mnsr 33

Question 1

— is a dark membrane which absorbs stray light.

Answer 1

choroid

Question 1

the – is the outer protective coating of the eyeball and is made from tough dense connective tissue

Answer 1

scalera

Question 2

Light enters the eyeball through the—- and passes through a fluid filled chamber containing —-

Answer 2

Conner, aqueous humour

Question 3

is the coloured ring behind the corner which regulates the amount of the light that enter through the —

Answer 3

iris, pupil

Question 4

the pupil varies in diameter from

Answer 4

7-8 to 2-3 mm

Question 5

then the light enter the —- of the eye, the shape is controlled by —-

Answer 5

crystalline lens, cillary muscles

Question 6

accomodation is the

Answer 6

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

Question 7

Behind the lens is a jelly-like substance is

Answer 7

vitrous humour

Question 8

the most sensitive at small retinal depression in the eye is the

Answer 8

yellow spot and the central position is the fovea centralis - 0.35 mm diameter and densly packed w cones. Responsible for direct vision . the eyeball normally rotates so that objects under examination are imaged directly onto the fovea.

Question 9

the most bending occurs when incoming light enters the

Answer 9

cornea

Question 10

the function of the crystalline lens is

Answer 10

provide fine adjustments to the refractive power of the eye to focus on objects at different distances. [The normal relaxed eye will focus parallel light onto the retina].

Question 11

light rays from an object as close as — to the eye is —-

Answer 11

6 metre is parallel, normal, and relaxed and can view sharp objects from 6m to infitinty without having to focus

Question 12

in the process of accommodation we need to

Answer 12

change the focal length to view objects closer than 6m for example bc the eyes have to focus

Question 13

the further away the near point is

Answer 13

the more difficult to see

Question 14

the near point varies depending on

Answer 14

the age
- child: few cm
- ppl in their 40s ~ 20cm
- age depend bc of the gradual decrease of elasticity of the lens and the hardening of the cillary muscle

Question 15

refers specifically to the numerical difference between the refractive power of the eye when relaxed (far point) and when fully accommodated (near point), i.e. maximum focussing power.

Answer 15

power of accommodation

Question 16

light is absorbed by the

Answer 16

photoreceptors cells which causes photochemical reaction and initiates an action potential. Rods are more sensitive than cones ( 350-550 nm)

Question 17

we can discriminate between different colours bc

Answer 17

we have thee different types of cones w/ different wavelengths.
L: long , red
M: med , green
S: short, blue

Question 18

different colours are included by

Answer 18

-different proportions of active.
-Our brain corrects for this interdependence of cones. Its decoding of the cone activity patterns is called the chromaticity diagram and restores the full colour range normally seen in an RGB colour mixing triangle

Question 19

we have extensive field of vision bc

Answer 19

-retina covers most of the back half of the eye
-The foveal field corresponds to the size of only-
a thumbnail at an arm’s length- a
35 cm diameter disk in 10 meter distance

Question 20

cones have excellent resolution bc

Answer 20

each cone in the fovea is connected directly to visual cortex

Question 21

the reason why rods have poor resolution

Answer 21

many rods are connected to the same nerve fiber

Question 22

the max density of rods are in an angle of

Answer 22

20 degree from the axis of vision and rods are not disturbed evenly in the retina

Question 23

cones are only active in — while rods are

Answer 23

• light adapted eye
• active all the time

Question 24

why do we see all cats gray at night?

Answer 24

the fovea is the most sensitive part of the retina in daylight conditions but can result in night time blindspot in our direct vision bc no rods are in the fovea even though our peripheral vision in the dark is good

Question 25

in bright light the iris reduces the pupil size to

Answer 25

3-4mm in 5 seconds , parasyptahtic, circular pillary sphincter constricts

Question 26

in dim light the iris needs

Answer 26

300 sec aka 5 minutes to open the pupil to 8 mm

Question 27

the reduction of the pupil in the bright condition will reduce

Answer 27

lens defects ( spherical aberration ) and improve the depth of focus

Question 28

optical illusions

Answer 28

1-. Like most sensory nerves, the nerve cells in the eye stop sending signals in the presence of a steady stimulus, that’s why our eyes jiggle to overcome this.
( the reason why we can see the blood vessels in our retina is bc of the steady supply of blood )
2-The eyes can play funny tricks in interpreting contrast between adjacent blocks of colour or toneThis perception is due to the interaction between adjacent groups of light sensors in the eye.This effect works to our advantage in discerning borders in X-ray images for example (note, the effect is diminished when the contrast is poor).In addition, our perception of darkness or brightness of an object also depends on the background colour behind the object, e.g.
3- Persistence of Vision.
4-Stereoscopic Vision:allows us to have ‘depth of field’, i.e. the ability to identify structures as being 3-d and to differences in distance from the eye.The brain processes the two images and fuses them together so that the combined image has components of both separate images and has a 3-d appearance( w/ slightly different angles )
5- perspection