A child’s vision continues to develop from birth until approximately 7 or 8 years of age. Assessing exactly how their vision is developing is a challenge.
When a child has retinoblastoma, it is important for the eye doctors to know what level their vision is in each eye. Often, the level of vision can influence treatment decisions. If there is little or no hope for any useful vision, consideration should be given to whether the treatment choice is in the best interest of the whole child.
The following guide was prepared by Sandra Staffieri, orthoptist and Retinoblastoma Care Co-ordinator, Royal Children’s Hospital Melbourne, Australia, together with WE C Hope Child Life Specialist, Morgan Livingstone.
Who Knows How to Test Children’s Vision?
Many health professionals are specially trained to assess vision.
Some will have the additional training or expertise required to assess children’s vision, particularly pre-verbal children. Different countries, or even states and jurisdictions within the same country, may have different personnel who have this training. Traditionally orthoptists, optometrists and ophthalmologists are the key personnel who have specific training, although many nurses and community health workers may also be well-trained.
Measuring Vision – Visual Acuity
The science behind measuring vision is complex, but basically relates to how far away an object can be located to be seen clearly. It can be recorded in either feet (20/20) or metres (6/6). Vision recorded as 20/20 means the individual sees an object 20 feet away that should normally be seen at that distance. 20/200 means the individual sees an object 20 feet away that should be clearly seen from 200 feet.
How Is Vision Tested?
The most familiar method to test vision is simply reading letters on a vision chart. The smaller the letters read, the better the central vision.
Children with retinoblastoma will often be too young to read a vision chart, however there are myriad other ways in which their vision can be tested.
Fixing and Following
Simply showing a baby or young child a small toy and watching them follow it, and even reaching out to grasp it can give a reasonable indication of what they can see. When this method is used, no sound or noisy toys will be used, so the examiner can be sure the child is responding with their vision and not their hearing.
To compare vision between the two eyes, the examiner may alternately cover each eye and compare their response. If the baby is happy to have one eye covered but not the other, it is clear the eye they are happy to have covered has the weaker vision.
An array of toys for assessing Fixing and Following
This type of vision test is only used by eye health care providers who regularly examine vision in young infants. A grid of narrowing stripes or a picture formed by increasingly narrow lines appear on a grey card.
If the baby is able to see the image or grid, they will naturally look to that side of the card. Once they can no longer see the image, they will just look from side to side and have no ‘preference’ for which side of the card they will look at. Ideally, the test is performed with each eye separately.
Teller Acuity Cards
Cardiff Acuity Cards
Pictures and Symbols
A variety of tests use pictures or symbols for the toddler to name. These tests are good because they transcend any language barriers and the child can name the pictures in the language most familiar to them. Again, each eye can be tested separately to compare the child’s response and determine whether one eye sees better than the other.
Kay Picture Test and LEA Symbols
By the time a child reaches about 3-3 ½ years of age, they will be able to match letters or shapes. Even with a little practice, they will be able to perform this task confidently. As the child becomes more familiar with the tests, the examiner can increase the difficulty by showing the child only a single letter at a time or pointing to a single letter in a row of letters.
Sheridan Gardiner Matching Test
A child completing the matching test