Squints & Lazy Eyes
What Is A Squint?
A squint is a misalignment of the two eyes so
that both the eyes are not looking in the same direction.
Usually the squinting eye turns in, but it may turn out, up or down.
Squints can sometimes also alternate between the eyes – the
eyes take it in turns to squint.
Squints may be visible all the time or only when the individual is
tired or focusing on an object close to them.
What Causes A Squint?
The exact cause of a squint is not fully understood.
They occur when the muscles controlling eye movement are not balanced
and working together. This may be due to muscular weakness, their
positioning or faulty brain and nerve control.
Most people with squints are born with them. There is a strong hereditary
link although sometimes there may be no other family members with
one.
Childhood illness such as measles or chickenpox can often unmask squints
that were previously present but controlled and therefore not noticeable.
Such diseases can weaken muscle control, allowing squints to become
visible.
In adults who have never previously had a squint, the most common
cause is illness or injury. Head traumas, cardiovascular disease and
tumours can damage one or more of the nerves that supply the muscles
that moves the eyes.
Focusing errors can also be a cause. In some adults and children focusing
to correct long sight induces a squint. This happens because there
is an indirect connection between the muscles that turn the eye in
and the focusing muscles. The nerves that supply these two muscles
share the same pathway. If a signal is sent to focus the eyes, it
will also make the eye inadvertently turn in as the other nerve is
also stimulated. In this type of squint, wearing glasses or contact
lenses to relax the focusing will keep the eyes straight.
Childhood Squints
These can sometimes be seen in infants under
the age of 12 months, but most commonly they are detected around the
age of two years.
Pseudosquints: Some babies have the appearance of a squint due to
a wide bridge of the nose or poor focusing, but this appearance is
lost as the vision and face develops. A child with a true squint will
not grow out of it
What Are The Effects Of A Squint?
If the two eyes are not pointing in the same
direction, double vision will result. Adults who develop a squint
will suffer from this. In children however, the brain will automatically
suppress the image from the squinting eye, to overcome seeing two
of everything.
Blanking off one eye in this way will lead to a lazy eye and poor
stereoscopic vision.
What Is A Lazy Eye?
This is an eye that even with glasses or contact
lenses cannot see very well. It may only be able to read the top few
lines of a letter chart.
The most common cause of a lazy eye is a squint, but it can also be
due to large uncorrected focusing errors.
Why Is The Eye Lazy?
In order for an eye to see well, it must be
used from a very young age. This is because using the eye sends signals
to the part of the brain that deals with processing of images. This
in turn stimulates the formation of neural connections and terminals
required to see finer detail.
Humans are not born with all the neural apparatus in place. It gradually
develops from birth through to the age of seven, but will only develop
if the relevant part of brains’ visual cortex is stimulated.
If the signals from an eye, such as one with a squint, are blanked
off the eye will be lazy.
How Are Squints Detected?
Large squints are visible – the eyes appear
obviously misaligned. Smaller squints are usually not seen simply
by looking at the physical appearance. It is therefore important for
children to be examined properly.
A number of tests are done during an eye examination that will check
for their presence. These include:
• Analyzing eye movements
• Grading the level of stereoscopic vision present
• Checking the sharpness of vision present
What Is The Treatment For A Squint?
How squints are treated depends on the type
of squint, its size and the age it develops. For childhood squints
the aim of treatment is to prevent the eye from becoming lazy and
to straighten it. To do this a combination of the following is used:
• Eye Exercises: to strengthen the eye muscles
• Glasses: these will straighten those squints that are caused
by focusing to correct longsight
• Surgery: necessary in large squints
Childhood squint treatment is done in conjunction with treatment for
the lazy eye. To reduce the laziness the good eye is patched (ie covered
up) for a period of time, in order to force the other eye to be used.
Adult squints are almost always treated with:
• Surgery: if persistent double vision is present or if bothered
by the cosmetic appearance
• Prisms: these are invisible triangular segments that are incorporated
within spectacle lenses. They eliminate double vision by moving the
images seen by each eye, so that they are fused together.
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