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Gelatt 6th Edition > Optics and Physiology of Vision > Flashcards

Optics and Physiology of Vision Flashcards

1
Q

What are the two part of the visual pigment molecule? What are their roles?

A

Opsin - determines the wavelength of light that the photopigment will absorb, thus determining color viison

Visual chromophore/retinal - uses the energy of the photon particle to undergo isomerisation and so starting conversion of light stimulus into electrical signal

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2
Q

what is the different between luminous intensity and luminance? And what are the units for each?

A

Luminous intensity - intensity of light source (candela)

Luminance - brightness reflected from a surface (candela/m2)

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3
Q

What are the 3 changes than light travelling in a vacuum undergoes when it strikes denser media?

A
  1. velocity is reduced
  2. wavelength shortens
  3. it bends (unless it struck the surface of the medium at a 90 degree angle)
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4
Q

what is an object that bends (or refracts) light called?

A

a lens

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5
Q

what happens to light rays when they strike a convex lens?

A

convergence

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6
Q

what happens when ray of light strike a concave lens?

A

divergence

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7
Q

what is unit for vergence power (amount of bending) of a lens?

A

diopters

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8
Q

what is the focal length of a lens?

A

the distance between the centre of the lens and the point at which parallel rays of light are brought into focus by that lens

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9
Q

True or false: the focal lens of a lens is directly proportional to it curvature radius

A

true

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10
Q

true or false: the vergence powers of lenses in a optical system are not addivitive

A

false, they are additive

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11
Q

what is accommodation?

A

rapid change in refractive power of the eye, intended to bring images of objects at different distances into focus on the retina

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12
Q

give the 4 mechanisms by which vertebrate eyes can accommodate

A
  1. changing the curvature or position of the lens
  2. changing the corneal curvature
  3. changing the distance between the cornea and the retina
  4. having 2 or more separate optical pathways of different refractive powers
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13
Q

true or false: accommodation is achieved in humans, primates and cats by changing the curvature of the lens

A

false: the feline lens capsule only has 5% of the elasticity in humans so cats are incapable of changing the lens curvature for accommodation

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14
Q

how do feline eyes accommodate and how is this possible?

A

translation - anteroposterior movement of the entire lens

abundance of meridonal (longitudinal) fibres in the feline ciliary body muscle with low amount of circular fibres

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15
Q

true or false: viewing distant objects is stimulated by the sympathetic nervous system

A

true

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16
Q

what 3 ciliary muscles control accommodative mechanisms in the chicken?

A

1/ anterior (cramptons muscle)

  1. intermediary (mullers muscle)
  2. posterior (bruckes muscle)
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17
Q

what are the unique anatomic adaptations that significantly increase the lenticular accommodative capability in chickens?

A

very large ciliary processes
ring of columnar epithelial cells at equatorial periphery of the lens (annular pad)
lenses are soft and malleable
corneoscleral sulcus permits a greater range of movement

18
Q

true or false: accommodation in chickens occurs from direct squeezing of the lens

A

true

19
Q

true or false: chickens cannot accommodate by changing the corneal curvature

A

false

20
Q

how is corneal accommodation mediated in chickens?

A

anterior ciliary muscle (cramptons muscle)

21
Q

true or false: chickens can accommodate independently in both eyes

A

true

22
Q

Apart from changing corneal and lens curvature, what else contributes to accommodation in chickens?

A

changing choroidal thickness

23
Q

does mydriasis increase or decrease the depth of focus of the eye?

A

decrease

24
Q

what is an emmetropic eye?

A

one in which parallel light rays from a distant object are focused on the outer segments when the eye is disaccommodated

25
Q

what is a myopic eye?

A

one in which parallel light rays from a distant object are focused on anterior to the retina (nearsighted)

26
Q

what is hypermetropic/hyperopic eye?

A

one in which parallel light rays from a distant object are focused posterior to the retina (farsighted)

27
Q

true or false: cycloplegia has a significant effect on refraction in most veterinary patients

A

false: it has no significance

28
Q

true or false: aphakia leaves the eye severely myopic

A

false: severely hypermetrophic

29
Q

what diopter power should the canine IOL have?

A

40-41.5D

30
Q

why is a 41D IOL needed to correct 15D of hypermetropia?

A

IOL is placed in a capsular bag filled surrounded by aqueous humour. This environment results in a reduction of its overall refractive power due to the small difference in refractive indices between the AH and the IOL

31
Q

what diopter power should the feline IOL have?

A

52-53D

32
Q

what is scotopic vision?

A

dim-light vision

33
Q

what are the characteristics of cone systems? (4)

A

high resolution of fine details
rapid responses
colour perception
low sensitivity to small fluctuations in light intensity

34
Q

what are the characteristics of rod systems? (4)

A

poor visual resolution
no colour perception
extremely sensitive to minute changes in light levels
detection of movement

35
Q

what is the fovea centralis in haplorrhine primates and many avian species?

A

a specialised, avascular area of the retina with higher cone density providing higher spatial resolution

36
Q

what are the four morphological parts of rods and cones?

A
  1. outer segment
  2. inner segment
  3. nucleus
  4. synaptic terminal
37
Q

what is the name of the rod photopigment?

A

rhodopsin

38
Q

what is the function of opsin?

A

determines the wavelengths of light that the photopigment will absorb

39
Q

briefly describe the phototransduction cascade

A

energy from photons transferred to chromophore
decrease in cyclic GMP levels leading to closure of the ion channels
hyperpolarisation of the photoreceptor
glutamate release decreased or terminated which affects second order neurons

40
Q

true or false: photoreceptors are hyperpolarised in the dark causing them to release glutamate

A

false: they are depolarised

41
Q

what are horizontal and bipolar cells?

A

second order neurons of the retina that connect the first order (photoreceptors) and third order (RGCs) neurons

Gelatt 6th Edition (7 decks)

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