Rods, Purkinje, Monochromacy, Color Vision, and Nagel Anomaloscope (M1) Flashcards
What is the fraction of incident photons that affect the eye?
Luminous efficiency
What are dark adapted or twilight conditions called?
scotopic
What measures the scotopic luminous efficiency function? 1. What are the methods to do this? 2
- photometry
2. absolute threshold in the dark or flicker photometry
What is the procedure for the absolute threshold measurement of the luminous efficiency of the eye in the dark?
- single flashes of light presented repeatedly
- each light has different wavelength
- intensity of each monochromatic light adjusted to just barely visible
- result is set of lights that are equated in visual effectiveness
What is the measurement of sensitivity relative to the threshold?
1/threshold = sensitivity
What controls the spectral sensitivity of the eye in the dark?
- spectral sensitivity of the rods (absorption spectrum of rhodopsin)
- transmission spectrum of the eye
What accounts for the loss in sensitivity in the scotopic spectral sensitivity as opposed to the rhodopsin absorption spectrum?
light being absorbed by the lens (variable per person)
What causes the increase in optical density with age?
exposure to UV-B radiation from sunlight
What controls photopic conditions?
cones
How is the photopic luminous efficiency function usually measured?
flicker photometry
What is the procedure of flicker photometry to measure the spectral sensitivity of the eye?
- pairs of lights (one usually white and the other monochromatic) alternate quickly
- intensity of the monochromatic light adjusted to minimize the flicker
Which is more sensitive at the max luminous efficiency: scotopic or photopic conditions?
scotopic
Which is more sensitive at long wavelengths luminous efficiency: scotopic or photopic conditions?
photopic slightly
Which cone has a minor contribution to the photopic luminous efficiency function?
S-cone
What is due to the relative spectral sensitivities of the photopic and scotopic luminous efficiency functions, and involves violets looking bright under scotopic conditions and roses looking brighter under photopic conditions?
Purkinje shift
What is the ability to make distinctions between visual stimuli, based only on the (wavelength) spectra they contain?
color vision
What does the spectral absorption function of each visual pigment relate to?
probability of absorption to the wavelength of light
What is a visual pigments probability of absorption of a certain wavelength of light called?
spectral absorption function
How do visual responses of a rod system to a stimulus vary from stimulus to stimulus?
vary in strength due to how many photons were absorbed (not wavelength)
What is a person that has only one photoreceptor type and one visual pigment called?
achromat or monochromat
If a patient requires only one knob to establish a match at any wavelength, what are they considered?
an achromat or monochromat
What does having more than one cone type provide to the patient that a patient that has only one cone type does not have?
ability to discriminate between two different wavelengths
What is a patient that can adjust every group of three primary lights to match the test light called? 1. How many knobs do they need to make a match on an anomaloscope? 2
- trichromat
2. 3
What is a patient that can adjust every pair of two primary lights to match a test light called? 1. How many knobs do they need to make a match on an anomaloscope? 2
- dichromat
2, 2
What is the region called after about 550 nm wavelength? 1. What is special about this region and why is it like this? 2.
- Rayleigh region
2. dichromatic region because S cones are extremely insensitive there
What are the uses for the Nagel anomaloscope?
- diagnose red-green color vision deficiency
- diagnose rod monochromacy
- demonstrate color matching
What is a patient with S-cones and M-cones but no L-cones called?
protanope
What is a patient with S-cones and L-cones but no M-cones called?
deuteranope
What is a patient with M-cones and L-cones but no S-cones called?
tritanope
When testing in the Rayleigh region using a Nagel anomaloscope what does a protanope act like?
monochromat
When testing in the Rayleigh region using a Nagel anomaloscope what does a tritanope act like?
dichromat
When testing in the Rayleigh region using a Nagel anomaloscope what does a deuteranope act like?
monochromat
What differs in the process of color matching between deuteranopes matching and protanopes matching?
deuteranopes match all colors a with a constant yellow (only need to alter wavelength to match) while protanopes need more yellow to match the green and less yellow to match the red
What differs in the process of color matching between protanopes matching and rod monochromats matching?
rod monochromats require a huge amount of yellow to match the green (can’t get enough for pure green) or yellow and less yellow to match the red
What is a person that has one pigment that is different from the normal L and M pigments called with one normal pigment?
anomalous trichromats
Do deuteranopes, protanope, or rod monochromats refuse the normal match?
rod monochromats and anomalous trichromats
What is the altered pigment sensitivity line for a deuteranomalous trichromat patient?
M-cone line
What is the altered pigment sensitivity line for a protanomalous trichromat patient?
L-cone line
If your patient accepts the match that you have made, what can rule them out as having?
anomalous trichromacy
If the patient accepts that match that you have made, you set the machine to the extreme red and then extreme green, and they can cannot match on adjustments by them then what are they not?
protanope or deuteranope
If the patient accepts that match that you have made, you set the machine to the extreme red and then extreme green, and they can can match on adjustments on both ends with the same luminance setting, what are they?
deuteranope
If the patient accepts that match that you have made, you set the machine to the extreme red and then extreme green, and they can can match on adjustments on both ends with varying luminance settings, what are they?
protanope
If the patient refuses your original match and makes adjustments that result in the red/green half being light green, what are they?
deuteranomalous trichromat
If the patient refuses your original match and makes adjustments that result in the red/green half being orange, what are they?
protanomalous trichromat
