hopefully help you understand the screening process and give you some information about the disease. Your doctor will answer any further questions or concerns you may have.
NORMAL DEVELOPMENT OF THE EYE
All babies use their eyes from the day that they are born. In order to see, light must pass through the cornea and the lens (the focusing parts of the eye) and come to a focus on the retina (the light sensitive part of the back of the eye). The retina then converts the light image into nerve signals which are transferred via the optic nerve to the visual part of the brain, stimulating it and developing a sense of vision. If a disruption in this pathway occurs and the visual part of the brain is not stimulated it can lead to permanent visual loss.
A baby’s eyes develop throughout the 40 week gestational period. Blood vessels begin to supply the retina with oxygen and nutrients from about 16 weeks gestation. They start at the optic disk and continue to grow outwards until the baby is 40 weeks (term) and the retina is fully vascularised.
WHAT IS RETINOPATHY OF PREMATURITY?
If a child is born prematurely the retina blood vessel’s development is incomplete. There will be non-vascularised parts of the retina that do not receive enough oxygen. This triggers the production of chemicals to produce new blood vessels. These new blood vessels are often abnormal in size or shape and can cause bleeding or scarring. This pulls the retina out of position, affecting the baby’s ability to see. This is called retinopathy of prematurity.
WHO IS AT RISK FOR RETINOPATHY OF PREMATURITY?
All babies who are born before 32 weeks gestation or weigh less than 1.5kg are at risk for ROP (some older babies who have had an unstable course are also at risk).ROP affects around 16 per cent of babies who are born prematurely. This increases to 65 percent of babies who are born before week 28 of pregnancy or weigh less than 1,250g (1.25kg) when they are born.
Many premature babies need oxygen when they are born to help their developing brain. Oxygen as well as other changes in the baby’s environment may interfere with the normal development of the retinal blood vessels. The amount of oxygen the baby receives should be monitored carefully to reduce this risk.
Other risk factors such as anaemia, poor weight gain, blood transfusion, respiratory distress, breathing difficulties and the overall health of the infant can also contribute to the severity of ROP.
HOW IS RETINOPATHY OF PREMATURITY NORMALLY DIAGNOSED?
The diagnosis of ROP is made by an ophthalmologist (a specialist eye doctor).
Before the examination, drops will be put in the baby’s eyes to dilate the pupil. This is necessary for the doctor to see the baby’s retina.
Once the baby’s eyes are dilated, the doctor will put an anaesthetic drop into both eyes. The doctor will hold your baby’s eyes open with a
small instrument and look closely at the back of the eye with a head-mounted ophthalmoscope (a tool that allows them to see inside the eye).
They may also use an indenter (a tiny rod) to gently press on the eyeball to get a better look. The examination only takes a few minutes. Your
baby may not like the examination but should only feel slight pressure – no pain. A drop of sugar which acts as a pacifier may be given
before the examination.
After examining your baby, the ophthalmologist will be able to see how much of the eye is affected and how severe any damage might be.
THERE ARE SIX STAGES OF RETINOPATHY OF PREMATURITY:
- Stage 0 – No ROP
- Stage 1 – Avascular zone: demarcated by a line dividing the avascular zone from normal vascular zone.
- Stage 2 – Formation of a ridge which divides the avascular zone from vascularised retina.
- Stage 3 – Vascularisation of ridge and vessels growing into the cavity of eye.
- Stage 4 – Subtotal detachment of retina.
- Stage 5 – Total retinal detachment.
- Plus Disease – vascular congestion and dilatation.
HOW IS RETINOPATHY OF PREMATURITY NORMALLY TREATED?
If the baby has a mild form of ROP, they may not need any treatment. It is likely that the ROP will resolve by itself and not cause any damage to their eyesight.
When ROP reaches a certain level of severity, the potential for retinal detachment (and possible permanent vision loss) becomes great enough to warrant treatment. Eyes that develop this disease have type 1 ROP and are usually treated. Treatment involves lasering the non-vascularised part of the retina which stimulates the growth of abnormal blood vessels.
The outcome of laser treatment is usually favourable with disappearance of the abnormal blood vessels. 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 sometimes be treated with a vitrectomy procedure. There is active research into the use of medications to retard the growth of the abnormal blood vessels (currently this is still controversial). Despite optimal treatment, some eyes with ROP progress to permanent and severe vision loss.
WHY ARE EYE EXAMINATION RECOMMENDED AFTER DISCHARGE FROM THE HOSPITAL?
Most premature babies, whose eyes do well initially, will continue to do well. However, all prem babies are at increased risk for developing eye conditions, not directly linked to ROP, as they get older. Some of these conditions include: amblyopia (lazy eye), squints, short sightedness and glaucoma (raised pressure in the eye). It is thus recommended that all babies who were born prematurely have regular eye examinations up till the age of 3-5years.