3- Psychophysics, Luminal Efficiency, and Rod Monochromacy

What is the method of constant stimuli?

predetermined range of stimuli are presented in random order + data is collected

What is the method of adjustment?

patient turns knob until stimulus is seen

What is the method of limits?

examiner adjusts knobs until criterion is obtained

What is the ascending method of limits?

start at a stimulus too low and then raise it until seen

What testing is ascending method of limits used for?

dark adaptation

What is the descending method of limits?

start at a stimulus too high and the lower it until just seen

What is the method of descending limits used for?

infant testing

What is the staircase method of testing?

examiner turns stimuli up if patient cannot see and down if patient can see, threshold is an average of stimulus at reversal points

What psychophysical method does automated visual fields use?

fancy staircase

What are examples of psychophysical methods used to find detection threshold?

method of constant stimuli

method of adjustment

method of limits

staircase

What is 2 alternative forced choice?

patient has to make a choice between two options (ex: is the stimulus on the right or the left)

What are the advantages of 2 alternate forced choice?

patient cant inflate their score

minimum instruction needed

What are the disadvantages of 2 alternate forced choice?

slow/takes a long time

rarely used correctly

Under fully scotopic conditions, any two lights (that has the same rate of absorption for rhodopsin) will?

look the same to the patient and give equal rod responses

What is luminous efficiency?

fraction of incident photons that affect the eye

What is the absolute threshold curve in the dark look like?

U-shaped

How is scotopic luminous efficiency measured?

by finding the absolute threshold of the eye in the dark

What light is toxic to the retina?

violet light (>390nm)

What light causes brunescence of the lens?

UVB light (280-315nm)

What UV light causes photokeratitis?

far UV light

How is photopic luminous efficiency measured?

flicker photometry

What is the purkinje shift?

in photopic conditions, red looks bright and violet looks dark, but in scotopic conditions, red looks dark and violet looks bright, as rods are more sensitive to shorter wavelengths

What is flicker photometry?

pair of lights (one monochromatic, one white) alternate quickly while intensity of monochromatic light is adjusted to match white until they are equated to each other

What is complete achromatopsia?

rod monochromacy: rods are normal, cone vision is completely absent

What is the VAs of someone with complete achromatopsia/rod monochromacy?

20/200 (poor vision)

What does red look like to someone with complete achromatopsia/rod monochromacy?

red looks black

What do we give to a complete achromatopsia/rod monochromacy?

long (red) wavelength pass filter to cut out the light an achromat is sensitive to (short wavelengths are bright to them), to cut out glare + photophobia

What is color vision?

the ability to make distinctions between visual stimuli based only on the wavelength of light

How many knobs does the rod monochromat require to make a match?

one knob (brightness)

Which cones is more sensitive to red light?

L cones