Looking Into the Eye Understanding Anatomy, Normal Vision, and Vision Problems By: Deniz Harland
May 10, 2015
Looking Into the Eye
Understanding Anatomy, Normal Vision, and Vision Problems
By: Deniz Harland
Fact or Fiction?• Fact:
– Eating Carrots Will Improve Your Sight– Looking Straight at the Sun Will Damage Your Sight– Using Artificial Sweeteners Will Make Your Eyes
More Sensitive to Light
• Fiction:– Reading in the Dark Will Weaken Your Eyesight– Sitting Too Close to the TV Will Damage Your
Vision– There's Nothing You Can Do to Prevent Vision Loss
Anatomy of the Eye
Outermost Layer
The Sclera maintains the shape of the eye
The Cornea is the front sixth of the sclera and is clear. All light must first pass
through the cornea when it enters the eye.
Extraocular Muscles
Sclera
Cornea
The Extraocular Muscles are attached to the sclera and move the eye
Second Layer
The Choroid (or Uveal Tract) is the second layer of the eye. It contains the blood vessels that supply blood
to structures of the eye.
The Iris is the colored part of the eye. The color is determined by
the color of the connective tissue and pigment cells. The iris is an
adjustable diaphragm around an opening called the pupil.
Choroid
Ciliary Body
Sphincter Muscle
Dilator Muscle
Iris
The Ciliary Body is a muscular area that is attached to the lens. It
contracts and relaxes to control the size of the
lens for focusing.
The Dilator Muscle makes the iris smaller and therefore the pupil larger, allowing more light into
the eye.
The Sphincter Muscle makes the iris larger and the
pupil smaller, allowing less light
into the eye.
Innermost Layer
Retina
Rod Cells
Fovea Centralis
Macula
Cone Cells
The Rod Cells are responsible for
vision in low light
The Cone Cells are responsible for color
vision and detail
The Retina is the light-sensing portion of the eye
The Macula is in the back of the eye and in the center of the retina
The Fovea Centralis is in the center of the macula, contains only cones, and is
responsible for seeing fine detail clearly.
Muscles
MuscleMedial rectus
Lateral rectus
Superior rectus
Inferior rectus
Superior oblique
Inferior oblique
Primary Function
Moves eye
towards nose
Moves eye away
from nose
Raises eye
Lowers eye
Rotates eye
Rotates eye
Six muscles attached to the sclera that control the movements of the
eye
Activity Slide
• What muscle are you using when you…– Move eyes towards nose…?– Move eyes away from nose…?
– ___________ raises the eye while the
– ___________ lowers the eye
• Which muscles rotate the eyes?– ___________ -and- __________
Understanding VisionLight enters the eye
Passes through the cornea, aqueous humor lens, and vitreous humor
Reaches the retina, where
rods handle vision in low light and
cones handle color vision and detail.
20 feet
20/20 Vision
If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what a "normal" human being can see.
Color Vision
• Cone Pigments: – color-responsive chemicals in the cones
– very similar to chemicals in the rods
– made up of retinal and photopsins
• The Three Kinds of Pigments:– Red-sensitive
– Blue-sensitive
– Green-sensitive
Fact: The Human eye can sense almost any gradation of color when red, green, and blue are mixed
Peak Absorbancy
• Measurement:
nanometers
• Reading the chart:- Blue-sensitive pigment
is 445 nanometers
- Green-sensitive pigment
is 535 nanometers
- Red-sensitive pigment
is 570 nanometers
Blind Spot Activity
Test the presence of the blind spot by
1- Covering your right eye with your hand
2- Staring at the yellow circle as you move closer to the screen
Or cover your left eye and stare at the red square as you move.
Result: the square (or circle depending on which eye in covered) will disappear
Vision Problems
• Astigmatism is an uneven curvature of the cornea and causes a distortion in vision.
• Night Blindness is when there is severe vitamin D deficiency which causes levels of light-sensitive molecules to be low
Blindness & Its Beginnings
• Legal blindness is usually defined as visual acuity less than 20/200 with corrective lenses
• Causes:– Cataracts - Cloudiness in the lens blocks light from
reaching the retina. It becomes more common as we age, but babies can be born with a cataract. Glaucoma - If the aqueous humor does not drain out correctly, then pressure builds up in the eye. Cells and nerve fibers die from the pressure Can be treated with medications and surgery.
Other Vision Problems
• Macular Degeneration - when the macula deteriorates with age for unknown reasons. This causes loss of central vision. Laser surgery can sometimes help with this condition
• Trauma - Direct trauma or chemical injuries can cause enough damage to the eyes to prevent adequate vision
• Retinitis Pigmentosa – An inherited disease that causes a degeneration of the retina and excess pigment. First causes night blindness and then tunnel vision, often gradually progressing into total blindness. No known treatment
• Trachoma - An infection caused by an organism called Chlamydia trachomatis. A common cause of blindness worldwide but is rare in the United States. Can be treated with antibiotics
Bibliography
• "The Human Eye." 19 December 2006 02 MAR 2008 <http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/Vision.html>.
• "Eye Health." WebMD 01 OCT 2005 02 MAR 2008 <http://www.webmd.com/eye-health/fact-fiction-myths-about-eyes>. – More information about Fact or Fiction: see this
site