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Chapter 2Chapter 2The Human Eye
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Physics ReviewPhysics ReviewLight
◦ Electromagnetic radiation
◦ Wavelength determines quality Measured in
nanometers
◦ Why light? Reliable: Travels
very fast and straight
Prevalent: Lots of it Informative:
Reflected/Absorbed by surface molecules
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The HeadThe HeadEye placement:
◦ Lateral vs. FrontalSkull: OrbitEye Movement
◦ 6 extra-ocular muscles: Conjugate: move
together Vergence: move
opposite
Eyelids:◦ Protection and
moisture◦ Blinking and Distance
Tears
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Eye FunctionEye FunctionImage: light distribution that
preserves the spatial ordering of locations in space
Image formation – reversing light divergence◦Optical power of:
1) cornea: 2/3rds of eye’s optical power 2) lens: flexing called accommodation
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Eye StructureEye StructureThree layers:
◦Protecting: Fibrous Tunic◦Nourishing: Vascular Tunic◦Detecting: Retina
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Fibrous TunicFibrous TunicSclera – “white” of eye, dense
material, gives eye it’s shapeCornea – transparent “bulge”,
allows light into eye
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Out of FocusOut of FocusCondition Common
nameEye Shape
Location of focus
Lens needed
Myopic Nearsighted
Too Long In front of retina
Concave
Hyperopic Farsighted Too Short Behind retina
Convex
Emmetropic
Normal Normal On fovea None
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Problems with LensProblems with LensPresbyopia:
◦loss of sight with age
Astigmatism:◦Distortion of cornea
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Vascular TunicVascular TunicChoroid
◦Pigment epithelium◦Contains blood vessels
and capillaries◦Reduces light scatter
and disposes of wasteAnterior Chamber
◦Manufactures aqueous humor
◦Contains: Iris/Pupil Lens
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RetinaRetinaContains
photoreceptors
Landmarks:◦ Macula (1.5mm
diameter): focus of eye, contains fovea
◦ Optic Disk: “blind spot”
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PhotoreceptorsPhotoreceptorsOrder of stimulation:
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PhotopigmentsPhotopigmentsTwo components
◦Opsin: large protein, 3 types◦Retinal: from vitamin A
Phototransduction
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Wavelength SensitivitiesWavelength Sensitivities
Cell Most Sensitive Wavelength
Relative “color”
Rods 500 nm Bluish-green
Cones440 nm Violet
530 nm Green
560 nm Yellow