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Strabismus may be classified as either
constant or intermittent, based on
the frequency with which an eye deviates.
When an eye deviates all of the time,
Strabismus is classified as constant.
If, on the other hand, an eye deviates
only some of the time, Strabismus
is classified as intermittent. Intermittent
cases of Strabismus usually result
from some other physical condition,
such as sickness or stress. Treatment
is available for both classifications
of Strabismus. There are also various
sub-classifications of Strabismus,
which determine the type of treatment
that may be needed.
Bilateral,
Unilateral and Alternating Strabismus
Strabismus may be classified according
to the laterality of the eyes. Strabismus
may be classified as bilateral, unilateral
or alternating. If both are eyes converge
or diverge, at the same time, Strabismus
is bilateral. If only one eye converges
or diverges, Strabismus is said to
be unilateral. If convergence or divergence
alternates between the eyes, such
that one eye is able to focus on an
object while the opposite eye is askew,
Strabismus is said to be alternating.
In many cases, both eyes deviate,
but only one eye appears to be askew.
Congenital
and Acquired Strabismus
Strabismus may be classified according to the
time at which the conditions onsets
When strabismus is developed during
infancy, it is called congenital. When
strabismus develops in adults, it is
called acquired. Research has not been
able to determine the reason for Congenital
Strabismus. Congenital Strabismus may
develop Amblyopia, which is referred
to as lazy eye. Amblyopia is a naturally
occurring condition in which the brain
ignores any input from a deviated eye.
Amblyopia in infancy causes problems
in the ability to perceive depth. Early
treatment of Strabismus or Amblyopia
greatly reduces the chance of developing
depth perception problems.
Acquired Strabismus in an adult,
who otherwise had proper alignment
of the eyes before the onset, is likely
to cause double vision, which also
known as diplopia. This is in contract
to orthotropia, which is characteristic
of eyes that are properly aligned.
With orthotropia, the brain is able
to fuse the two different objects
seen by each eye into one three dimensional
object. Orthotropia is also characterized
by a high degree of depth perception.
Acquired Strabismus is typically caused
by injury to the eye orbit or injuries
to the brain, such as with a stroke
or head injury. Loss of vision from
Acquired Strabismus usually results
in a gradual development of an exotropia
condition, rather than Amblyopia.
Exotropia is the condition where the
eye turns outward, away from the nose.
Vision is already developed in adult
brains and an adult brain will not
compensate for deviation as children’s
brains do. In other words, the adult
brain is already developed and trained.
It is not able to ignore images acquired
by a strabismic eye.
Esotropic,
Exotropic and Hypertropic Strabismus
Strabismus may be classified according to the direction in which the eye turns. Eyes that turn inward characterize Esotropic Strabismus, the most common form of Strabismus. The symptoms of Esotropic Strabismus are usually visible by 6 months and the condition will only worsen with age.
Accommodative Esotropia is a form of Esotropia that develops in farsighted children, almost exclusively after 6 months of age. The condition is termed accommodative since it relies upon the degree of accommodation necessary for a farsighted child to bring an object into focus. The degree of accommodation is proportional to the degree of farsightedness. In some children, an over-convergence of the eyes is necessary to bring an object in focus. This over-convergence is Accommodative Esotropia. Eyeglasses are usually able to correct this condition
Eyes that turn outward, away from the nose, characterize Exotropic Strabismus. The degree of turn is typically greater in children as they focus on more distant objects since focusing on close objects forces their eyes to converge. Unlike children with other types of Strabismus, bright sunlight tends to make exotropic children squint. While some children may benefit from eyeglasses or prisms, most children require surgery to correct the misalignment.
Hypertropic Strabismus is characterized by
a vertical misalignment where an eye
turns up or down in relation to the
other eye. It is common for medical
professionals to regard the condition
relative to the upwardly skewed eye.
Hypertrophic Strabismus may exist
along with other types of Strabismus.
Pseudostrabismus
Pseudostrabismus is a false appearance
of Strabismus. Strabismus is usually
falsely anticipated when the patient
has a flat, wide bridge of the nose
and a fold of skin in the corner of
the eye that makes the eye appear
to be turned inward (esotropic). Pseudostrabismus
is typically found in infants and
children. As children age, the systems
of Pseudostrabismus disappear since
the bridge of the nose tends to narrows
and eliminate any folds in the corner
of their eyes. Strabismus may be differentiated
from Pseudo Strabismus as early as
6 to 9 months.
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