University of Edinburgh
 

Medical Information on Prematurity and VI

by Dr Andrew Blaikie for VI Scotland

This document is written with the minimum use of medical terms and jargon. It is impossible to avoid all medical terms but where we have used them we have attempted to explain them as clearly as we can. Although the information is intended to describe most aspects of the condition each child is different and there will always be exceptions to the rule. As far as we can determine these pages are true and accurate and have been written in good faith.

What this information is not for?

This document is not a substitute for a consultation with a Health Professional and should not be used as a means of diagnosing a condition.

We hope the information will help you to:

  • Have a better understanding of the condition
  • Know what tests and treatments are normally available
  • Know when to seek professional advice
  • Be able to discuss the condition in a more informed way
  • Make the most of consultations with carers, teachers and health professionals
  • Be reassured and more able to cope

Due to staffing limitations we are not able to offer telephone or email advice to parents of children.

Medical Information on Prematurity and VI

What we see is made in the brain from signals given to it by the eyes. What we see is in fact made in the brain. The brain makes sight from signals given to it by the eyes.

What is the normal structure of the eye?

The eye is made of three parts.

  • A light focussing bit at the front (cornea and lens).
  • A light sensitive film at the back of the eye (retina).
  • A large collection of communication wires to the brain (optic nerve).

A curved window called the cornea first focuses the light. The light then passes through a hole called the pupil. A circle of muscle called the iris surrounds the pupil. The iris is the coloured part of the eye. The light is then focused onto the back of the eye by a lens. Tiny light sensitive patches (photoreceptors) cover the back of the eye. These photoreceptors collect information about the visual world. The covering of photoreceptors at the back of the eye forms a thin film known as the retina. Each photoreceptor sends its signals down very fine wires to the brain. The wires joining each eye to the brain are called the optic nerves. The information then travels to many different special 'vision' parts of the brain. All parts of the brain and eye need to be present and working for us to see normally.

Why do children born prematurely develop visual impairment?

Most babies born prematurely do not develop visual impairment. A small number may however develop visual impairment. There are two main reasons why this might happen. They include:

  • Retinopathy of prematurity; and
  • Periventricular leucomalacia

What Is Retinopathy Of Prematurity?

A premature baby's retina is prone to scarring and detachment. This leads to visual impairment. Retinal detachment is when the thin retinal film peels off from the back of the eye. Scarring and detachment of the retina in a premature baby is called Retinopathy of Prematurity.

Why does the retina scar and detach?

Because the baby has been born early, before they were expected to be due, some parts of the body have not had time to grow fully. The blood supply has not usually spread fully to all areas of the retina. Quite often areas of the retina around the edges do not have any blood supply when a premature baby is born. The blood supply normally grows to the edges of the retina over the first few weeks of life. During these few weeks the retina can become damaged because it is starved of blood. The damage can lead to scarring. The scar tissue can then shorten and pull the retina off the back of the eye. This is called a retinal detachment and causes visual impairment. Damage is more likely the more premature the baby is and the smaller their birth weight.

How is retinopathy of prematurity diagnosed?

An eye doctor can usually diagnose Retinopathy of Prematurity during an examination. All babies who are born at least 8 weeks early or weigh less than 1500 grammes (less than about three pounds) need to be examined every 2 weeks. Examinations should start 6 weeks after the child is born. Examinations can stop when the blood supply to the retina has near fully grown. This is usually a couple of weeks before the date the baby was supposed to be due.

About half an hour before the examination a nurse will usually place drops in the baby's eyes. The drops will make the pupils go bigger. This lets the eye doctor see all of the back of the eye. By looking into the eye using a special lens and torch the retina can be seen. The eye doctor can say how much of the retina does not yet have a blood supply. They can also see if any scarring or retinal detachment has started. Based on the examination the eye doctor can decide if any treatment is needed.

What can be done to help?

Most babies with Retinopathy of Prematurity do not need any treatment. If the baby's eyes do need treatment this is usually organised by the eye doctor. The treatment reduces the chance of a child developing visual impairment by between one half and one quarter.

What is Periventricular Leucomalacia?

The brain of a premature baby is prone to damage from lack of blood and oxygen. This is because the normal blood supply has not yet spread to all parts of a premature baby's brain.

The brain has within it spaces that are filled with water. These water spaces are called 'ventricles'. The parts of the brain around the water spaces often have the poorest blood supply. The medical word for 'around' is 'peri'. 'Periventricular' means 'around the water spaces'.

It is these periventricular areas in premature babies that are most likely to suffer damage from lack of blood and oxygen. If damage occurs the nerves in this part of the brain die. The area softens and becomes scarred. On a picture of a head scan the scars appear white. 'Leuco' is a medical word for white and 'malacia' for softening. Periventricular Leucomalacia is the description of how a premature baby's brain looks on a scan that has suffered damage from lack of blood and oxygen. It means 'white soft areas around the water spaces of the brain'. Periventricular Leucomalacia (PVL) can lead to visual impairment. Most premature babies do not develop PVL but a small number do.

Why might PVL lead to Visual Impairment?

The periventricular areas of the brain help carry visual information from the eyes to the special vision parts of the brain. Scarring in this area can slow or block passage of information. Children with PVL may then have difficulties understanding what visual information means. This can lead to a type of visual impairment known as Cerebral Visual Impairment.

What is Visual Field Loss?

Visual field is the medical word for the full area that we can see: our visual world. If an area of our visual world is blurred or missing with the rest clear then visual field loss is present. It is due to damage to some of the special vision parts of the brain. The relationship between brain damage and visual field loss is all opposite to what you might think.

The right side of the brain is responsible for seeing the left side of the visual world. The left side of the brain sees the right side of the visual world. If the right side of the brain is damaged the left side of the visual world may not be seen. In the same way the upper part of the back of the brain is responsible for seeing the lower part of the visual world. A child with damage in this area will not see the ground when looking straight ahead. The child may then tend to trip over things.

What can be done to help?

There are lots of things that can be done to help children with CVI and retinopathy of prematurity see better.

We use our vision to get around, learn new things and to meet other people and make friends. It is important to consider what your child's particular problems with vision might be now and in the future.

If your child has been prescribed spectacles, contact lenses or a Low Visual Aid (LVA) it is important that they are encouraged to wear and use them. This will help your child see more clearly and ensure the vision parts of the brain grow and develop.

Problems at school may be due to some of the reading books being hard to see. This often means it takes longer and more effort to do the work. If the size of print is increased and letters and words spaced more widely most children will find schoolwork easier. Good bright lighting and crisp black print on a clean white background will also make things easier. Sometimes placing reading books on a slope, which tilts the print towards the child, will improve reading speed as well. When reading it can be helpful to read one line at a time through a 'letter box' placed over the page. Placing a piece of blue tack below the line they are reading, at the beginning of the next sentence, can help some children find their way back to the start of the next line more quickly.

Some children may also benefit from using a computer program while reading. The program only shows one word of a sentence at a time. The word is in the middle of the computer screen. This reduces the need for fast eye movements. It can increase reading speed and reduce tiredness. One programme is called AceReader. There are many others.

It is also worth watching carefully to find out what the smallest toys are that a child can see and play with. Then try to only play with toys that are the same size or bigger. Placing one toy on a plain background will often help children see it more readily. Placing lots of toys of different size and colour close together on a patterned background can make them 'invisible' to many children with CVI.

Recognising facial expressions can often be difficult. It is worth trying to find out at what distance facial expressions can be seen and responded to. Then always try to talk and smile from within this distance. This helps a child to learn what facial expressions mean and to copy them. There is a special part of the brain that helps children 'make sense' of faces. Sometimes this part is also damaged. These children may have difficulty responding to smiling even if their vision is clear enough. If the child has visual field loss try to place objects in the part of the child's vision that is working.

Cerebral Visual Impairment commonly occurs in children who have difficulty controlling both head and eye movements. Careful positioning of the head to prevent it falling to the side or falling forward can help a lot.

Infants and young children need to learn about the world around them. Home visiting teachers, physiotherapists and occupational and speech therapists may all add to the child's care and education. It is important to continue the programmes that they recommend. If the child is involved in family activities vision can improve and new skills can develop.

Even if a child has very poor vision many useful and practical things can be done to improve the ability of the child to get around, interact with other children and learn.

Who wrote these documents?

These pages are the consensus of opinion of many different people. They include parents of visually impaired children, visually impaired children themselves, Community Paediatricians, Ophthalmologists, Educationalists and Psychologists.

The main author and person responsible for their content is Dr Andrew Blaikie who was an Ophthalmology Research Fellow with Visual Impairment Scotland and is a member of the Royal College of Ophthalmologists.

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