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Y2 LCRS Neuro Fwong > Structure and Function of the Eye (B) > Flashcards

Structure and Function of the Eye (B) Flashcards

1
Q

Where is the lacrimal gland located?

A

Superio-laterally to the orbit

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2
Q

Describe the innervation of the cornea.

A

The cornea is very sensitive and it is innervated by the ophthalmic branch of the trigeminal nerve (CN V)

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3
Q

What two things regulate how much light reaches the retina?

A

Pupil
Pigmented Uvea

uvea is pigmented so that the iris (part of uvea) can block out excessive light to retina

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4
Q

What is the term given to perfect focusing ability?

A

Emmetropia

Adequate correlation between axial length and refractive power, parallel light rays fall on the retina

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5
Q

What is the technical term for long-sightedness? Why does it happen?

A

Hypermetropia/hyperopia same thing
Focal point behind the retina
Caused by:
short globe (axial hyperopia, more common)
Insufficient refractive power (refractive hyperopia)

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6
Q

How can long-sightedness be corrected and what is it caused by?

A

Convex lenses
It is usually caused by having short eyeballs
It is occasionally caused by a flat corneal surface

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7
Q

What is the technical term for short-sightedness? Why does it happen?

A

Myopia
Focal point is anterior to retina. Can be caused by:
-long globe ie high axial length (axial myopia, more common)
- XS refractive power (refractive myopia)

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8
Q

How can short-sightedness be corrected? (what sort of lens)

A

Concave lenses

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9
Q

What is astigmatism?

A

The cornea is oval rather than round
This means that the refractive power varies in different planes (in some planes you will be hypermetropic, and in others you would be myopic)

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10
Q

Which nerve is responsible for accommodation?

A

Oculomotor Nerve (CN III)

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11
Q

What is the near response triad?

A
  1. Pupillary Miosis (constriction of sphincter pupillae) – increases the depth of field
  2. Convergence – the medial recti of both eyes contract
  3. Accommodation – ciliary muscles contract which makes the zonules relax, this makes the lens rounder and increases its refractive power
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12
Q

What is the term given to naturally occurring loss of accommodation with age? What is the treatment

A

Presbyopia
Reading glasses with convex lenses. This INCREASES refractive power which moves the focal point anteriorly (normally done by accommodation but function is lost). More deets on types of glasses see slides

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13
Q

What is the name of visible part of the optic nerve

A

optic disc. NB When looking at the blood vessels next to the optic disc, the thick ones are the venules and the thin ones are arterioles

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14
Q

Describe the difference in perfusion between the outer and inner parts of the retina.

A

Inner 2/3 of the retina = retinal arteries

Outer 1/3 of the retina = choroidal vasculature

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15
Q

What part of the retina is responsible for central vision?

A

Fovea (it has the highest concentration of cones)

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16
Q

What is peripheral vision responsible for?

A

Shape, movement, night vision

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17
Q

Describe the structure of the retina.

A

The structure is counter-intuitive because the cones and rods are actually ‘behind’ the ganglion cells when the light shines in (see slide).

From superficial to deep of eyeball:

  1. retinal ganglion cells (3rd order neurons). Their axons then go off and become part of optic nerve
  2. bipolar cells (2nd order neurons)
  3. photoreceptors ie rods/cones (1st order neurons)

Next to photoreceptors is retinal pigment epithelium

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18
Q

What is the function of the retinal pigment epithelium?

A

Transports nutrients from the choroid to the photo-receptor cells and removes metabolic waste from the retina back out

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19
Q

Describe how the fovea appears on a cross-section of the macula.

A

It appears as a foveal pit due to the absence of overlying retinal ganglion cells

20
Q

Describe the recycling of photopigments.

A

Photopigments are synthesised in the inner photo-receptor segment and then are transported to the outer segment discs
The distal discs with deactivated photo-pigments are shredded from the tips and phagocytosed by retinal pigment epithelial cells
The deactivated photo-pigments are regenerated inside the retinal pigment epithelial cells and are then transported back to the photo-receptors

21
Q

What is the rod photopigment?

A

Rhodopsin

It is a G-protein coupled receptor system

22
Q

What is another term for night vision?

A

Scotopic vision

23
Q

What is another term for day-time vision?

A

Photopic vision

24
Q

Describe the distribution of rods and cones across the retina.

A

Rods have the highest density just outside the macula
They decrease in density the further you move away from the macula
There are NO rods in the macula
Cones are MAINLY found in the macula
The highest density of cones is in the fovea
no photoreceptors near the blindspot (optic disc)

25
Q

Where is the physiological blind spot located? Why is there a blindspot?

A

20 degrees temporal to central vision

This is because there are no photoreceptors (rods/cones) at the optic disc

26
Q

What are the three types of cone photopigment and which colours do they respond maximally to?

A

S-cone – short wavelength – BLUE
M-cone – medium wavelength – GREEN
L-cone – long wavelength – RED

27
Q

What is the most common colour vision deficiency and what is it caused by?

A

Deuteranomaly
It is caused by the shifting of the M-cone (green light) towards the L-cone (red) caused by mutation

so loss of green peak, cannot distinguish difference between green and red.

28
Q

What is the term given to shifted peaks?

A

Anomalous trichomatism

29
Q

What test is used to diagnose colour blindness?

A

Ishihara Test

30
Q

Describe how your eyes adapt to darkness

A

Dark adaptation: Light sensitivity increases. (biphasic process, cones 7mins, rods 30 mins)

Pupil adaptation eg dilation (minor)

31
Q

What happens during adaptation to brighter environment

A

Light adaptation:
-photopigment bleaching
the pigments become almost transparent. Transparent objects do not ABSORB light, they transmit it. Therefore, less light absorbed by photopigments
- neuro-adaptation (increased tolerance to light)
-inhibiting rod and cone function (increasing threshold intensity, ie greater intensity needed to generate a response, ie less sensitive.)

Pupil adaptation (minor) eg constriction

32
Q

What part of the eye is responsible for central vision and where is it located? What is the centre of this region called?

A

Macula- located near the centre of the retina, temporal to the optic nerve/optic disc
Macula is also called macula lutea because of the yellow patch when you look at it down the scope.
Fovea is the centre of the macula. Fovea of the macula is the most sensitive part of the retina (highest cone concentration but low rod conc). It gives us ability for detailed vision for tasks like reading

33
Q

Compare central and peripheral vision and explain the reasons behind this.

  • detail
  • recognising colour
  • recognising motion
  • day/night vision
A 
Detail: Central > peripheral
Colour: Central > peripheral
Motion: Peripheral>central
Night vision: Peripheral> central
Day Vision: Central>peripheral
Navigation vision: mainly peripheral- patient may fail to navigate if peripheral vision is lost.

Reason is due to more cones in the fovea which is responsible for central vision and more rods elsewhere. Look at word file comparing cones with rods table but basically the above list applies for the difference between cones and rods.

34
Q

State the test for central and peripheral vision

A

Central - visual acuity assessment (acuity= sharpness)

Peripheral- visual field assessment

35
Q

What scan can be used to assess the macula and fovea

A

OCT scan

Optical coherence tomography

36
Q

Compare cones and rods

A 
Outer segment (part that absorbs light and contains photosensitive pigment): 
Rods > cones

Speed of response to light:
Cones>rods

Sensitivity to light: Rods>cones so better for night vision (this is NOT acuity of vision)

Acuity/resolution: Cones>rods

Location: Rods= more in periphery. Cones= more in macula/fovea

Colour: only cones

Abundance: more rods than cones

You still see colour in peripheral vision because you still have cones outside of macula, just not much

37
Q

What are cone and rod vision also called

A

Scotopic vision (rod)= means dim light vision

Photopic vision (cone)= means bright light vision

38
Q

2 most common colour blindness problems?

A

Deuteranomaly (less sensitive to green, most common colour blindness because the green curve shifts towards red) and protanomaly (less sensitive to red as red curve shifts towards green)

Deuter= second
Proto= first
look at the absorption curves of red green and blue in the slides. Red is furthest right then green then blue on left.

39
Q

What is the index of refraction?

A

every medium has this.

Speed of light in vacuum (c)/speed of light in new medium (Vm)

denominator is always smaller. This value has no units. Greatest possible value is 1.

40
Q

PLEASE LOOK AT PDF TO REVIEW GCSE LEVEL OPTICS

A

/

41
Q

What is the general term used to describe mismatch between axial length and refractive power such that the light rays dont fall on retina? (eg myopia, hyeropia, astigmatism, presbyopia)

A

Ametropia is the general term for all of these refractive disorders

42
Q

Symptoms of hyperopia and myopia

A

look at slides

43
Q

What is amblyopia

A

this is also called lazy eye. If one of your eyes is weaker than the other (either myopic or hyeropic or due to other pathological reasons.) overtime, your brain will start to prefer the stronger eye over the weak one and so the neuronal connections to the weak eye will be tuned down. If this is left untreated, amblyopia can develop and basically you wont be able to see well even with glasses because the brain has switched off the neuronal connections to the weaker eye. To fix this, children may be forced to use the weaker eye more by covering up the strong eye.

44
Q

What is astigmatism

A

multiple focal points rather than one due to the refractive media not being spherical. Eg if cornea is not circular dome shaped but rugby ball dome shaped then it will refract light differently at different points. (see word file for better explanation)

45
Q

Astigmatism symptoms and treatment?

A 
Symptoms
– asthenopic symptoms ( headache , eyepain)
– blurred vision
– distortion of vision
– head tilting and turning

Treatment
– Regular astigmatism: cylinder lenses with or
without spherical lenses(convex or concave), Sx (surgery)
– Irregular astigmatism : rigid Contact lens , surgery

Y2 LCRS Neuro Fwong (22 decks)

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