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Human Responses To The Environment > Human Eye > Flashcards

Human Eye Flashcards

1
Q

How is the eye held in position?

A

By SIX EXTERNAL MUSCLES, that control the movement of the eye.

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2
Q

What cushions and protects the eye?

A

Fatty tissue

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3
Q

What is the function of the lachrymal gland?

A

Produces salty tears and washes away dust

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4
Q

What is the function of the tear duct?

A

Drains excess fluid into nasal cavity.

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5
Q

What is the function of the eyelashes and eyelids?

A

Protect eye from dust, too much light and foreign bodies

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6
Q

What is the function of the glands of Meiboom?

A

Secrete oily fluid to lubricate eyeball.

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7
Q

What is the structure and function of conjunctiva?

A

S: delicate mucous membrane, covers front of the eye and lines the eyelids

F: 1. Pain receptors for eyelids to close prevent foreign bodies enter.
2. Produce lubricating mucous, prevent eye drying out

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8
Q

What is the structure and function of Sclera?

A

S: tough, white in elastic layer made up of connective tissue.

F: protects internal parts of eye.
Provide points of attachment for six muscles
Inelasticity maintain shape of eye.

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9
Q

What is the structure and function of Cornea?

A

S: more convex than rest of eyeball
Transparent, has no blood vessels
Covered by conjunctiva (thin membrane)

F: transparency allow light rays pass through to light cells
Causes converging refraction of light rays
Many pain receptors, so eyelid close.

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10
Q

What are the three components of the Middle Vascular layer?

A

Choroid
Ciliary body
Iris

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11
Q

What is the structure and function of Choroid?

A

S: thin, dark layer containing pigments and blood vessels

F: pigment absorbs excessive rays of lights, preventing reflection - blurring.
Blood vessels supply food and O2 to cells of retina

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12
Q

What is the Structure and function of Ciliary body?

A

S: thickened part, extension of choroid, contains circular ciliary muscles

F: control curvature of lens

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13
Q

What is the structure and function of the Iris?

A

S:continuation of cHoroid, forms a circular coloured curtain with a hole in centre
Circular structure contains brown pigments
Two sets of involuntary muscles occur in the iris- circular and radial - when one contracts, other relaxes
Pupil is circular opening (not a struc) appears black of dark cavity.

F: controls the amount of light entering the eye. By PUPILLARY MECHANISM- reflex action

In BRIGHT LIGHT:
circular iris muscle contracts
Radial iris muscle relax
Size of pupil reduces (constricts)

Less light enters the eye. Prevent damage to retina

In DIM light:
Radial muscles contract
Circular muscle relax
Pupil dilates

Allow max amount. Of light to enter eye for clearest vision

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14
Q

What does the Retina consist of?

A 
Pigmented layer
2. Nervous layer 
A) photoreceptors
Rod cells
Cone cells
B) neutral layer
Blind spot
Yellow spot
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15
Q

What is the structure and functions of pigmented layer?

A

S:layer of cuboidal cells, borders on the choroid

F: dark pigment absorbs light

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16
Q

What is the structure of the nervous layer- photororecptors?

A

S: 2 types of photoreceptors - Rods and cones
Modified neutrons
Both sensitive to light.

F: convert light stimuli into nerve impulses.

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17
Q

What is the structure and function of rod cells?

A

S: thin, elongated cells
Found in peripheral regions of retina

F: respond to low-intensity light and provide night( black and white.)
Provide peripheral vision.

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18
Q

What is the structure and function of cone cells?

A

S: found in yellow spot of retina
Red, blue, green cones respond to diff wavelengths of light

F: respond to bright light intensities, enable colour to be seen.
Provide sharp, clear vision.

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19
Q

What is the structure and function of neural layer?

A

S: photoreceptors synapse with 2 layers of neutrons
axons of 2nd layer form optic nerve, leave the eye.

F: neutrons carry impulses from photoreceptors?
Optic nerve conduct impulses to occipital lobe of cerebral cortex, where interpreted as sight.

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20
Q

What is the structure and function of blind spot?

A

S: No rods or cones where optic nerves leave eyeball
Where blood vessels enter and leave.

F: not sensitive to light stimuli

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21
Q

What is the structure and function of yellow spot?

A

S: Near centre of retina,side of blind spot. An oval area
Contain mainly cones

F: where vision is sharpest.

22
Q

What are the inner parts of the eye?

A
  1. Lens

2. Eye cavities - anterior cavity, posterior cavity

23
Q

What is the structure and function of the lens?

A

S: round,biconvex,flexible, transparent struc,me closed in elastic
capsule.
Held in place by suspensory ligament
No blood vessels.

F: change shape to allow sharp, precise focusing of light rays on retina

24
Q

What is the structure and function of anterior cavity?

A

S: filled with water fluid, aqueous humour.

Aqueous humour:
F: provides nutrients and O2 to lens& cornea and carries away waste.
Provides correct pressure in anterior cavity.

25
Q

What is the structure and function of posterior cavity?

A

S: filled with jelly -like fluid, vitreous humour
Vitreous humour:
F: provides pressure within eye, holding retina firmly against choroid.
Prevents eyeball from collapsing.

26
Q

What is Accommodation of the eye?

A

Process of producing a finely focused image on the retina

27
Q

How is accommodation carried out

A

By the action of the ciliary muscles which change shape of lens

28
Q

What happens when lens is more convex?

A

Light rays are bent

29
Q

What happens of the lens is flatter?

A

The less the light rays are bent.

30
Q

When does accommodation take place?

A

When viewing objects NEARER THAN 6 METRES.

31
Q

What happens for close vision?

A

Make active adjustments , to form a clear, sharp image on the retina

32
Q

Why does light on a close object diverge?

A

So lens BULGE OUT MORE TO BEMD LIGHT RAYS MORE, to focus image on retina

33
Q

What is Accommodation?

A

Lens become more convex, so incoming diverging rays of light are bent more sharply for clear focusing to take place.

34
Q

How is accommodation brought about?

A

The circular,ciliary muscles contract

Action pulls ciliary body inwards towards pupil

35
Q

Where is the eye situated?

A

Eyeball fits into a BONY SOCKET situated anteriorly in CRANIUM

36
Q

What is another name for short-sightedness?

A

Myopia

37
Q

What is short-sightedness?

A

See and read close objects clearly but distant obj are blurred

38
Q

How is short-sight caused!

A

Eyeball too long

Cornea/ lens being convex

39
Q

What does short sight result in?

A

Light rays converging to form image in front of retina

40
Q

How can it be solved?

A

Wear concave lenses, which diverge light rays

41
Q

What is another name for long sightedness?

A

Hypermetropia

42
Q

What is long- sightedness?

A

See distant obj clearly, close obj not very clear

43
Q

What is long sight caused by?

A

Eyeball too short

Curvature of lens to flat

44
Q

What does long sight result in?

A

Light rays converging to form an image behind retina

45
Q

How can it be solved?

A

Wear convex lenses, that converge light rays so image on retina

46
Q

What are the causes of Astigmatism?

A

An irregularly shaped :
Cornea- corneal astigmatism shaped like rugby ball than soccer ball
Lens - lenticular astigmatism

47
Q

What does this defect cause?

A

Causes light rays to focus on 2 points rather than one leading to blurred image.

48
Q

What is Keratoconus?

A

A disease that causes gradual thinning of cornea.

49
Q

How can astigmatism be treated?

A

Spectacles, contact lenses , refractive laser surgery.

50
Q

What is Cataracts?

A

When protein clumps together and cloud a small area of the lens

Human Responses To The Environment (10 decks)

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