Betzold 89947 Handbuch Seite 20

ciliary muscle
ciliary muscle
zonular fiber
zonular fiber
eye lens
eye lens
Illustration 4: negative accommodation, ciliary muscle relaxed
When the ciliary muscle contracts, it expands in length and its diameter is reduced. Thereby the tension on the zonular fibers
is released. The lens thickens to a rounder shape and increases its curvature. Nearby objects can be seen clearly (positive
accommodation).
ciliary muscle
ciliary muscle
zonular fiber
zonular fiber
eye lens
eye lens
Illustration 4: positive accommodation, ciliary muscle is contracted
By the way, contrary to farsightedness, it is not possible for a nearsighted person to compensate nearsightedness by accommo-
dation. The ciliary muscle cannot relax any more than it already is. Nearsighted people try to minimize the size of distraction on
the retina by blinking. Therefore the image sharpness is improved (stenopaeic vision).
The following text is also available as a fill-in-the-blanks text (see 7.1).
Nearsightedness / Farsightedness
If the eyeball is too long or the refractive power of the eye's lens is too strong it is called nearsightedness. The position of the
focal point falls to the front and lies before the retina. Nearsighted people can see nearby objects very well, whereas objects in
the distance cannot be focused clearly.
Farsightedness occurs when an eye is too short in proportion to its focusing power or the refractive power is not strong enough.
The focal point of the eye is set back and lies beyond the retina. People with farsightedness can see distant objects very well,
but have difficulty focusing on objects that are up close.
The ciliary muscle is relaxed and the lens flattens when looking into the distance.
Nearby objects can be seen when the ciliary muscle contracts and the lens thickens to a rounder shape and increases its
curvature.
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