So, if you're watching this video, there's a good chance that you
have heard the term 'astigmatism' and perhaps you've heard that
every single time you go in for your eye exam.
Well, in this video, we're covering exactly what astigmatism is
how astigmatism affects our vision and our prescriptions.
So, let's take a look.
Hey, guys! This is Doctor Joe Allen from DoctorEyeHealth bringing you
the very best in tips and education about your eyes
and your vision and here on this channel you'll find a lot of
different product reviews as well as educational videos just
like this one so if you're new here, considering subscribing
and at any point in the video make sure to check out the show notes and links below for
further information about anything we forget to mention.
Otherwise, let's go over astigmatism. So astigmatism
is arguably one of the most common things I
have been talking about with my patients every single day.
It's a very common diagnosis and it is something most of us, probably
have to some degree. The most simple way to explain
astigmatism is basically that the structures within the eye
are not perfectly round; they're a little bit warped
and because of that, it causes light to bend
or refract a little bit uneven inside of the eye
and that causes your vision to be blurry, and distorted.
However, the good news is that astigmatism isn't
actually a disease, it's just a condition, and we can
correct for that with glasses, contact lenses, and even
eye surgeries, like LASIK. Now, to better
explain what astigmatism is, I want to show you the
cornea. The cornea is the front window surface
to the eye. It protects the inside of the eye
from the outside environment, and acts as a lens to
bend light toward the inner eye. In an ideal world
it is a smooth and evenly curved surface to that light
passes through it in a uniform fashion.
However, most of us have some unevenness
on the surface of our cornea, and that uneven curvature
is what is called corneal astigmatism. The uneven
curve of the cornea can be determined by
finding the difference between the flattest and the steepest curve
of the corneal surface. Most corneas have some
curvature somewhere between 39 and 49 diopters
and that number
tells us the amount of curvature or power
that the cornea has to bend light. If there
isn't astigmatism, as in this example, we'll say maybe
the curvature is 43 diopter in one place
and maybe 41 diopter in another.
The amount of astigmatism in this example being the difference
being between 43 and 41 is two so
the answer is 2 diopters of corneal astigmatism.
Now, your eye doctor can actually measure this curvature
to the eye using a couple of different instruments.
Classically, we would use one called a Keratometer which only measure about the
first three millimeters centrally of the cornea.
But nowadays, we actually use new technology
called a topographer, and the topographer will not only
just measure the central three millimeters, but they'll measure
but they'll measure the entire front surface of the cornea making it
a little bit easier to identify disease as well as
to treat and manage those conditions, such as with
specialty contact lenses or even with corrective eye
surgery. Now, when light passes through a cornea with astigmatism,
that causes the light to be focused irregularly
inside and that causes our vision to not just be
really foggy and blurry, but
can cause your vision to be distorted.
Almost in an extreme example, it would look like a fun
house mirror, where everything can kind of
be wonky and warped. Now most of us are actually born with
some level of corneal astigmatism, and it may
change in the first couple of months and then it tends to
stabilize out for the rest of your life. Now there is another type
of astigmatism, and we call that lenticular
astigmatism.
And that has to do with the shape of the lens inside the eye.
And that astigmatism does tend to change throughout
our lifetime. First in our adolescent years, as
we're under more visual stress, and then again
in our later years as the lens begins to stiffen.
Now, when the doctor measures and corrects for your astigmatism,
they actually correct for the combination
of the two: both the cornea and the lenticular
astigmatism. Usually, your doctor won't measure the lenticular
astigmatism by itself because it requires
very expensive and high-tech equipment and it really just
doesn't give us that any much useful information. Now, if
you don't know if you have astigmatism or not, we can actually figure that out
by looking at your most recent glasses prescription.
So, let me guide you through how to read those numbers.
So, if we look at a prescription pad here
and zoom in here we are going to see, of course, the first and last name,
a date of birth, and then down below we are going to have the expiration
date and your doctor's signature.
Now, looking here on the left side you will see two rows, one is labeled
OD which stands for the right eye and one is labeled OS,
which stands for the left eye. On the top, we have
several columns which we can actually work through
individually, the first column here is labeled as
SPH, which stands for sphere,
which is the easiest type of lens that can be made. Under that
you'll see some numbers, the higher the number the stronger
the prescription. The number will also have a positive or
a negative symbol in front of it, which tells us
if the lens is correcting for far-sightedness, or hyperopia,
when it's a positive symbol and near-sightedness, or
myopia, when it's a negative symbol.
These next two columns here are going to tell you if you have astigmatism.
That first column is
the cylinder, and the higher the cylinder number,
the stronger your astigmatism correction will be.
Again, in front of this number you may see a positive or
a negative symbol. However, it is more common
to have a negative symbol here because when an optician makes glasses,
it has to be in the negative format.
If your prescription does have a positive symbol here,
well, then your optician has to do extra work to convert it
and it increases the likelihood of errors when
glasses are made. The next part is called the axis, and
the axis number indicates the
position of the overall astigmatism through the visual field.
And this number will be between 0 and 180.
To illustrate this better, we can divide the eye into
a pie with twelve equal sections. The astigmatism lies
along one of the divisions of this circle.
In this case, the astigmatism is along the 120-degree
line in the right eye, and 20-degree
line in the left. The
axes are darkened on the illustration to indicate this.
It is actually more common for the prescription
when we are young to have an axis closer
to the 180 line, and then gradually becomes
closer to 90 as we age.
So, if you have these number, that's going to tell you that you have
astigmatism. However, the last two sections here
describe what is called the add or the
additional lens needed to help someone see up close as in
the use for bifocals, and the there's the prism which
isn't used very often, but is necessary for those individuals who have
fusion difficulties and may end up seeing double.
Now, the good news is that we can correct for astigmatism
with glasses, contact lenses, and again
forms of corrective surgery like LASIK. The most simple way to correct
for astigmatism is with glasses.
However, glasses aren't always the best way to correct for it
because we can get some optical distortions
because they're looking through a piece of glass or plastic. And you can
kind of experience that distortion by holding up
your lenses and looking at a distant object that's
straight up and down.
And then rotating the lenses so you can see how the
world starts to warp left and right or side to side.
And that's why some people will say that it feels like
they're almost having tunnel vision while looking through glasses
as compared to some options, like contact lenses.
Contact lenses are fantastic because it actually forms to the
surface of the eye, giving you a wider field of
view, and can correct for that astigmatism,
all at the same time. Now, most contact lenses for astigmatism
may actually be called toric lenses
and these lenses have a little dash mark that's
etched into the lens and you can hold up the
lens to the light and sometimes you can see that little marking.
That mark is there so that the doctor can read where the lens is
sitting on the eye, and then make adjustments
so that you can get the best prescription and
comfort in those lenses. Many types of corrective
eye surgery can actually correct for astigmatism
as well ,such as LASIK. LASIK can actually
actually correct up to almost 5 or 6 diopters
of astigmatism. So, make sure you ask your doctor
if you are a good candidate for those procedures.
Now, let me show you what somebody sees when they're not
wearing correction for their astigmatism.
I'll give you the best frame of reference we have a vision chart in the clinic here on the left side and we have some distant objects
outside here on the right. We'll start off
to showing what 1 diopter of corneal astigmatism
set at about and axis 90 degrees looks like
and then we can rotate it so the axis is closer to
180 degrees. We can also
do the same thing with 2 diopters of corneal astigmatism,
and then we can go over to 3 diopters
and then over to 6 diopters.
And here at 6 diopters, you can see how warped
or bent someone's vision would be if they were walking
around without correction for their astigmatism.
Now, again the good news is that astigmatism isn't really
a disease, it's just a condition that we correct for.
However, there are some extreme cases
where people will have really high levels of astigmatism
and that can actually be classified into diseases.
One of those diseases is called Keratoconus, where the surface
of the eye, the cornea, actually starts to bulge out
into a shape of a cone. Other cases such as
Pellucid Marginal Degeneration describes
where the cornea begins to thin inferiorly,
causing again high levels of astigmatism.
Now some people may have had trauma to the eye or scarring
that actually caused astigmatism and that again can be corrected
with special contact lenses and maybe even just glasses
by themselves.
Alright, guys, thanks for checking out our video
about astigmatism and how it affects your eyes and your vision.
If you like what you saw, make sure to hit that like, subscribe
and go ahead and share this video with friends and family who may be
interested more in what astigmatism actually is.
Otherwise, again, this is Dr. Joe Allen from DoctorEyeHealth,
bringing you the very best in tips and education about your eyes
and your vision. Keep and eye on it! We'll talk to you soon.
*beep*
*woo sounds* putting on my cool glasses.
Putting on my cool glasses.
Ooh, it felt good!