General shape, size and position of the eye Flashcards

1
Q

What is photoreception?

A

the process by which light energy from the environment produces changes in specialised nerve cells in the retina- the rods and cones

the changes result in nerve action potentials which are relayed to the optic nere and then to brain where information processed and consciously appreciated as vision

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2
Q

What are all the structures within the eye other than the photoreceptors (rods and cones) for?

A
  • may be aprt of the system for focusing and transmitting light onto the retina (cornea, lens, iris, ciliary body)
  • may be necessary for nourishing and supporting tissues of eye (choroid, aqueous outflow system, lacrimal apparatus)
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3
Q

What is the approximate shape and size of the eye?

A

approximately a sphere 2.5cm in diameter with volume of 6.5ml

in reality more of the parts of two spheres - smaller one anteriorly, cornea, and the sclera which constitutes large sphere

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4
Q

What proportion of the circumference of the globe is formed by the cornea?

A

one sixth

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5
Q

How does the curvature of the cornea compare with the sclera?

A

the cornea has a greater curvature than the sclera

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6
Q

What is the raidus of the cornea?

A

7.8mm

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7
Q

What is the radius of the sclera?

A

11.5mm

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8
Q

What is the average axial lenngth of the globe of the eye?

A

24mm (range 21-26mm varies between individuals)

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9
Q

What is the diameter of the globe?

A

23mm

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10
Q

What is the horizontal length of the globe?

A

23.5mm

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11
Q

Are small eyes hyperopic (hypermetropic) or myopic?

A

hyperopic (aka hypermetropic)

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12
Q

What is the cut off axial length of the globe to be consider a small eye?

A

<20mm

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13
Q

Are large eyes hyperopic (hypermetropic) or myopic?

A

myopic

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14
Q

What is the the cut off axial length of an eye to be consiered a large eye?

A

26mm - 29mm

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15
Q

Where within the orbit is the eye situated?

A

anterior portion, closer to the lateral than the medial wall and nearer the roof than the floor

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16
Q

What is another name for the layers/ coats that make up the eye?

A

tunics

17
Q

What are the 3 coats (tunics) that make up the eye?

A
  1. Fibrous (corneo-scleral) coat
  2. Uvea or uveal tract (composed of choroid, ciliary body and iris)
  3. Neural layer (retina)
18
Q

What are the three things that the uveal tract is composed of?

A
  1. choroid
  2. ciliary body
  3. iris
19
Q

What do the three coats of the eye surround?

A

the orbital contents: the lens and the transparent media (aqueous humour and vitreous body)

20
Q

What are 2 key functions of the cornea and sclera?

A
  1. form tough fibrous envelope that protects the ocular tissues
  2. fibrous coat provides important structural support for intraocular contents and attachment of the extaocular muscles
21
Q

Name the following on the eye diagram:

  • corneal epithelium
  • cornea
  • iridocorneal angle
  • limbus
  • canal of schelmm
  • pupil iris
  • conjunctiva
  • posterior chamber
  • lens zonules
  • cilia body
  • anterior chamber
  • lens
A
22
Q

Identify the three tunics of the eye on the diagram (fibrous coat, uveal tract, neural layer).

A

neural = purple

uveal tract = red

fibrous = blue

23
Q

Label the following on the eye diagram:

  • vitreous
  • hyaloid (Cloquet’s) canal
  • optic disc
  • choroid
  • retinal pigment epithelium
  • retina (neural layer)
  • optic nerve
  • dura mater
  • subarachnoid spae
  • lamina cribrosa
  • fovea
  • sclera
  • parsa plana
  • ora serrata
  • rectus muscle tendon and belly
A
24
Q

What is the name of the point at which the cornea meets the sclera?

A

limbus (or corneoscleral junction)