Eye Coordination (Alignment)
Defects - ESOTROPIA
Good control of eye movements and teaming of the eyes, also requires
a healthy neuro-muscular system. An imbalance of the ocular muscles
can lead to an eye turn (strabismus)
in the presence of a weak neuro-muscular system. Whether or not
strabismus results depends on the magnitude of the genetic defect,
the extent of lack of the necessary nutrition and on other factors
such as lack of visual experience etc.
It would be ideal to have all newborns
examined by an eyecare practitioner at three
months of age. This is mainly so as to detect
those children who are significantly long-sighted.
These infants should be followed up more
carefully at regular intervals, in case an eye-muscle
imbalance develops which may lead to esotropia
(inward turn of one of the eyes). Should there be
any sign of esotropia in the presence of long-sightedness,
corrective lenses should be prescribed as soon as
It is believed by certain workers in the field
(and the author agrees with this view), that
significant amounts of long-sightedness can lead
to esotropia even within the first few months of
life. Without corrective lenses, long-sighted
infants must constantly focus more than the usual
amount in order to see clearly. As accommodation
(focusing) is normally accompanied by convergence
(aiming of the eyes at a closer distance) in a
reflex manner, an excessive amount of focussing
will lead to excessive convergence or crossing of
There are several factors that determine
whether the eyes will remain "crossed"
or become realigned. These are mainly related to
the extent to which the eyes are crossed
and to the ability of the infant to fuse
the images from both eyes into one single image
derived from both eyes.
The extent to which the eyes are
"crossed" is mainly determined by the
magnitude of the long-sightedness and whether
there is a genetic tendency for an excessive
amount of convergence of the eyes in response to
focussing. The anatomical starting alignment of
the eyes at birth would also play a role.
The ability to fuse is governed by several factors. One
such factor is whether there is clear and equal
vision in both eyes. The most common cause of unequal vision and
a potent contributing factor to esotropia, is anisometropia.
An example of this condition is when one eye is significantly more
long-sighted than the other. Pathology such as cataract or retinal
damage can also be the cause of reduced or unequal vision.
The alertness of the infant that enables it to
sense the lack of single and cohesive
vision, and the strength of the neuro-muscular
system in opposing the excessive reflex
convergence due to accommodation, are also
important in instigating fusion. Some workers
believe that the inherent ability to fuse two
superimposed images, which is present in most
infants, may be somewhat lacking in some infants.
The underlying cause would probably be of a