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Year 2 - LCRS - Neuroscience and Mental Health > Structure and Function of the Eye > Flashcards

Structure and Function of the Eye Flashcards

1
Q

How is the orbit structured?

A
  • 7 bones contribute to the framework of the orbit (frontal, lacrimal, zygomatic, maxilla, ethmoid, spheroid and palatine)
  • there are holes in the orbit (e.g. optic canal, ethmoidal foramina)
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2
Q

What are the three types of tear production?

A
  • basal tears - nourish, lubricate and protect the cornea.
  • reflex tears - in response to irritation
  • crying (emotional) tears
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3
Q

Reflex tears

A
  • Afferent – Cornea – CN V1 (Ophthalmic branch of Trigeminal Nerve)
  • Efferent – Parasympathetic
  • Neurotransmitter – Acetylcholine
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4
Q

The lacrimal system - how are tears produced?

A
  • Tear produced by the Lacrimal Gland – Tear drains through the two puncta, opening on medial lid margin
    – Tear flows through the superior and the
    inferior canaliculi
    – Tear gathers in the Tear Sac
    – Tear exits the Tear Sac through the tear duct into the nose cavity
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5
Q

What produces tears?

A
  • the lacrimal gland
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6
Q

What are the functions of the tear film?

A
  • Tear film maintains smooth cornea-air surface
  • Oxygen Supply to Cornea – Normal cornea has no blood vessels
  • Removal of Debris (Tear film and Blinking)
  • Bactericide
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7
Q

What is the structure of the tear film?

A

It has 3 layers:

  • Lipid layer
  • Water layer
  • Mucin Layer
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8
Q

What is the function of the lipid layer of the tear film?

A

Superficial Oily Layer to reduce tear film evaporation (produced by a row of Meibomian Glands along the lid margins)

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9
Q

What is the function of the water later of the tear film?

A

Aqueous Tear Film (Tear Gland)

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10
Q

What is the function the Mucin layer of the tear film?

A

Mucinous Layer on the Corneal Surface to maintain surface wetting

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11
Q 
Which layer in the tear film protects the tear film from rapid evaporation?
– A) Lipid Layer
– B) Water Layer
– C) Mucinous Layer 
– D) All Three Layers
A

A)

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12
Q

Conjunctiva

A
  • the thin, transparent tissue that covers the outer surface of the eye.
  • It begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids.
  • It is nourished by tiny blood vessels that are nearly invisible to the naked eye.
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13
Q

What is the diameter of the eye in adults?

A

~24 mm (anterio-posterior diameter)

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14
Q

What are the 3 layers that coat the eye? What are their properties?

A

– Sclera – Hard and Opaque (outermost)
– Choroid – Pigmented and Vascular
– Retina – Neurosensory Tissue (innermost)

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15
Q

Sclera

A
  • commonly known as “the white of the eye”
  • the tough, opaque tissue that serves as the eye’s protective outer coat.
  • High water content
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16
Q

Cornea

A
  • transparent
  • dome-shaped window covering the front of the eye
  • powerful refracting surface, providing 2/3 of the eye’s focusing power (Convex curvature, Higher refractive index than air)
  • Low water content
    – Front-most part of Anterior Segment
    – Continuous with the Scleral Layer
  • physical barrier
  • infection barrier
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17
Q

What gives the eye its focusing / refractive power?

A
  • 2/3 is the cornea

- 1/3 is the lens

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18
Q

What is the structure of the cornea?

A
  • front-most part in the anterior segment of the eye
  • continuous with the scleral layer
  • has 5 layers:
    • Epithelium
    • Bowman’s membrane
    • Stroma
    • Descemet’s membrane
    • Endothelium
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19
Q

Stroma (layer of the cornea)

A
  • regularity contributes towards transparency
  • Corneal nerve endings provides sensation and nutrients for healthy tissue
  • No blood vessels in normal cornea
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20
Q

Endothelium of the cornea

A
  • pumps fluid out of corneal and prevents corneal oedema
  • Only 1 layer of endothelial cells
  • No regeneration power
  • Endothelial cell density decreases with age
  • Endothelial cell dysfunction may result in corneal oedema and corneal cloudiness
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21
Q

What conditions cause red eyes? How can you differentiate them?

A

Conjunctivitis and Uveitis (inflammation of the iris); also conjunctival hyperaemia.

Bacterial conjunctivitis will come with pus, viral without. there is also fungal and allergic.

Diffuse redness is usually conjunctivitis; in uveitis you see a red ring around the cornea.

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22
Q

What happens when you hydrate the cornea?

A
  • it becomes white / milky
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23
Q

What are the components of the uvea?

A
  • Iris
  • ciliary body
  • choroid

These three portions are intimately connected and a disease of one part also affects the other portions though not necessarily to the same degree.

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24
Q

What is the uvea?

A
  • Vascular coat of eye ball and lies between the sclera and retina
  • composed of three parts (iris, ciliary body and choroid)
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25
Q

Choroid

A
  • lies between the retina and sclera

- composed of layers of blood vessels that nourish the back of the eye.

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26
Q

Iris

A
  • coloured part of the eye
  • controls light levels inside the eye (similar to the aperture on a camera)
  • The round opening in the centre of the iris is called the pupil.
  • It is embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil size.
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27
Q

Lens

A
  • gives the eyes 1/3 of the refracting power (the other 2/3 is the cornea)
  • Outer Acellular Capsule
    – Regular inner elongated cell
    fibres – transparency
    – May loose transparency with age – Cataract
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28
Q

What are the functions of the lens?

A
  • transparency (regular structure)
  • accommodation (elasticity)
  • refractive power ( 1/3 power; Higher refractive index than aqueous fluid and vitreous)
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29
Q

What are lens zonules?

A

The lens is suspended by a fibrous ring known as lens zonules, consists of passive connective tissue.

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30
Q

Retina

A
  • very thin layer of tissue that lines the inner part of the eye.
  • It is responsible for capturing the light rays that enter the eye (Much like the film’s role in photography)
  • These light impulses are then sent to the brain for processing, via the optic nerve.
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31
Q

Optic nerve

A
  • The optic nerve transmits electrical impulses from the retina to the brain.
  • It connects to the back of the eye near the macula.
  • The visible portion of the optic nerve is called the optic disc.
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32
Q

Macula

A
  • The macula is located roughly in the centre of the retina, temporal to the optic nerve.
  • It is a small and highly sensitive part of the retina responsible for detailed central vision.
  • The fovea is the very centre of the macula. The macula allows us to appreciate detail and perform tasks that require central vision such reading.
  • ~ 6mm diameter
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33
Q

How is the eye divided into anterior and posterior segments?

A
  • anterior: ocular structures in front of the lens

- posterior: ocular structures behind the lens

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34
Q

How many chambers are there in the eye?

A

2

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35
Q

Anterior chamber of the eye

A
  • Between Cornea and Lens
    – Filled with Clear Aqueous Fluid
    – Supplies nutrients
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36
Q

What structure in the eye secretes aqueous humour?

A

The ciliary bodies

37
Q

Ciliary bodies

A
  • Ciliary body secretes aqueous fluid in the eye
  • Intraocular Aqueous Fluid flows anteriorly into the Anterior Chamber along the green arrow
  • Aqueous Fluid supplies nutrient
  • Trabecular Meshwork drains the fluid out of the eye
  • drained via canal of Schlemm -> into the nose
38
Q

Normal Intraocular Pressure

A

12- 21mmHg

now up to 24 mmHg? NICE

39
Q

Aqueous flow (drainage)

A
  • 80 - 90% TM canal of Schlemm

- rest uveal scleral outflow (is this correct?)

40
Q

“Optic neuropathy with characteristic structural damage to the optic nerve, associated with progressive retinal ganglion cell death, loss of nerve fibres and visual field loss”

A

Glaucoma

41
Q

Glaucoma

A

– Medical Condition of Sustained Raised Intraocular Pressure (risk factor)
– Retinal Ganglion Cell Death and Enlarged Optic Disc Cupping
– Visual Field Loss, Blindness

42
Q

What are the different types of glaucoma?

A

– Primary Open Angle Glaucoma – Commonest
– Closed angle glaucoma - can be acute or chronic

(angle refers to angle between the cornea and the iris)

43
Q

Primary open angle glaucoma

A
  • commonest

- trabecular Meshwork Dysfunction

44
Q

Closed angle glaucoma

A
  • can be acute to chronic
  • Increased pressure pushing the iris/lens complex forwards, blocking the trabecular meshwork – vicious cycle
  • Risk factors - small eye (hypermetropia), narrow angle at trabecular meshwork
  • May present with sudden painful red eye with acute drop in vision
  • Can be treated with peripheral laser iridotomy to create a drainage hole on the iris
45
Q 
Which type of cells in the eye are primary affected in glaucoma?
– A) Photoreceptors
– B) Retinal Pigment Epithelial Cells 
– C) Bipolar Cells
– D) Retinal Ganglion Cells
A

D)

46
Q

Blind Spot

A

Where the optic nerve meets the retina there are no light sensitive cells. It is a blind spot.

47
Q

Fovea

A
  • it is at the very center of the macula
  • Your fovea is the most sensitive part of the retina.
  • It has the highest concentration of cones, but a low concentration of rods.
  • This is why stars out of the corner of your eye are brighter than when you look at the directly.
  • But only your fovea has the concentration of cones to perceive in detail.
48
Q 
Whatisthe corresponding anatomic landmark for the physiological blind spot?
– A) Macula
– B) Fovea
– C) Optic Disc 
– D) Ora Serrata
A

C)

49
Q

Central Vision

A 
– Detail Day Vision, Colour Vision – Fovea has the highest concentration of cone photoreceptors
– reading, facial recognition
– assessed by visual Acuity Assessment
– Loss of Foveal Vision 
– Poor visual acuity
50
Q

Peripheral Vision

A 
– Shape, Movement, Night Vision
– Navigation Vision
– Assessed by Visual Field Assessment 
– Extensive loss of Visual Field 
–  unable to navigate in environment patients might need a white stick even with perfect visual activity
51
Q

How is the retina structured on a cellular layer?

A
  • Outer Layer – Photoreceptors (1st Order Neuron) – Detection of Light
  • Middle Layer – Bipolar Cells (2nd Order Neurons) – Local Signal Processing to improve contrast sensitivity, regulate sensitivity
  • Inner Layer – Retinal Ganglion Cells (3rd Order Neurons) – Transmission of Signal from the Eye to the Brain
52
Q

What way do the photoreceptors face?

A

They face the back of the eye, the light is refracted from there.

53
Q

Macula, Fovea and Foveal Pit

A
  • Macula Lutea (yellow patch), pigmented region at the centre of the retina of about 6 mm in diameter
    – Fovea forms the pit at the centre of the macula due to absence of the overlying ganglion cell layer
    – Fovea has the highest concentration of photoreceptors for fine vision
    – Clinicallycanbeassessed with an OCT scan (Optical Coherence Tomography)
54
Q

What are the 2 types of photoreceptors?

A
  • rods

- cones

55
Q

Rod photoreceptors

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

56
Q

Cone photoreceptors

A
  • Less sensitive to light, but faster response
  • Responsible for day light fine vision and colour vision (Photopic Vision)
  • 6 million cones
57
Q

Scotopic vision

A
  • Rod Vision
  • Peripheral and Night Vision
  • (More Photoreceptors, More Pigment, Higher Spatial and Time Summation)
    – Recognizes motion
58
Q

Photopic Vision

A

Cone Vision
– Central and Day Vision
– Recognizes colour and details

59
Q 
Where can one find the highest concentration of Rod Photoreceptors in the retina?
– A) Optic Disc
– B) Fovea
– C) 10-20 degrees away from Fovea 
– D) 20-40 degrees away from Fovea
A

D)

60
Q

Which photoreceptors detect which frequencies?

A

frequencies = colours (wavelength in nm)

  • S cones: blue
  • Rods: black
  • M cones: green
  • L cones - red
61
Q

What percentage of people have normal colour vision?

A

92%

62
Q

Ishihara test

A
  • Colour Perception Test
  • Ishihara Isochromatic Plates can test for red-green deficiencies only
  • Consists of plates of circle of dots appearing randomly in size
  • Subjects with normal red- green vision will recognize the correct pattern in the form of a 2-digit number
  • Patients with colour vision deficiencies will not recognize any pattern or recognize the wrong pattern
63
Q

What is the test with numbers presented as blops on a background of different coloured blops called?

A

Ishihara test

64
Q

What number on Ishihara test should everyone see?

A
  • 25

- if they say they don’t see it they are very likely lying as even patients with achromatopsia can see them

65
Q

Achromatopsia

A
  • black and white vision
66
Q

Light dark adaptation

A

Dark Adaptation:
– Increase in light sensitivity in dark
– Biphasic Process: Cone adaptation 7 minutes; Rod adaptation 30 minutes – regeneration of rhodopsin;

Light Adaptation: 
– Adaptation from dark to light
– Occurs over 5 minutes
– Bleaching of photo-pigments
– Neuro-adaptation
– Inhibition of Rod/Cone function
Pupil Adaptation (minor):
– constriction of pupil with light
67
Q

Whichisthe commonest form of colour vision deficiency in humans?
– A) Absence of all cone photoreceptors
– B) Absence of M-cone (green) photoreceptors
– C) Abnormal L-cone (red) photoreceptors
– D) red-green confusion

A

D)

68
Q

Refraction

A
  • based on light passing from 1 medium to the other
  • As light goes from one medium to another, the VEOLCITY changes!
  • As light goes from one medium to another, the PATH changes!
69
Q

What change when light passes from 1 medium to the other?

A

Velocity

Path

70
Q

Convex lense

A

A converging lens (Convex) takes light rays and bring them to a point.

71
Q

Concave lense

A

A diverging lens (concave) takes light rays and spreads them outward.

72
Q

Focal length

A

length between focal point and lens

73
Q

Emmetropia

A

= normal vision

  • Adequate correlation between axial length and refractive power
  • Parallel light rays fall on the retina (no accommodation)
74
Q

Ametropia (refractive error)

A

• Mismatch between axial length and refractive power
• Parallel light rays don’t fall on the retina (no accommodation)
– Nearsightedness (Myopia)
– Farsightedness (Hyperopia)
– Astigmatism
– Presbyopia

75
Q

Myopia

A

= nearsightedness
- focal point anterior to the retina
- Etiology : not clear , genetic factors
- Causes:
excessive long globe (axial myopia): more common excessive refractive power (refractive myopia)
- correction with diverging lenses, contact lenses or surgical lens removal

76
Q

Symptoms of Myopia

A

– Blurred distance vision
– Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
– Headache

77
Q

Hyperopia

A

= farsightedness
- focal point posterior to the retina
- Etiology: not clear, inherited
- Causes:
excessive short globe (axial hyperopia) more common insufficient refractive power (refractive hyperopia)
- correction with converging lenses, cataract lens, contact lens

78
Q

Symptoms of Hyperopia

A
  • visual acuity at near tends to blur relatively early
    • nature of blur is vary from inability to read fine print to near vision is clear but suddenly and intermittently blur
    • blurred vision is more noticeable if person is tired , printing is weak or light inadequate

– asthenopic symptoms : eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis

79
Q

Amblyopia

A

uncorrected hyperopia > 5D

80
Q

Astigmatism

A
  • Parallel rays come to focus in 2 focal lines rather than a single focal point
    • Etiology : heredity
    • Cause : refractive media is not spherical–>refract differently along one meridian than along meridian perpendicular to it–>2 focal points ( punctiform object is represent as 2 sharply defined lines)
81
Q

Symptoms of Astigmatism

A

– asthenopic symptoms ( headache , eyepain)
– blurred vision
– distortion of vision
– head tilting and turning

82
Q

Treatment of astigmatism

A
  • Regular astigmatism :cylinder lenses with or
    without spherical lenses(convex or concave), Sx
  • Irregular astigmatism : rigid CL , surgery
83
Q

Near response triad

A

= Adaptation for near vision

– Pupillary Miosis (Sphincter Pupillae) to increase depth of field
– Convergence (medial recti from both eyes) to align both eyes towards a near object
– Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision

84
Q

Presbyopia

A
  • Naturally occurring loss of accommodation (focus for near objects)
  • Onset from age 40 years
  • Distant vision intact
  • Corrected by reading glasses (convex lenses) to increase refractive power of the eye (reading glasses, bi-/trifocal glasses, progressive power glasses)
85
Q

Types of optical correction

A

• Spectacle lenses
– Monofocal lenses : spherical lenses , cylindrical lenses
– Multifocal lenses

• Contact lenses
– higher quality of optical image and less influence on the size of retinal image than spectacle lenses
– indication : cosmetic , athletic activities ,
occupational , irregular corneal astigmatism , high anisometropia , corneal disease
– disadvantages : careful daily cleaning and
disinfection , expense
– complication : infectious keratitis , giant papillary conjunctivitis , corneal vascularization , severe chronic conjunctivitis

• Intraocular lenses
– replacement of cataract crystalline lens
– give best optical correction for aphakia , avoid significant magnification and distortion caused by spectacle lenses

• Surgical correction
– Keratorefractive surgery :RK, AK, PRK, LASIK,
ICR, thermokeratoplasty
– Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL

86
Q

Accommodation Mechansims

A

• Accommodation Mechanism
– Contraction of the Circular Ciliary Muscle inside the Ciliary Body
– This relaxes the zonules that are normally stretched between the ciliary body attachment and the lens capsule attachment
– Note that zonules are passive elastic bands with no active contractile muscle
– In the absence of zonular tension, the lens returns to its natural convex shape due to its innate elasticity
– This increases the refractive power of the lens
• Mediated by the efferent Third Cranial Nerve

87
Q

• Which statement is false for Myopia?
– A) May be associated with large globe
– B) Light ray converges behind the retina
– C) May be associated with increased corneal curvature
– D) Unable to see objects clearly at distance without glasses or other optical correction

A

B)

88
Q

Inaccommodation, which one of the following events does not take place?
– A) Relaxation of Circular Ciliary Muscle
– B) Relaxation of Zonules
– C) Thickening of Lens
– D) Increase of Lens Refractive Power

A

A)

Year 2 - LCRS - Neuroscience and Mental Health (21 decks)

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