Chapter 3 Flashcards
Light:
form of electromagnetic radiation that travels as a wave
Properties of Light
Amplitude: perception of brightness
Wavelength: perception of colour
Purity: mix of wavelengths; perception of saturation
Light enters through the _____ then passes through the ____
cornea, lens
Lens is capable of adjustments – called
accommodations
When you focus on a close object the lens of your eye gets fatter (rounder) to give you a clear image
When you focus on distant objects, the lens flattens out to give you a better image of objects
Retina:
absorbs light, processes images, and sends information to the brain
Fovea:
middle point at the back of our light, high concentration of our cones-most refinement
Optic disk:
where the optic nerve leaves the eye/blind spot
Receptor cells
Rods, cones
Rods:
black and white/low light vision
Communicate information about movement, bright or dark
Cones:
colour and daylight vision
Communicate information about detail
Adaptation:
becoming more or less sensitive to light as needed
Distribution on retina
Fovea consists solely of cones
Peripheral retina has both rods and cones
More rods than cones in periphery (outside of the fovea)
Blind spot:
place where optic nerve leaves the eye
blind spot-We don’t see it because:
One eye covers the blind spot of the other
It is located at edge of the visual field
The brain “fills in” the spot
Cornea is ___, but accounts for ___
fixed, ~80% of focusing
Lens makes _____ and accounts for the remaining __
accommodations, 20%
Ciliary muscles tighten, lens thickens
Light rays pass through the lens more sharply and focus near objects on the retina
Near point:
lens can’t adjust for too close objects
Inability to Focus
1- Presbyopia
2- Myopia
3-Hyperopia
Presbyopia: “old eye”
Distance of near point increases
Due to hardening of lens and weakening of ciliary muscles (muscles can’t focus enough to see things close)
Corrective lenses are needed for close activities, such as reading
Myopia:
“nearsightedness;” inability to see distant objects clearly
Image is focused in front of retina
Myopia Caused by:
Refractive myopia: cornea or lens bends too much light
Axial myopia: eyeball is too long
Hyperopia:
“farsightedness;” inability to see nearby objects clearly (eye is short)
Image is focused behind the retina
Usually caused by an eyeball that is too short
Constant accommodation for nearby objects can lead to eyestrain and headaches
Receptors have outer segments, which contain:
Visual pigment molecules
Visual pigment molecules have two components:
Opsin: a large protein
Retinal: a light sensitive molecule
Visual transduction occurs when the retinal____
absorbs one photon
Retinal changes its shape (isomerization)
Dark adaption:
process of increasing sensitivity in the dark
Measured by determining a dark adaptation curve
Visual Pigment Regeneration 1
Light causes the retinal part of the visual pigment molecule to change its shape (A → B)
Leads to separation of retinal and opsin (C)
Visual pigment bleaching (changes in color)
Visual Pigment Regeneration 2
Bleached pigments are unable to react to light
process of reforming the visual pigment molecule by re-attaching the retinal
In normal light levels, both bleached and intact visual pigments present (balance)
In low light levels, more intact visual pigments than bleached leads to increased sensitivity
Cone vs Rod Regeneration
William Rushton measured regeneration of visual pigment in humans using darkening of retina associated with dark adaptation
Cone pigment regenerates in ~ 6 min
Rod pigment regenerates in 30+ min
Rates match dark adaptation for cones and rods
Spectral Sensitivity
Sensitivity of rods and cones to different parts of the visual spectrum
Use monochromatic light to determine threshold at different wavelengths
Threshold for light is lowest in the middle of the spectrum
1/threshold = sensitivity
Produces the spectral sensitivity curve
Rod spectral sensitivity
More sensitive to short-wavelength light
Most sensitivity at 500 nm
Cone spectral sensitivity
Most sensitivity at 560 nm
Purkinje shift:
enhanced sensitivity to short wavelengths during dark adaptation when the shift from cone to rod vision occurs
Difference in spectral sensitivity is due to absorption spectra of visual pigments
Rod pigment absorbs best at 500 nm
Cone pigments absorb best at 419nm, 531nm, and 558nm
Absorption of all cones equals the peak of 560nm in the spectral sensitivity curve
Difference in spectral sensitivity is due to absorption spectra of visual pigments
Rod pigment absorbs best at 500 nm
Cone pigments absorb best at 419nm, 531nm, and 558nm
Absorption of all cones equals the peak of 560nm in the spectral sensitivity curve
1-Rods and cones send signals ____ through:
2-Signals are sent ___:
1) vertically
Bipolar cells
Ganglion cells
Ganglion axons
2) horizontally,
Between receptors by horizontal cells
Between bipolar and between ganglion cells by amacrine cells
1-Rods and cones send signals ____ through:
2-Signals are sent ___:
1) vertically
Bipolar cells
Ganglion cells
Ganglion axons
2) horizontally,
Between receptors by horizontal cells
Between bipolar and between ganglion cells by amacrine cells
