The lens is disc shaped like a Smartie. It sits inside the eye, just behind the black pupil and the coloured iris, and normally in a child it is a transparent, elastic bag, the lens capsule, full of a clear protein jelly rather like the white of a raw egg. The lens changes shape when an eye focuses. If you take a flash photograph sometimes in the centre of the coloured part of the eye there is a red circle, ‘red eye’. This is caused by light passing through the clear window of the front of the eye, the cornea, through the circular gap in the coloured iris of the eye, the pupil, through the clear lens of the eye behind the pupil and reflecting back from the red lining of the eye, the retina. For more on this, see our article, How the eye works.
A cataract is a lens that is not clear. The lens may be cloudy or totally white. There may be fine dots throughout a lens or a blob at the front or at the back of the centre of the lens. Only light is seen through a dense white cataract. It is like trying to look through a white sheet of paper, but if there are only scattered blobs within a lens it is like looking through frosted glass. You can see colours and shapes, but not clearly and you are dazzled by bright lights.
You may or may not be able to see the cataract in your child’s eye, depending on how dense white it is and whether the cloudy part is towards the front or the back of the lens. The word ‘cataract’ comes from a Greek word meaning ‘white water’, but unlike water the lens cannot become clear again. The lens is made up from proteins that are usually laid down in smooth layers to make the transparent lens. For some reason (see What causes cataracts? for more), either the proteins were not laid down smoothly in the first place, or they became damaged, so the lens is not clear. The result is a bit like egg white that has been cooked and the only way to remove the cataract is to remove the lens.
You may have been told, or want to ask about, the type of cataract that your child has; different types of cataract are mostly described by their shape and where they are in the lens. Different types may have different causes and are sometimes slightly different in other ways. If you want to know more about this, there’s a very good article on the PGCFA website about it.
How are childhood cataracts different from the ones that older people get?
An adult who grows up with good eyesight and who only develops a cloudy lens (cataract) later in life usually will regain good eye sight after a routine surgical operation to replace the cataract with an artificial lens inside the eye. After the operation often the adult can see very clearly without any glasses. The eye is measured before the operation and a lens implant of the correct size to fit and to focus the eye exactly is implanted. Usually an adult’s cataract is caused by ageing of the lens proteins and not by an illness. The situation is more complicated for a child and the outcome much more variable.
Most children will be otherwise well and have no problems apart from their eyes. However, a cataract may be a sign that a child will have other problems in their development and with other organs. Most children will with early treatment and wearing glasses or contact lenses will be able to go to a mainstream school, but will often need their work enlarged. A few children will gain excellent vision and be able to drive and a few will have very poor vision and not be able to see to read large print. The eye may be under developed or abnormal in other ways apart from the cataract. The nerve that passes information from the eye to the brain, the optic nerve, may be small. Even if a successful operation enables the eye to focus well if the nerve is small this limits how clear vision will be.
A child’s brain is still ‘learning to see’ and must have good input from the eyes in the first few weeks of life for the vision areas to develop properly. If a baby is born with dense cataracts and the cataracts are only removed when the child is older the child will see movement, colours and crude shapes but not be able to focus as the brain has not developed the ability to process vision. A child’s eye may be too small to safely place an artificial lens inside. The artificial lenses available at present cannot be safely changed so if a lens is put inside the eye and as the eye grows it will not focus the eye exactly and glasses or contact lenses will need to be changed as your child gets older.
Surgical operations are much more difficult on a young infant eye than on an adult or older child’s eye. This is not just due to the eye being smaller but the tissues of the eye are very different and the eye is more likely to become inflamed after surgery. To help the eye heal, frequent eye drops are used that contain steroids. Often the doctor will recommend postponing immunisation with live vaccines until your baby has finished treatment with steroid eye drops.
How common are childhood cataracts?
Childhood cataracts are much rarer than adult cataracts, with only about 200 children born in the UK each year with them (against 2.4 million older adults who have cataracts). A few children develop cataracts later in childhood, although some of these might be cataracts that were there at birth, but that were so small that they were only spotted later. Some other children develop cataracts later in childhood when the lens is damaged because of an eye injury or during eye surgery for another problem.
Checked for medical accuracy by Miss Isabelle Russell-Eggitt, Consultant Paediatric Ophthalmologist, Great Ormond Street Hospital, London