Flashcards in 9- Duplex Retina Deck (65):
T/F the human visual system operates over a remarkably broad range of light levels
What makes it possible for the human eye to see something very bright and small
What does the pupil changing its diameter allow us to do
Help control the amount of light that falls on the retina
What is the formula for retinal illuminance
Td: (nits)(pupil are in mm)
Pupillary diameter changes account for what portion of adaptation
1 log unit
What accounts for 9 log untis of adaptation
The existence and properties of the rods and cones
What are the conditions of scotopic vision
Very sensitive to dim lights
Poor VA (20/200)
No color discrimination
What are the conditions of photopic vision
Poor sensitivity to dim lights
Excellent VA (20/20)
What does the existence of rods and cones create
What photoreceptor works under mesopic conditions
Both roads and cones
What is the rod photopigment?
Where is it found?
How many rods in the human eye?
How many disks does a rod have
How many rhodopsin molecules are there per rod disk?
How many rhodopsins are there per eye
How many photons of light can one molecule of rhodopsin absorb
T/F the absorption on one molecule is sufficient to activate a rod
What is the first step of vision
Absorption of light that hyperpolarizes the photoreceptors
What is the principle of univariance
Once a quantum of light is absorbed all information regarding its wavelength is lost
What quanta wavelength has the greatest probability of being absorbed
T/F the absorption and transmission curves are reciprocal s of each other
When is a molecule of rhodopsin bleached?
When it absorbs ligt
How many quanta of light are needed to bleach a molecule of rhodopsin
When a rhodopsin molecule is in the bleached state can it capture another quatua?
NO, but it will transmit a quanta of light incident on it
T/F a bleached molecule will NOT spontaneously revert back to unbleached state
False, it will
What is the half life for rhodopsin regeneration
Can the scotopic system differentiate color and wavelengths?
What is the minimum amount of energy required for detection of a stimulus
A low threshold indicates a high or low sensitivity
T/F one quantal absorption is sufficient to activate one rod
How many quantal absorptions result in detection
10, but they must occur within a certain space and time
Fewer than 20% of the quanta incident on the retina are absorbed by rhodopsin
What is the peak of the of the photopic sensitivity curve?
What cones contribute to the photopic spectral sensitivity curve
L and M
What is the photochromatic interval
The difference in sensitivity between scotopic and photopic systems for a given wavelength
When is the scotopic system greater than the photopic system sensitivity
At all wavelengths EXCEPT long wavelength region
T/F photochromatic intervals increase with retinal eccentricity
What is the order of the cones sensitivity in the fovea
What is the order of the cones sensitivity in the peripheral retina
What is the purkinje shift
As lighting conditions change from scotopic to photopic the wavelength that we are most sensitive to increases from 507 to 555 nm
How many cones do we have
IS the M and L cone ratio the same in everybody?
No, it varies
How are the S cones different from teh M and L cones
There are a lot less of them (5-10%)
They are not found in the fovea
What is dark adaptation
Gradual improvement in vision after exposure to a bright adapting light
Recovery is based on the regeneration of photopigment molecules
What is the reduction in threshold over a 35 minute period
5 log units
Rods do not become more sensitive then cones until what percentage of rhodopsin is regenerated
What is the value for the photochromatic interval?
3 log units
Look at it
What is light adaptation
The visual systems abiity to adapt to changes in the illumination levels
Can be studied with an increment procedure
What are the stages of scotopic light adaptation
1. Dark light
2. Square root law
3. Weber law
4. Rod saturation
Is the photopic system more sensitive than the scotopic system?
Yes, but he absolute sensitivity is less
The Weber fraction for scotopic vision is
What is the Weber fraction for the photopic vision
Rods are connected in a manner that they do what to information?
What does this do?
Sum up info over space.
Greater sensitivity, poor resolution
Do rods or cones have greater resolution
What is the summing up of information over space
Slides 46, 47
_____ system has excellent spatial summation
______ system has excellent spatial resolution
The ____ system has greater temporal summation
The ____ system has superior temporal reolsution