Vision

Question 1

What’s the role of the retinal pigment epithelium?

Answer 1

• controls nutrient environment
• its pigmentation means that the light that reaches the retina is absorbed, not reflected.
• phagocytose outer segments// remove damaged material

Question 2

What types of cones we have?

Answer 2

red, green, blue

Question 3

What is rhodopsin?

Answer 3

• pigment found in rod photoreceptors,

- which operates at light levels that are too dim to activate cones.

Question 4

Why don’t you have colour vision at low light levels?

Answer 4

• bc only of the rod is sensitive enough and you need multiple photoreceptors to with different absorption to be able to compare between them.

Question 5

What are the wavelengths of blue and red?

Answer 5

blue=  small wavelength, high frequency
red= large wavelengths, low frequency

Question 6

How is our perception of colour determined

Answer 6

• the extent to which the different sensors/photoreceptors are excited

Question 7

How is our perception of colour determined

Answer 7

• the extent to which the different sensors/photoreceptors are excited/ tuned to different wavelengths

Question 8

Which absorption spectra overlap?

Answer 8

• red and green
• The blue spectrum overlaps little with these 2. The blue cones are also rather less sensitive than the red and green cones.

Question 9

What happens to colour-blind people?

Answer 9

• they lack one or more set of cones a

- or they have cones that respond to different peak frequencies

Question 10

the Snellen test chart

Answer 10

• routine test of visual acuity
• all of the letters at a give distance occupy 5 mins of arc but you need to discriminate them in 1 min of arc ( this is the limit of resolution/ acuity of the normal eye )

Question 11

Why is everything blurred under water?

Answer 11

focusing depends on the curvature of the cornea, lens and difference in refraction index between the eye and surrounding medium.
- bc of the small difference of refraction index between water and the eye, the amount of curvature needed by the lens increases, it must become very curved (humans can’t curve the lens that much), so vision is blurred

Question 12

As myopics and hypermetropics age, which group will develop sooner a problem with reading? why?

Answer 12

hypermetropics because they already have problems with focusing light from objects at short distance,and as they age (they lose accommodation, the lenses lose the ability to focus light) , the problems worsen

Question 13

color- blinding

Answer 13

the S and M/L wavelengths don’t overlap so your ability to distinguish colours decreases

Question 14

Why does atropine applied to the eye not only cause everything to appear excessively bright, but blurred as well? (atropine blocks the action of acetylcholine at parasympathetic effector organs?

Answer 14

atropine block the action of acetylcholine at the muscarinic receptors that control contraction of the muscles of the eye which in turn control the openning of the pupil and shape of the lens (therefore losing the ability to accommodate and thus the blurred vision) . Therefore, atropine opens the pupil allowing excess of light to come in.

Question 15

Why do blue flowers appear brighter than yellow flowers in moonlight?

Answer 15

because at night, the rod are more sensitive to blue light