1. 10.9 – Sense of Sight

2. The Eye as an Organ Lies w/ the Orbit
Made of bone & contains fat, bl. Vessels, nerves, & connective tissue
Provides vision along with accessory organs
Eyelids
Thinnest skin of body
Lined with conjunctiva – mucous membrane that folds back to cover surface of eye as well
Lacrimal apparatus
Lacrimal gland + ducts
Secretes tears continuously – lubrication & antibacterial enzyme
Extrinsic eye muscles
Attach to sclera
Move eye in all directions
Eyelids & lacrimal = protect eye
- Eyelids: 4 layers: skin, muscle, conn. tissue, conjunctiva
- lacrimal ducts carry tears to nasal cavity
Muscles = move eye

4. Structure of the Eye Fluid-filled hollow sphere with 3 layers (tunics)
Outer Tunic
Fibrous tunic
Transparent cornea
White sclera
Optic nerve & bl. vessels pierce the back

5. Structure of the Eye Middle Tunic Choroid coat Ciliary body Iris
Vascular, darkly pigmented
2 functions
Nourish other tissues
Keep inside of eye dark
Ciliary body
Forms ring around front of eye
contains ciliary muscles & ligaments = holds lens in place & changes its shape to focus objects
Called accomodation
Iris
Thin, smooth muscle
Adjusts to amount of lilght entering the pupil
Iris muscles – radial & circular set of muscles
Pupil – hole in the iris

6. Structure of the Eye Middle Tunic cont. Anterior Cavity consists of:
Anterior Chamber
b/w cornea & iris
Posterior Chamber
b/w iris & vitreous body housing the lens
Filled with aqueous humor
Fluid that circulates from one chamber to the other through the pupil

8. Structure of the Eye Inner Tunic
Covers back side of eye to the ciliary body
Retina – contains photoreceptors
Fovea Centralis = back of retina, point of sharpest image
Optic disk = nerve fibers leave eye; causes blind spot
Open cavity of the eye in front of the retina is filled with vitreous humor
Fovea capitis is in the center of the macula lutea (lining of the back of the eye)
Optic disk is medial to the fovea capitis

11. Light Refraction Light waves must be focused – called refraction
Cornea & lens bend light
Bent light is focused on retina
Aqueous & Vitreous humors also help to bend/refract the light

12. Visual Receptors 2 kinds: Rods Cones Elongated
Sensitive to light; function in dim light
Produce colorless vision
Cones
Provides sharp images in bright light
Produces vision in color
Fovea centralis contains the most cones
Note about cones:
- to see something in detail, the person moves the eye so the image falls on the fovea centralis, which contains the highest percentage of cones
- proportion of cones decreases with distance from the fovea centralis

13. Visual Nerve Pathways
Axons of ganglion cells leave eyes to form the optic nerves
Fibers from the medial half of the retina cross over in the optic chiasma
Impulses are transmitted to the thalamus
Then sent to the visual cortex of the occipital lobe for final association

14. Optical Device – The Eye
Myopia – nearsighted
Eyes are too long
Hyperopia – farsighted
Eyes are too short
Astigmatism
Cornea misshapen
Cataracts
Clouding of the lens
Floaters
Cell fragments break off
Make drawings of Myopia, Hyperopia, and Astigmatism
Floaters: not really moving, the eye just tries to track them

16. Lasik eye surgery