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  • (light orchestral music)

  • - Oh that's better, thanks.

  • (upbeat instrumental music)

  • 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.

  • (brite instrumental music)

  • 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 ...

  • (brite string music)

  • 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.

  • (light orchestral music)

  • Last ... (coughing)

(light orchestral music)

Subtitles and keywords

B1 INT US lens crystalline eye human eye cloudy object

What Is Presbyopia?

  • 215 0
    wei   posted on 2018/12/15
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