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THE EYE
Bushong Ch. 29 p 358 - 359
Appendix #1 State Fluoro Syllabus
pg 77
Reference: Ch. 14 Carltons
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Early Fluoroscopy
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The eyes are the window to the soul……….
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Red goggles for dark adaptation
•Fluoroscopy was performed
•in total darkness
•so the eyes had to be adjusted
•for 20 - 30 minutes by wearing red goggles
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• FOVEA CENTRALIS
• CENTRAL PART OF
RETINA
• CONES TIGHTLY
PACKED
• REMAINDER –
CONES DIMISH =
MORE RODS
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Human Vision
• Light passes through the lens, where light
is focused onto the retina.
• Between the cornea and the lens is the
iris, which acts like a camera diaphragm =
controls the amount of light admitted into
the eye
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the retina
• The retina is important because it
contains the rods and cones.
• The sharpest point of vision is located in
the center in an area called the fovea
centralis.
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RETINA
• contains millions of specialized
photoreceptor cells called rods and cones
• That convert light rays into electrical
signals that transmitted to the brain
through the optic nerve.
• Rods see in dim light and
• Cones provide the ability to see in color
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Visual Physiology
2 types of light receptors
RODS
•
•
•
•
NIGHT VISION
SCOTOPIC
PERCEIVE GRAYS
PERIPHERY OF
RETINA = DIM
OBJECTS SEEN
BETTER – 1000 X
MORE SENSITIVE
• 30 min dark
adaptation
CONES
•
•
•
•
•
DAYLIGHT
PHOTOPIC
PERCIEVE COLOR
CENTER OF RETINA
BETTER VISUAL
ACUITY
New II much brighter
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The rods
• These are located at the periphery of the
retina
• There are fewer of them and they are
sensitive to low levels of light.
• Night vision (scotopic vision) uses the rods
of the eye to see
• The rods are colorblind
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The cones
• Cones are located at the center of the
retina in the fovea centralis
• They respond to intense light levels. As
such, these are used for our daylight
(phototropic vision).
• Cones have better visual acuity and better
contrast perception.
• Cones perceive color
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Eat the ice cream
CONE
in the DAYLIGHT!
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Macula & Fovea centralis
• The macula, located in the center of the retina,
is where most of the cone cells are located.
• The fovea, a small depression in the center of
the macula, has the highest concentration of
cone cells.
• The macula is responsible for central vision,
seeing color, and distinguishing fine detail.
• The outer portion (peripheral retina) is the
primary location of rod cells and allows for night
vision and seeing movement and objects to the
side (i.e., peripheral vision).
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CORNEA
• The cornea is a thin transparent protective
covering that protects the eye.
• It has no blood vessels and it helps focus light
onto the retina
• Light rays bounce off all objects. If a person is
looking at a particular object, such as a tree,
light is reflected off the tree to the person's eye
and enters the eye through the cornea
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IRIS
• located between the cornea and the lens
• colored part of the eye
• It controls the amount of light that is admitted to
the eye by dilating or constricting the pupil.
• Bright light causes contraction of the iris
allowing only a small amount of light to hit the
pupil
• In dim light, the pupil enlarges to allow more
light to enter the eye.
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IRIS
• The structure which gives the "color" to
the eye.
• The pupil is the hole in the iris.
• Contraction of the iris makes a pupil
small.
• Relaxing of the iris makes the pupil large.
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LENS & PUPIL
• focuses the light that passes through the
pupil onto the retina where the light
receptors are located
• The pupil is the opening to the eye. As the
iris opens and closes, it causes the pupil
to dilate or contract.
• Light has to pass through the pupil to
reach the retina
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VISUAL ACUITY
• ABILITY TO PERCEIVE FINE DETAILS
• INTEGRATION TIME = 0.2 SEC (how
long it takes to identify something)
• Photopic acuity is 10 x greater than
scotopic
• Contrast perception is our ability to detect
differences in brightness
• Normal viewing distance 12 – 15 inches
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Binocular vision
• is the best we can see at and is 12-15 inches
from the object we are looking at.
• We have a blind spot at about 9 inches and can’t
see from the periphery of the eye.
• Remember… integration time: 0.2 sec. and it is
the ability to see and recognize everything we
will
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•
•
•
•
•
VISION
EYE SEES 32 SHADES OF GRAY
COMPUTER 256 – 8 bit to 1024 12 bit depth SHADES
REGARDING CINE:
32 FRAMES SOME FLICKER (OLD MOVIES)
60 FRAMES = NO FLICKER
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The Eyes & Radiation Dose
• What is the allowable annual limit for the
eyes? _______________________
• What problems with the eyes were seen
with early Radiologists?
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The Eyes & Radiation Dose
• Cataracts (cataractogenic effects)
P49 RAD – RHB SYLLABUS
• Formation of Cataracts – dose of several 110
rads
• Fibers in lens of eye are specialized to transmit
light
• Damage to these (particularly to the developing
immature cells – can result in cataracts)
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Now your turn..
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The Early years
• Because of the high dose to the patient
and to the operator’s eyes, radiation
damage was noted shortly after the
invention.
• Thomas Edison noted that his vision was
deteriorating because of the radiation.
• The possibilities of this new find
outweighed the dangers.
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•CATARACS
•Dangers of early fluoro
•DOSE RESPONSE ??
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