Betzold 89947 Handbuch Seite 19

Illustration 2: Myopic eye. The eyeball is too long, the focal point lies in front of the retina.
Farsightedness occurs when an eye is too short in proportion to its focusing power or the refractive power is not strong enough.
People with farsightedness can see distant objects very well, but have difficulty focusing on objects that are up close. With
farsightedness, the focal point of the eye is beyond the retina. To a certain degree the lens of the eye is able to help adjust the
focus between near and far. Children have a very flexible eye lens, but with increasing age the elasticity of the lens decreases.
Presbyopia is a condition associated with aging in which the eye loses the ability to see clearly at close range.
Illustration 3: Farsighted eye. The eyeball is too short, the point of focus lies beyond the retina.
In order to understand why a person has a vision impairment it needs to be explained how near and far objects are focused by
the eye: The eye lens is an elastic capsule filled with transparent fluid. The ciliary muscles change the shape of the lens, and
therefore also the focal point of incoming rays of light. This is how the eye adjusts the ability to see near and far.
When in a relaxed state the ciliary muscle is large in diameter, but does not expand in length.
Fibers (zonular fibers) attaching the ciliary muscle to the lens become taut, flattening the lens. This enables long range focus
(negative accommodation).
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