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THE EYE

Bushong Ch. 29 p 358 - 359Appendix #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

12 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

25VISION

• 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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