1. Special Senses - Eyes

2. External Anatomy of the Eye
Eyelids
Eyelashes
Conjunctiva – A membrane that lines eyelids and covers part of the outer surface of the eyeball
Conjunctivitis
Inflammation of the conjunctiva (example – pinkeye)
Caused by a bacterial or viral infection

3. External Anatomy of the Eye
Lacrimal glands
Above the lateral end of the eye
Secrete dilute salt solution (tears) onto the anterior surface of the eyeball

4. Internal Anatomy of the Eye
The eyeball is consisted of three tunics (coats)
Sclera – outer tunic (white of the eye)
Choroid – middle tunic (has a dark pigment that prevents light from escaping the eye)
Retina – inner tunic (has photoreceptors called rods and cones)

5. Sclera
Choroid
Retina

6. Internal Anatomy of the Eye (cont.)
Photoreceptors – respond to light
Rods
Detect black and white
Process dim light
Used for peripheral vision
120 million rods in one eye
Cones
Detect color
Process bright light
Most are found in the center of the retina
7 million cones in one eye

7. Internal Anatomy of the Eye (cont.)
Optic nerve – sends information from the eyes to the brain
Optic disk – part of the eye where optic nerves travel through
Does not have any photoreceptors
Known as the blind spot
Fovea centralis
Near the optic disk that contains only cones
The area of sharpest vision

9. Internal Anatomy of the Eye (cont.)
Cornea – Clear membrane that forms the front of the eye
Iris – pigmented portion of the eye
Pupil – The expanding and contracting opening in the iris through which light passes to the retina
Cornea
Pupil
Iris

10. Internal Anatomy of the Eye (cont.)
Lens
Allows light to reach the retina to focus an image
Held in place via suspensory ligaments
Lens
Suspensory ligaments

11. Internal Anatomy of the Eye (cont.)
The lens divides the eye into two chambers
Aqueous humor – Anterior segment that contains a clear watery fluid
Provide nutrients for the lens and cornea which lack a blood supply
Vitreous humor – Posterior segment that’s filled with a gel-like substance
Helps prevent the eyeball from collapsing inward by reinforcing it internally

13. Pathway of Light Through the Eye
Cornea
Aqueous humor
Pupil
Lens
Vitreous humor
Retina
Choroid
Optic disk
Optic nerve

14. Malfunctions of the Eyes
Cataract
As one ages, the lens becomes hard and cloudy.
Causes vision to become hazy and possibly blindness

16. Malfunctions of the Eyes
Glaucoma
If drainage of aqueous humor is blocked, pressure within the eye increases dramatically compressing the retina and optic nerve.
This can cause pain and possibly blindness.