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What is squint (strabismus)?
Squint is a misalignment of the
two eyes so that both the eyes are
not looking in the same direction.
Squinting of eyes may occur occasionally
or may be present throughout the
day. It may appear in only one eye
or may alternate between the two
eyes.
It is a common condition among children
but may also occur in adults.
Types of Squint
It could be :
Convergent squint also known as
esotropia, where one eye is turned
in towards the nose. This is the
most common form of squint seen
usually in children.
Divergent squint also known as exotropia,
where one eye turns out away from
the centre of the face.
Vertical deviations known as hypo
or hypertropias are also seen but
are not common.
What causes squint?
Squinting eye could be because of
one of the following reasons
- Refractive (focusing) abnormality
- Eye muscle imbalance
- Injury
- Due to other diseases or
illness or associated with some
syndrome.
The movement of each eye is controlled
by six muscles. Each of these muscle
acts along with its counterpart
in the other eye to keep both the
eyes aligned properly. A loss of
coordination between the muscles
of the two eyes leads to misalignment.
Sometimes a refractive error hypermetropia
(long sight) may lead to inward
deviation of the eye. Poor vision
in an eye because of some other
eye disease like cataract, etc.
may also cause the eye to deviate.
Squint can become obvious after
chronic illness and it can also
run in families.
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What is binocular vision?
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Under normal circumstances, when
both the eyes have good vision and
they are aligned properly, they
focus on the same object. Each of
the eyes sends picture of the same
object, viewed from a slightly different
angle. These two images reach the
brain, where they are fused to form
a single three-dimensional picture
with depth perception. This is known
as binocular single vision.
What are the problems with squint?
When the eyes are not aligned properly, each of the eyes is focusing on a different object and sends signal to the brain. These two different images reaching the brain lead to confusion and may have either of the two effects:
A child would ignore the image coming from the deviated eye, and thus sees only one image. But in the process, he loses the depth perception. This suppression of the image from the deviating eye results in poor development of vision in this eye, which is known as amblyopia.
An adult cannot ignore the image from either eye, and therefore has double vision. This can be very annoying and may interfere with work.
What are the symptoms of squint?
In a child, the parents may notice
the deviation of eyes. It is important
to remember that the eyes of a newborn
are rarely aligned at birth. Most
establish alignment at 3-4 weeks
of age. Therefore squint in any
child who is more than one month
old must be taken seriously and
should be evaluated by an ophthalmologist.
Adults may notice double vision,
or misalignment of the eyes.
How is squint diagnosed?
The squint is diagnosed by the ophthalmologist.
He or she would do a few special
tests to confirm the squint, to
try and find out the cause and to
quantify the amount of deviation.
In some cases there may be a false
appearance of squint due to broad
nasal bridge in a child. An ophthalmologist
will be able to differentiate between
a true squint and false squint.
The aims of treatment of squint
in order of importance are:
- Preserve or restore vision
- Straighten the eyes
- Restore binocular vision
The different treatment modalities
are four O’s:
- Optics (Spectacles)
- Occlusion (Patching)
- Orthoptics (Eye Exercises)
- Operation (Surgical Correction)
First of all, the eyes are checked
to see if they have any refractive
error that may be responsible for
squint. If there is any significant
refractive error present, it is
treated first. In some cases (accommodative
squint) a correction of refractive
error is all that may be required
to treat squint.
Next the eyes are checked for presence
of amblyopia. It is important to
treat the amblyopia before the surgery
for squint.
The squint is treated by surgery
of either one or both the eyes.
The surgery involves weakening or
strengthening of the relevant muscles
to restore the balance and to get
a good coordination. In some cases
with double vision, prisms may be
added in the glasses to ease the
symptoms.
When should the squint be treated?
In a child, the treatment of squint
and any associated amblyopia should
be started as soon as possible.
Generally speaking, the younger
the age at which amblyopia is treated;
the better is the chance of recovery
of vision. Remember that the child
would never grow out of squint.
A delay in treatment may decrease
the chances of getting a good alignment
and the vision.
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