So nearsighted versus farsighted in this video
I'm going to be reviewing what it means to be nearsighted so that you can better understand how our eyes and vision works
So let's take a look
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So now to better understand nearsightedness versus farsightedness
Let's go over the basic fundamentals of how the eyes actually work
Now when light hits objects all around us that light then bounces off those objects and enters into our eye
When it hits our eye
It goes through three different refractive
Structures that help bend the light and these structures include the tear film the very front surface of the eye
you have the cornea which is the window to the eye and then you have the crystalline lens and that's the
focusing lens inside of the eye
when light goes through these structures
Those structures actually bend the light and help focus it to the back of the eye and hopefully that light gets focused onto the human
retina that
retina is basically like the satellite dish that picks up all that light information and then sends it to the visual processing centers of the
Brain, and that's what gives you your eyesight now whether you have nearsightedness farsightedness or astigmatism
we refer to that as refractive error and
Refractive error means that the strength powers of the eye are either too strong
They're too weak or that the retina itself is either too far back in
Reference to where that light is focusing or it's too far forward and the end result is blurred vision
however
In most cases we can correct for that with glasses, contact lenses or corrective eye surgery
to get that light to focus onto the retina correctly giving clearer vision. Now if somebody is nearsighted in the medical world
We call that person having myopia or being myopic and that means that when they see things in the distance things are not in focus
Things are too blurry
However, when they're looking up close at something like their phone then things are nice in focus
They're sharp. And again that person is nearsighted
Now this happens because when an eye is fully relaxed looking in the distance
The light isn't focused cleanly onto the retina and in fact, the light is focused too strongly
It converges in front of the retinal surface or it could be that the eyeball itself
Is actually stretched out and is longer meaning that retina is pushed further behind where that light is focusing
Actually when we fix or prescribe glasses or contact lenses to correct for nearsightedness
We actually prescribe minus lenses
these lenses are actually made to weaken the power of the eye and
push that focusing light to the retina to help you see that is why when you look at a
prescription for glasses for someone with nearsightedness you'll actually see a little
Minus symbol in front of those numbers now the reason for somebody who is nearsighted to be able to see up close
Without any form of correction on has to do with some physical
properties of light that comes off of near objects the light that comes off of a near object we call
Divergent light and that means that the light is actually spreading outward from that near object
Now the reason if somebody can see you'll see up close
With that divergent light is because it's balanced out by the focusing powers of the eye and that makes the light land perfectly
Onto the retina even without glasses and again, that's why they can see clearly up close
So that's what it means to be nearsighted. Did you get all that now?
Let's compare that to someone with just the opposite. They are farsighted or in the medical world. We call that having
hyperopia, or hypermetropia now, I explaining hyperopia or farsightedness is a little bit trickier than nearsightedness and that's because of
The involvement of the crystalline lens. Now the crystalline lens together is one of the focusing powers of the eye
but the crystalline lens is under the influence of a muscle inside the eye called the ciliary body and when this muscle
Flexes the lens inside the eye can change shape and therefore focus the light inside of the eye
Hopefully to the retina on its own
It's actually one of the most amazing parts of the human eye
And that's the ability to focus light on its own just like a camera lens that done autofocus now an eye care
We like to assume that the refractive powers of the crystalline lens are fully relaxed
However, that's not really true. Almost always people are using their eye muscles just a little bit
In fact, it's nearly impossible to fully relax your eye muscles on your own
However, in the clinic we can use different medications in the form of eye drops to help relax those muscles
completely and we call that a cycloplegic refraction and that gives us a lot more information about how somebody's actually
Utilizing their eye muscles and the exact refractive powers of the eye now for this example
Let's imagine somebody who is farsighted that cannot use their eye muscles at all
And they're looking in the distance in that case the light being focused inside of the eye is being focused to weakly
It's not strong enough
and the light is actually focused behind the retina or it could be that the eye itself is too small and the light again is
Focused again behind the retina and not giving us a clear image in that case
somebody's prescribed plus lenses
These are magnifying lenses that actually help move that light in front
Toward the retina giving them clear vision now in many cases
somebody who is farsighted may not need glasses at all or for maybe not at least most of the time and that is because that
focusing power of the eye
if they are able to utilize their eye muscles and focus the crystalline lens inside the eye then it basically
Acts like a magnifying lens. That is fluid
and allows us to adjust its power again without needing that farsighted prescription
However, the powers of that crystalline lens are limited
In fact, that lens grows every year of life and as it gets bigger year after year
The lens actually becomes more rigid and difficult to flex meaning that your power or ability to move that focusing plane
Forward to the retina, it's more difficult and more difficult over time, especially
When somebody's looking up close meaning that a lot of people who are farsighted again, they take the glasses off
They can see pretty well, but when they're looking up close it's more difficult. So they need reading glasses
in fact
that's really one of the reasons why a lot of people end up not having glasses until they're
40s ended up needing glasses to read as they get older and we call that presbyopia
Which has literally Latin for old eyes
But when somebody is young and has the ability to focus that lens inside of the eye
They can overcome quite a bit of farsightedness on their own without glasses
the tough part is that some people are using those muscles all day long just to see clearly even that distance and
eventually those muscles that whole
Dynamic process of using those eye muscles and focusing can break down
resulting in
kind of a muscle spasm
Inside the eye it can end up with eye fatigue or even really - things like headaches and so some people end up still needing
to wear glasses for their
Farsightedness at all distances just to help relax those eye muscles and prevent that eye fatigue and that's it
That's basically the difference between nearsightedness and farsightedness
However, when somebody is nearsighted or myopic it's usually not that the focusing powers of the eye are too strong
It's more likely that the eye itself has grown and stretched out through adolescence and this can happen because of either genetic influences
environmental factors
But that I actually does tend to stretch out and that's concerning for me as an eye care
professional because when the eye starts to stretch out the higher amounts of nearsightedness are
associated with different eye diseases that can potentially lead to vision loss and this can include cataracts glaucoma a
certain condition called myopic maculopathy
you can lead the eye floaters retinal tears and
Detachments and even in some extreme cases the retina can actually stretch out so much that it begins to crack open
And little blood vessels can grow inside the eye and those new blood vessels can destroy the retina completely
So yeah, having excessive amounts of nearsightedness can put the eye at higher risk certain eye diseases
It's a major concern in fact in eye care
There's a whole growing kind of sub specialty called myopia control and that's utilizing different strategies
Different types of lenses to help influence the eyes us to slow down and stop it from progressing
and growing longer and
The entire point of that is to get slowed down and prevent these different diseases from occurring and becoming more prevalent
Actually just recently did an interview with one of my doctor friends here in Minnesota. Dr. Roman Gerber of Wink Family
Eye Care who's very passionate about myopia control if you'd like to check out that video
I have hooked up a link to that in the description below as well as in the YouTube card up above
All right eye health question of the day. Are you near-sighted? Are you farsighted?
Do you wear glasses do wear contacts or have you had some sort of corrective surgery like LASIK go ahead and comment in the section
Below, I'd love to hear from you. Alright guys. Thanks so much for watching. Again. This is dr. Joe Allen hear from dr
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