>> In this video,
we will go over the basics of refractive errors.
We hope that this will serve as a guide for patients and
families to understanding blurry vision and the use of glasses.
Our eye is like a camera,
constantly taking in images of the world around us through a lens
and projecting it onto the screen
in the back of the eye called the retina,
where these images can then be processed by the brain.
Refractive errors occur when structures of the eye involved in
this process fails to focus the object exactly on the retina.
This results in a blurry image.
Just like when your camera is out of focus.
There are four main types of refractive error.
Myopia, hyperopia, presbyopia, and astigmatism.
We will go over each of these in detail in the subsequent slides.
Refractive errors are very common in the general population.
The majority of individuals have some degree of refractive error,
although most do not require correction.
Refractive errors requiring correction
are uncommon in preschool children.
However, by late adolescence,
nearly 20 percent of children develop
refractive errors that require the use of glasses.
Now, we will go over each of
the different types of refractive error.
Myopia, also known as nearsightedness,
is when the focusing power of the eyes too
strong or the eyes too long,
such that the image of an object is
focused before it reaches the retina.
This problem is worse when objects are far
away and require less focusing power.
Thus, things further away are
especially blurry for people with Myopia.
Myopia rates increases throughout
childhood with the greatest number occurring
during and after puberty when the eye
undergoes a growth spurt just like the rest of the body.
As the eye grows through childhood,
myopia also tends to become more severe
before eventually stabilizing upon reaching adulthood.
In contrast, hyperopia or farsightedness is when
the focusing power of the eyes too weak or the is too short,
such that the image of an object doesn't
focus until after it has reached the retina.
This problem is worse with
near objects that require more focusing,
making near objects more blurry for hyperopic people.
Mild hyperopia is normal in
infants and children and usually does not require
correction as the lens can squeeze to
increase its focusing power to compensate.
Presbyopia happens when our lens loses
that squeezing power as hardens with age.
This is especially problematic when
we're looking up close or reading as
our lens usually work extra hard to
converge the light and focus it on the retina.
Because the elasticity of the lens decreases with age,
this is more common in older adults,
and similar to hyperopia,
results in an image focused behind the retina.
Astigmatism is when the surface of the eye,
called the cornea, is not perfectly spherical.
Instead of being shaped like a basketball,
it is more like a football.
However, unlikely exaggeration shown in this picture,
the changes are usually subtle and not visible to the naked eye.
The problem with having a non-spherical cornea is that,
the lanes is not the same in all directions, therefore,
light coming from different directions
cannot focus at the same point.
This leads to multiple images of
the same object at different places along the visual axis,
making it blurry from the real point of the retina.
This can happen whether the object is near or far.
Astigmatism may also occur in combination with
myopia or hyperopia in the different directions.
Treatment options for refractive errors include glasses,
contact lenses, and/or refractive surgeries.
Not all refractive errors require treatment.
Many small errors do not require any treatment.
The threshold for when a child should be corrected
depends upon the severity of the refractive error,
the age of the child,
the caretakers preference and other factors.
Symptomatic refractive errors, even when small should be treated.
The end goal of all of these treatments is to allow
light to focus back onto a single image on the retina,
whether that is through using
extrinsic lenses in the case of glasses or contacts,
or permanently altering the intrinsic refractive structures
of the eyes through surgery.
For example in myopia,
because the focusing power of the eye is too strong,
we add a diverging or minus lens to
allow the light to spread out more before reaching the eye,
balancing out the extra focusing power.
In hyperopia, we do the opposite and add
the converging or plus lens to help
the eye focus the light a little bit more.
Similarly with presbyopia, we have a converging,
plus lens to compensate for the loss of focusing power of
the hardened and flexible lens so that light focuses a little
sooner as it reaches the retina.
For astigmatism, where the eye is not perfectly round,
we use a cylinder to balance it out,
stretching the light coming in from
one direction without changing other directions.
We can even change the direction the cylinder's
oriented to balance it in any direction the eye is tilted.
Regardless of the type of
refractive error which will determine the type of lens used,
the first step is to give a precise measurement of
these errors so we can find the correct lens to fix it.
These are some common equipment we may use in
the clinic to get your measurements.
Finally, when should you worry
about refractive errors in your child?
Blurry vision is the most common symptom.
Children may also complain of
eyestrain and tiredness or headaches,
especially after activities requiring vision.
In children who are not yet able to complain of these symptoms,
you may know the signs such as squinting or rubbing the eye,
closing the eye as they try hard to focus on
near objects or other behaviors
suggestive of a vision problem.
If you notice any of these signs in your child,
you may want to consider bring them in for detailed eye exam.