Vision tests in children are specifically tailored to age and ability and are routinely performed to look for defects that may delay normal development and learning. The need for glasses can be assessed in infants using tests such as retinoscopy, while older children may be asked to match shapes or letters. Once a child can read, a Snellen chart may be used to look for vision defects (see Vision tests).
This test can be performed on infants. Eyedrops are given about 30 minutes beforehand to dilate the pupils and prevent focusing. A beam of light is shone from an instrument called a retinoscope into each eye in turn. The effect of different lenses on the beam of light determines whether glasses are needed.
This test is designed for children of about 3 years of age. A child is given a card with letters printed on it. The doctor then holds up letters of decreasing size at a distance of 3 m (10 ft) and asks the child to identify the same letters on the card. By using an eye patch, each of the eyes can be tested separately.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.