Duplex Retina Flashcards
A source with which of the following color temperature will appear most red
2000k
The color temperature of an incandescent bulb is 3300K. This means
The bulbs spectral distribution matches that of a blackbody radiator whose temperature is 3300K
A neutral density filter transmits 50% of 450nm light that is incident upon it. If 40W of 550nm are incident on the filter, how many watts are transmitted
20
40x50%=20W
Wavelengths doesn’t matter, it transmits all wavelengths equally
The least amount of distortion is present with sunglasses made with a
Neutral density filter
Which of the following light sources has more energy concetrated in the blue region of the spectrum
LEDs
What is the adaptional range of the human eye
10^-6 to 10^10
What makes it possible for the human eye to see something very bright and something very feeble in the night sky?
The pupil, but the pupil is good for only 1 log unit, the rest is from the retinal photoreceptors
How does pupil help make humans able to see bright and dark
By changing its diameter in response to light, helps to control the amount of light that falls upon the retina
How many log units does the pupil contribute to sensitivity of light
1 log unit
How can the eye adjust to a 10-log unit range of retinal luminance if the pupil can only account for 1 log
Retinal photoreceptors, rods and cones
Things about scotopic vision
- sensitive to dim lights
- poor VA
- absence of color discrimination
- mediated by rods
Photopic vision things
- poor sensitivity to dim lights
- excellent VA
- color discrimination
- cones mediate photopic vision
The existence of two classes of photoreceptors, each operating under different lighting conditions, referred to as a
Duplex retina
Under _____________conditions, both rods and cones contribute to vision
Mesopic conditions
Contained within the discs of the rods outer segment
Rhodopsin
One eye contains about ______ rods
120 mill
Each rod contains ______ disks
1000
Each disk within a rod contains ________rhodopsin molecules
10,000
How many rhodopsin molecules per eye
10^15
Each molecule of one rhodopsin is capable of absorbing ______ photon of light
One
The absorption of _____photon (s) is sufficient to activate a rod
One
The large number of rhodopsin molecules capture light and contributes to our exquisite _______ under nighttime lighting conditions
Sensitivity
The absoprtion of light quanta by the photosensitive pigment in the outer segment causes the photoreceptor to become ____________. This is the first step in a sequence of events that ultimately leads to vision.
Hyperpolarized
Light quanta that are incident on the rhodopsin, but not transmitted, have been ________
Absorbed
Relationship of the absoprtion curve and the transmission curve
Reciprocal
Light quanta of _______nm have the highest probability of absorption in rods
507nm
Wavelengths other than 507 in rods
Are absorbed, but with less probability
Once a quanta of light is absorbed, all information regarding its wavelength is lost, a principle referred to as ______________
Univariance
A molecule of rhodopsin becomes ______when it absorbs light
Bleached
The absoprtion of __________ is required to bleach a molecule of rhodopsin
One quantum of light
When a rhodopsin meolcule is in the bleached state, it is not capable of capturing another quantum, it will
Transmit a quantum of light incident on it
A bleached molecule will _________ to the unbleached state
Spontaneously revert back
50% of the rhodopsin will recover in 5 minutes. This is referred to as
The half life of rhodopsin
What is the half-life for rhodopsin
5 minutes
If you irradiate the retina with 1000 quanta of light at 507nm, you might successfully bleach _______ rhodopsin molecules
200 or 20%
If you irradiate the same part of the retina with 1000 quanta of light at 580nm, you might bleach _____ rhodopsin molecules, since the longer wavelength is absorbed less effectively
100
If you double the irradiance of 580nm light to 2000 quanta of light, you would bleach appx _______the number of rhodopsin molecules. This is equal to the result of bleaching the retina with 1000 quanta of 507nm light
Double the number (200)
Physiological response of the visual system to 1000 quanta of 507nm light and 2000 quanta of 680nm light
It is the same
Since the scotopic (rod) system produces one physiological response irrespective of wavelength, and it is possible to match the output signal for all wavelengths, by adjusting the brightness of the light. Therefore the scotopic system is _________; it has not wavelength discrimination
Colorblind
Our ability to detect stimuli under scotopic conditions is circumscribed by the _________
Rhodopsin absorption curve
Rhodopsin adsorption curve
- Dark adapt someone for 45 minutes, maximizing the regeneration of the rhodopsin
- the minimum amount of energy required for the person to detect stimuli of various wavelengths is determined.
The minimum amount of energy required for detection of a stimulus is referred to as the _______ for that stimulus
Threshold
The sensitivity curve is the ________ of the threshold function. A low threshold indicates a high sensitivity
Reciprocal
What is human scotopic spectral sensitivity function determined by
The absorption characteristics of rhodopsin
_______ is sufficient to activate one rod
One quanta absorption
How many rods activate a ganglion cell
10
How many ganglion cells needed for there to be detection
10
For these 10 quantal absoprtion to result in detection, they must
Occur within certain space and time constraints
_______ of the quanta incident on the retina are absorbed by rhodopsin
Fewer than 20%
Is a stimulus that emits 10 quanta visible?
No because many quanta are either reflected or absorbed by tissues inner to the photoreceptors (preretinal and retinal) or not absorbed by rhodopsin
What are the 3 cone pigments
- cyanolabe/blue/426/S cone
- chlorolabe/green/530/M cone
- erythrolabe/red/557/L cone
How many photopigments do each cone contain
One
Where is the photopic spectral sensitivity
555
Photopic spectral sensitivity shows a single broad peak in the region of
555nm
What does the photopic spectral sensitivity curve represent
The addition of M and L cone absorption spectra
S cones and the photopic spectral sensitivity
It is though that S cones make little, if any contribution to spectral sensitivity
Where does the blue peek
Shorter than the rod (black line)
The difference in sensitivity between scotopic and photopic systems, for a given wavelength is referred to as the
Photochromatic interval
When is the photochromatic interval largest
At shorter wavelengths
Where is the photochromatic interval medium
At medium wavelengths
Where is the photochromatic interval switched, with the photopic being higher than the scotopic?
Longer wavelengths
When does the photochromatic interval equal 0?
650nm
When isthe photochromatic interval approximately zero and rods and cones are almost equally sensitive
Longer wavelengths
Photochromatic interval beyond 650nm
The photopic system is slightly more sensitive than the scotopic system
Photochromatic intervals ________with retinal eccentricity
Increase
Photochromatic intervals int he fovea
Greatest for short, then medium, then long wavelengths
Photochromatic wavelengths in the periphery
The order for short and medium wavelengths is reversed. The interval size for short and medium wavelengths increases at a negative rate and for long wavelengths at a positive rate
Photochromatic intervals vary with
Stimulus size
As lighting conditions change from scoptopic to photopic, the wavelength to which we are most sensitive increases from ______ to _____
507 to 555nm
The relative increase in the brightness of longer wavelength stimuli as lighting conditions change from scoptopic to photopic
Purkinje shift
How many rods in one eye
120 mill
How many cones in one eye
6 mill
What do the cones look like as you get further from the fovea
They get larger and mroe spaced out
Ratio of L and M cones in people
Varies from person to person
S cones distribution
Show a different retinal distribution than other cones. Not only are there considerably less numerous than either M or L ones, constituting appx 5-10% of the cone population, they are not found int he central 0.3-0.4 degrees of the human fovea
What cones are not found in the fovea
S cones
What cones are found in much less numbers in the retina
S cones
Gradual improvement in vision, after exposure to bright-adapting light
Dark adaptation
Rod and cone sensitivity recover
Recover at different rates, after exposure to bright lights
What is recovery in sensitivity in rods and cones related to
The regeneration of photopigment molecules
After 35 min in the dark, the eye is ______ more sensitive to light
100,000 times
Cone plateau
10 minutes
Rod-cone break
12 minutes
From the point of cone plateau to the rod-cone break (10-12) minutes, what detects the stimulus
The cones
Rod plateau
35 minutes
Where does the rod cone break occur
At that point in time when the rods become more sensitive than the cones
When do rods become more sensitive than cones
Rod-cone break, 90% of the rhodopsin as regenerated
The different between the cone plateau, which represents the minimum photopic threshold for a stimulus, and the rod plateau, which represents the minimum scotopic threshold for this same stimulus
Photochromatic interval
The photochromatic interaval is about ____ log units
3
Bleaching to rod recovery is about ____ log units
5
After _____ log units, sensitivity for rods increases
5
What form does the dark adaptation curve take if the stimulus is 650nm?
It shows only oa cone portion, the rod aspect is missing, since the photochromatic interval for 650nm is 0. And because the scotopic system is not more sensitive than the photopic system, there is not an obvious rod-cone break
The photochromatic interval for the 420nm stimulus
Large, consequently, this stimulus produces a dark adaptation curve with a prominent rod-cone break
____ are not mroe sensitive than ____ for long wavelengths
Rods
Cones
The stimulus used to generate the dark adaption curve
Is large and central fixeted. Such a stimumuls falls on both the fovea and surrounding retina
What happens when you make the stimulus small when doing dark adaptation
Only a cone function is obtains, the absence of a rod function reflects the absence of rods in the fovea.
