How the eye works
We need light to see what is around us and to see colour. Light bounces off the objects we look at. These reflect different amounts of light which we see as different colours.
Front of the eye
Light rays enter the front of our eye through the clear cornea and lens. It is very important that both the cornea and lens are clear as this allows the light to pass directly through the front of the eye to the retina.
The cornea and lens bends light so that it can focus on the retina at the back of our eye. This gives us a clear, precise image. The cornea focuses the light towards our retina. The lens fine tunes the focussing of this light
Our tears form a protective layer at the front of the eye and also help to direct the light coming into our eye.
The iris, the coloured circle at the front of our eye, changes the size of the pupil which allows different amounts of light into our eye.
The pupil is the dark hole in the middle of the coloured part of our eye. The pupil gets smaller in bright conditions to let less light in. The pupil gets bigger in dark conditions to let more light in.
Middle of the eye
The middle of our eye is filled with a jelly-like substance called the vitreous. The vitreous is clear and allows light to pass directly from the front to the back of our eye.
Back of the eye
The retina at the back of the eye is a light-sensitive layer which consists of rod and cone cells. These cells collect the light signals directed onto them and send them as electrical signals to the optic nerve at the back of our eye.
Rod cells are concentrated around the edge of the retina. They help us to see things that aren't directly in front of us, giving us a rough idea of what is around us. They help us with our mobility and getting around by stopping us from bumping into things. They also enable us to see things in dim light and to see movement.
Cone cells are concentrated in the centre of our retina where the light is focused by the cornea and lens. This area is called the macula. Cone cells give us our detailed vision which we use when reading, watching TV, sewing and looking at people's faces. They are also responsible for most of our colour vision.
The optic nerve is made up of thousands of nerve fibres. These fibres pass the electrical signals along to our brain where they are processed into the image we are looking at. This connection is known as the visual system and develops through use from birth to around 7 years of age after which it does not develop further. For this system to develop normally all parts of the eye need to be functioning well
How we see
Seeing can be likened to the process of taking pictures on a film with a camera which you then get developed. The retina is like a camera film which stores an image of what we are looking at. The image directed onto the retina is then sent along to the brain where it is processed, like developing a camera film. Therefore we actually "see" in our brain with the light information sent to it from our eyes. This whole process happens very quickly so that everything we see is in focus.
About congenital cataracts
A cataract is a clouding of the normally clear and transparent lens inside the eye. It can cause blurry or hazy vision and be a bit like trying to look through frosted glass. It is not a layer of skin that grows over the eye or eyes.
A cataract is called congenital when it is present at birth. It is also known as 'infantile cataract' if it develops in the first six months after birth. It can affect one eye, which is known as 'unilateral cataract' or both eyes, which is known as 'bilateral cataracts'. Most children with cataract in only one eye usually have good vision in the other.
There are many types of cataract. Some affect vision and others never do. A cataract located towards the centre of the lens is more likely to affect vision and visual system development, although this will depend on its size and how dense the cataract is. Very developed cataracts can cause blindness in babies if left untreated.
Congenital cataracts can continue to develop, although this normally takes months to years. The ophthalmologist (eye doctor) will take all this into account when considering treatment.
Causes of congenital cataracts
Cataracts form when the protein in the lens clumps together which produces a 'clouding' or frosted affect. There are a number of reasons for this, including hereditary factors, infection (such as Rubella during pregnancy) and metabolic disorders, but in the majority of cases cataracts are idiopathic, meaning they have no known cause.
Approximately 200 children in the UK are born with some form of congenital cataract every year. Around one fifth of these have a family history of congenital cataract.
Cataracts can be dominantly inherited - that is passed on from one or other parent to a child because of a faulty gene. The parent may know that they have cataracts themselves but sometimes they may only have a tiny cataract which does not affect their vision and which they are unaware of. This is why it can be helpful for the ophthalmologist (eye doctor) to examine the eyes of the parents of a child with cataract, even if they are unaware of a problem with their eyes.
Most children who are born with or develop infantile cataracts do not have other medical problems but some do. This possibility will always be looked at by the ophthalmologist who will refer a child onto a paediatrician (a child specialist) if necessary.
The majority of children with congenital cataract will be able to attend mainstream school, read, play and go on to live full lives.
Cataract and visual system development
The visual system, that is the route of communication between the eye and the brain, goes on developing up until around the age of seven. During this period of development the eye needs to produce a clear image otherwise the system will not fully develop.
If one eye is sending poorly focused, unclear images to the brain, the brain will learn to ignore these images in favour of those provided by the 'good' or 'stronger' eye. This prevents the visual system from developing properly in the 'weaker' eye. This is known as 'amblyopia' or lazy eye. Amblyopia may result in permanent visual loss in one eye.
With unilateral congenital cataracts the brain tends to rely on the eye without a cataract and learns to switch off from the eye with reduced vision. In these cases it can be difficult to encourage the visual system to develop in the eye with the cataract.
If a child has bilateral cataracts the visual system will still develop but it would be limited and might result in some vision being lost permanently. Bilateral cataracts can cause amblyopia to develop in both eyes.
Diagnosis
Every baby needs to be screened within the first 24-28 hours after birth as part of the National Screening procedure. Babies are normally checked again by a health visitor around six weeks of age. If a parent is concerned at any stage that their baby is not seeing normally, they should discuss this with their family doctor.
If the obstetrician or hospital doctor suspects that a child has a congenital cataract they, will arrange a full examination of the eye and lens. An ophthalmologist (eye doctor) would carry out this examination at hospital. If a child's cataract or cataracts are likely to have a significant effect on the child's vision, surgery may be considered under the age of three months. In these cases it is very important to get a referral to an ophthalmologist as quickly as possible following diagnosis.
The ophthalmologist would normally use an instrument called an ophthalmoscope which allows them to examine the inside of a child's eyes. The ophthalmoscope is held close to the eye but will not touch it. Sometimes a child will be given a general anaesthetic to allow the ophthalmologist to carry out an eye examination. This allows the doctor to look thoroughly at the baby's eye whilst he or she is still without causing any distress.
If cataracts develop later on in childhood, there may be noticeable outward signs if they affect vision. For example sometimes a child may appear to have difficulty focusing on certain objects or has to hold their head at a certain angle or they may develop a squint. In these cases the GP will refer you to see an eye specialist.
In only a few cases would a cataract change the appearance of an eye. A very advanced cataract can cause a child's pupil to look white, as the cloudy cataract can be seen through it. However, there are other causes of a 'white pupil' which would need to be checked as an emergency, as they can be serious.
Treatment
Some cataracts do not cause visual problems and surgery would not be needed. If the cataract does affect vision, surgery will usually be considered to remove the affected lens from the eye.
During surgery, a small opening is made in the side of the cornea at the front of the eye through which the cloudy lens is removed using suction. A child will normally be kept in overnight so that the hospital can make sure they are recovering well.
Once the cataract lens has been removed, it may be replaced by a lens placed inside the eye (intraocular lens or IOL), although in most cases this does not happen and glasses or contact lenses will be required.
The consultant may recommend using a contact lens for a young child or baby rather than an implant. Because contact lenses are not implanted into the eye they are much easier to change or remove if this becomes necessary. Glasses and contact lenses will also often be worn by children who do not require or have surgery.
After cataract surgery
Following the operation the eye may feel slightly uncomfortable or itchy. The eye will be covered for a few days to help it heal and protect it. The hospital will provide you with eye drops which will help to prevent inflammation or infection, and are usually used for a month or two to help the healing process. Eye drops are used as soon as the dressing covering the eye is removed. This usually happens the day after the operation. If the eye seems to be uncomfortable, the hospital may also consider a pain reliever.
The doctors will monitor post-surgery recovery and check on progress. They will also advise on the use of any medication. The nurses will show parents or carers how to put drops into a child's eye before he or she is discharged from the hospital. They will also go over any post-operative care techniques, such as bathing the child, wearing a plastic eye shield, or keeping the eye clean without wiping inside the eye or washing it out.
It is important to protect the eye and keep it clean following surgery, including being careful not to get dirty water or shampoo in the eye. This is to give the eye the best chance of recovery and to minimise the risk of infection
The hospital may provide an eye shield to place over the child's eye, especially at night. This helps to protect the eye as it can usually stop the child from rubbing it after surgery. The hospital would also say when and for how long the shield should be used. Patients or carers are normally given a sheet of post-operative care instructions which includes this kind of advice.
Post-operative complications
Later complications such as glaucoma, eye infection and retinal detachment may occur following surgery in around two per cent of cases. There is treatment available for these conditions and information is available from the RNIB.
Complications are more common when a child under the age of one has had surgery for congenital cataract. A child will have more frequent check ups in these cases.
If you notice any swelling, bleeding, a lot of stickiness, pain or redness in or around the operated eye, then prompt medical attention is required.
These problems can often be treated successfully if they are caught early enough. If you have any concerns about your child's eye or post-operative care, contact the hospital where the surgery took place. Parents and carers will often be given 24 hour contact details before leaving the hospital.
Patching
Following surgery, vision in one eye may be better than in the other and patching might be necessary. Patching is when one eye is covered with a patch to encourage a child to use their other eye.
-
the 'stronger' eye may be patched for several hours a day in early childhood
-
patching aims to encourage the visual system in the 'weaker' eye to develop
-
if the consultant's patching advice is strictly followed, the better the chance of visual system development in the weaker eye
-
patching may also be used in cases where surgery is not considered necessary, for example if the cataract is not considered to be dense or large enough to merit an operation
-
sometimes drops can be put in the stronger eye to blur vision rather than wearing a patch
-
the orthoptist at hospital will be able to advise on the various ways to help a child to develop their vision as much as possible, such as glasses, eye exercises and patching.
What next?
Talk to someone
The RNIB Helpline is your direct line to the support, advice and products you need. We'll help you to find out what's available in your area and beyond, both from RNIB and other organisations.
Whether you want to know more about your eye condition, buy a product from our shop, join our library, find out about possible benefit entitlements, be put in touch with a trained counsellor, or make a general enquiry, we're only a call away.
RNIB Helpline
Telephone: 0303 123 9999
Email: helpline@rnib.org.uk
We are ready to answer your call Monday to Friday 8.45am to 5.30pm. Outside these times leave us a message and we'll get back to you as soon as possible.
Unfortunately, RNIB can only answer email enquiries from the UK.
RNIB discussion forums
Join our discussion forums - share your ideas with others and have your say about the issues that affect you.
Get information
RNIB's guide to Adapting to sight loss offers ideas for people with sight problems on making life easier and ways of getting the most out of life.
You may also find the following useful:
Useful contacts
-
LOOK UK is an organisation which helps support families with children aged between 0-16 with vision problems. They have family support officers and help support families at home and in school.
Look National Office
c/o Queen Alexandra College
49, Oak Court Road
Harbourne
Birmingham
B17 9TG
Tel: 0121 428 5038
-
National Blind Children's Society (NBCS) can offer information, support and advice to parents and carers of children with sight loss or an eye condition.
Head Office
Bradbury House
Market Street
Highbridge
Somerset
TA9 3BW
Tel: 01278 764 764
Family Support & Information - 01278 764770
Fax: 01278 764 790
Email: enquiries@nbcs.org.uk
-
Families can use Contact a Family's Freephone Helpline for advice, information and, where possible, links to other families through their web-based linking service Making Contact.org
About this guide
Thanks to Kings College Hospital for allowing the RNIB to use parts of their "Care after your cataract operation leaflet".
Updated Feb 2007
Eye Health Information Disclaimer
Your feedback
What do you think of this eye condition page? Is it useful, easy to read and detailed enough - or could we improve it? Send your comments about this page to webeditor@rnib.org.uk
For general comments about the website please fill in our website feedback form.
For all other RNIB enquiries or comments please email helpline@rnib.org.uk, call 0303 123 9999 or use our online contact form.