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Y2 Neuroscience and Mental Health > The Structure of the Eye > Flashcards

The Structure of the Eye Flashcards

1
Q

Label the eye

A 
Cornea
Anterior chamber
Pupil
Iris
Lens
Conjunctiva 
Sclera
Ciliary body 
Vitreous body 
Optic disc
Optic nerve
Choroid
Retina
Macula
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2
Q

What is the anterior-posterior diameter of the orbit in adults

A

24mm

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3
Q

What type of humour is in the two segments and what are they separated by

A

Anterior segment - aqueous humour
Posterior segment - vitreous humour

separated by the lens

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4
Q

What are the two anatomical spaces within the anterior segment

A 
Anterior chamber (cornea → iris)
Posterior chamber (iris → lens)
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5
Q

Describe the optic disc

A

Part of the optic nerve visible at the back of the eye

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6
Q

Describe the zones/suspensory ligaments

A

Fibrous strands that hold the lens in line with the pupil

Connected to pupil by ciliary muscles.

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7
Q

Describe the cornea

A

Transparent window
2/3 refraction
Physical and infection barrier

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8
Q

Describe the uvea

A

Vascular coat

= iris +ciliary bodies + choroid

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9
Q

Describe the iris

A

Coloured part of eye

Controls the diameter and size of the pupil and therefore the amount of light reaching the retina

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10
Q

Describe the retina

A

Captures light rays that fall on the eye

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11
Q

What are the layers of the eye

A

Sclera
Choroid
Retina

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12
Q

Describe the sclera layer of the eye

A

Hard
Opaque
Protects and maintains the shape of the eye

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13
Q

Describe the choroid layer of the eye

A

Pigmented
Vascular
Shields out unwanted scattered light
Provides circulation to the eye

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14
Q

Describe the retina layer of the eye

A

Neurosensory tissue

Converts lights to neurological impulses that are transmitted via optic nerve

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15
Q

What is the ciliary body

A

Ring shaped tissue surrounding the lens between the anterior and posterior segments and is located behind the iris
Contains the ciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces aqueous humor

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16
Q

What are the layers of the iris

A

Anterior Layer Stromal Layer containing muscle fibres

Posterior Layer -Epithelial

17
Q

What is the normal intra-ocular pressure and how is fluid drained

A

12-20mmHg

Drained via the tribecular network

18
Q

What are the 2 portions of intraocular fluid

A

Aqueous humor - in front of lens, freely flowing

Vitreous humor - between posterior surface of the lens and the retina, gelatinous mass held by proteoglycan molecules, little change

19
Q

Describe aqueous humour

A

Nourishes the cornea and lens by supplying nutrition such as amino acids and glucose.
Transports vit C in the front segment to act as an antioxidant agent.
Each eye forms AH at 2-3 microlitres/minute

20
Q

What is uveoscleral outflow

A

drainage of ocular aqueous humour from the anterior chamber to anterior chamber angle that is NOT through the trabecular network

21
Q

Describe the pathway of intraocular fluid drainage

A
  1. Ciliary body
  2. Anterior chamber of the eye
  3. Trabecular meshwork
  4. Canal of Schlemm (thinly walled vein that extends circumferentially all around the eye)
  5. Extraocular veins
22
Q

Describe glaucoma

A

Condition caused by sustained, raised intraocular pressure
Axons of the optic nerve are compressed at the optic disk. causing a lack of appropriate nutrition to fibres
This results in retinal ganglion cell death and cupping of the optic disc

23
Q

What is the optic cup

A

The central portion of the optic disc, of which there is an increase in glaucoma

24
Q

Describe primary open angle glaucoma

A

Commonest type

Due to a blockage in the trabecular meshwork

25
Q

Describe closed angle glaucoma

A

Increased pressure in the eye pushes the lens/iris forward, making it difficult to drain aqueous humor
Patients present with painful red eyes and an acute drop in vision

26
Q

What are the risk factors for closed angle glaucoma

A

Small eyes

Narrow trabecular meshwork

27
Q

What are the 2 main photoreceptors in the retina

A

Rods – 120 million present, 100X more sensitive to light

Cones – 6 million present, Less sensitive to light but faster response

28
Q

What occurs with photoreceptors during dark and light adaptation

A

Dark adaption - retina increases sensitivity so that cones are suppressed and rods take over

Light adaptation - rod function is suppressed and cone function takes over

29
Q

Describe refraction of light in the eye

A

Light is refracted by thecorneaandlensto focus the incoming light rays onto the retina to form a clear image
The refractive power of the lens = 1/3
The refractive power of the cornea = 2/3

30
Q

What is emmetropia

A

Perfect correlation between the axial length of the eye and it’s refractive index
Therefore, parallel light waves fall perfectly on the retina and there is 20:20 vision

31
Q

What is ametropia

A

Axial length of the eye does not match its refractive power
As a result, parallel light rays don’t fall on to the retina
People with ametropia require corrective lenses

32
Q

Give 4 examples of ametropia

A

Nearsightedness (Myopia)
Farsightedness (Hyperopia)
Astigmatism
Presbyopia

33
Q

Describe myopia

A

Near-sightedness

Parallel rays converge at a focal point anterior to the retina

Due to a long globe or excessive refractive power

Requires a concave lens

34
Q

Describe hyperopia

A

Far-sightedness

Parallel rays converge at a focus point posterior to the retina

Due to a short globe (axial hyperopia - more common) or inadequate refractive power (refractive hyperopia)

Requires a convex lens

35
Q

Describe astigmatism

A

Parallel rays do not come to focus on a single point, instead we end up with two focal lines
This occurs because the eye is an irregular shape: oval/not circular
It can be hereditary

36
Q

Describe presbyopia

A

Naturally occurring loss of accommodation with old age as the lens hardens and is unable to change shape
Onset from age 40 years
Distant vision intact
Corrected by reading glasses (convex lenses)

37
Q

What is anisometropia

A

Condition where 2 eyes have unequal refractive power

38
Q

What is the near response triad

A
  1. Pupillary Miosis – mediated by the sphincter pupillae
  2. Convergence of the eyes – mediated by the medial recti muscles
  3. Lens Accommodation (becomes thicker) – mediated by the circular ciliary muscle

Y2 Neuroscience and Mental Health (22 decks)

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