「Nerve06/eyes and ears/focus adjustment」の版間の差分

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From a certain point, light spreads to all directions (Fig 2A).  This light reaching the eye, some distance away, will have a certain spreading angle at the lens (B).  Since the lens can refract (bend) the path of the light, it can converge this spreading angle.  When the paths converge to one point at the retina, the point A will not be blurred and can be seen sharply.  This is called 'in focus'.  Secondly, if point A was in a far distance, then the path of the light reaching the would be parallel (C).  In a normal eye, when the lens is thinnest (with least refractive bending power), the light path from a far distance converges to one point.  However, if the light originated closer to the eye, the light path will converge to one point behind the retina if the lens remains thin (D).  Thus, at this circumstance, the refractive power (thickness) of the lens need to be increased for focusing.   
From a certain point, light spreads to all directions (A).  This light reaching the eye, from some distance away, will have a certain spreading angle at the lens (B).  Since the lens can refract (bend) the path of the light, it can converge this spreading angle.  When the paths converge to one point at the retina, the point A will not be blurred, but rather clearly seen.  This is called 'in focus'.  Secondly, if point A is at a far distance, then the path of the light reaching the lens would be parallel (C).  In a normal eye, when the lens is thinnest (with least refractive bending power), the light path from a far distance converges to one point.  However, if the lens remains thin and the light originates closer to the eye, the light path will converge to one point behind the retina (D).  Thus, in this circumstance, the refractive power (thickness) of the lens needs to be increased for focusing.   


[[ファイル:00739.jpg|500px]]
[[ファイル:04222.jpg|500px]]


The ciliary body surrounds the lens like the rings of the saturn, pulling the lens outwards, which makes the lens thin.  Also, when the the muscles in the ciliary body, which are in the circular direction, contract, the diameter of the ciliary body decreases, and the lens, being pulled less outwards, becomes thicker.  So, when the ciliary muscle are dilated, the diameter is increased, pulling the lens outwards, decreasing the thickness and the refractive (bending) power of the lens (Fig 2C).  When the point is near, the ciliary muscle contracts, the diameter is decreased, pulling the lens less outwards, increasing the thickness and the refractive (bending) power of the lens (Fig 2B).  This is done by the parasympathetic nerve activity of the oculomotor (III cranial) nerve.   
The ciliary body surrounds the lens (like the rings of saturn) and pulls the lens outwards, making the lens thin.  When the circular muscles in the ciliary body contract, the diameter of the ciliary body decreases, and the lens becomes thicker.  So, when the ciliary muscles are dilated, the diameter is increased, pulling the lens outwards, thereby decreasing the thickness and the refractive (bending) power of the lens.  When the point is near, the ciliary muscle contracts, the diameter is decreased, increasing the thickness and the refractive (bending) power of the lens.  This is done by the parasympathetic nerve activity of the oculomotor (III cranial) nerve.   


{{QuizTitle}}
{{QuizTitle}}
<GIFT>


<GIFT>
//LEVEL:2
//LEVEL:2
//RAND
//RAND
When focusing on a near point, the ciliary muscle {=contract.~dilate}, and the lens becomes {=thick.~thin}.
When focusing on a near point, the ciliary muscle {=contracts~dilates}, and the lens becomes {=thick~thin}.
 
</GIFT>
</GIFT>

2014年11月18日 (火) 21:47時点における最新版

From a certain point, light spreads to all directions (A). This light reaching the eye, from some distance away, will have a certain spreading angle at the lens (B). Since the lens can refract (bend) the path of the light, it can converge this spreading angle. When the paths converge to one point at the retina, the point A will not be blurred, but rather clearly seen. This is called 'in focus'. Secondly, if point A is at a far distance, then the path of the light reaching the lens would be parallel (C). In a normal eye, when the lens is thinnest (with least refractive bending power), the light path from a far distance converges to one point. However, if the lens remains thin and the light originates closer to the eye, the light path will converge to one point behind the retina (D). Thus, in this circumstance, the refractive power (thickness) of the lens needs to be increased for focusing.

04222.jpg

The ciliary body surrounds the lens (like the rings of saturn) and pulls the lens outwards, making the lens thin. When the circular muscles in the ciliary body contract, the diameter of the ciliary body decreases, and the lens becomes thicker. So, when the ciliary muscles are dilated, the diameter is increased, pulling the lens outwards, thereby decreasing the thickness and the refractive (bending) power of the lens. When the point is near, the ciliary muscle contracts, the diameter is decreased, increasing the thickness and the refractive (bending) power of the lens. This is done by the parasympathetic nerve activity of the oculomotor (III cranial) nerve.

Challenge Quiz

1.

When focusing on a near point, the ciliary muscle contracts dilates , and the lens becomes thick thin .