Delayed Visual Maturation (DVM) is
characterized by an otherwise normal eye exam in an infant that does not
fix or follow or otherwise respond (e.g., blink to threatening object or
bright flash of light) to a visual object. In an infant with DVM, the
eyes, including the retinas and optic nerves, appear normal and the
infant is otherwise neurologically normal. Infants with DVM do not have
nystagmus and typically do not have "wondering" eye movements. Yet, the
infant does not fixate on objects or track, even with jerking eye
movements (saccades), objects that move across his/her visual field. By
definition, however, at some point in time, usually by about 6 months of
age, the infant will start to fix and follow and will then appear as a
visually normal infant.
The typical infant with DVM is 2 to 4
months old and is otherwise healthy. The parents or grandparents
become concerned because the infant does not appear to see things or
track things like most infants their age. The parents end-up seeing an
eye doctor and the eye exam is normal, except for the fact that the
infant doesn't fix or follow objects placed in front of him/her.
Depending on the situation, the eye doctor often will simply tell the
parents that the child is delayed in vision abilities and that he/she
will catch-up in a few months (and to come back and see the doctor in a
few months). And sure enough, the infant will indeed start to fix and
follow by about 6 months of age confirming the diagnosis of DVM.
In terms of vision development, some
infants with DVM, parents report, act as though a switch in the brain
has been turned-on and all of a sudden the infant starts to look at
things and respond to objects in their visual space. Other infants with
DVM start off slower and may first look at salient objects,
periodically, and gradually start to fixate and tract objects. Very
soon thereafter the infant with DVM appears normal in every respect and
causes no further concern for the parents.
Nothing is harder for parents than
waiting - waiting to see IF and WHEN their infant will start seeing. To
alleviate fears and concerns, the eye doctor may have a Visual Evoked
Response (VER, also called a Visual Evoked Potential, VEP) undertaken on
the infant to ensure that the early visual pathways are intact and
functioning. The VER to pattern stimulation is typically normal in
infants with DVM. Often between the time that the VER is ordered and
performed, say 2 weeks, the infant with DVM will start to respond to
visual objects. If, however, the VER is abnormal or worse yet "flat"
additional testing may be indicated. Additional testing might include
the electroretinogram (ERG) to assess retinal function and CAT scan or
MRI to evaluate brain structures.
What causes DVM? Nobody really knows
what causes DVM. However, it is possible that DVM is the result of a
delay in cortical maturation (or delay in myelination of cortical areas)
- particularly the maturation of cortical areas responsible for
"awareness" of visual objects. Recent research has shown that one
particular cortical area called the Angular gyrus plays an important
role in object awareness. For example, adults that have had damage to
the Angular gyrus cannot identify an object by sight alone, but can
identify the object if it makes a sound or has a familiar smell. For
all practical purposes, people with damage to the Angular gyrus don't
see - much like infants with DVM don't see. A big difference between
adults with damage to the Angular gyrus and infants with DVM is that the
later will eventually see.
What happens if the infant is older
than 6 months and still doesn't fix or follow? If the infant is older
than 6 months and still doesn't fix or follow then it may be necessary
to undertake additional testing, including those discussed previously.
Although rare, infants that do not fix or follow may have more serious
vision problems including Leber's Congenital Amourosis or
monochromatism. Usually, infants with more serious vision problems that
are present at birth also exhibit other signs of vision loss such as
nystagmus, or will exhibit self visual stimulating behavior like pushing
the thumb, fingers or whole hand into the eye and rubbing vigorously.
Can anything speed-up the development
of vision in an infant with DVM? Research is moot on this point.
Nevertheless, experience suggests that infants that are continuously
stimulated with visual objects including those that make sounds or/and
that the infant can hold may facilitate vision development. Probably
the most important stimuli for an infant with DVM are activities with
the parents (feeding, talking, playing, holding) and, particularly,those
undertaken by other older children or sibs.