VOP - The Eye And The Visual Stimulus - Topic 1 Flashcards
What is the iris?
– is the loose open muscular membrane that is perforated in the center forming the pupil.
What is the pupil?
– the central opening of the iris that allows light to enter the eye. Pupil size varies with the amount of light
What is the Cornea?
– domelike optical structure covering the pupil and iris. Together with the lens, comprises the refracting elements of the eye
What is the Sclera?
– sclera is the tough fibrous outer coat that provides structural strength to the eye. It is covered by the conjunctiva.
- The white part of the eye
What is the Conjuctiva?
- provides protection and lubrication of the eye by the production of mucus and tears.
- It lines the inside of the eyelids(palpebral) and provides a covering to the sclera.
What is the Tear Film?
covers the cornea and conjunctiva
What is the Limbus?
– this is the region where the cornea and conjunctiva/sclera meet
What is the Cilia?
the eyelashes
What the is Punctum Lacrimalis?
– the opening to the tear drainage system (the canaliculus)
What is the Lacrimal caruncle?
– small pink/whitish raised area in the medial corner of the eye
What is the Aqueous Humor?
– occupies the anterior chamber of the eye comprising a clear fluid (mostly water)
What is the Lens?
– crystalline, transparent structure suspended by thin fibrils attached to the ciliary body. Its shape changes by the action of the ciliary muscle (accommodation)
What is the Vitreous?
– sits behind the lens, comprises a clear jelly-like structure.
What is the Choroid?
– vascular layer that sits between the retina and sclera and provides nutrients to the eye.
What is the Retina?
– light sensitive organ containing neural elements including the photoreceptors (rods and cones)
What is the Macula?
– macula surrounds the fovea and appears yellow in colour due to the presence of pigment.
Define Radiometry?
Measurement of energy across the electromagnetic radiation/ spectrum.
Define Photometry?
- Measurement of the amount of ‘visible’ radiation
- Photometric quantities take into account of sensitivity of eye
Define Luminous Power/ Flux(F) ?
The total amount of light emitted by a source (in all directions).
Define Luminous Intensity (l) ?
Measure of light (luminous flux, F) delivered in a solid angle from a point source PARTICULAR direction
Define Luminance (L) ?
The amount of light coming OFF an extended surface in a particular direction.
Define ILluminance (E) ?
The amount of luminous power falling ONTO a unit area of a certain surface.
What does the amount of light that falls onto the retina depend on?
1• Luminance of the stimulus.
2• The optical transmittance of the eye (i.e. how much of the light gets to the retina).
3• The area of the pupil
When does visual response begin?
It begins when light passes into the rods and cones in eye.
What is the unit for the amount of light reaching the retina?
Troland
What is one Troland?
One (1) Troland is the amount of retinal illuminance (Eret) arising from a light source emitting a luminance (L) of 1 cd/m2 through a pupil area (s) of 1mm2.
-Eret = L x s
Give 6 sources of visible radiation?
- Sun and sky – bright daylight. (cones only)
- Thermo-luminescent sources (e.g. tungsten globe).
- Reading light.
- Twilight.
- Moon and stars.
- Driving at night.
- Absolute darkness (rods only)
The amount of energy (in joules) in a quantum is given by the equation?
E = h*ν
‘E’ is energy in joules
‘h’ is Planck’s constant 6.626 x 10^-34 (joules-seconds)
‘ν’ (Greek letter ‘Nu’) is frequency in Hertz (cycles per second of the quantum)
Frequency is also related to wavelength by the equation:
λ = c/ν (wavelength is inversely proportional to frequency)
‘c’ is speed of light in a vacuum (3 x 10^8 m/sec)
‘λ’ (Greek letter lambda) is wavelength in m
‘ν’ (Greek letter ‘Nu’) is frequency in Hertz (cycles per second of the quantum)
The amount of energy (in joules) in a quantum, without v, is given by the equation:
E = h*c/λ
‘E’ is energy in joules
‘h’ is Planck’s constant 6.626 x 10^-34 (joules-seconds)
‘c’ is speed of light in a vacuum (3 x 10^8 m/sec)
‘λ’ (Greek letter lambda) is wavelength in m
nanometre to metre?
x 10^-9 (1nm= 10^-9 m)
metre to nanometre?
x 10^9 (1m=10^9 nm)
What is the typical wavelengths of light for humans?
between 380nm and 750nm
What are the 4 Radiometric quantities and their units?
- Radiant power Fe – Watts (joules/sec)
- Radiant intensity Ie – watts/steradian
- Irradiance Ee – watts/m2
- Radiance Le – watts/steradian/m2
What are the 5 Photometric Quantities?
- Luminous power F – lumen
- Luminous intensity I – candela
- Illuminance E – Lumens/m2 or lux
- Luminance L – cd/m2
- Troland Eret – Retinal illuminance(trolands)
