Medical Information on Glaucoma
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 to 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
Medical Information on Glaucoma
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 the parts of the brain and eye need to be present and working for us to see normally.
Eyes are pumped up with water
Eyes keep their shape by being pumped up with water. It is a bit like a football being pumped up and inflated with air. You can feel the 'pressure' in your own eyes by gently feeling them through your closed eyelids. The amount of pressure depends on the flow of water in and out of the eye. If the flow of water out of the eye becomes blocked the pressure goes up. High pressure in the eye can cause damage to the optic nerve.
Glaucoma is when the optic nerve is damaged by high pressure in the eye.
Water drains out of the eye through a narrow gap between the coloured part of the eye (iris) and the clear curved window at the front (cornea). Sometimes this narrow gap can become blocked. This leads to high pressure in the eye. Eye doctors often call the drainage gap the 'drainage angle' or 'trabecular meshwork'.
There are many different causes of a blocked drainage gap
Some children are born with a thin skin blocking the drainage gap. This is known as Primary Congenital Glaucoma. Congenital means 'to be born with'.
Other children are born with an open drainage gap, but later on develop a blocked drainage gap. This is known as Secondary Glaucoma. The drain becomes blocked in these children because of another eye condition (the first or primary condition). Common conditions that can also cause Glaucoma include Iritis or Retinopathy of Prematurity. See the VI Scotland documents on these conditions.
Why are some children born with a blocked drainage gap?
Most cases of Primary Congenital Glaucoma occur by chance. Sometimes glaucoma can run in families. Occasionally children whose parents are cousins or more distant relatives may be born with glaucoma. This is called 'recessive inheritance'.
There is a wide range of congenital glaucoma conditions
There is a wide range of congenital glaucoma conditions. Some conditions only affect the trabecular meshwork where the water in the eye drains out at the drainage gap. In other children the iris can show obvious changes as well. The child may have extra pupils or an unevenly shaped pupil. This is called Reiger's Syndrome. Sometimes the iris is missing altogether. This is called Aniridia.
Are there any other conditions associated with Glaucoma?
Children with Glaucoma usually only have problems with their eyes. Rarely if a child has glaucoma they may also other conditions as well. A child is more likely to have other conditions if the iris and pupil are affected as well.
In Reiger's Syndrome, where the pupil appears unevenly shaped, the child may also have a flattened appearance to the nose and face. They may also have fewer teeth than normal. Very rarely they may also have poor hearing, learning difficulties and problems with the heart.
Some children with Aniridia, where the iris is missing altogether, develop tumour of their kidneys. They may need regular scans to look for this.
Children with Glaucoma sometimes do not like bright light or going outdoors. This is called photophobia. The child's eyes may also water constantly. Sometimes parents notice their child's eyes to be larger than other children. If the pressure in the eyes is very high the cornea may look hazy and not as clear as usual. If parents notice these signs they can ask their Family Doctor to arrange an examination by an Eye Doctor.
The damage to the optic nerve from the high pressure however does not initially cause any problems with vision. If though the high pressure is not treated the optic nerve damage can become worse. The child may slowly develop haziness of vision that creeps in from the edges to cause blurred central vision.
High pressure in an eye of a child can also make the eye grow bigger than usual. This is called 'buphthalmos'. Children with bigger eyes are more likely to need spectacles to see clearly. Children with buphthalmos are also more likely to develop a squint or lazy eye. See the VI Scotland Documents on these conditions.
Sometimes the cornea can be hazy. This is most often seen when the pressure is high. If the pressure is lowered then the cornea usually becomes clear again. After the cornea clears small 'cracks' on the inside surface of the cornea might still be seen. They are called Haab's Striae and do not usually affect vision.
Glaucoma can be diagnosed during an eye examination. The eye doctor looks for typical features. The most important signs include:
- checking the pressure in the eye
- examining the drainage angle and
- looking at the optic nerve.
If the pressure is high then Glaucoma is likely. Sometimes using a small mirror it is possible to look at the drainage angle. Water in the eye drains out at the drainage angle. In Glaucoma it can often look different from usual. If the angle looks blocked or not fully developed then this might explain why the pressure is high. The way the optic nerve looks can also help to make a diagnosis. In Glaucoma damage occurs to the optic nerve. This causes some of the wires within it to wear out and disappear. By looking into the eye with a special instrument all these wires can be seen 'end on' as they exit the eye and pass to the brain. This is the 'head' of the optic nerve. If none of the wires are damaged then the 'head' of the optic nerve looks yellow and pink. If many wires are missing then the optic nerve looks pale and white. This is the common appearance in Glaucoma. Eye doctors often describe the damage to the optic nerve head as 'optic disc cupping'.
Younger children can be difficult to examine when awake. It is easier while they are asleep, under a short anaesthetic. While asleep the eye doctor can check the pressure in the eye and the appearance of the head of the optic nerve. Most young children will need short anaesthetics once or twice a year to do this.
If the pressure in the eye is lowered the damage to the optic nerve usually stops. The pressure can be lowered by several different kinds of operation. All the operations work by trying to increase the flow of water out of the eye. This usually helps to lower the pressure and prevent further damage to the optic nerve.
If a skin is blocking the drainage gap of the eye it can be cut open. This is called a Goniotomy. This allows more water to drain out of the eye and lowers the pressure. If this does not work other kinds of operations can be done (e.g. Trabeculectomy or Drainage Tube Insertion). Sometimes drops can also be given to help lower the pressure.
How can parents, family, friends and teachers make a difference?
We use our vision to get around, learn new things and to meet other people and socialise.
If your child has been prescribed spectacles or a Low Visual Aid (LVA) it is important that they are encouraged to use them. This will help your child see more clearly and ensure the vision parts of the brain grow and develop correctly. Wearing a hat and tinted glasses can also help reduce symptoms of photophobia. If your child has also been prescribed drops they should be used regularly as advised by the nurses and doctors at the eye clinic.
Most children with Glaucoma have few problems getting around. Their behaviour can therefore give the impression that their vision is normal. It is important however to recognise their particular limitations of vision.
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 most children will find schoolwork easier, especially if they also use their LVA. If a child has been given an (LVA) then they should be encouraged to use it.
It is 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.
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.
Even if a child has very poor vision many useful and practical things can be done to help.
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.