Today we're going to start a short video series called Astigmatism Made Easy.

今日から「乱視を簡単に」という短いビデオシリーズを始めます。

I recently received a comment on one of the videos I did covering the 10 types of astigmatism in that they wish there were more examples on it and to be honest it was a really short video for a lot of information that was just kind of condensed into it.

最近、乱視の10タイプについて取り上げたビデオについて、もっと多くの例を挙げてほしかったというコメントをいただきました。正直なところ、多くの情報が凝縮されている割には、本当に短いビデオでした。

So this will be a time for us to kind of evaluate some different points in that video but on a slower level and kind of breaking it down a little better.

だから今回は、あのビデオのさまざまなポイントを評価する時間になる。

So first off, what is astigmatism?

まず、乱視とは何でしょうか？

Astigmatism is when light does not come to a singular point focus on the retina.

乱視とは、光が網膜上で一点に焦点を結ばないことである。

We want light to generally focus on the macula and the fovea centralis of the retina.

私たちは一般的に、光が網膜の黄斑と中心窩に焦点を結ぶことを望んでいる。

That's the point on the light sensitive tissue of the eye that receives the light image.

眼球の光に敏感な組織で、光のイメージを受け取る点だ。

So it has all the cone photoreceptor on it that have our clear central vision, our color vision, right?

つまり、中心視力や色覚をつかさどる錐体視細胞がすべてそこにあるわけだ。

So with astigmatism, light doesn't come to a singular point focus.

乱視があると、光は一点に集中しない。

It comes to a linear focus.

直線的なフォーカスになる。

So the light is kind of it's spread out.

だから光が広がっているんだ。

It's not to that singular sharp point and we illustrate this with a lot of times the oversimplification of a football image and I want to show that because it is a great illustration.

私たちはこのことを、サッカーのイメージを単純化しすぎた例で説明することが多い。

So this is a football.

だからこれはフットボールなんだ。

We'll put the laces on there just for for the fun of it and you know we're going to compare that to a soccer ball or basketball or whatever.

サッカーボールやバスケットボールと比較するんだ。

So with a round spherical shape like a soccer ball, if you can imagine this radius is going to be the same curve as this radius.

つまり、サッカーボールのような丸い球形の場合、この半径がこの半径と同じカーブになると想像してもらえればいい。

They're going to be the same steepness, right?

同じ急勾配になるんだろう？

So from there to there it's going to be the same pattern and you could do that all throughout, right?

だから、あそこからあそこまでは同じパターンになるし、それをずっと続けることもできるよね？

So that is the same.

だからそれは同じだ。

That line is going to be the same steepness as this line here.

このラインはこのラインと同じ急勾配になる。

That's if your eye was perfectly spherical and you did not have astigmatism.

あなたの目が完全な球形で乱視がなかったらの話です。

It doesn't mean you don't have a refractive error, right?

屈折異常がないわけではないですよね？

Because your eye could be too long like a myope or too short like a hyperope but it could still mean that light's coming to one singular point.

近視のように眼球が長すぎたり、遠視のように眼球が短すぎたりしても、光が一点にしか届かないということはあり得るからだ。

Astigmatism means more like a football that this meridian, right?

乱視というのは、この子午線よりもサッカーボールのようなものだろう？

Our vertical 90 you know might be steeper and if you can imagine this curve on a football it's much less drastic.

私たちが知っている縦の90度はもっと急かもしれないし、サッカーボールのこのカーブを想像してもらえればわかると思うが、もっと激しくない。

It's flatter, right?

もっと平らでしょう？

So a football laying like this is a good example of with the rule of astigmatism.

つまり、このようなサッカーの敷設は、乱視のルールと相性が良い例なのだ。

Just something to remember your vertical meridian is steeper so it'd be like the cornea is steeper in the vertical meridian but this is astigmatism.

ただ覚えておいてほしいのは、縦経線の方が急なので、角膜が縦経線で急になっているようなものですが、これは乱視です。

Light is entering at different steepnesses you know a flattest point and a steepest point and it's causing that light to enter and and fall upon the retina in a linear fashion instead of that point that we really want.

光は異なる急勾配で入射し、最も平坦な点と最も急勾配な点があり、光は私たちが本当に望む点ではなく、直線的に網膜に入射し、落下する。

So if that's what astigmatism is then we also need to define you know the anatomy of the eye that can cause astigmatism or yeah so like what are the refractive medium of the eye?

乱視がそうであるならば、乱視の原因となる目の解剖学的構造を定義する必要があります。

What are the parts of the eye that are creating astigmatism?

乱視を作り出している目の部分とは？

Well to refract means to bend, right?

屈折するということは、曲がるということだよね？

So we're talking about bending light so if the cornea was completely spherical like our soccer ball right no matter how light entered it it would enter at the same radius of curvature and it would provide the same refraction same refractive properties but then we have the if this is the anterior view of the eye coming through then you have the crystalline lens which is behind it kind of suspended in the anterior chamber of the eye.

角膜がサッカーボールのような完全な球面であれば、光がどのように入射しても同じ曲率半径で入射し、同じ屈折率、同じ屈折特性を示します。

That's another lens of the eye and it too can have torricity which is you know and create astigmatism.

これも目のレンズのひとつで、乱視を作るトーリシティがあります。

Much more common on the cornea but you can find it on the crystalline lens.

角膜によく見られるが、水晶体にも見られる。

So the cornea supplies roughly 43 diopters of strength that's plus 43 it's a plus power lens you know and just to take a step back of how amazing it is that the cornea is like half a millimeter thick in the center it's supplying 43 diopters of strength and the crystalline lens supplies on average about plus 17 diopters and that gives us our 60 diopters of strength but either one of those surfaces can be torric right can have a cylindrical component on it which is going to make light enter it differently.

つまり、角膜はおよそ43ディオプターの強度を供給しており、これはプラス43であり、プラス度数のレンズなのです。角膜の厚さは中心部で0.5ミリほどですが、これが43ディオプターの強度を供給し、水晶体は平均してプラス17ディオプターの強度を供給しています。

So the big question is you know how do we measure astigmatism?

そこで大きな疑問は、乱視をどうやって測定するかということだ。

Well the main instrument that's used to measure astigmatism is the keratometer.

乱視の測定に使われる主な機器はケラトメーターです。

The keratometer is what we get our k readings from and interestingly it just measures the central three millimeters three to four millimeters of the cornea right so we know our cornea horizontally measures about 12 millimeters right and then vertically maybe 10 and a half millimeters.

角膜の中心3ミリ、3～4ミリを測定するだけなので、角膜の水平方向は約12ミリ、垂直方向は10.5ミリということになる。

So we're talking about you know the corneal cap it's measuring about three millimeters just this zone of it and it's measuring the steepness it's finding out what the flattest meridian is and what the steepest meridian of the cornea is.

角膜の角膜蓋を3ミリほど測り、角膜の最も平らな子午線と最も急な子午線を見つけるのです。

The average keratometer is going to measure from 36 to 52 diopters and and what that's measuring is the power of the cornea but also the steepness of the cornea.

平均的な角膜度数は36から52ディオプターで、角膜の度数だけでなく角膜の急峻さも測定します。

Also remember just helpful on your test you can add a negative one auxiliary lens it's going to bring your case down to 30 diopters or you could add in the in the positive direction a plus one and a quarter lens and that's going to bring you up up nine more diopters up to 61 diopters from 52 to 61.

また、テストに役立つだけでなく、補助レンズをマイナス1枚追加すると30ディオプターになり、プラス方向にプラス1.4枚追加すると52から61ディオプターまで9ディオプター増えることを覚えておいてください。

That's just a side note neither here nor there but we measure corneal astigmatism with k readings and I'm just going to give you an example of that.

これは余談ですが、角膜乱視の測定にはK測定が用いられます。

So let's say our k readings are 42 at 180, 43.50 at 90.

つまり、Kの数値が180で42、90で43.50だったとしよう。

What this is telling us and I'll do another drawing here across our vertical meridian our 90 the power of the cornea is 43.5 diopters at our 180 it's 42 diopters.

この図からわかることは、垂直子午線を挟んで90°の角膜の度数は43.5ディオプター、180°の角膜の度数は42ディオプターということです。

So the difference between those two our steepest and our flattest meridian is going to be our corneal astigmatism.

つまり、最も急な子午線と最も平らな子午線の差が角膜乱視になる。

So 43.50 from you know 42 from a 43.50 that's one and a half diopters of those two values that's the amount of toricity that's the amount of cylinder value on ascribed to the cornea because remember a keratometer or an ophthalmometer you might refer to as only measures corneal astigmatism.

つまり、43.50と42.50では1.5ディオプターの差があり、これが角膜に割り当てられたトーシティの量であり、シリンダー値の量なのです。

I'm going to do one more example of that so if we have um I'll read this out so it's actually clear okay 44.50 at 70 and then 45 at 160.

もう1つ例を挙げますので、もしよろしければ......70で44.50、そして160で45と、はっきりわかるように読み上げます。

So our flattest meridian our 44.50 is at 70 and we have 45 diopters of strength at the 160.

つまり、最も平らな子午線44.50は70にあり、160の強度は45ディオプターある。

So there is a difference of what a half a diopter between those two uh meridians the steepest and the flattest meridian so there's a half a diopter of corneal astigmatism and this brings up a great point now um so if defining astigmatism there is regular astigmatism and irregular astigmatism.

つまり、最も急な子午線と最も平坦な子午線という2つの子午線の間には、なんと半ディオプターの差があるのです。

Regular astigmatism means that the principal meridians are 90 degrees apart from one another so this is measured by keratometry um you could have with the rule against the rule oblique astigmatism these are all regular astigmatism but then you have irregular astigmatism.

正乱視とは、主経線が互いに90度離れていることで、これはケラトメトリーで測定される。

Irregular astigmatism cannot be we can't use a cylindrical eyeglass lens we can't use a cylindrical contact lens to correct irregular astigmatism.

非正規乱視は、円筒形の眼鏡レンズを使うことはできません。非正規乱視を矯正するために円筒形のコンタクトレンズを使うこともできません。

Keratoconus is commonly associated with irregular astigmatism you know that's a thinning of the cornea and you have a an oblate like a protrusion of the cornea um pelucid marginal degeneration is kind of like keratoconus it's a thinning of the anterior um inferior part of the cornea the lower part of the cornea um you could have if trauma something you know punctures the cornea um different disease can cause um corneal thinning that gives you an irregular corneal shape so another word to remember now um i'll write on the board it's a fun word this is like bonus stuff right here ectasia so it's even fun to ectasia so you'll hear corneal ectasia that is thinning so this word means thinning so it's a thinning of the cornea um thinning of the cornea can create an irregular surface so we have irregular astigmatism which is like an ectasia of the cornea you know and for these for these patients you need to use some sort of a gas permeable lens you know a lens that's rigid enough that it's going to create a tear film behind the lens and it's going to provide a brand new optical surface um because we're it's not going to be able to you can't use like a soft contact lens that drapes the cornea to correct for irregular astigmatism so that's kind of the the foundation of astigmatism here shortly in the next video series i'm going to go over with the rule against the rule and oblique astigmatism and just do some examples and some example prescriptions with that um and then you know i'm going to do another uh video after that on like compound myopic simple myopic you know mixed astigmatism those types of classifications and you know that way we could just bring it all together and you could really have a solid foundation of what is astigmatism if this video has been helpful i definitely encourage you to subscribe to the channel share it with your friends and really just to keep watching it because you know i'm truly you know a firm believer in especially as opticians contact lenses it's you know it's really just um the heart of the medical side of what we do and just uh the more that we are subject matter experts on this the more that we'll be able to help our patients and provide good service to them because you know with just a surface uh level knowledge of contact lenses we're really not doing our patients any service so just keep watching if you're studying for your ncle um trust me just just watch the videos and study your material uh find a good comprehensive guide and just read through it um there's a number of good resources out there i know carrie wilson has a great book for ncle but if you're pairing the the question the answers up with these videos i know you'll be a success on the test you know these these videos truly are just geared towards the theory behind the material and helping you to understand it better if you're not necessarily like a textbook person and you weren't fortunate enough to go to opticianary school or be able to be lectured to these are kind of hopefully supplementing and taking the place of that so anyway stay tuned and i'm going to have another video in this series coming up shortly thank you

円錐角膜は、一般的に不正乱視と関連しています。角膜が薄くなり、角膜が突出したような楕円形になります。病気によって角膜が薄くなり、角膜の形が不規則になることがある。角膜が薄くなると、乱視が生じます。角膜の外乱のようなものです。このような患者には、ある種のガス透過性レンズを使用する必要があります。乱視を矯正するために角膜をドレープするソフトコンタクトレンズを使用することはできません。このビデオが役に立ったなら、ぜひチャンネル登録することをお勧めします。コンタクトレンズの表面的な知識だけでは、患者さんのためにな