1. Eye presentation Uly, Elizabeth, Zulema Period 4

2. General Function ❏ light detection ❏ focus ❏ balance ❏ depth perception ❏ works with brain to provide us with vision

3. Parts of Eye and Function Outer Tunic (Fibrous) ● Cornea o Clear front window of the eye o Transmits and focuses (sharpness or clarity) light into the eye ● Sclera o White outer coat of eye surrounding iris o Acts as a tough protection from injury o provides attachment for the extraocular muscles that move the eye ● Conjunctiva o Thin, transparent tissue covering the outer surface of eye o Begins in outer edge of cornea, covering the visible part of sclera, and lining the inside of the eyelids o Nourished by tiny blood vessels

4. Continue... Middle Tunic (Vascular) ● Choroid o Lies btw retina and sclera o Composed of blood vessels that nourish the back of the eye ● Ciliary Body o Releases transparent liquid (aqueous humor) within the eye o accommodation  ciliary muscle changes shape of lens when eyes focus on something ● Iris o Colored part of eye o Regulates the amount of light entering the eye o Closes when there’s bright light to let in less light, and opens when there’s low light to let in more light ●Pupil ○ ark center opening in the middle of the iris ○ Changes size to adjust for amounts of light available (smaller for bright Light and larger for low) ●Lens ○ Transparent and can be replaced ○ Focuses light rays onto the retina ●Suspensory Ligaments ○ Adjust the shape of lends ■ more or less curved ■ increase or decrease the refraction of light ○ Connect the ciliary muscles to lens to hold them in place

5. Continued... Inner Tunic (Nervous) ● Macula o Area in retina containing special light- sensitive cells o These cells allow us to see fine details clearly in the center of our visual field ● Optic Nerve o Bundle of more than 1 million nerve fibers carrying visual messages from retina to brain o Transfer visual info from retina to visual centers of the brain via electrical impulses ● Retina o Nerve layer lining the back of the eye o Senses light and creates electrical impulses that are sent through the optic nerve to brain ● Fovea o Center of medulla o Provides sharp vision ●Vitreous Humor ○ The clear gel that fills the space between the lens and the retina of the eyeball ○ Often referred to as the vitreous body or simply “the vitreous”

7. Neurons Involved ● Sensory o Detect info through receptors and travels through the nerves to the brain ● Bipolar o Transfer signal from receptor cells to the ganglion cells o Signals carry visual info to the brain through optic nerve ● Ganglion o Located in the inner surface of the retina o Transmits image and non-image visual info to many regions o Consists of axon and dendrite structures that send and receive nerve impulses ●Amacrine ○ Integrate for ganglion cells the signal coming from bipolar neurons ○ Interneurons ○ 22 types of amacrine cells ○ Supplement the action of horizontal cells ●Horizontal ○ Integrate and regulate the input from receptor cells ○ Allows eyes to adjust to dim and bright lights ●Photoreceptors ○ Responds to the stimuli after receiving signals ○ Convert light into signal ○ 2 types: rod and cones

8. Visual Receptors ●Visual processing begins at retina. ●Light enters eye and passes through 1.Cornea 2.Anterior Chamber 3.Lens 4.Vitreous 5.Photoreceptor cells: ●Cones ●Rods

9. Rods ● Located mainly near your peripheral sides of the retina ● Nerve fiber coverage ● contains light sensitive pigment called rhodopsin. ● provides vision in dim light and also provides colorless vision. ● Produces response to single photon. ● 100-120 million rods in a human retina

10. Cones ● Detect colors ● 4-6 million cones ● Nonconvergent ● Densely packed with fovea centralis ●Attached to pigmented epithelium ● Contains iodopsins 3 types- 1.Erythrolabe 2.Chlorolabe 3.Cyanolabe

11. Chambers ● Anterior Chamber -Small area filled with aqueous ●Posterior Chamber -Behind peripheral part of iris -Anterior to lens -Contains aqueous humor ●Vitreous Chamber -Large space between lens and retina -Filled with vitreous humor

12. Fluids ● Aqueous Humor - Fluid nourishes cornea and lens - Gives the eye its shape -Produced by ciliary body ● Vitreous Humor -80% eye volume -98% water -Contains collagen, salt and sugar -Large molecules of hyaluronic acid

13. Accessory Organs ● Conjunctiva - inner layer eyelids laying on cornea. ● Lacrimal glands - Secretes tears, water, enzymes, salts, oxygen, and nutrients. ● Tarsal glands- Next to eyelashes, secretes substance to keep eyelids from sticking together. ●Ocular Muscles -Lateral rectus -Medial rectus -Superior rectus -Superior oblique -Inferior oblique ●Eyebrows - Catch sweat or debris coming off forehead into the eye ●Eyelids -Hairs growing at the edge of the eyelids are very sensitive, tactil receptors. ●Fasciae - Envelopes bulb of eye from optic nerve to cilia region.

14. How we interpret sight

15. Refraction Once light enters the eye it must make it past: ● the cornea, ● aqueous humor, ● lens, ● vitreous humor, and several layers of the retina before reaching the eye. An image of what is seen focuses upon the retina then the light rays must bend to be focused on, this is called a refraction. Refraction occurs when light waves pass at an oblique angle from a medium of one optical density into a medium of a different optical density.

16. Refraction pictures

17. Convergent vs Divergent waves ● Lens with a convex surface causes light waves to converge. (inward) ● Lens with a concave surface causes light waves to diverge. (outward) ● Converging means to come together from different points to eventually meet at one point. ● Diverging means to separate or to split apart from the main direction and to go to a different direction

18. Concave and convex reflections

19. How an image is flipped 1.Normal shaped eye 2.Light waves are focused sharply on the retina. 3.Those waves formed on the retina make an image appear upside down and reversed from left to right. 4.When the visual cortex of the cerebrum interprets such an image, it will then correct it, and objects are seen in their real position.

20. Example of a flipped image

21. Dark vs light vision Rhodopsin ● light sensitive pigment in rods photoreceptors ● they are embedded in membranous discs that are stacked within the receptor cells. Iodopsins ● light sensitive pigment in cones

22. Dark vs light cont In light: rhodopsin molecules break down into molecules of a colorless protein called opsin and a yellowish organic molecule called retinal. In darkness: the sodium channels in receptor cell membranes are opened by nucleotides, cyclic guanosine monophosphate (cGMP), when the molecules absorb sunlight they change shape and release opsin.

23. Stereoscopic vision ● Simultaneously perceives distance, depth, height, and width of objects. ● 3D Vision ● Pupils 6-7 cm apart make this possible. ● This involves two eyes, so a one eyed person is less able to judge distance and depth accurately ● Bad or good?

24. stereoscopic vision

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