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What are the structures of the eye and how do they work so that we see?…
What are the structures of the eye and how do they work so that we see?
Structure of the eye (86)
Crystalline Lens (K)
Accomodation
Lens can vary focus by changing shape
Emmetropic
Hypermetropia (Farsightedness)
Difficulty bringing near objects into focus
If eye is too short or light not bent sharp enough
Myopia (Nearsightedness)
If eye is too long or light is bent too sharply
Difficulty bringing far objects into focus
The eye's ability to accommodate (focus) normally
Capacity depends on eye-shape & amount of light
Damage/injury
Presbyopia (Old-sighted)
Lens loses elasticity with old age
Refractive error
Item's held further away inorder to focus
Cataracts
Distorted image from clouded lens
3 types:
Secondary --> from disease
Traumatic --> from injury
Congenital --> from birth
Function:
Accountable for 20%-30% of eye's ability to focus
Sharpens focus of image onto retina
Curvature determines amount that light is bent
Retina (D)
Pigment epithelium
Light absorbing dark layer
Reduces amount of reflected/scattered light
Function:
Neural screen at the back of the eye
Light/image is focused onto here
Transduces light waves into neural signals
3 layers of neural tissue
Outer layer contains
photoreceptors
Rods (long/thin)
Cones (short/thick)
Middle layer contains
bipolar cells
Connects photoreceptors and ganglion cells through synapses
Inner layer contains
ganglion cells
Cells with lateral connections:
Horizontal cells
Amacrine cells
Damage/injury:
Retinitis pigmentosa
Loss of night vision, or resulting blindness
caused by retinal degeneration
Diabetic retinopathy
Diabetes causes neovascularization leading to vision loss
Pupil (I)
Light reflex
Controls size of the pupil
Function:
Pupil contracts --> increasing or decreasing it's size
Increases size to let in more light
Decreases size to let in less light
Fovea (C)
Macula lutea
Yellow pigmented area around origin of optic axis
Fovea centralis
Small circular depression
Optic axis
Imaginary line passing through center of pupil to center of retina
Function:
Foveal region gives us the sharpest image
Densely packed with cones
Iris (J)
Function:
Controls amount of light entering the eye
Colored membrane surrounding the pupil
Optic Nerve (B)
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Cornea (G)
Aqueous humor (H)
Nourishes cornea and lens
Small chamber filled with fluid (similar to cerebro-spinal-fluid)
Function:
Accountable for 70%-80% of eye's ability to focus
First structure light waves pass through
Damage/injury
Astigmatism --> Cornea isn't spherical; blurry images
Less transparency --> distorted retinal projection
Sclera (F)
Elastic membrane/socket protecting the eye in the skull
White coating that surrounds the iris
Vitreous humor (A)
Jelly-like substance that fills up eye chamber
Blind spot (L)
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Area that neural signal exits retina
Doesn't contain any photoreceptors
Choroid (E)
Layer of blood vessels inbetween sclera & retina
Neural responses (36)
Receptive fields
Region of retina where light alters cell's firing-rate
Optic nerve
Optic disk
Neural axons exiting eye form a circular pattern
Function:
Bundle of axons
Transmits visual info from eye to the brain
Rods & Cones
Duplex retina theory
Night-blindness
None, or non-functioning rods
Day-blindness
Non-functioning cone system
Schultze claims there are two separate visual systems
Dim light (Rods) & bright light (Cones) conditions
Photopic (Day vision)
Vision under bright light
Scotopic (Night vision)
Vision under dim light
Pigments
Rhodopsin
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Visual red
Breaks down into retinal and opsin
In rods: Scotopsin
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Iodopsin
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Visual pruple
Breaks down into retinal & opsin
In cones: Photopsin
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Rods
Respond to dim light
120 million distributed along perihperal retina
Cones
Respond to color
6 million distributed along retina (1% in fovea)
Function:
Cells containing light absorbing pigments
Visual properties (18)
Visual Acuity
Cones are more sensitive to light
Eyes ability to solve details
Measured with recogntion acuity
Visual sensitivity
Rods are more sensitive to light
Light adaptation
Dark adaptation
Illusions
White's Illusion
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Lateral inhibition
Rectangles appear different shades because of surroundings
Hermann Grid
Lateral inhibition
Perceiving black spots at intersections of grid
Simultaneous contrast
Falsely perceive brightness of area
Caused by the surrounding or neighboring area
Anatomy