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Neuroscience and Mental Health > Structure and function of the eye > Flashcards

Structure and function of the eye Flashcards

1
Q

Macula

A
  • ~centre of retina
  • temporal to optic nerve
  • small and highly sensitive
  • responsible for detailed central vision
  • fovea (necessary for sharp, central vision) at the centre of the macula
  • macula allows appreciation of detail and ability to perform tasks requiring central vision (eg: reading)
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2
Q

Tear film

A
  • maintains smooth cornea-air surface
  • oxygen supply to cornea (normal cornea has no blood vessels)
  • debris removal (achieved by tear film and blinking)
  • bactericide
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3
Q

Conjunctiva

A
  • thin, transparent tissue covering outer surface of the eye
  • begins at outer edge of cornea, covers visible eye part and lines inside of eyelids
  • nourished by tiny blood vessels (nearly invisible to the naked eye)
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4
Q

3 layers of the coat of the eye

A
  • Sclera
  • Choroid
  • Retina
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5
Q

Schlera

A
  • ‘white of the eye’
  • hard, opaque tissue
  • eye’s protective outer coat
  • high water content
  • maintains eye shape
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6
Q

Choroid

A
  • pigmented
  • vascular (layers of blood vessels nourish back of the eye)
  • between retina and sclera
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7
Q

Retina

A
  • neurosensory tissue

- converts lights to neurological impulses that are transmitted via optic nerve

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8
Q

Cornea

A
  • transparent, dome-shaped window
  • covers front of the eye (front-most part of anterior segment)
  • continuous with scleral layer
  • powerful refracting surface (2/3 of the eye’s focusing power)
  • low water content
  • physical barrier and infection barrier
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9
Q

5 layers of the cornea

A

(outer) 1) Epithelium
2) Bowman’s Membrane
3) Stroma
4) Descemet’s Membrane
(inner) 5) Endothelium

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10
Q

Stroma of the cornea

A
  • regularity contributes towards transparency
  • corneal nerve endings provide sensation and nutrients for healthy tissue
  • no blood vessels in normal cornea
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11
Q

Endothelium of the cornea

A
  • pumps fluid out of corneal and prevents corneal oedema
  • 1 cell thick
  • no regeneration power
  • decrease in endothelial cell density with age
  • endothelial cell dysfunction-> corneal oedema and corneal cloudiness
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12
Q

Parts of the uvea

A

1) iris
2) ciliary body
3) choroid

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13
Q

Iris

A
  • coloured part of the eye
  • controls light levels inside eye (amount of light reaching the retina)
  • round opening in centre of iris is the pupil
  • iris embedded with tiny muscles that dilate and constrict pupil size (iris controls size and diameter)
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14
Q

Structure of the lens

A
  • outer acellular capsule
  • regular inner elongated cell fibres
  • may loose transparency with age (cataracts)
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15
Q

Functions of the lens

A
  • transparency
  • refractive power
  • accommodation
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16
Q

Lens zonules

A
  • fibrous ring suspending the lens

- consists of passive connective tissue

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17
Q

Retina

A
  • very thin tissue layer

- lines inner part of eye

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18
Q

Functions of the retina

A

-capturing light rays entering the eye-> light impulses then sent to the brain for processing via the optic nerve

19
Q

Optic nerve

A
  • transmits electrical impulses from retina to brain

- connects to the back of the eye near the macula

20
Q

Optic disc

A

Visible portion of the optic nerve

21
Q

Blind spot

A

Point where the optic nerve meets the retina (no light sensitive cells so insensitive to light)

Test:

  • draw dot on piece of paper with ‘X’ 10cm to the left of the dot
  • close right eye and hold paper at arms length
  • look at dot and move paper towards you
  • ‘X’ disappears into blind spot
22
Q

Fovea test

A
  • Paper has star in centre and series of letters on either side of star
  • Look at star and try to read letters
23
Q

Hyperopia symptoms

A
  • visual acuity at near tends to blur relatively early (Nature of blur varies from inability to read fine print to clear near vision but suddenly and intermittently blur. More noticeable blurred vision if tired patient, printing is weak or light adequate)
  • asthenopic symptoms (eyepain, headache in frontal region, burning eye sensation, blepharoconjunctivitis etc)
24
Q

Amblyopia

A

LAZY EYE

-uncorrected hyperopia >5D

25
Q

Types of lenses

A
  • Converging lens (convex)

- Diverging lens (concave)

26
Q

Myopia treatment

A

Concave lens to decrease refraction on the light

27
Q

Hyperopia treatment

A

Convex lens to increase refraction power

28
Q

Astigmatism

A
  • Parallel rays come to focus in 2 focal lines rather than a single focal point
  • heredity aetiology
29
Q

Spectacle lenses

A
  • Monofocal lenses (spherical lenses, cylindrical lenses)

- Multifocal lenses

30
Q

Contact lenses

A
  • higher optical image quality and less influence on retinal image size compared to spectacle lenses
  • indications: cosmetic, athletic activities, occupational, irregular corneal astigmatism, high anisometropia, corneal disease
  • disadvantages include expense and careful daily cleaning/disinfection
  • complications include infectious keratitis, giant papillary conjunctivitis, corneal vascularisation, severe chronic conjunctivitis
31
Q

Intraocular lenses

A
  • cataract crystalline lens replacement
  • best optical correlation for aphakia
  • avoid significant magnification and distortion caused by spectacle lenses
32
Q

Surgical correction

A
  • keratorefractive surgery: RK, AK, PRK, LASIK, ICR, Thermokeratoplasty
  • intraocular surgery: clear lens extraction (with or without IOL), phakic IOL
33
Q

Photoreceptors in the retina

A
  • Rod photoreceptor

- Cone photoreceptor

34
Q

Rod photoreceptor (rods)

A
  • longer outer segment with photo-sensitive pigment
  • 100 times more sensitive to light than cones
  • slow response to light
  • responsible for night vision (Scotopic Vision)
  • 120 million rods
35
Q

Cone photoreceptor (cones)

A
  • less sensitive to light compared to rods
  • faster response to light than rods
  • Responsible for day light fine vision and colour vision (Photopic Vision)
  • 6 million cones
36
Q

Anterior segment

A

Ocular structure anterior to the lens

37
Q

Posterior segment

A

Ocular structure posterior to the lens

38
Q

Anterior chamber

A
  • between cornea and lens
  • filled with clear aqueous fluid
  • supplies nutrients
39
Q

Glaucoma

A

/

40
Q

Types of Glaucoma

A
  • Primary Open Angle Glaucoma

- Closed Angle Glaucoma

41
Q

Primary Open Angle Glaucoma

A
  • commonest type

- due trabecular meshwork dysfunction (meshwork cannot drain properly leading to fluid build-up)

42
Q

Closed Angle Glaucoma

A
  • acute or chronic
  • increased pressure pushes iris/lens complex forwards which blocks the trabecular meshwork (inability to drain aqueous humour)->vicious cycle
  • risk factors include small eyes, narrow angle at trabecular meshwork etc
  • patients may present with sudden painful red eye with an acute drop in vision
  • treatment with peripheral laser iridotomy (laser beam creates drainage hole on the iris for the aqueous humour)
43
Q

Fovea

A
  • most sensitive part of the retina
  • highest concentration of cone photoreceptors but low concentration of rod photoreceptors (why stars out of corner of eye are brighter than looking directly at stars)
  • only fovea has concentration of cone photoreceptors to perceive in detail
44
Q

3 layers of the tear film

A
  • Superficial oily layer (reduces tear film evaporation and is produced by row of Meibomian Glands along lid margins)=lipid layer
  • Aqueous tear film (Tear Gland)=water layer
  • Mucinous layer on the corneal surface (maintains surface wetting)=mucin layer

Neuroscience and Mental Health (18 decks)

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