Refraction and
Converging Lenses
THE HUMAN EYE
SUAAD MOHAMMAD
ERIN OLSON
Refraction is the way
that light bends when
going from one medium
to another. Converging
lenses are types of lenses
where the light enters
the lens, and refracts
towards the normal. An
example of a thin
converging lens is the
human eye. In the
human eye, the light
comes in, and bends
towards the retina,
where the picture is
formed. The picture that
is formed is an inverted
picture. The human
brain must then flip the
image formed in order
for us to see the world
right side up.
Refraction
The human eye is a
convex lens in which
rays of light converge.
Light is refracted on the
cornea and lens, and
meets on the back of the
retina, creating a clear
picture.
The Normal Human Eye
Nearsighted vision is
when the light focuses in
front of the retina.
There can be different
causes for this problem.
1.1. The eye is too long
and the light focuses
before hitting the retina.
2.2. Astigmatism – The
cornea is not perfectly
spherical causing light to
refract at a different
angle.
3.3. Curvature – If the
lens is steeply curved it
causes nearsightedness.
Nearsighted
Farsightedness takes
place when the light is
not completely focused
before hitting the retina.
The reasons for this
condition are opposite
for those of
nearsightedness.
1.1. The eye is too short
causing the light to focus
beyond the retina.
2.2. Astigmatism – The
cornea is not spherical
causing the light
refraction to be off.
3.3. Curvature – If the
lens is too flat, it causes
farsightedness.
Farsighted
If you are having trouble
with your vision, an eye
doctor will perform what
is called a refraction test
to determine if there is a
need for correction.
During this test, an eye
doctor will use different
lenses to refract the light
differently to determine
if one of the lenses helps
you to see more clearly.
If correction is needed,
they may write you a
prescription for glasses
or contacts.
Refraction Test
To correct a vision
problem, eye glasses can
be prescribed. The lens
works to refract the light
in such a way that
focuses the light
correctly on the back of
your retina to create a
sharper image. Contact
lenses are used in the
same fashion.
Corrective Lenses
Another way to correct
vision in a more
permanent way than with
contacts or glasses is
LASIK Eye surgery.
During the LASIK
procedure, the doctor uses
a laser to reshape the
cornea. To do this, the
doctor must first cut the
flap on top of the cornea
to reshape it. An
alternative to the LASIK is
the photorefractive
keratectomy or PRK. This
procedure also uses a laser
to reshape the cornea, but
does not peel back the
flap, but scratches the
surface. Both procedures
work for patients who are
nearsighted, farsighted or
have astigmatism.
Lasik Eye Surgery
Sources Used
HTTP://WWW.ALLABOUTVISION.COM/EYEEXAM/REFRACTION.HTM
HTTP://WWW.WEBMD.COM/EYE-HEALTH/LASIKLASER-EYE-SURGERY
HTTP://WWW.ALLABOUTVISION.COM/VISIONSUR
GERY/PRK.HTM