Eye Notes You tube video below E1MvRmWg7I

Parts of sight sense Eyes Accessory organs –Eyelids (palpebrae)-thinnest skin Protect eye –Canthus-corners of the eye –Eyelashes-hairs that prevent particles from getting into the eye –Conjuctiva-membrane inside eyelids (prevent eyelids from sticking together) Conjunctivitis-pink eye –Lacrimal apparatus-has a gland that produces tears/pink tissue in corner of eye Tears have lysozymes-antibacterial enzyme –6 muscles

Parts of outer eye Fibrous Tunic-mechanical & physical protection help to focus image Cornea-transparent window of the the eye –Focus entering light –Covers colored portion of the eye –Limited repair Sclera-white portion of eye –Made of collagen and elastin –Protect eye and attaches muscles Optic nerve Blindness-loss of transparency of cornea Can receive a donor cornea/no blood involved so successful

Vascular Tunic (middle eye) Regulate amount of light entering the eye Control shape of lens (an essential part of the focusing process) Choroid coat –Vascular and nutritive –Joined to sclera –Melanocytes (pigments)-absorb excess light and keep inside eye dark (tons of pigments) Ciliary body-forms a ring around the eye Composed of muscles and ligaments Holds lens in position

Middle Eye (cont) Lens-behind the iris and pupil –Held in place by suspensory ligaments –Ciliary muscles and ligaments help to change its shape in order to focus Accomodation –Relaxation creates flat shape to see distance –Contraction creates convex shape to see close Cataracts-lens become cloudy and opaque –Can cause blindness

Iris-part of middle eye Thin diaphragm of connective tissue and smooth muscle Colored portion of eye –Thickness and # pigments determines eye color –More is black, brown colors; less is blue and gray –melanin Adjusts the amount of light that enters the pupil –The pupil is the opening at the center of the iris. –Dark part of eye Aqueous humor-fluid between cornea and lens –Provides nourishment and maintains shape

Smooth Muscle Role Regulates light by regulating pupil size –Contract-small size so less light –Relax-big size so more light

Glaucoma Rate of aqueous humor formation is more than its rate of removal Builds pressure on the eye –Blood vessels shut-rob cells of nutrients Cells die and may cause blindness

Inner Eye Parts Retina –Photoreceptors –Thin and delicate –Contains a depression called fovea centralis –This produces the sharpest vision Optic Disc –Where nerve fibers leave the eye and join the optic nerve –Lacks receptor cells-known as blind spot –Vitreous humor-liquid that fills the posterior cavity Floaters-when clumps form in this liquid

Light Refraction (bending of light wave) Convex surface of cornea and the lens refracts light and converges the rays onto the retina –Image is upside down and reverse –Distant objects Lens thinner, muscles relax, less convex, refract less –Close objects Lens thicker, muscles contract, more convex, refract more Visual cortex interprets this image correctly

Visual Receptors Rods –Long and thin –Provide black and white vision –More sensitive to light –Provide vision in dim light Cones –Short and blunt –Color vision –Sharp image –High in fovea centralis –Cone numbers decrease as you move away from fovea centralis

Visual pigments in Rods  Rhodopsin (purple pigment)  light sensitive  Breaks down into a protein called opsin (clear color), and yellow retinal (made from vitamin A) in the presence of light  Sends nerve impulse to brain  In dim light, opsin and retinal make rhodopsin

Visual Pigments of Cones  Made of retinal and the opsin protein  There are 3 types of opsin proteins  Sensitive to red light  Sensitive to green light  Sensitive to blue light  The wavelength of light determines the color perceived from it  The color perceived depends upon which sets of cones the light stimulates  If all 3 stimulated-white  if none are stimulated-black Colorblindness-lack of cone pigments

Nearsightedness-myopia –Concave lens Farsightedness-hyperopia –Convex lens Ophthalmoscope-used to examine the interior of the eye