wk 2 SP Flashcards
when light changes in intensity, we perceive this as a change in…
brightness
when light changes in wavelength, we perceive this as a change in…
colour
what range of wavelength in nm can humans see
400-700nm
Pupil between ~2 mm and ~___ mm diameter
9
Cornea –__% focusing power
Lens –__% but can change shape due to action of _____muscles
80
20
ciliary
Lens becomes fatter to focus _____objects
close
Lens becomes thinner to focus ______objects
far
Myopia
light focused ____ of retina
corrected with ____ lens
nearsightedness
in front
concave
Hyperopia
light focused ____ of retina
corrected with ____ lens
farsightedness
behind
convex
photoreceptors
how does transduction occour
light sensitive cells
carry out transduction
by visual photopigments reacting to light and trigger electrical signals
2 types of photoreceptor
+ approx number
Rods (120 million)
Cones (6 mil)
Rods vs cones in sensitivity
Rods
Very sensitive, respond well in very dim light
Most useful at night, useless in daylight
Cones
Less sensitive
Work best in daylight, useless at night
scotopic
only rods active
photopic
only cones active
mesopic
both cones and rods active
Bright light bleaches ________ so ______ stop responding
Going from bright to dark the _______ have to ‘recover’ or regain sensitivity.
photopigments
photoreceptors
photoreceptors
Dark adaptation
increase in eye’s sensitivity in the dark
After 20-30 minutes in the dark, sensitivity is about __________ times greater than the sensitivity in light
100,000
rods or cones are Responsible for colour vision
cones
3 types of cone, sensitive to different wavelengths of light:
Red (_____ wavelengths)
Green (_____ wavelengths)
Blue (______ wavelengths)
long
medium
short
Rods
Produce ________ vision
(colour)
monochromatic
how many types of rod cells are there, what are they most sensitive to
1 type - most sensitive to medium wavelengths (green light)
Purkinje shift
- at night red looks darker than green
On average…
___ rods send signals to 1 ganglion cell
__ cones send signals to 1 ganglion cell
120
6
Rods have greater convergence – this leads to
lower acuity
can’t see fine details
Cones have less convergence - this leads to
higher acuity
can see fine details
