Chapter 2-Light sensitivity Flashcards
what is the duplex retina
what must the 2 thigns operate
- one operates under dim conditions and is more sensitive to short wavelengths
- a second that operates under bright conditions and is more sensitive to long wavelenths
what is scotopic vision
rod mediated mech
operates under dim lighting conditions
doesnt perceive color
poor VA
what is photopic visoin
cone mediated mech
operates under bright lighting conditoins
perceives colors
best VA
what do rods contain in their outer segment?
how is that activated?
rhodopsin
it is very sensitve to light and it can be activated by only 1 photon
-can trigger rod to transmit signal to rod-bipolar cells
-DOES NOT mean we perceive this photon as light
what happens when rhodopsin is activated by a photon
becomes inactive and it is not sensitive to light anymore
BLEACHING is the inactive site
- cont. regenerates and reverts to the active state after some time
- after regnerated it is able to absorb another photon and etc.
how many rhodopsin molec does a single rod contain, what about the whole retina
how long does it take for all of these molec to become active (NOT BLEACHED)
10^7
10^15
40 min (in ocmplete darkness this is when we can measure scotopic threshold)
how can we obtain a similar function to scotopic spectral sensitivie for photopic conditions?
no dark adaptation, bright background and stimulus to stimulate cones
how long does it take for the regneration of the 3 cone opsins
5-10 min
what is the photochromatic interval
the difference btwn the scotopic and photopic spectral sensitivity function
in a radiometry, where will the output be
the radiant power (or radiant flux) of the source in Watt (W)
what does photometry deal w/
the effect a certain wavelength has on the visual system and how it compares w/ other wavelengths
or
how efficient a wavelength is at stimulating the visual system
photopic and scotopic luminosity functions
what is luminous power
the perceived power of light, not the physical power
what is abney’s law of additivity
add the total luminous power by adding all of the indiv wavelenghts
what is dark adaptation?
waht is light adaptation
dark: adaptation to dark conditions (or scotopic conditions(
light: adapatation to light conditions (or photopic)
what are the 2 def of dark adapattation
- how fast our visual system adapts to darkness after exposure to bright light
- how fast our sensitivity recovers after exposure to bright light
after bleaching w/ a very intense light the subject sets his/her threshold for up to _______ in complete darkness
40 min
what are the factors affecting dark adaptation curve
bleaching stimulus size stimulus location stimulus wavelength rhodopsin regneration
what is bleaching
the process when the photopigments become inactive and the regeneration process starts
what does the amt of bleached photopigment depend on
the intensity (I) and the duration (t) of the light used for bleaching
bleached photopigment = f(I,t)
what is the photochromatic interval
the difference in spectral sensitivity btwn photopic and scotopic system
what is the half life of rhodopsin regneration
cone?
Rods: T=5 min
in other words, in 5 min, 50% of the bleached rhodopsin is regnerated
Cones: 1.5 min
when causes dark adaptations to start sucking for pts?
- age-photoreceptor loss and thickening of bruch’s
- retinal/neural sources-RP, AMD, congenital stationary night blindness
- vascular changes
- choroideremia,
- gyrate atrophy - vit A deficiency
- chronic liver disease (cirrhosis)
- chronic GI tract dieases (malabsorption)
- alcoholism
what is the visual cycle also known as
retinoid cycle
when photopigments molec are active (ready to react to light) they are opsins bound with a …..
a photon is absorbed by that and it chnages its form to what?
chromophore called 11-cis-retinal (rhod etc)
a photon is absorbed by 11-cis-retinal which then changes its form to all trans retinal
