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- Oh that's better, thanks.
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Hello and as always I would like to welcome you
to the Laramy-K Optician Works Training Center.
Last week we covered seven of the eight
refractive errors of the human eye.
And as promised today we're gonna wrap it up
with number eight, Presbyopia.
Last time that we got together we talked about
seven of the eight refractive errors of the human eye.
And I said that I don't really like
calling Presbyopia a refractive error.
I think it's a more of refractive condition
which most of us end up having if we live long enough.
And I'll talk about that in just a minute,
after we get through this section.
Same eye, same cornea, same retina, same fovea, same macula.
From there things get a little but different
than those other seven we talked about last time.
This is about a lens, the crystalline lens
that's inside the eye.
And because it's inside the eye
it's really none of our business.
There's nothing we can do about it.
We need to know the why of what's happening
so that we can figure out the how
we can overcome it with lenses.
That's our job, were opticians not docs.
When that crystalline lens which is a biconvex shape,
it's a plus lens, plus shape in very simple terms.
When we are looking out in the distance here.
We're looking at our big A, out past 20 feet.
The lens is relaxed, it's as flat as it can be.
As our object moves from distance to near
it passes our 20 foot mark roughly.
As the object gets closer and closer to us
this crystalline lens changes
either the zonules or ciliary muscles
and it allows the lens to change it's shape.
It becomes more biconvex, more plus.
And it allows us to see that object as it comes in clearly.
And kind of an important note,
something kind of fascinating is happening here in our brain
is that the object doesn't become larger.
I mean we think of a magnifying glass,
we think of making something larger.
But it doesn't, it actually just stays clear as it comes in.
Which is kinda cool, at least I think it's kinda cool.
Oddly enough the ciliary muscles contract,
release the pressure off the zonules
and that's what allows this lens to increase in size.
So that's the why, how we fix it
obviously we'll get into that in other videos.
But we use our common ordinary prescriptions
for our other seven refractive errors
combined with an add power.
We give back some of that plus that's lost
when this can no longer do what it's supposed to.
Let's talk about that for a few minutes.
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Let me talk just briefly a little bit more
about the why behind this.
What is happening to this poor
crystalline lens inside our body.
Well there are a couple of things
happening in very simple terms.
One is ...
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One is, cells die off.
Cells die in the body, you know skin cells
and they flake off and they go away, get vacuumed up.
They have a place they can go when they die.
The crystalline lens is a capsule.
It's enclosed, it's inside the vitreous humour.
Inside the eye, inside the body, inside the skull.
The cells as they die off inside the crystalline lens
over time as we age, they have no place to go.
They're trapped in there, they start taking up space.
They are no longer young and soft and able to move.
They start making that lens stiff.
It can't change shape anymore.
The muscles, just like the muscles in our body.
As we age, and we're creeping along and we're sore
and we can't move like we use to.
Same for these, the zonules and the ciliary muscles
they get old, they get tired.
Instead of reacting in milliseconds, they react in seconds.
Can't make that nice change rapidly,
don't allow it to expand and contract like it use to.
Related to this is cataracts, not direct relationship.
But over time because of the dead cells
and reaction possibly to UV light, or our age, or time.
This becomes cloudy and as that becomes cloudy
that's what you'd have what's called cataracts.
And of course light can't pass through the cloudy lens
and hit the retina nice and clean and sharp.
So they end up taking this out and replacing it.
But then again that's kind of
something a little but different.
But it's kinda sorta related to Presbyopia
and you understand why.
When this changes, if they change the power here
then our job out here changes as well.
That is a little but of an overview
of the refractive condition of Presbyopia.
We have covered the other seven in last weeks video
and of course soon we will be going on
to how we use lens, our job what Opticians do,
design lenses to overcome those eight refractive errors.
Thank you so much for watching.
Make sure you also watch the video
on the other seven refractive errors of the human eye.
Because soon we will tying lens design
to the correction of those errors.
Please hit the like button and please leave me a comment.
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Last ... (coughing)