Sense of Vision. Chapter 8. The Eye and Vision. The Eye Orbit. Eyebrows, Eyelids, Eyelashes. Accessory Organs 5/3/2016.

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1 Sense of Vision Chapter 8 Special Senses The Eye and Vision 70 percent of all sensory receptors are in the eyes Each eye has over 1 million nerve fibers Protection for the eye Most of the eye is enclosed in a bony orbit A cushion of fat surrounds most of the eye The Eye Orbit Eyeball site in an orbit of 7 bones 1. Frontal 2. Lacrimal 3. Ethmoid 4. Zygomatic 5. Maxilla 6. Sphenoid 7. Palatine (posterior) Accessory Organs The eyebrows, eyelids, and eyelashes Protection The Lacrimal apparatus = gland and ducts Protection, moistens, traps debris The extrinsic muscles of the eye Eye movement Eyebrows, Eyelids, Eyelashes Eyebrows short hair on the supraorbital ridge Shade protection from perspiration and debris Eyelids extension of skin Protection from debri Inner surface lining = conjunctiva Secretes mucus to lubricate eye Eyelashes associated with eyelids Sebaceous glands (eyelashes) lubrication Inflammation sty 1

2 Lacrimal gland Lacrimal sac Nasolacrimal duct Lacrimal Apparatus Function: Produce tears Saline solution to wash eyeball Extrinsic Muscles 3 pairs of muscles that anchor the eye Attach sclera to the bone Rotates counterclockwise Rolls eye upward turns eye inward turns eye outward Rotates clockwise Rolls eye downward Figure 8.3c Extrinsic muscles of the eye. Structure of the Eye (c) Name Action Controlling cranial nerve Lateral rectus Moves eye laterally VI (abducens) Medial rectus Moves eye medially III (oculomotor) Superior rectus Elevates eye and turns it medially III (oculomotor) Inferior rectus Depresses eye and turns it medially III (oculomotor) Inferior oblique Elevates eye and turns it laterally III (oculomotor) Superior oblique Depresses eye and turns it laterally IV (trochlear) Layers forming the wall of the eyeball Fibrous layer: outside layer Vascular layer: middle layer Sensory layer: inside layer Humors are fluids that fill the interior of the eyeball Cavities & Chambers Anterior Cavity Cornea Lens (filled with aqueous humor clear liquid) Posterior Cavity Lens Retina (filled with vitreous humor) Anterior Chamber Cornea iris Posterior Chamber iris lens Vitreous Chamber 2

3 1. Sclera 2. Choroid 3. Retina Three layers of the Eye Sclera Fibrous Layer Outer layer, white (except cornea) Cornea: transparent anterior portion, allow light to pass (window of the eye), repairs itself easily, only human tissue that can be transplanted without fear of rejection Vascular Layer Choroid Blood rich nutritive layer Absorbs stray light that is not absorbed by receptors. Ciliary body smooth muscle attached to lens (controls shape of lens) Iris: regulates size of pupil Pigment is your eye color Pupil: opening in iris allows light to enter Retina contains 2 layers Outer pigmented layer absorbs light Inner contains photoreceptors Rods detect light, used for night vision Cones detect color Figure 8.5a The three major types of neurons composing the retina. Figure 8.5b The three major types of neurons composing the retina. Pigmented layer of retina Rod Cone Bipolar cells Central artery and vein of retina Pigmented layer of retina Neural layer of retina Optic disc Ganglion cells (a) Pathway of light (b) Optic nerve Sclera Choroid 3

4 Neurons of the retina and vision Rods Most are found toward the edges of the retina Allow vision in dim light and peripheral vision All perception is in gray tones Neurons of the retina and vision Cones Allow for detailed color vision Densest in the center of the retina Fovea centralis lateral to blind spot Area of the retina with only cones Visual acuity (sharpest vision) is here No photoreceptor cells are at the optic disc, or blind spot Figure 8.8 The posterior wall (fundus) of the retina as seen with an ophthalmoscope. Fovea centralis Macula Blood vessels Optic disc Retina Lens Bends and focuses as light rays pass thru Suspensory ligaments support lens and attach to ciliary body Lateral Medial Lens Cataracts result when the lens becomes hard and opaque with age Vision become hazy and distorted Eventually causes blindness 4

5 Accomodation of the Eye Optic Disk where the optic nerve leaves the posterior eyeball. There are no photoreceptors here so it s your blind spot Pathway of Incoming Light Cornea Aqueous Humor Pupil Lens Vitreous Humor Retina Optic Nerve Optic chiasma (where nerves cross) Thalamus Visual cortex in Occipital Lobe Visual Association Area A Closer Look Emmetropia eye focuses images correctly on the retina Myopia (nearsightedness) Distant objects appear blurry Light from those objects fails to reach the retina and are focused in front of it Results from an eyeball that is too long A Closer Look Hyperopia (farsightedness) Near objects are blurry, whereas distant objects are clear Distant objects are focused behind the retina Results from an eyeball that is too short or from a lazy lens A Closer Look 8.2 Bringing Things into Focus. (a) Emmetropic eye (b) Myopic eye (nearsighted) Focal plane Correction None required Concave lens Convex lens (c) Hyperopic eye (farsighted) 5