The method of vision assessment varies with the patient’s
age. Normal infants can fixate at birth, in particular on their
mother’s face. This response is well recognized by parents feeding
their child. Asking the parents of an infant, especially when they
have previously raised a normal child, whether their child sees is
a remarkably accurate assessment of the child’s vision.
In the first 1 to 2 months of life, infants should at least respond
to lights by blinking when a bright light is shone into the eyes.
When the lights are turned off, the eyes often open, sometimes with
the upper lids retracting such that the superior sclera (white of the
eyes) becomes visible, a primitive response known as the eye-popping
reflex. Many infants will track fairly well shortly after birth,
but it is not abnormal to have minimal tracking at this early age.
A 3-month-old infant should be able to fixate on a toy held in the
examiner’s hand and should track the object back and forth
as the examiner moves it. This is initially done with both eyes
open. However, because an infant may track well if the vision is
good in only one eye, it is important that the vision in the two
eyes be assessed independently. This is done by covering each eye
separately (usually with the examiner’s or caretaker’s
hand) and monitoring whether the infant tracks equally well with
either eye. If the child consistently tracks well with one eye covered
but becomes upset or refuses to track when the opposite eye is covered,
this strongly suggests that there is a vision problem in the first
eye that was covered. An important caveat, however, is that some
children get upset when either eye is covered, even if both eyes
see well. Therefore, if the child becomes agitated equally with
either eye covered, one may not be able to accurately judge the
vision based on this behavior. In addition to distracting the child
with interesting toys as vision stimuli, it is also important to
try avoiding direct contact with the child’s face when
occluding one eye. This can be achieved by placing the examiner’s
hand slightly in front of, but not directly in contact with, one
side of the face. Also, the examination should be conducted fairly
quickly. If there is a difference in the visual responsiveness of
one eye versus the other, it will often be readily apparent.