1. THE EYE
CHAPTER 10

2. THE EYE
There are 4 cranial nerves: Optic (II), Oculomotor (III), Trochlear (IV), and Abducens (VI).
People of Asian descent have an EPICANTHIC FOLD in the upper eyelid; no functional difference.

3. The eye 3 layers (tunics/coats)
70% of sensory receptors in the body are found here.
Housed in the orbit of skull and surrounded by fat, blood vessels, nerves, and connective tissues.
2.5cm in diameter
3 layers (tunics/coats)
Outer layer (fibrous)
Protective, refracts light
Includes cornea and sclera
Middle layer (vascular)
Contains pigments to keep eye dark inside
Includes choroid coat, ciliary body, lens, iris, pupil, aqueous humor.
Inner layer (nervous/sensory)
Visual receptors
Contains retina, fovea, optic disc, vitreous humor

5. External/Accessory Structures
Eyelids – covers & protects/thin skin
Eyelashes – fine hairs grow from eyelid; protect/ catch foreign particles
Eyebrow – coarse hairs catch foreign particles/ sweat

6. PINK EYE - also known as CONJUNCTIVITIS
CONJUNCTIVA is a clear, thin covering around the eye and under the eyelids.  
PINK EYE - also known as CONJUNCTIVITIS 
(from bacteria, very contagious)
Pink Eye Slide Show from Web MD

7. GLANDS OF THE EYE
LACRIMAL GLANDS are the largest set. They are on the superior lateral eyelid and they produce tears, which drain into the nasal cavity via the LACRIMAL DUCT.
The function is to moisten and lubricate the eye surface, and it has enzymes (lysozyme) to kill bacteria (which thrive in warm, moist conditions).

8. Figure 16.5b

9. Extrinsic/External Eye Muscles
Lateral rectus – moves eye laterally
Medial rectus – moves eye medially
Superior rectus – elevates eye
Inferior rectus – depresses eye
Inferior oblique – elevates & turns eye laterally
Superior oblique – depresses & turns eye laterally
Orbicularis oculi – opens & closes eyelid

10. Extrinsic Eye Muscles 5 1 3 4 6 2

12. Outer Tunic
Cornea – transparent covering; focuses light rays. It has many nerve endings with pain fibers; can repair itself (Only tissue in body that can be transplanted from one person to another w/o rejection b/c it has no blood vessels)
Sclera – protection, thick white connective tissue, outer layer
Optic Nerve – connection from eye to occipital lobe; exits at the optic disk and transmits visual info from eye to brain
Keratoconus is an eye condition in which the normally round cornea thins, causing a cone-like bulge to develop.
Source: NPR

13. Middle Tunic
Choroid coat – supplies blood vessels Ciliary body – 2 smooth muscle structures connected by suspensory ligaments (changes shape of lens & secretes aqueous humor) Lens – disc-shaped structure that bends/refracts light to be focused on the retina Iris – pigment (color) around pupil contains melanin (blue eyes = no melanin) Pupil – round opening through which light passes Aqueous humor – watery fluid b/w cornea & iris; helps maintain intraocular pressure & provides nutrients for lens & cornea

14. Figure 16.7a

15. Inner Tunic
Vitreous humor – jellylike substance that gives the eye its shape & prevents it from collapsing inward
Retina – innermost layer that contains rods & cones (visual receptor cells)
Fovea Centralis – area of retina where only cones are found (clearest vision)
Optic disc – area of retina lacking cones & rods/where nerve fibers leave the eye creating blind spot
Canal of Schlemn – drains fluid that accumulates in eye located at the junction of the sclera & cornea

16. Retina
The retina is made up of PHOTORECEPTORS, which are sensors for light.

17. Photoreceptor cells – found in retina
Rods
Cones
125 million
7 million
Coarse detail
Fine detail
Black and white
Color
More sensitive to low light
Less sensitive to low light
Used for peripheral and night vision
Used for central and detailed vision

18. Rods = monochromatic (b&w)
Cones  = color vision

20. **Visual cortex of occipital lobe interprets the images**
Pathway of Light
Cornea
Aqueous humor
Pupil
Lens
Vitreous humor
Retina
**Visual cortex of occipital lobe interprets the images**

22. EYE PHYSIOLOGY
Refraction: the cornea and lens bend light waves to focus an image on the retina
Normal vision
Image viewed by the eye are upside down
Visual cortex of brain interprets it in its proper position

23. R.O.Y.G.B.I.V
Rainbows are seen after rain because light is passing through water droplets.  This separates the white light into the individual colors of the spectrum

25. Refraction
Visual Nerve Pathway Journey Through the Visual System

28. Accommodation: Lens changes shape to focus on objects.
Physiology cont…
Accommodation:
Lens changes shape to focus on objects.
Ciliary muscles and suspensory ligaments aid in doing this
When the ligaments pull outward, the lens flattens and focuses on distant objects (muscle relaxed)
When ligaments are
relaxed, the lens is
more convex (thickens)
focusing on closer
objects (muscle contracts)

29. Accommodation
Lens Accommodation

30. VISUAL ACUITY
Ophthalmoscope: instrument that illuminates the interior of eyeball allowing the inside to be seen.
Snellen eye chart:
measure acuity
20/20 normal vision
The higher the bottom
number, the poorer
the vision

31. Eye problems Myopia: nearsighted Hyperopia: farsighted
Emmetropia: normal vision
Astigmatism: cornea/lens developed an irregular shape
Strabismus: cross-eyed
Diplopia: double vision (can be caused by one eye deviating from line of vision).

32. Myopia = nearsightedness
You can see near objects fine, but distant objects appear blurry

33. Hyperopia = farsightedness
You can see distant objects fine, but close objects appear blurry

34. ASTIGMATISM is when the cornea has an irregular shape. ‘
Part of the field of view is out of focus.

36. Eye Videos
Lasik Surgery: Eye Surgery Video Myopia vs. Hyperopia Vision Problems

37. Cataracts: lens becomes cloudy (laser surgery to fix) Cataracts video
Glaucoma: increase in intraocular pressure, caused by an increase in aqueous humor
Tonometer: instrument measuring pressure

38. Blindness: totally sightless in both eyes
Common Causes of blindness include diabetes, macular degeneration, traumatic injuries, infections, glaucoma, and inability to obtain any glasses, loss of transparency of the cornea
Treatments depends on cause
Cornea transplant (high success rate b/c no blood vessels)
Night blindness: poor vision in dim light resulting from a vitamin A deficiency.

39. What causes red-eye?
The flash on a camera is bright enough to cause a reflection off of the retina -- what you see is the red color from the blood vessels. Many cameras have a "red eye reduction" feature. In these cameras, the flash goes off twice -- once right before the picture is taken, and then again to actually take the picture. The first flash causes people's pupils to contract, reducing "red eye" 

40. Why are babies born with blue eyes?
Melanin is a brownish pigment that adds color to your hair, eyes, and skin. At the time babies are born, melanin hasn't yet been "deposited" in the eyes' iris. Hence, they appear blue. 
After about six months, eyes change color depending on the amount of melanin. If you have a lot of it, your eyes will turn dark brown.  If you have little, they'll stay blue. And if you have no melanin, your eyes may appear pink (albino). .

41. Color Blind   Normal Vision
Color Blindness: Genetic trait carried on the X chromosome. Most common is
red/green color blindness.
 Normal Vision
Color Blind 

42.  Normal Vision
Color Blind 