Study Guide for Exam 4 Vision Parts 1 2 3 I have gathered the information necessary to study for Exam 4 and compiled it into a single document There ARE DIFFERENCES in this study guide from the study questions at the ends of the PowerPoint lectures 1 What does the visual spectrum refer to To which wavelengths are humans maximally sensitive Even if we can t see it is there other electromagnetic radiation that we somehow respond to Know an example of an animal that uses more of the electromagnetic spectrum Light Electromagnetic radiation o Waves wavelength light when it moves around the world hue o Made up of particles photon light when it is absorbed number intensity brightness We are sensitive to only a limited portion of the spectrum 380 760 nm Light the visual spectrum Electromagnetic radiation o energy produced by vibrations of electrically charged material Radiation energy emitted in form of waves light or particles photons o S for short wave length let us see blue o M for medium wavelength let us see green o L for long wavelength let us see red Light waves themselves are not colored after our visual system interprets them we perceive them as having a color IR Infrared we don t see but it is there o Night vision devices o Animal Pit vipers rattlesnakes detect UV we don t see but tissue damage sunburn 2 FYI of photons perception of intensity wavelength perception of color 3 Differentiate between radiance and illuminance What does it mean to say that light is reflected Absorbed Transmitted Refracted Radiance Illuminance o energy from source intensity of a light beam The sun radiates light o energy from source to object the amount of light falling onto patch of unit surface area the sun illuminates the Earth When the light hits the surface it can be reflected absorbed or transmitted If a surface looks lighter it is reflecting most of the light If a surface looks dark it is absorbing most of the light If transmitted some is refracted bent Example when light goes into through the water or the eyeball Luminance energy reflected off object means emitting or reflecting light measure of the brightness of a surface 4 What is the main purpose of the eye as an organ To control light entry to focus light on receptors to transduce photons of light to electrical signals the brain can interpret 5 Know the parts of the eye Be able to label them on a picture and know what they each do IN DETAIL Retina Macula Iris Cornea Pupil Lens o only part of the body where we can see arteries and veins directly so good diagnostic for entire vascular system o center of retina center of its fovea 2 layers of ganglion cells o Circular band of muscles dilator sphincter that controls the size of the pupil and therefore controls light entry o transparent tissue covering the front of the eye o Light is transmitted and refracted here o Nerve endings to detect touch and to force eye to close and produce tears if the cornea is scratched o Nerves Afferent branch Trigeminal V efferent Facial VII o hole in the center of the iris where light passes through o transparent tissue o Bends light that is passing through the eye to focus image on retina o Accommodation near far focus o By bending itself ciliary muscles control its curvature Ciliary muscle o a round muscle o Connected to lens by Zonules like spokes on a wheel o Relaxed o Contracts in o Focus on distance Zonules of Zinn o stretched o Relaxed less tension o Lens bulges o Focuses on close objects Aqueous humor o fluid derived from blood o Just behind cornea o Supplies oxygen and nutrients to cornea and lens o Removes waste from cornea and lens o Helps maintain shape of eye and intraocular pressure too much production or too little drainage in glaucoma Vitreous humor o between lens and retina o Clear jelly like fluid o 80 of internal volume of eye o Refracts light o Maintains shape of eye Sclera o the white of the eye o Tough opaque tissue that serves as the eye s protective outer coat o Six tiny muscles connect to it around the eye control the eye s movements o Optic nerve is attached to the sclera at the very back of the eye o layer of blood vessels providing nutrition for the eye o Heavily pigmented high melanocyte content so absorbs extraneous light entering eye this reduces reflection within the eye it would blur the image o Attached to sclera o Viscous kind of like egg white o 4th time light is refracted in the eye o point of central focus o Blind in dim light Choroid Fovea Optic disc Optic nerve Fundus o hole in back of eye where optic nerve fibers exit and blood vessels enter o leaves the eye through the optic disc o back surface of eye including retina optic disk macula center of retina center of it is fovea 2 layers of ganglion cells fovea 6 What is the pupillary light reflex AKA Whytt s reflex What cranial nerves are involved Why does red eye occur in photographs How is that different from red eyes due to studying or reading too long etc This has to do with blood vessels in the whites of the eyes and not the choroid reflection that creates red eye in a photograph Pupillary light reflex o AKA Whytt s reflex o Immediate constriction of pupil in response to bright light o CNs II Optic nerve and III Oculomotor nerve Red eye o dim light pupil dilated too much light in reflected back from fundus thru choroid latter gives reflection red appearance o causes dilation of blood vessels o Fundus back surface of eye including retina optic disk macula center of retina center of it is fovea 2 layers of ganglion cells fovea 7 What is accommodation and how is it accomplished What shape do you need your lens flat or bulging to see close by What about to see far away What is presbyopia and what causes it Accommodation dynamic Presbyopia arm s reach o so as opposed to other parts of the eye the refractive power of the lens is o Ability to accommodate decreases with age o By 40 50 years old cannot accommodate enough to focus on things within o Why Lens becomes harder and capsule surrounding it loses elasticity o Some vertebrates fish accommodate by moving lens in relation to retina Move forward to focus on nearby object back to focus on distant object like camera lens Why do we accommodate o Light enters the eye refracted converges at a point on the retina o Light rays from object less than 20 feet away are parallel o Light rays from closer object are divergent and must be sufficiently refracted or will not meet on a single focal point 8 What are cataracts What causes them
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