The eye and vision

70% of all sensory receptos are in the eyes

each eye has over a million nerve fibers

protection of the eyes

most of the eye is enclosed in a bony orbit

a cushion of fat surrounds most of the eye

human adult eye - hallow speherical stucture and 2.5 cm diameter

  • iris - color portion

protection of the eye

  • eye socket - less 20% of the surface of eyeball

  • eyelash - tarsal gland produce an oily secretion that lubricates the eye and ciliary glands are located between the eyelashes

  • eyelids - shades the eye during sleep and protects the eye from exessive light and foreign objects

  • tears apparatus - tears clean, lubricates and mostens the eye

  • flow of tears - lacrimal gland, lacrimal ducts, lacrimal canals, nasolicrimal duct, nasal cavity

accessory strcuture of the eye

  • function of the lacrimal aparatus - protects, moistens, and lubricates the eye and empties into nasal cavity

  • lacrimal secreation (tears) - diluate salt soluation, mucus, antibodies, lysozyme

lacrimal aparatus = lacrimal gland + ducts

  • lacrimal gland - produces lacrimal fluid; situated on lateral aspects of each eye

  • lacrimal canaliculi - drain lacrimal fluid from eye medially

  • lacrimal sac - provides passage of lacrimal fluid towards nasal cavity

  • naslocrimal duct - empties lacrimal fluid into the nasal cavity

  • conjuctiva - membrane that lines the eyelids, connects to the outer surface of the eye, secreates mucus to lubricate the eye and keep it moist

  • extrinsic eye muscle - six muscle attach to the outer surface of the eye & produce eye movement

sense of sight

  • sclera - protection - ( white of eye ) a tough protective layer of connective tissue that helps maintain the shape of the eye & provides an attachment for the muscle that move the eye

  • cornea - the clear, come shaped part of the sclera coverin the front eye through which light enters the eye

  • vitreous humor - a thick, transpart liquid that fills the center of the eye - it is mostly water & gives the eye its form & maintains eyeball shape

  • retina - sensory tissue that lines the back of the eye. it contains millions of photorecpetos (rods for black and white & cones for colors) that converts light rays into electrical impluses that are relayed to the brain via optic nerve

  • optic nerve - the nerve that transmits eletrcial impluses from the retina to the brain

  • if a blood vessle has white streek indicates high blood pressure high colestral

  • if a blood vessle looks bleeding indicate diabites

  • fovea - central vision

  • lens - a crystaline strcuture located just behind the

  • iris - it focuses light onto the retina & the pigmented ront portion of this chorid layer & contains the blood vessles - it determines the eye color

  • choroid layer - middle layer of the eye containing may blood vessles

  • aqueous humor - the clear fluid that fills that anterior chamber of the eye & helps to maintain the shape of the cornea providing most of the nutrients for the lens & the cornea & involved in waste management in the front of the eye

  • pupil - the opening in the center of the iris - it changes size as the amount of lights changes the more light and smaller the hole

  • ciliary body - is a circcular bond of muscle that is connected & sits immediately behind the iris - produces aqueous humor, changes shape of lens for focusing

sense of sight

  1. light enters through the pupil

  2. light passes through the lens & vitrous humor to the back of the eye the retina

  3. the image projected from the lens on the back of the eye is upside down

  4. the retina has photorecptors cells that direct light

  5. impluses from the rods & cones in the retina are sent to the optic nerve

  6. the optic nerves each eye cross at the optic chaism

  7. visual integration center in the occipital lobe process visual input

  • rods - black & white vision

  • cones - color vision & details

vision disorders

  • farsigtedness : trouble seeing close - up eye too short and/ or lens too weak light foucses behind retina correct with “ convex” lens to add power (hyperpia)

  • nearsightedness: trouble seeing far away is too long (myopia)

  • presbyopia (oldsightedness) : the crystaline lens tends to harden with age, the near point of distinct vision moves further and further away

  • astigmatism: abnormal curvature of the cornea

  • color - blindness - red - green color blindness due to sex linked gene

  • nonsex linked condition ( blue color blindess) - misslinh blue cones or pigments

  • monochromats : ppl who are totally colorblind

  • glucoma : damage to the optic nerve occurs due to increased eye preassure

  • cataracts: clouding of the lens that affects vision