MNSR 34 -Eye and Vision

Question 1

Iris function

Answer 1

a coloured ring behind the cornea which adjusts in size to regulate the amount of light entering the eye through the Pupil

Question 2

where does light enter the eye

Answer 2

enters through crystalline lens

Question 3

what controls the shape of the crystalline lens

Answer 3

ciliary muscles

Question 4

an example of accommodation in the eye

Answer 4

The ability of the ciliary muscles to change the shape of the
lens to focus objects at different distances onto the retina

Question 5

where is the eye most sensitive

Answer 5

most sensitive in small retinal depression called yellow spot or fovea - dencely packed with cones

Question 6

normal horizontal field of view

Answer 6

60 - 95 degrees L and 95 degrees R

Question 7

Normal vertical field of vision

Answer 7

135 degrees
60 degrees up
75 degrees down

Question 8

what does refractive index determine and how does it influence how light travels in the eye.

Answer 8

determines how fast light travels and if it goes from one material to different material with different refractive index

Question 9

where does most of light bending occur in the eye

Answer 9

most f light bending occurs as light enters the cornea
the greatest difference in refractive index is between light and cornea (refractive index difference = 0.337) greatest difference =greatest bending

Question 10

what is the function crystalline lens in regards to refractive index

Answer 10

adjusts in accordance to refractive power of the eye to focus on objects at a distance

Question 11

why does the crystalline lens not have to adjust its shape w/ objects further than 6 metres?

Answer 11

Light rays from an object as close as 6 m to the eye are essentially parallel, so the normal, relaxed eye can view sharp
images of objects from 6 m to infinity without having to focus.

Question 12

how does accommodation process change with age and explain why?

Answer 12

decreases gradually

due to the loss of elasticity of lens and hardening of ciliary muscles

Question 13

what does power of accommodation refer to specifically?

Answer 13

numerical difference between refractive power of the eye when relaxed (far point) and when fully accommodated (near point)

Question 14

2 structural differences between rod and cones

Answer 14

rod - contains membrane lined vesicles in centre
- contains pigment rhodopsin
cone - membrane surface folds in on itself
- contain pigment iodopsin

Question 15

what photoreceptor cell is more sensitive and in what wavelength range?

Answer 15

rods are more sensitive within 350 - 550 nm range

Question 16

3 cones in eye

Answer 16

blue (S) cone (short wavelength)
Green (M) cone (Medium wavelength)
Red (L) cone (Long wavelength)

Question 17

chromaticity diagram

Answer 17

decoding of the cone activity patterns within the cones
restores the full colour range
normally seen in an RGB colour mixing triangle.
cones that detect colour - in corner
how it is perceived - in the centre

Question 18

what are cones responsible for?

Answer 18

for daytime and colour vision.
for our ability to resolve fine detail.
direct vision - mainly in fovea

Question 19

how do cones in the eye give excellent resolution

Answer 19

Each cone in the fovea centralis is connected directly to the visual cortex

Question 20

how come the resolution of the rod much poorer than that of the cones even though there are more rods than cones?

Answer 20

most of the rods are connected to the same nerve fibre

Question 21

why is the pupil in the centre of the iris black?

Answer 21

because all of the light that enters is

absorbed inside the eye.

Question 22

how does iris respond to bright and dim light and how long does it take?

Answer 22

does not respond instantly
in bright light - reduces pupil size to 3-4mm in 5 seconds
in dim light - iris opens pupil to 8mm in around 5 mins

Question 23

purpose of reducing pupil size in bright conditions

Answer 23

to reduce lens defects (spherical aberrations) and

improve depth of focus

Question 24

why can’t we see blood vessels of retina?

Answer 24

see time stamp of 42 mins

Question 25

how does eye perceive different brightness

Answer 25

maximises contrast in shades
the intensity may actually be more homogenous than we perceive it to be
due to interaction between adjacent groups of light sensors in the eye

Question 26

persistance of vision

Answer 26

eye can’t process more than 25 images a second

Question 27

stereoscopic vision

Answer 27

images taken from both eyes are from different angles

brain combines them and allows image to have depth

Question 28

how can stereoscopic vision be used

Answer 28

one can take pictures of object at dif angles

show left image at left eye but right image at right eye. - create sense of depth in. examination of tumours