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BAB > The eye and vision > Flashcards

The eye and vision Flashcards

1
Q

Where is the anterior compartment located?

A

Anterior to the lens. Composed of an anterior and posterior chamber to the iris. Contains aqueous humour.

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2
Q

What is the function of aqueous humour?

A

Function:
Nurishes the avascular cornea, providing nutirents.
Maintains intraocular pressure.
Contributes to refraction of light.

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3
Q

How is aqueous humour secreted and reabsorbed?

A

Secreted into the posterior chamber between the iris and lens, by ciliary processes. Moves into anterior chamber between cornea and iris. Reabsorbed through scleral venous sinus.

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4
Q

Where is the posterior compartment of the eye?

A

It is located posterior to the lens and filled with jelly-like vitreous humour.

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5
Q

What is the function of vitreous humour?

A

Maintains intraocular pressure, gives eye its shape, holds retina and lens in place.
It is transparent to let light through whilst being involved in refraction.

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6
Q

What is glaucoma?

A

Ischaemia of the retina as a result of raised intraocular pressure due to decreased removal of aqueous humour. The pressure transmits to the back of the eye and cuts off blood supply. High risk of blindness.

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7
Q

What are the two causes of glaucoma?

A

1) Angle closure - Iris adheres to cornea blocking drainage angle of the eye. Causes acute, rapid rise in pressure.
2) Open angle - Sclerosis of veins preventing drainage. Most common form and affects elderly more.

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8
Q

What is the treatment for glaucoma?

A

Surgery
B blocker eye drops - block sympathetic innervation to reduce production of aqueous humour.
PG analogue eye drops - Vasodilation for increased drainage

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9
Q

Draw a diagram of the eye and its structures

A

See lecture

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10
Q

Draw the structure of the retina and label the cells involved. indicating the direction of light and direction of signal.

A

See lecture

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11
Q

What are photoreceptors?

A

Receptors composed of rods and cones that detect the lambda wavelength of light. They convert light energy to signals that can travel along the optic nerve.

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12
Q

What is the function of a Rod and what pigment does it contain?

A

Contains rhodopsin within intracellular membrane disc for a high density. Each disc is separate from one another, creating a large SA = high sensitivity suitable for NIGHT vision / low light intensities.

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13
Q

What is the function of a cone and what 3 pigments does it contain?

A

Contains red, green and blue pigments within infoldings on the surface membrane of the cone. Has a lower density of pigment and smaller SA than rods = COLOURED vision at higher light intensities.

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14
Q

What do the ganglion cells form?

A

Their axons form the optic N.

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15
Q

What is the function of horizontal and amacrine cells?

A

They modulate transmission of information.
Horizontal cells receive output from rods and cones.
Amacrine cells receive output from bipolar cells.

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16
Q

What structures form the retina?

A

Photoreceptors + bipolar cells + ganglion cells + horizontal and amacrine cells.

17
Q

What is the blind spot?

A

It is located in the retina where the optic N leaves the eye, forming the optic disc. There are no photoreceptors present, only axons of ganglion cells.

18
Q

Which photoreceptor is dominant at the centre of the retina?

A

Cones. They increase in number, closer to the centre. Further from the centre is mostly rods.

19
Q

What is the sensitivity and acuity of the peripheral retina?

A

High sensitivity as mostly rods present. Many rods connect to 1 ganglion = low visual acuity. This combining of information at a ganglion reduces the level of detail processed.

20
Q

What is the sensitivity and acuity of the central retina?

A

Low sensitivity as contains only cones. Requires a sufficient light intensity to induce a signal. 1 cone connects to 1 ganglion = high visual acuity. Allows for sharp central vision of high detail.
Each cone will detect a different light intensity of an image providing a better representation of light and dark areas.

21
Q

Where is the macula located?

A

An oval, yellow area at the centre of the retina responsible for the centre of field of vision.

22
Q

Where is the fovea located and how is it involved in producing detail of an image?

A

Forms a dip in the centre of the macula. Focusing light into the fovea produces detail as it contains only cones.

23
Q

What is the pigment rhodopsin composed of?

A

Retinal (atoms that absorb light to excite) and opsin (GPCR within the cell).

24
Q

What happens to a rod in the dark?

A

1) Rhodopsin is inactive in the dark
2) Therefore cyclic GMP gated cation channels are open
3) Allows Na influx that dominates K efflux
4) Produces a dark current causing depolarisation.
5) Rods have a low resting membrane potential and are easily depolarised.
6) Depolarisation causes glutamate release at bipolar cell synapse.

25
Q

What happens to a rod in the light?

A

1) Photons of light hit retinal and change its conformation by breaking C=C bonds.
2) H atom flips to II-cis position
3) Activates opsin
4) GTP binds to G protein alpha subunit which splits off from beta and gamma.
5) GTP activates PDE
6) PDE breaks down cGMP to GMP
7) Cation channels close = hyperpolarisation
8) No glutamate release

26
Q

What is the direct pathway of light transmission in the retina?

A

Photoreceptor —> Bipolar cell —> Ganglion cell

27
Q

What happens to all photoreceptors in the light?

A

HYPERPOLARISE

28
Q

Why does the response to light vary if all photoreceptors hyperpolarise?

A

The response to light is dependent on the type of bipolar and ganglion cells involved in the pathway.

29
Q

What are the two types of bipolar or ganglion cells and what happens to them in the light and dark?

A

ON: In the DARK = HYPERPOLARISED (glutamate released)
In the LIGHT = DEPOLARISED (decreased glutamate)

OFF: In the DARK = DEPOLARISED
In the LIGHT = HYPERPOLARISED

They have different responses to glutamate due to presence of different receptors.

30
Q

What is the indirect pathway in light transmission in the retina?

A

Each bipolar cell has a receptive field within the retina. The receptive field has a central component that is directly connected to bipolar cell and a peripheral component with indirect connections via horizontal cells.
Light detection in the peripheral field induces the OPPOSITE response in the bipolar and ganglion cell to the direct pathway. This is due to horizontal and amacrine influence.

31
Q

Why is the indirect pathway important?

A

Allows increased contrast at the image borders to discriminate between light intensities in the image.

32
Q

Which area of the receptive field has a greater influence on the ganglion cell?

A

The centre field dominates over the peripheral field when stimulating the ganglion cell.

e. g. if centre hyper and peripheral depolarise —> low firing
e. g. if centre depolarised and peripheral hyper —> increase in firing

33
Q

What information is carried in the Left optic tract?

A

Carries all information to visualise the Right visual hemifield. Composed information from the left temporal retina and right nasal retina.

34
Q

Damage of the left optic tract causes…

A

Right homonymous hemianopia = loss of right visual hemifield (left temporal retina + right nasal retina)

35
Q

Damage of the optic chiasm…

A

Bitemporal hemianopia = Loss of left and right nasal retina

36
Q

Damage of the left optic nerve…

A

Monocular blindness = loss of left temporal and nasal retina (loss of left eye function)

37
Q

When does the optic nerve become the optic tract? Where does the tract relay information to?

A

The optic nerve is formed by the axons of ganglion cells and becomes the optic tract after the optic chiasm.
Relays information to the ipsilateral lateral geniculate nucleus, superior colliculus and pretectal nuclei.

BAB (11 decks)

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