Chapter 2 Study Guide The First Steps in Vision Key terms 1 Duplex in reference to the retina consisting of two parts the rods and the cones which operate under different conditions 2 Eccentricity the distance between the retinal image and the fovea 3 Emmetropia the condition in which there is no refractive error because the refractive power of the eye is perfectly matched to the length of the eye ball 4 Scotoma A blind spot in the visual field 5 synaptic terminal the location where axons terminate at the synapses for transmission of information by release of a chemical transmitter 6 Properties of light a Absorb to take up light noise or energy and not transmit it at all b Contrast the difference in luminance between an object and the background or between lighter and darker parts of the same object c Filter an acoustic electrical electronic or optical device instrument computer program or neuron that allows the passage of some frequencies or digital elements and blocks the passage of others d Photoactivation activation of light e Reflect to redirect something that strikes a surface especially light sound or heat usually back toward its point of origin f Scatter to disperse light in an irregular fashion g Transduce referring to the conversion from one form of energy e g light to another e g electricity h Transmit to convey something e g light from one place to another i Wave an oscillation that travels thought a medium by transferring energy from one particle or point to another without causing any permanent displacement of the medium 2 Anatomy of the eye lens iris rods cones pigments fovea cornea ect and what each part does a Cornea the transparent window into the eyeball i Has sensory nerve endings that force the eye to close and produce tears if the cornea is scratched ii Most powerful refracting surface in the eye which contributes to 2 3 of eye s focusing power b Aqueous humor watery fluid derived from blood in the anterior chamber of the eye i Supplies oxygen and nutrients to and removing waste from the cornea and crystalline lens b Crystalline lens the lens inside the eye that enables changing focus c Pupil the dark circular opening at the center of the iris in the eye where light enters the eye d Iris the colored part of the eye consisting of a muscular diaphragm surrounding the pupil and regulating the light entering the eye by expanding and contracting the pupil i Controls amount of light that reaches the retina via pupillary light reflex b Vitreous humor the transparent fluid that fills the vitreous chambers in the posterior part of the eye i Compromised of 80 of the internal volume of the eye eye maintain its spherical shape and refracts light rays g Retina a light sensitive membrane in the back of the eye that contains rods and cones which receives an image from the lens and send it to the brain through the optic nerve i Much of the light energy will have been lost in space or the atmosphere because of absorption and scattering ii A good deal of light becomes lose in the eyeball so only half the starlight that arrives at the cornea actually reaches the retina iii The role of the retina is to detect light and tell the brain about aspects of light that are related to objects in the world 1 Where seeing really begins b Ciliary muscle Ciliary muscles are responsible for changing the shape of the lens to bring objects into focus i When they contract the lens becomes thicker which brings close objects into focus ii When the ciliary muscles relax the lens becomes thinner bringing far away objects into focus iii The ciliary muscles are connected to the lens by tiny fibers called the zonules of Zinn b Pigments rhodopsin c Fovea A small pit near the center of the macula that contains the highest concentration of cones and no rods It is the portion of the retina that produces the highest visual acuity and serves as the point of fixation 8 Rods and Cones where they are what they do when kind of cells are the information pass through what pigment is found in rods night vs day vision There are many more rods about 90 million than cones about 4 5 million have many different geographic distributions in the retina a Rods photoreceptors specialized for night vision i Completely absent from center of the fovea and their density increases to a peak at about 20 degrees then declines ii Function relatively well under conditions of dim scoptic illumination which is why all animals with all rod retinas are nocturnal iii Rods have the same type of photopigment they cannot signal differences in color 1 Rhodopsin the visual pigment found in rods b Cones photoreceptors specialized for day light vision fine visual acuity and color i More concentrated in the center of the fovea and their density drops off dramatically with retinal eccentricity distance between retinal image and the fovea ii Cones require brighter photopic illumination e g sunlight or room lights to operate efficiently iii Cones have three different photopigments that differ in wavelengths at which they absorb light most efficiently 1 Cones provide basis of our color vision 9 Myopia a common condition is which light entering the eye is focused in front of the retina and distant objects cannot be sharply seen nearsightedness a Hyperopia a common condition in which light entering the eye is focused behind the retina farsightedness b Astigmatism a visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye usually the cornea