Vision I Light Eye Anatomy Optics and Introduction to the Retina What does the visual spectrum refer to 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 Waves wavelength light when it moves around the world hue Made up of particles photon light when it is absorbed number intensity brightness S for short wave length let us see blue Electromagnetic radiation is energy produced by vibrations of electrically charged material Radiation energy emitted in form of waves light or particles photons M for medium wavelength let us see green 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 we don t see but it is there Night vision devices Animal Pit vipers rattlesnakes detect UV we don t see but tissue damage sunburn FYI of photons perception of intensity wavelength perception of color Slide 5 know the terms in red Radiance energy from source intensity of a light beam The sun radiates light Illuminance 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 o o o 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 Know the parts of the eye Be able to label them on a picture and know what they each do Retina only part of the body where we can see arteries and veins directly so good diagnostic for entire vascular system Macula center of retina center of its fovea 2 layers of ganglion cells Iris circular band of muscles that controls the size of the pupil controls light entry Cornea transparent tissue covering the front of the eye Light is transmitted and refracted here Nerve endings to detect touch and to force eye to close and produce tears if the cornea is scratched Nerves Afferent branch Trigeminal V efferent Facial VII Pupil hole in the center of the iris where light passes through Lens transparent tissue Bends light that is passing through the eye to focus image on retina Accommodation near far focus By bending itself ciliary muscles control its curvature Focus on distance Ciliary muscle a round muscle Connected to lens by Zonules like spokes on a wheel Relaxed Contracts in Zonules of Zinn stretched Relaxed less tension Lens bulges Aqueous humor fluid derived from blood Removes waste from cornea and lens Just behind cornea Supplies oxygen and nutrients to cornea and lens Focuses on close objects Helps maintain shape of eye and intraocular pressure too much production or too little drainage in glaucoma 80 of internal volume of eye Vitreous humor between lens and retina Clear jelly like fluid Refracts light Maintains shape of eye Sclera the white of the eye Tough opaque tissue that serves as the eye s protective outer coat Optic nerve is attached to the sclera at the very back of the eye Choroid layer of blood vessels providing nutrition for the eye Heavily pigmented high melanocyte content so absorbs extraneous light entering eye this Six tiny muscles connect to it around the eye control the eye s movements reduces reflection within the eye it would blur the image 4th time light is refracted in the eye Attached to sclera Viscous kind of like egg white Fovea point of central focus Blind in dim light Optic disc hole in back of eye where optic nerve fibers exit and blood vessels enter Optic nerve leaves the eye through the optic disc What is the pupillary light reflex What cranial nerves are involved Why does red eye occur in photographs Pupillary light reflex Whytt s reflex immediate constriction of pupil in response to bright light CNs II and III Red eye occurs because of dim light the pupil is dilated or too much light goes in it is reflected back from the fundus through the choroid What is accommodation 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 what causes it Accommodation so as opposed to other parts of the eye the refractive power of the lens is dynamic Ability to accommodate decreases with age Presbyopia by 40 50 years old cannot accommodate enough to focus on things within arm s reach 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 Light enters the eye refracted converges at a point on the retina Light rays from object less than 20 feet away are parallel Light rays from closer object are divergent and must be sufficiently refracted or will not meet on a single focal point What are cataracts What causes them How do they affect vision Cataracts clouding of the eye s natural lens Opacities in the lens caused by irregularity in the crystallins Crystallins densely and regularly packed proteins that make up the lens and whose organization dense and regular gives the lens its translucence Causes risk factors Congenital rare Age related usually after 50 in most people after 70 Diabetes Being struck by lightening Penetrating or non penetrating eye trauma Sun exposure Affect vision absorbs and scatter more light than the normal lens What are emmetriopia hyperopia myopia Emmetriopia no refractive error because the refractive power of the eye is perfectly matched to the length of the eyeball Hyperopia Farsightedness usually present at birth runs in families Eyeball is too short for refractive power of eyes so focus behind retina Correct with plus convex lenses to converge rays before they enter the eye Most newborns are hyperopic because optical components of eyes are well developed at If you are young you can correct this by accommodating birth compared with lengths of eyeballs Myopia Nearsightedness eyeball is too long for refractive power of eye so focus image in front of the retina instead of on it Correct with negative minus concave lenses which diverge the rays before they enter the eye What is an astigmatism Occurs when cornea isn t spherical curved more steeply in one direction than the other like going from a basketball to a football Vertical lines might be focused just in front of retina and horizontal lines
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