Intro to the Eye Flashcards

1
Q

What are the layers of the eye?

A

Outer Fibrous Coat

  • Cornea Anteriorly
  • Sclera Posteriorly & Laterally

Vascular Coat:

  • Iris & Pupil
  • Ciliary Body
  • Choroid

Sensory Coat:
- Retina

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2
Q

What are the histological layers of the Cornea?

A
  • Stratified Squamous non-keratinized Epithelium
  • Bowman’s Membrane (basement membrane)
  • Stroma (regular connective tissue - collagen)
  • Descemet’s Layer (basement membrane)
  • Endothelium (single layer)
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3
Q

What would be the reason for examining Bowman’s membrane in an ocular injury?

A

It the injury only affects the epithelium it will heal to normal.

If it breaks the bowmans membrane then it will heal with collagen and form a scar, affecting corneal transparancy and therfore sight

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4
Q

How do we maintain corneal transparency?

A
  • No blood vessels in the stroma
  • Regular arrangement of the stroma
  • Pumps in the endothelium keep out the aqueous humor
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5
Q

How does nutrition reach the cornea?

A

From the:

  • Tear Film
  • Blood vessels in the sclera
  • Aqueous Humor
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6
Q

How is the avascular nature of the cornea relevant to surgery?

A

Because its avascular theres a low chance of foreign antigens being noticed, this means theres a lower chance of corneal graft rejection than any other type of transplant.

This has led to the cornea being dubbed an “immune-privileged” site

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7
Q

How do we divide up the eye (segments/chambers)

A

Anterior Segment and Posterior Segment divided by the lens.

The anterior segment is split into the ant/post chambers divided by the iris.

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8
Q

Where is aqueous humor produced/

A

The ciliary body in the posterior chamber of the anterior segment

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9
Q

Explain the passage of aqueous humor

A
  • Produced in the ciliary body
  • Passes between lens and iris into anterior chamber
  • Then drains through the trabecular meshwork and out schlemm’s canal
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10
Q

What is the choroid?

A

A part of the vascular coat.

Its a layer of fenestrated blood vessels of varying diameter below the retina

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11
Q

Explain the layers of the retina?

A

Split into 10 layers, these are not all separate cell layers, the organisation of the cells make them appear like 10 layers.

The important layers are:

10) Pigment Epithelial layer
9) Rods and cones layer (dendrites of the lowest neuron layer)
2) Nerve Fibre layer (Axons of the highest neuron layer)

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12
Q

Explain the blood supply of the retina?

A
  • Outer layers are supplied by the choroid by diffusion

- Inner Layers are supplied by branches of the central retinal artery

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13
Q

What do you see with an opthalmoscope

A

The retina and its blood vessels (branches of the central retinal artery)

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14
Q

What is special about the central part of the retina?

A

Fovea Centralis!

It has the densest packing of cones/rods anywhere in the retina so its where the image is sharpest.

The outer layers of the retina are also pushed aside at the fovea centralis to expose the rods/cones.

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15
Q

What suspends the lens?

A

Suspensory Ligaments (Zonules)

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16
Q

Why do cataracts form?

A
  • Lens absorbs lots of UV light
  • Lens cant shed its old cells like skin or remove them through blood.
  • So over time it opacifies leading to cataracts
17
Q

What shape is the lens?

A

Biconvex

18
Q

What makes up the eyelid?

A

They are given shape by the tarsal plates (connective tissue).
They contain glands that contribute to tears.

The lids also contain the palpebral part of the orbicularis oculi

19
Q

How many layers are there in the tear film?

A

Three.
1 - Mucinous Layer - 30%
2 - Aqueous Layer - 69%
3 - Oily Layer - 1%

20
Q

how do we inspect the tear film?

A

With a dye called Fluorescein

21
Q

What are the functions of the tear film?

A
  • Prevents drying of cornea
  • Washes away foreign bodies
  • Contains lysozymes and antibodies to fight off microbes
  • Maintains smooth corneal surface for refraction
22
Q

Whats the function of the mucinous layer of tear film?

A

Overcomes surface tension of the eye to prevent the aqueous layer simply rolling off

23
Q

Whats the function of the oily layer of the tear film?

A

Prevents the aqueous layer from evaporating too fast

24
Q

How does tear secretion occur?

A

Parasympathetic fibres from cranial nerve VII (Facial) trigger the conjunctival sac to secrete tears

25
Q

What triggers blinking?

A

When the aqueous layer evaporates enough for the oily layer to contact the mucinous layer it triggers reflex blinking

26
Q

What does the eye develop from embryologically?

A

Optic Vesicles grow outwards from the diencephalic part of the neural tube

  • Grows towards the surface ectoderm forming optic cup
  • Surface Ectoderm invaginates forming lens vesicle

Together they form the eye