Works somewhat like a camera.It takes in light for imageto be “understood/seen”,It must be processed in the brain.Eyes are actually extensions of the brain
ANATOMY OF THE EYEThe eye is round, like a ball or a balloon.It is made of many separate components and tunics (layers).Only 1/6 of the eye is exposed/visible (the rest is enclosed in fat and bone).
Interior apparatus associated with the eye: lacrimal glands nasolacrimal ductTears contain antibodies and lysozymes (enzymes that kill bacteria).
Six external eye muscles control eye movement:4 rectus muscles (up, down, left and right)2 oblique muscles Inferior oblique (elevates eye & moves it laterally) Superior oblique (depresses eye & moves it laterally)
Tunic Layers :a) Sclera (outermost layer): thick, tough, whites of the eye.b) Choroid (middle layer of eye): blood rich tunic, that contains a dark pigment that prevents light from scattering in the eye.c) Retina (inner back of the eye): innermost delicate tunic, that contains millions of receptor cells (rods & cones) that receive and respond to light. sclera choroid retina
Internal Anatomy of the Eye:Two hard lenses (cornea & lens) help bend lightappropriately in order to focus light onto the retinaso image can be clearly seen. cornea lens
Attached to the lens are ciliary bodies (smooth muscles)and the iris (pigmented “color” part of the eye).The ciliary bodies pull on the iris which dilatesand constricts to regulate light input.
Two “liquids” in eye:a) Aqueous humor: watery liquid just behind cornea. Helps bathe cornea and give it oxygen & nutrients.b) Vitreous humor: thick, jelly-like substance which makes up bulk of eyeball. Give eye structure and maintains ocular pressure. Aqueous humor Vitreous humor
On the back of the eye is the retina.The retina contains thousands of photoreceptors.Photoreceptors are nerve cells that receive light.Light passingthrough Retinaeyeball (& photoreceptors)
The role of photoreceptors…•Photoreceptors are distributed all over the entire retina,at the back of the eye (except where the optic nerve leavesthe eyeball = optic disc/“blind spot”).•When light from an object is focused on the optic disc, it disappearsfrom our view. “blind spot”
There are two types of photoreceptors: a) Rods:slender, elongated neurons. Rods allow us to see in black, white, and shades of gray. Rods also allows for peripheral vision. rods conesb) Cones: fatter, more pointed neurons(blue cones, green cones, and red cones). Rods (skinny)Cones allow us to see in color. Cones (fatter)Also allows us to focus clearlyon objects in the center of our view.
Vision results from:Light enters eye as wavelengths. These stimulate neurons atback of eye (retina). These neurons start an action potential(electrical impulse) which pass from the photoreceptors tobipolar cells, then to ganglion cells, and then leave the opticnerve. Photoreceptors on retina get stimulate and pass electrical impulses to brain via optic nerve.
The nerve impulses travel very quickly along optic nerve tothe occipital lobe of the the cerebral cortex which allowsus to process and interpret these electrical signals, resultingin “vision”. eyes occipital lobe
Cataract• A cloudy or opaque area in the lens of the eye• Can be caused by smoking or heredity• ! 32
Glaucoma• A group of ocular conditions that contribute to the loss of retinal nerve ﬁbers thus vision loss• A disease of the optic nerve• The higher the pressure inside the eye the greater the chance of optic nerve damage 33