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AHS2 > PB - special senses: vision > Flashcards

PB - special senses: vision Flashcards

1
Q

How is the aqueous humour removed from the eye?

A

By the venous plexus in the anterior chamber

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2
Q

What pressure is required in the eyeball to maintain eyeball shape?

A

Slightly +ve

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3
Q

What is the consequence of a high intraocular pressure?

A

Impairs vascular perfusion.
Ischaemic damage
Physical damage
Risk of detached retina.

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4
Q

What does the term mydriasis mean? Which nerve is stimulated and what muscle is activated?

A

Dilation of the pupil in dim light. Parasympathetic efferents causes radial muscles (iris dilator) of the pupil to contract.

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5
Q

What does the term miosis mean? Which nerve is stimulated and what muscle is activated?

A

Constriction of the pupil in bright light. Sympathetic efferents causes circular muscles (iris sphincter) to contract and constrict the pupil

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6
Q

How is a dilated pupil maintained?

A

Maintained by a lack of PS activity and a basal level of S activity. This maximises the sensitivity to light.

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7
Q

What does melanopsin contain, which is stimulated by light?

A

Retinal ganglion cells.

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8
Q

What is the pathway, which causes pupillary constriction in response to light?

A 
Retinal ganglion cells
Pretectal nucleus of the midbrain
PS motor nucleus of oculomotor nerve
Ciliary ganglion
Circular muscle
Constriction
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9
Q

What does the pupillary light reflex test show?

A

This is a bilateral response. So this test shows whether the efferent pathway of each eye is intact.

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10
Q

Why does a close image require a thicker lens to focus?

A

The light focusses at a more distant point behind the lens.

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11
Q

How is a thinner lens achieved?

A

Relaxation of the ciliary bodies increases their diameter.

This exerts tension on the zonular fibres, which causes the lens to become thinner.

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12
Q

How is a thicker lens achieved?

A

Contraction of the ciliary bodies is stimulated by PS control.
This decreases the tension of the zonular fibres.
Thicker lens results due to the elasticity of the lens.

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13
Q

Do the ciliary bodies need to be relaxed or contracted for more distant vision?

A

Relaxed

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14
Q

What is the effect of pupil constriction of the depth of field? How does this happen?

A

Increases the depth of field because the rays of light are brought closer to the visual axis.

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15
Q

What is aberration caused by?

A

Rays of light passing through the periphery of the lens.

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16
Q

What is chromatic aberration?

A

Different wavelengths are refracted to different extents. So they are focussed at different points.

17
Q

What is spherical aberration?

A

This is caused by the shape of the lens.

Light passes through the periphery of the lens, which reduces image quality.

18
Q

What is the primary function of binocular vision? Which type of animals benefit from this?

A

Comparison of images allows for the perception of depth.

Primates and predators.

19
Q

What is the primary function of monocular vision? Which type of animals benefit from this?

A

Does not provide depth for distant images because each image is arriving at the same time.
Uses size, haze and overlap to judge distance.
Prey animals.

20
Q

How does the receptor density vary across the retina?

A

Low receptor density in the periphery.
High receptor density in the area centralis.

Directly correlates with the number of retinal ganglion cells, which is related to visual acuity.

21
Q

Why is the optic disc a blindspot?

A

This is where the optic nerve leaves the eye, so there are no photoreceptors in this region.

22
Q

Do carnivores or herbivores have a circular area centralis? What is the function of this?

A

Carnivores.

Allows for a central area of sharp detailed vision, which is useful for recognising prey.

23
Q

Do carnivores or herbivores have a ‘visual streak’ area centralis? What is the function of this?

A

Herbivores.

Elongated strip has a high photoreceptor density, which allows for high visual acuity for horizon scanning.

24
Q

What determines the position of a species blindspot?

A

Eye position

25
Q

What is the effect of vergence movements on the area centralis?

A

Moves the area centralis of each eye to investigate objects at different distances

26
Q

What are the types of vergence movements?

A

Convergence and divergence

27
Q

What are convergent movements of the eye?

A

Movement of the eye medially.
Slow - 25 degrees per second. This allows for eye movements in response to sensory feedback.
Velocity is primarily rapid and slows down as the eyes get to a fixation point.
Associated with accomodation to change focus of the eye and pupillary constriction to change the depth of field

28
Q

What are divergent movements of the eye?

A

Movements of the eyes laterally.

Shifts the point of focus to a more distant image.

29
Q

What is the effect of saccadic eye movements on the area centralis?

A

Moves the area centralis from 1 visual field to another.

30
Q

What are saccadic movements of the eye?

A 
Microsaccades = subconscious. Movement around the visual image.
Saccades = conscious. Associated with head movements.

500 degrees per second. Fast.

  • So is too fast for sensory feedback
  • If inaccurate, sensory feedback drives a microsaccade.
  • Parametric feedback for the future.
31
Q

What are tracking eye movements?

A

Slow steady movements until limit is reached.

Rapid saccade in the opposite direction to reset the eyes.

32
Q

What is a nystagmus defined as?

A

The direction of the rapid saccade.

33
Q

What are 2 examples of physiological nystagmus?

A

Optokinetic reflex - tracking objects in the visual field.

Vestibulo-ocular reflex - stabilising gaze during head movements.

34
Q

What is a pathological nystagmus?

A

If there is a dysfunction in the neural pathway underlying the tracking responses.

35
Q

What are the 3 main adaptations of the avian eye?

A

Clear nictitating membrane -> prevents the eye drying out

Striated ciliary muscle -> The lens can change shape much more quickly than in mammals.

Pecten -> projects into the vitreous humour from close to the optic disc. Main function is to supply O2 and nourishment.

AHS2 (12 decks)

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