If your child has a total cataract your child may be able to see just light and dark and maybe some colours. Not all congenital cataracts are totally opaque (like a sheet of thick paper rather than like tissue paper), some babies can still see movement and large shapes. Rarely the cataract affects vision very little, at least early in life, especially if the cataract is like a cloud of tiny dots in the lens rather than a white sheet
If he or she has a partial cataract, what they can see could vary between seeing everything normally and not being able to see much detail or much in the distance, or being able to see less when it’s bright. Bright light may be dazzling in cataracts due to a cloud of tiny dots in the lens as these scatter the light. This is like trying to see the view through frosted glass of a bathroom on a sunny day as compared to a dull day, or to trying to read a street sign when an oncoming car has their lights on high beam.
‘Cataract’ means that part or all the lens is cloudy or opaque. In general, if the opaque area is in the centre of the lens in the pupil, particularly in the posterior (back) part of the lens this will stop the lens focusing and be more ‘visually significant’. If the opacities are towards the front pole of the lens, affects only the edges, or are less dense, they are likely to block vision and are less ‘visually significant’.
How are a baby’s eyes tested?
The ophthalmologist will usually assess your child’s vision using a method appropriate for age and compare the result with the usual result for this age. If your baby is very young they may be sleepy at the time you see the doctor. If the doctor knows from experience and from the type and density of the cataract that this will seriously impair vision, further testing of vision behaviour may not be necessary when deciding whether your baby will need a cataract operation.
Vision is tested qualitatively by watching what a baby looks at and what they will track (follow with their head and eyes). A parent’s or grandparent’s input is often valuable as they compare with their other children at the same age.
The doctor looks for abnormal flickering or roving eye movements and notes whether the two eyes move together.
Quantitative tests of vision (with numbers like 6/60) are much harder to perform in a very young child or if the child has developmental delay. The tests used are either ‘preferential looking’ tests or ‘electrodiagnostic tests’. Preferential looking tests rely on a child’s interest in patterns from an early age and a stripy black and white pattern is shown to them on a grey card with the same brightness as the stripy pattern if it is blurred. The baby will only look at the pattern if they see the detail. The tester will know they are seeing by watching their eyes and varying whether the pattern is on their right or left and by moving the pattern and seeing if the baby’s eyes follow.
Electrodiagnostic tests are only available in a few specialist centres and can be helpful if the doctor is not certain how much a partial cataract is impairing a baby’s vision and if the cataract is becoming denser.
The Ophthalmologist can work out how much the cataracts are likely to be affecting your child’s vision from all this information. They will when deciding when and whether to recommend surgery take into account other eye conditions and other conditions your child may have. They will examine you and ask about other members of the family who have had early problems with their eyes. They will then advise whether the cataract should be removed now, or later, or to wait and see whether they grow (‘progress’).
Young babies with normal eyesight do not see as clearly as an adult or an older child so if your newborn, for example, gets a result that is poorer than 6/60 (they are able to see at six metres what an adult with normal vision is able to see at sixty metres), this may be a normal result for their age; the test results aren’t adjusted for age although the type of test that’s done is. Babies’ vision usually develops so they are able to see almost as much detail as an adult (6/6 or 20/20) by around their third birthday. Vision continues to develop until the child is about eight years old, so if your child is a late starter learning to see (after cataract surgery for example) they may not develop their best vision until they are a lot older than usual.
An older child who has suffered an eye injury that has caused a cataract has already done their learning to see and their eye has developed normally so it is much easier for the older child in this situation to get really good visual results after the surgery if there aren’t any other problems with the eye. A newborn baby must be able to see a reasonable amount within the first weeks and months of life or he or she will never be able to learn to see well, if at all because their eyes and brain needed the stimulation during that time window, but there are no hard and fast rules and children’s visual development can vary a lot even in the same situation. Children also vary a lot in how well they use the vision they have.
Why won’t the ophthalmologist tell me more?
Many Ophthalmologists will not tell you very much about what your child is likely to be able to see, especially if you’ve just been told about the cataract(s). While your child is very young, they are not able to get clear test results and his or her vision is still developing.
Many of us need time to get used to the situation before asking for more information. You may need to explain that you would rather have another appointment later when you will be better able to take in information (although this might be more difficult if you need to make a quick decision about surgery, it should be possible). Or you might need to explain that you really want to know as much as possible in order to know what help your child might need and to get access to the best help and services as soon as possible. You may need to accept that there aren’t definite, clear-cut answers to every question.
Checked for medical accuracy by Miss Isabelle Russell-Eggitt, Consultant Paediatric Ophthalmologist, Great Ormond Street Hospital, London