1. Structure and Function of the Eye
SPE 516

2. The Bony Orbit
This is the orbit of the eye. Which one? right (optic nerve passes between bone nasally)
These and other diagrams are linked for Web Lesson 1

3. The Muscles of the Eye (Extraocular muscles)
5 of the 6 muscles come out of a cone from the back of the orbit. The inferior oblique comes in nasally.

4. Superior and Inferior rectus
Superior rectus
Attached to the eye at 12 o’clock
Moves the eye up.
Inferior rectus
Attached to the eye at 6 o’clock
Moves the eye down.

5. Inferior oblique is outside (on top) of the inferior rectus
The superior oblique is inside (under) the superior rectus

6. Lateral Rectus Lateral Rectus Also called the external rectus
Attaches on the temporal side of the eye
Moves the eye toward the outside of the head (toward the temple)
I typically ask “Why don’t I use clock positions to describe this? E.g. 9 o’clock?
The idea is to make them realize that they have to reverse the positions based on which side of the head they are talking about

7. Medial Rectus Medial Rectus Also called the internal rectus
Attached on the nasal side of the eye
Moves the eye toward the middle of the head (toward the nose)

8. The Superior oblique originates behind the eye with the others (except the inferior oblique) but uses the Trochlea as a pulley to actually approach the eye from the front allowing it to pull the eye down and inward toward the nose

9. Superior Oblique Attached high on the temporal side of the eye.
Passes under the Superior Rectus.
Moves the eye in a diagonal pattern -- down and in.
Travels through the trochlea

10. Inferior Oblique Attached low on the nasal side of the eye.
Passes over the Inferior Rectus.
Moves the eye in a diagonal pattern -- up and out.

11. The Nerves That Control the Muscles of the Eye
Third Cranial Nerves
Fourth Cranial Nerves
Sixth Cranial Nerves
Nerve palsy- what is it going to look like?
The 3rd nerve does most of the eye movement as well as pupil and lid function
The 4th nerve does the superior oblique (may cause double vision or manifest as a head tilt – to stop double vision) called throchlear nerve
And the 6th is responsible for the lateral rectus
The 2nd cranial nerve is pure sensory- carries information to the brain (Optic Nerve)
NOT ON THE TEST

12. Lids and Lashes Main function is the protection of the eye.
They also help to distribute tears which wash and lubricate the eyes.

13. The Lacrimal System -- Tears
Tears flow across the eye and drain down into the nasal cavity.

14. Conjunctiva covers the sclera and inside of lid
DOTS ALONG THE BASE OF THE BOTTOM LID -Gray line and orifices of tarsal gland –produces oils -meibum an oily substance that prevents evaporation of the eye’s tear film, prevents tear spillage onto the cheek, makes the closed lids airtight and acts as a blockade for tear fluid, trapping tears between the oiled edge and eyeball. There are approximately 50 glands on the upper eyelids and 25 glands on the lower eyelids

15. The Refractive Structures
These structures bend the light so that a clear image is produced.
They are:
tears
conjunctiva
cornea
aqueous humor
lens
vitreous humor
Three chambers in the eye
1. Anterior chamber – from cornea to iris
2. Posterior chamber – from iris to zonules and lens –
These two are responsible for the production and drainage of the aqueous which is produced continuously throughout your life
produced in the posterior chamber by the ciliary body travel through the iris to drain out the anterior chamber (through the Canal
of Schlemn)
3. Vitreous – gel like –gives the eye its shape not produced – damage or loss can cause retinas to fall or tear

16. Chambers of the Eye 1. Anterior chamber – from cornea to iris
2. Posterior chamber – from iris to zonules and lens –
These two are responsible for the production and drainage of the aqueous which is produced continuously throughout your life.
Aqueous is produced in the posterior chamber by the ciliary body travel through the iris to drain out the anterior chamber (through the Canal of Schlemn)
3. Vitreous – gel like –gives the eye its shape not produced – damage or loss can cause retinas to fall or tear

18. Which eye? Looking down from the ceiling to the top of the head –right eye
What plane? Horizontal plane
See the indentation in the back of the eye that is the fovea- fovea means dent (fovea Centralis)
This is the center of the macula which produces the sharpest vision
Macula means yellow spot
Tell them to know this….they MIGHT see it again

19. The Sclera changes into the cornea at the corneal limbus..
Changes/differences?
Color/clarity, and layers
Both very tough

20. Layers of the eye Sclera and Cornea uveal tract retina Choroid Iris
Ciliary body
retina
Three layers –outer, middle, and inner
Essentially sclera-choroid-retina are the three layers
Cornea and limbus

21. Sclera and Cornea
Form the outer layer of the eye – 1/6 cornea and 5/6 sclera
Cornea is clear- sclera is white (they transition at the limbus)
Very tough and provide protection
Sclera maintains shape of the eye
Cornea is the major refractor of the eye
Limbus can be a site of certain diseases
maintains the shape of the globe, offering resistance to internal and external forces, and provides a place for the extra-ocular muscles to attach

22. Uveal Tract
Choroid – vascular layer, major supplier of nutrients and blood supply to the eye
Iris – Controls light that enters eye
Cilliary body- produces aqueous humor to bathe lens and provide nutrients to lens and cornea and provides accommodation.
Uveal tract also provides light absorption. The uvea improves the contrast of the retinal image by reducing reflected light within the eye (analogous to the black paint inside a camera), and also absorbs outside light transmitted through the sclera, which is by no means opaque.

24. The Retina The retina is made up of cones and rods
Rods -peripheral retina
Motion, low light, no color
Cones -central retina
Highly centralized in the fovea
Color
Fine detail
There are essentially three types of Cones in humans - red, green, and blue
We have approx 18 times more rods than cones (4.5 million cone cells and 90 million rod cells)

25. The optic nerve is always temporal…there is no vision where the nerve attaches…USEFUL STUFF page has a link to an activity where you can verify this
This image is skewed- the fovea would be centered if you were looking directly into the eye

26. This yellow spot is NOT the macula- this is the optic disc
Vascularization of ma

27. The Optic Pathway Begins at the optic nerve.
Impulses cross and partially split at the optic chiasm.
After the chiasm, it becomes the optic tract.
Lateral geniculate bodies (sensory way stations)
Some fibers go to the colliculus (located in the mid brain)

28. Optic Pathway (cont.)
The other fibers fan out into the visual cortex which is located at the top and back of the brain.

30. Vision and the Brain Primary visual cortex (Striated Cortex) --
spatial organization of a scene
shapes of objects
brightness and shading of parts of objects
Secondary visual cortex (Prestriated Cortex) --
pattern recognition

31. The Brain and Vision (cont)
Temporal Lobes
center for visual learning
recognition by sight
Midbrain -- Limbic sector
emotional responses to visual stimuli
Midbrain -- Superior Colliculus --
guides visual attention