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Y2 LCRS Neuro Fwong HR > Structure and function of the eye > Flashcards

Structure and function of the eye Flashcards

1
Q

What are the inner and outer corners of the eye referred to as?

A

Medial and lateral canthus

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2
Q

What name is given to the border between the cornea and the sclera?

A

Corneal limbus

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3
Q

What is the clinical significance of the corneal limbus?

A

Common site for corneal epithelial neoplasm

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4
Q

Describe the nervous innervation of the cornea

A

Highly sensitive

Ophthalmic branch of trigeminal nerve

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5
Q

Describe the nerve supply to the lacrimal gland

A

PNS-mediated

CNV

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6
Q

Recall the drainage of tear film

A

Tear film: lacrimal gland, movement accross eye = superolateral to inferomedial, drainage through puncta to superior/ inferior canaliculus –> lacrimal sac –> nasolacrimal duct

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7
Q

Recall 3 functions of tear film

A
  1. Bactericide
  2. O2 and nutrient supply to ant. seg
  3. Smooth surface mainenance
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8
Q

Recall the layers of tear film from deep to superficial

A

Mucous, thick aqueous, oily

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9
Q

Describe the fx of each layer of tear film

A

mucous: protect eye surface, adhere tear film to eye
Thick aqueous: lubricant, bactericide, nutrition
Oily: prevention of evaporation

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10
Q

Where is the mucous layer of tear film produced?

A

Goblet cells in conjunctiva

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11
Q

Where is the oily layer of tear film produced?

A

Meibomian glands within eyelids

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12
Q

What sign in the eyes is indicative of intermittent hypertension?

A

Rupture of tiny vessels in conjunctiva

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13
Q

What surrounds the retina?

A

Uvea

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14
Q

What is the uvea made up of?

A

Predominantly vascular

  1. Choroid
  2. Ciliary body
  3. Iris
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15
Q

What does the choroid lie between?

A

Retina and sclera

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16
Q

What is the choroid made up of?

A

Vasculature supplying posterior segment of eye

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17
Q

What is the main component of the sclera?

A

Collagen

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18
Q

Recall and describe the most significant osmotic gradient that is maintained in the eye

A

Sclera = high H2O, cornea = low H2O
Sclera has protective fx
Cornea must remain transparent

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19
Q

How is the transparency of the cornea maintained?

A

Corneal endothelium actively removes water

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20
Q

In emmetropia, what provides the refractive power of the eye?

A

Cornea = 2/3 of power, lens = 1/3

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21
Q

Recall one advantage and one disadvantage of the barrier function of the cornea?

A

Ad: prevents infection
Disad: prevents drug entry

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22
Q

What are the 5 structures that make up the cornea, working superficial to deep?

A 
Epithelium
Bowman's membrane
Stroma
Descemet's membrane
Endothelium
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23
Q

Which element of the cornea cannot regenerate?

A

Endothelium

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24
Q

What characteristic of the lens makes it transparent?

A

Regular structure

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25
Q

Recall the pathophysiology of age-related cateracts

A

Hydration of lens –> loss of transparency

26
Q

Describe the shape of the lens

A

Aspheric: anterior and posterior surfaces have differing curvature

27
Q

Recall the attachments of the lens

A

Attached all around by zonules/ lens zonulae, anchored to ciliary body

28
Q

Recall what happens when the ciliary muscles contract?

A

Pressure on zonules decreased, lens gets smaller and thicker

29
Q

Recall what happens when the ciliary muscles relax?

A

Pressure on zonules increases, lens gets wider and thinner

30
Q

How can the optic nerve be identified with an ophthalmoscope?

A

Optic nerve head appears as bright optic disc

31
Q

Where is the macula?

A

Roughly in centre of retina

32
Q

Where is the aqueous humour found?

A

Anterior segment of eye (in front of lens)

33
Q

Where is the vitreous humour found?

A

Posterior segment of eye (behind lens)

34
Q

What is the fx of aqueous humour?

A

Nutrient and oxygen delivery

35
Q

Recall the flow of aqueous humour

A

Ciiary body –> anterior chamber –> trabecular meshowrk (lies in limbus) –> Schlemm’s canal/ uveal-scleral flow

36
Q

Describe the 2 methods of aqueous humour drainage

A
  1. Schlemm’s canal = modified vein

2. Uveal-scleral flow = passive, PG analogues act here

37
Q

Describe the composition of vitreous humour

A

99% water, collagen, GAGs

38
Q

What is the fx of vitreous?

A

Mechanical support

39
Q

What is a normal IOP?

A

12-21mmHg

40
Q

Recall the names of the layers and sublayers of the retina

A

Layers: retinal pigment epithelium and neuroretina

Sublayers of neuroretina: outer/ middle/ inner

41
Q

Recall the composition of each of the layers of neuroretina

A

Outer: photoreceptors
Middle: bipolar cells
Inner: ganglion cells

42
Q

Recall 2 functions of the retinal pigment epithelium

A
  1. Waste removal

2. Transport nutrients from choroid to photoreceptor cells

43
Q

Recall the differences between rod and cone photoreceptors

A

Cones: colour, central vision, detail, fast response to light; n = 6 mill
Rods: B&W, peripheral vision, sense movement; N = 120 mill

44
Q

What is the fx of bipolar cells?

A

Fine-tuning of afferent info

45
Q

Where do retinal ganglion cells synapse with 4th order neurons?

A

Lateral genticulate nucleus

46
Q

What are the 2 oritentations of retinal ganglion cell, and what is the relevance of this

A
  1. On-centre: stimulated by light falling on centre of its receptove field and inhibited by light falling on edge
  2. off-centre: opposite
47
Q

What is the receptive field of a neuron?

A

Retinal space within which incoming light can alter the firing pattern of a neuron

48
Q

Which type of photoreceptors have lower convergence, and what is the clinical relevance of this?

A

Cones = finer visual acuity as smaller receptive field

49
Q

What is the main test for colour-blindness?

A

Ischiara test

50
Q

What are the 2 possible causes for colour-blindness?

A
  1. Shift in the peak of photo-pigment sensitivity

2. Absence of 1 or more of the 3 cone photpigment subtypes

51
Q

Describe the mediation of light dark adaptation

A

Photoreceptor bleaching –> inhibition of rods/ cones accordingly (deending on whether it is light –> dark or dark –> light)

52
Q

Which type of photoreceptor adapts to changes in light level more quickly?

A

Cones

53
Q

What name is given to perfect vision?

A

Emmetropia

54
Q

What is the mechanical problem in visual impairment?

A

Parallel lens converges to a point anterior/ posterior to the retina, or to more than one point

55
Q

What term is used to describe convergence of the parallel lens anterior to the retina?

A

Myopia (short-sightedness)

56
Q

What term is used to describe convergence of the parallel lens posterior to the retina?

A

Hypermetropia (long-sightedness)

57
Q

What sort of glasses are used to correct myopia?

A

Concave

58
Q

What general term is given to eyes that have a refractive error?

A

Ametropia

59
Q

What is astigmatism?

A

Parralel lens focuses on not one point but two

60
Q

What causes astigmatism?

A

Elliptical cornea

61
Q

What term is given to a naturally-occuring loss of accommodation?

A

Presbyopia

62
Q

What causes presbyopia?

A

Stiffening of lens

Y2 LCRS Neuro Fwong HR (17 decks)

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