VOP - The Eye And The Visual Stimulus - Topic 1

Question 1

What is the iris?

Answer 1

– is the loose open muscular membrane that is perforated in the center forming the pupil.

Question 2

What is the pupil?

Answer 2

– the central opening of the iris that allows light to enter the eye. Pupil size varies with the amount of light

Question 3

What is the Cornea?

Answer 3

– domelike optical structure covering the pupil and iris. Together with the lens, comprises the refracting elements of the eye

Question 4

What is the Sclera?

Answer 4

– 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

Question 5

What is the Conjuctiva?

Answer 5

• 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.

Question 6

What is the Tear Film?

Answer 6

covers the cornea and conjunctiva

Question 7

What is the Limbus?

Answer 7

– this is the region where the cornea and conjunctiva/sclera meet

Question 8

What is the Cilia?

Answer 8

the eyelashes

Question 9

What the is Punctum Lacrimalis?

Answer 9

– the opening to the tear drainage system (the canaliculus)

Question 10

What is the Lacrimal caruncle?

Answer 10

– small pink/whitish raised area in the medial corner of the eye

Question 11

What is the Aqueous Humor?

Answer 11

– occupies the anterior chamber of the eye comprising a clear fluid (mostly water)

Question 12

What is the Lens?

Answer 12

– crystalline, transparent structure suspended by thin fibrils attached to the ciliary body. Its shape changes by the action of the ciliary muscle (accommodation)

Question 13

What is the Vitreous?

Answer 13

– sits behind the lens, comprises a clear jelly-like structure.

Question 14

What is the Choroid?

Answer 14

– vascular layer that sits between the retina and sclera and provides nutrients to the eye.

Question 15

What is the Retina?

Answer 15

– light sensitive organ containing neural elements including the photoreceptors (rods and cones)

Question 16

What is the Macula?

Answer 16

– macula surrounds the fovea and appears yellow in colour due to the presence of pigment.

Question 17

Define Radiometry?

Answer 17

Measurement of energy across the electromagnetic radiation/ spectrum.

Question 18

Define Photometry?

Answer 18

• Measurement of the amount of ‘visible’ radiation

- Photometric quantities take into account of sensitivity of eye

Question 19

Define Luminous Power/ Flux(F) ?

Answer 19

The total amount of light emitted by a source (in all directions).

Question 20

Define Luminous Intensity (l) ?

Answer 20

Measure of light (luminous flux, F) delivered in a solid angle from a point source PARTICULAR direction

Question 21

Define Luminance (L) ?

Answer 21

The amount of light coming OFF an extended surface in a particular direction.

Question 22

Define ILluminance (E) ?

Answer 22

The amount of luminous power falling ONTO a unit area of a certain surface.

Question 23

What does the amount of light that falls onto the retina depend on?

Answer 23

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

Question 24

When does visual response begin?

Answer 24

It begins when light passes into the rods and cones in eye.

Question 25

What is the unit for the amount of light reaching the retina?

Answer 25

Troland

Question 26

What is one Troland?

Answer 26

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

Question 27

Give 6 sources of visible radiation?

Answer 27

1. Sun and sky – bright daylight. (cones only)
2. Thermo-luminescent sources (e.g. tungsten globe).
3. Reading light.
4. Twilight.
5. Moon and stars.
6. Driving at night.
7. Absolute darkness (rods only)

Question 28

The amount of energy (in joules) in a quantum is given by the equation?

Answer 28

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)

Question 29

Frequency is also related to wavelength by the equation:

Answer 29

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)

Question 30

The amount of energy (in joules) in a quantum, without v, is given by the equation:

Answer 30

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

Question 31

nanometre to metre?

Answer 31

x 10^-9 (1nm= 10^-9 m)

Question 32

metre to nanometre?

Answer 32

x 10^9 (1m=10^9 nm)

Question 33

What is the typical wavelengths of light for humans?

Answer 33

between 380nm and 750nm

Question 34

What are the 4 Radiometric quantities and their units?

Answer 34

• Radiant power Fe – Watts (joules/sec)
• Radiant intensity Ie – watts/steradian
• Irradiance Ee – watts/m2
• Radiance Le – watts/steradian/m2

Question 35

What are the 5 Photometric Quantities?

Answer 35

• Luminous power F – lumen
• Luminous intensity I – candela
• Illuminance E – Lumens/m2 or lux
• Luminance L – cd/m2
• Troland Eret – Retinal illuminance(trolands)