the eye and the visual stimulus Flashcards
what is the iris
loose open muscular membrane in the centre forming the pupil
what is the pupil
centre opening of iris that allows light to enter
why does the pupil change size
it varies with light intensity and size
what is the cornea
domelike optical structure covering the pupil and iris and is the refracting element of the eye
what is the sclera
tough fibrous outer coat that provides structural strength
what is the conjuctiva
covers the sclera and extends over the eyelids
what is the tear film
it covers the cornea and conjuctiva
what is the limbus
where cornea and sclera meet
what is the punctum lacrimalis
opening to the tear drainage system
lacrimal caruncle
small white/pink raised area in the corner of the eye
what is the aqueous humour
clear fluid in the anterior chamber
what is a lens
crystalline transparent structure attached to the ciliary body and suspended by thin fibrils
how does the lens shape change
by action of the ciliary muscle
what is the choroid
vascular layer that sits between retina and sclera. It also provides nutrients to the eye
what is the vitreous
clear jelly like structure which sits behind the lens
what is the retina
light sensitive organ containing photoreceptors
what is the fovea
central retinal pit that contains only cones
what is the macula
surrounds the fovea and appears yellow due to pigment
what is the visual and optical axis
visual axis- line drawn from the fovea to the point an eye is gazing at
optical axis- line through the optical centre
what is light
a wave and stream of particles
what is a quantum
unit of energy
what is light as waves used for
to explain diffraction, interference and polarisation
what is light as rays used for
to understand the optical pathway through systems
what is light as quanta used for
to understand processes in the photoreceptors
what is frequency
number of cycles per sec
what is the energy equation
E= hv
h= planks constant(6.626 x 10^-34) joules per sec
v= frequency in Hz
OR
E+hc/λ
c=speed of light
λ= wavelength
what is the wavelength equation
λ=c/v
c=speed f light in a vacuum
v=frequency
what is the relationship with frequency and wavelength
the lower the frequency the longer the wavelength
what is the unit for wavelength
nanometers
what is radiometry
measurement of the quantity of energy of the electromagnetic radiation using physical energy units and radiometric devices.
what Is photometry
measure of visible radiation (usually between 380-750nm)
What is luminance flux/power (F) and what is it measured in
total amount of light emitted by a source in all directions- its photometric unit is in unit of lumen lm and its radiometric is radiant power or flux joules/sec
what is luminous intensity(l)
Measure of light from a solid angle from a point source in a particular direction- its photometric unit is in candela cd(one lumen=one candela) and its radiometric unit is radian intensity watts
what is luminance and its units
amount of light coming off an extended surface in a particular direction- its photometric unit is candelas/m2 and its radiometric is in radiance watts
what is illuminance and what are its units
amount of luminance power falling onto an area of a certain surface- its photometric unit is unit of lumens(lumens/ m2) and its radiometric unit is irradiance Ee
How does the visual response begin
When light passes into the rods and cones in the eye
what does the amount of light that falls on the retina depend on
it depends on the luminance of the stimulus, the optical transmission of the eye(how much light gets into the retina) and the area of the pupil
what is the unit for the amount of light reaching the retina
Troland
How do you work out the retinal illuminance
E ret= L(luminence) x a(pupil area)
what is brightness
perception of the amount of light (also depends on the surround)
what is the lightness
perception of the surface colour
