Task 2 Flashcards
(30 cards)
Accommodation
Accommodation enables the power of the lenses to vary. There are accommodated and unacommoated lenses.
Lenses are attached yo ciliary muscles through tiny fibers (Zones of Zinn). When the Hilary muscles are relaxed then the lenses are unacommodated, whereas the zones of Zinn are under tension.
When the clarity muscles are contracted then then lenses are accommodated, meaning that the zones of Zinn are relaxed.
Accommodation- changes in lenses shape, ciliary muscles at the font of the eye tighten and increase the curvature of the lenses -> gets thicker.
Refractive errors
occur when the eyeball is too short( hyperopia) or too long(myopia) , relative to the power of the 4 optical components which are the: cornea, aqueous humor, lenses, and vitreous humor. *The nr. of errors that can affect the ability of the cornea and or lenses to focus the visual input onto the retina.
Transduction in short
transformation from one energy to another. Visual transduction happens in photoreceptors (rods & cones). Transform light into electricity.
Steps:
1. Molecules light sensitive visual pigment in outer segments of photoreceptors.
*long protein :opsin
*smaller light sensitive component: retinal
when these 2 are combined= results in molecules absorbing light
1.1. Light hits the retina- visual pigment molecule absorbs the light
2. Which causes retinal within molecule to change shape: Izomerization- from being bent to straight-> creates a chemical reaction .
3. Activates thousands of charged molecules to create electrical signals in receptors.
4. Amplification leads to activation of entire photoreceptor. Electical signal has now been created. Transduction complete.
Focus + pupil (depth of field)
Cornea (80%)- transparent covering, fixed in place
Lens (20%)- adjustable, thanks to ciliary muscles
* 20/20 vision( normal vision): if an object is > 20 away, the light rays that reach the eye are parallel, and the cornea + lens focuses them
blindspot
Where ganglion cells leave the eye to form the optic nerve. There are no photoreceptors.
Measuring cone adaptation
look directly at the test light-> image falls on all-cone fovea
Dark adaptation curve
1) first cones then rods more relevant
dark adaptation is almost 30 minutes -> time after when person can see the surroundings in comparison to light adaptation time that take up to 5 minutes
Red- cone break- place where rods begin to determine the dark adaptation curve instead of the cones is called the rod-cone break.
Purkinje effect
The phenomenon, now known as the Purkinje effect, explains why colors look different depending on how much light is present.
all colors are seen as grey in the dark
Purkinje shift- enhanced perception of short wavelength during dark adaptation
Visual pigment regeneration/ blenching
Visual pigment blenching- change in shape and separation of retinal from opsin causes the molecule to become lighter in color.
Visual pigment regeneration- in order to be useful again, retinal needs to return to its bent shape and become reattached to opsin.
when turning off the lights
visual pigments continue to regenerate but there is no isomerization, the concentration of regenerated pigments builds up so retina contains only intact visual pigment molecules.
Ruthon’s measurements & conclusions
Cone pigment- 6 minutes to regenerate completely
Rod pigment- 30 minutes
Rate of cone dark adaptation matched cone pigment regenerations, same for Rods
What happens to vision if something prevents visual pigments from regenerating ?
Pigement epithelium
condition: detached retina
Pigment epithelium
person’s retina becomes detached from layer containing enzymes needed for pigment regeneration.
Blenched pigment’s separated retinal and opsin can no longer be recombined. Condition called detached retina, caused by traumatic injuries of the eye or head. Baseball player is hit in the eye. Laser surgery
Spectral sensitivity curve
the relationship between wavelength and sensitivity. Rods and cones differ in the way they respond to light in different parts of the visible spectrum. Measuring a spectral sensitivity curve.
*threshold higher at short and long wavelengths
-> less light is needed to see wavelengths in the middle of the spectrum
Rod and cone pigment absorption
Cone pigment regenerates faster than rod
Pigments absorption spectrum- plot of the amount of light absorbed vs wave length of the light
3 absorption spectra
S(419nm)+ M(531 nm)+ L(558 nm) = psychophysical spectral= 560 nm sensitivity curve
Photopigment regeneration
*photopigments are used up & replaced in receptor cells
*rods provide better sensitivity than cones do
* rod system is capable of detecting a single quantum of light
*after a photopigment molecule is blenched, molecules must be regenerated before it can be used again to absorb another photon.
Neural circuity
Receptive field- region on the retina and corresponding region in visual space in which stimuli influence the neurons firing rate.
Visual acuity (ability to see in detail)
less convergence causes cones to have better acuity than rods
*cones have better visual acuity because they have less convergence
high convergence vs low convergence
High convergence results in high sensitivity= poor acuity (rods)
Low converges results in low sensitivity= high acuity (cones)
Optic nerve
signals from photoreceptors travel though retina-> reaching retinal ganglion cells. The axons of the ganglion cells leave the retina as fibers of the optic nerve
neuron’s receptive field
the region of the retina that must receive illumination in order to obtain a response in any given fiber.
*Receptive field of many different ganglion cells overlap
Shining light on a particular point on the retina activates many ganglion cells
center surround receptive fields
concentric circles: inhibitory and excitatory
