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THE HUMAN EYE14.2 – Pages 449-455
A) Types of Vision
Monocular Binocular Peripheral Tunnel Vision
B) Layers of The Eye
Sclera (A): Outer white part of the eye tough Resists punctures, is under fluid pressure from below
Choroid (G): Middle layer contains numerous blood vessels Contains a black pigment darkens the interior of the
eye Ensures the eye ball is a “dark room”
Retina (L): Contains the Photoreceptors Rods & Cones Converts light into nerve impulse to the Occipital
lobe
C) The Photoreceptors:
Rods- Located in
periphery- 120 million/Eye- Detects movement- Detects Black &
White- Night Vision- Dim light (dawn &
dusk)- Pigment:
Rhodopsin
Cones- Located in center- 6 million/Eye- Detects Color - Red, blue, green- Sharpness of
vision- Bright Light (Day)- Pigment:
IodopsinCalled “Visual Purple” and both contain Vitamin A
Colorblindness
Inherited through X Chomosome The genetic information for certain
cones in the eye are missing Only lets the person see parts of
the color spectrum clearly
Color SpectrumThe first spectrum is normal and the next two are the spectrums thatpeople with Protanopia and Deuteranopia see.
Test For Colorblindness
There is no cure for colorblindness at the present time.
There is a way to test for it.
Test
Test
Test
Missing Red
Missing green
Missing blue
Fun facts….
About 8% of men all men have some sort of color deficiency; about half of 1% of all women do
Humans are born color-blind. Cone cells don’t begin functioning until a baby is about 4 months old
Color-blindness is also known as Daltonism, named after John Dalton, who wrote the first scientific paper about the condition (which he had) in 1794. In 1995, 150 years after his death, reserarchers determinded that Dalton suffered from deuteranopia. How? They did a DNA analysis of his preserved eyeball.
Complete color-blindness, or rod monochromacy, is extrememly rare, except on the pacific island of Pohnpei, where 8% of the population has it.
Color-detecting cones work best in bright light. In very dim light only non-color detecting rods are used, which is why everything seems to be in black and white in dim light.
Rods are more numerous in the periphery of the retina. In dim light, use your peripheral vision – it sees better
Most mammals are dichromatic: they have two types of cone cells and can see fewer colors than we can. Honeybees, like humans, have three types. But honeybees can see colors in
the ultraviolet range, humans can’t.
Source: Uncle John’s Slightly Irregular Bathroom Reader, 2004
D) Protection of the Eye:
Bony socket Eyebrow deflects water and debris Eyelashes have “blink” reflexes that
respond to potential danger Lacrimal Gland (tears): (top/side of
eye) Tears flow from top/temple to bottom/nasal Tears contain an antibiotic Tears drain into the nose
Protection cont’d:
Tarsal Gland (oil): (located in the lid) Secretes an oil to moisturize the eye
Lids sweep the eye Sclera to resist puncture
E) Eye Anatomy
Cornea (B)- outer transparent skin of the eye, no blood vessels, helps to focus image (refracts light towards pupil)
Iris (D)- circular muscle that helps control pupil size
Pupil (E)- allows light to enter the eye Ciliary Muscles (F) – control the shape
of the lens for focusing
Anatomy cont’d:
Lens (H) – focuses the image (inverts it too)
Aqueous Humour (I) – clear fluid in front between cornea and lens, circulates to nourish the cornea
Vitreous Humor (K) – clear pressurized fluid to maintain ball shape
Retina (L) – contains photoreceptors Fovea Centralis (M) – 90% of cones
are located here for color and sharpness of vision; most light sensitive area of the eye
Anatomy cont’d:
Blind Spot (N) – where optic nerve leaves the eye, no photoreceptors here
Optic Nerve (O) – contains 1 million axons to occipital lobe
F) Vision
Retina: Three layers of cells Rods and cones are closest to choroids;
generate nerve impulses in response to light (pigments change shape)
Middle layer contains bipolar cells Innermost layer contain ganglionic cells, the
axons of which form the optic nerve Impulse travels from rods and cones
bipolar cells ganglionic cells optic nerve optic chiasma occipital lobe
Vision cont’d…
• Focusing: Bending Light• Light rays must be bent (refracted) to focus on the
retina• Bent by: cornea, lens and to a lesser extent, humors
• Accommodation Reflex – ability of lens to adjust in order to see close or distant objects.
• For distant objects the lens is flat and the ciliary muscle relax
• For close objects the lens becomes round and the ciliary muscles contract
• With aging, lens loses some elasticity and is unable to accommodate.
Accommodation animation
HOW THE EYE WORKS
Depth Perception
Depth perception is due to each eye forming an image from a slightly different angle.
Images on each side of the brain are interpreted as a whole.
G) Vision Defects:
Glaucoma: build-up of aqueous humor Treatment: topical eye drops Cause: high blood pressure; diabetes
Cataracts: clouding and/or hardening of lens Treatment: removal; strong eyeglasses Cause: age, trauma
Astigmatisms: irregular shaped cornea (or lens) Treatment: glasses or contact lenses
Myopia: near sightedness; image is focused in front of fovea Treatment: biconcave lens
Hyperopia: far sightedness; image focused behind fovea Treatment: biconvex lens
Focusing Problems Animation
Eye Dissection
Eye Dissection – pg 463 in textbook Identify the following parts:
Inside:• Lens• Humors (jelly)• Iris (scrape off
cornea)• Retina (white,
scrapes off easily)• Blind spot
Outside:• Optic Nerve
(stump)• Cornea• Sclera
To Do:
Work on Human Eye Worksheet Quiz tomorrow (Tuesday after the turkey
coma!) on the EYE!
