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