another important part of human eye are ciliary
muscles, to understand the working of ciliary muscles which we have studied in the previous
section that these are holding the eye lens at its position. lets understand a fact about
converging lens. we already studied in previous topic that if there is a converging lens or
a convex lens on which parallel light rays falls onto it. these light rays converges
to a point we call focal point or focus of the lens. the distance of this focus from
the lens is called focal length it is denoted by, the symbol small f. now in eye lens also
there is a focal length of eye lens. which decides where, the image of an object which
we are looking at will be produced. now in this situation here we can write. first we
study about ciliary muscles. and then we’ll, use this, concept of focal length in understanding
the working of ciliary muscles. about ciliary muscles we can write these are. muscles. holding
the eye lens, this we already studied in the previous section. now the important thing
about ciliary muscles, is. by contraction. in ciliary muscle. curvature of. eye lens
increases. due to which. its focal length. decreases. and a clear image. of modified
object. modified object means the object which is seen. the image is produced by, relaxation
or contraction in the ciliary muscles. and the object is modified and it can be seen.
here we can write that image is modified object is the one which we are looking at. and all
near by objects which are placed. anywhere in surrounding if we look at any nearby object.
due to contraction or relaxation in ciliary muscle the curvature changes here we have
written that by contraction the curvature of eye lens increases. due to which focal
length decreases and vice versa also that we can also write here. when ciliary muscles.
are relaxed. then curvature of eye lens. decreases. and its focal length. focal length is the
distance from eye lens where, eye lens converges all parallel light rays onto it. this increases.
so always remember in relaxed state of ciliary muscle focal length is large and in contracted
state of ciliary muscles focal length is less. if focal length increases and. a clear image
of. a distant object. can be seen. so in nearby objects, we can write the images are modified
due to the contrition in ciliary muscles and the image of such, nearby objects. can be
seen by contraction in ciliary muscles and when we look at the distant objects, which
are look at far away from eye, in relaxed state of ciliary muscles we can see the clear
image that’s why. you might be aware. that when, you wish to see the clear image of a
very close by object you need to strain your eyes. here you can see in this picture, this
is the picture of eye lens along with ciliary muscles. so when eye will look at far away,
objects from which the light rays are almost parallel in relaxed state the image is produced
at the focal point. but when we have a look. on very nearby objects here you can see, the
ciliary muscles compresses and contracts the eye lens due to which its curvature increases,
and. because of which the focal length decreases so a close by object, can be seen as its image
is produced on retina.