1. Special Senses
The Eye

2. Overview of the Eye Eye acts like a camera
Lens adjusts to bring object into focus
Pupil constricts to allow less light to enter in bright setting or dilates to allow more light to enter in darker setting
Through bending of light rays, images reaches retina
Sensitive nerve cell layer of eye
Image is transmitted to brain for interpretation

3. Front view of the eye Sclera = white portion of eye
tough, maintains shape of eyeball
serves as protective covering for the eye
Iris = colored portion of the eye
Pupil= opening in center of eye that controls amount of light entering eye

4. Lacrimal gland = produces tears
Conjunctiva = thin mucous membrane that lines the eye and inner part of eyelid
Lacrimal gland = produces tears
located at upper outer edge of each eye
Lacrimal Duct = Tears drain thru duct
located at inner edge of eye

5. ■ Vitreous humor = fluid that prevents eye from collapsing forward
Cornea = transparent layer covering colored part of eye that holds in fluid
Aqueous humor = maintains pressure to keep outer cornea inflated & helps fight infection
Lens = colorless biconvex structure that focuses image clearly on retina
Aqueous Humor
Vitreous humor
■ Vitreous humor = fluid that prevents eye from collapsing forward

6. Retina Sensitive nerve cell layer Nerve cells of retina
changes energy of light rays into electrical nerve impulses
transmits nerve impulses via optic nerve to brain for interpretation
Nerve cells of retina
Rods are responsible for vision in dim light and for peripheral vision
Cones responsible for colors and vision in bright light

7. Cones The retina contains approximately 6 million cones.
contained in the macula, the portion of the retina responsible for central vision.
They are most densely packed within the fovea, the very center portion of the macula.
Cones function best in bright light and allow us to appreciate color.
Fovea

8. Rods There are approximately 125 million rods.
They are spread throughout the peripheral retina and function best in dim lighting.
The rods are responsible for peripheral and night vision.

9. How the eye focuses
Lenses and cornea focuses image precisely on the retina
Cornea of eye is overly curved or eyeball is too long. This combination brings images of distant objects to a focus point in front of the retina.
Normal Vision
cornea of eye is not curved enough or eyeball is too short. This combination causes the focus point of the eye to be located behind the retina.
Near-sighted Vision
Astigmatism
Far-Sighted Vision
Cornea of eye has a football shape and does not bring light to focus at a single point. Instead, it focuses images over a range of points producing a blurred image

10. Figure 35-14 The Eye Section 35-4 Choroid Retina Blood vessels
Optic nerve
Fovea
Vitreous humor
Sclera
Ligaments
Iris
Pupil
Cornea
Aqueous humor
Lens
Muscle

11. Pathway for Vision Reception
Light
Cornea
Iris and pupil
Lens
Retina to photoreceptors
Rods
Cones (macula and fovea)
Optic Nerve
Brain