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H+N and Dermatology > Special Senses: Eye > Flashcards

Special Senses: Eye Flashcards

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Dermatology Board Prep flashcards
1
Q

What are the histological layers of the Cornea?

A

1 - Epithelium

2 - Bowman’s membrane

3 - Stroma

4 - Descemet’s Layer

5 - Endothelium

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2
Q

How is Transparency maintained in the Cornea?

A
  • Histologically: regular arrangemnt of collagen in the stroma
  • No blood vessels (!!!)
  • Endothelium cell layer: has a pump that actively keeps the aqueous humor out
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3
Q

Why is the healing of wounds not ideal in the Cornea?

A

Because it leads to loss of corneal transparency (corneal opacity)!!!

-> This is bc the healing of wounds in the cornea leads to fibrous tissue being laid down

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4
Q

Why is the Cornea an “immune-privileged” site?

A
  • Bc of the avascularity of the Cornea -> aids in corneal transplants because there is a lesser chance of graft rejection by the recipient
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5
Q

What are the most important layers in the Retina?

A
  • Nerve fibre layer (layer 9)
  • Layer of Rods + Cones (layer 2)
  • Pigment Epithelial layer (layer 1)
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6
Q

What is the function fo the Choroid?

A

Choroid supplies outer layers of Retina with blood (nutrients and oxygen) by diffusion

(itself is supplied by the short posterior ciliary arteries)

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7
Q

Where does the Retina get its blood supply from?

A
  • The Choroid (outer layers)

- The Central Retinal Artery (inner layers)

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8
Q

What is the Fovea Centralis?

A

Point of maximum visual acuity in the retina of the eye

-> (packed with cones!)

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9
Q

What is the Lens?

A
  • Transparent, crystalline biconvex structure
  • Suspended by zonules from the ciliary body
  • Able to change shape (ie. becomes less or more convex)
  • Transparent
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10
Q

What is Lens opacification called? What predisposes it to becoming opaque later in life?

A
  • Lens opacification = cataracts
  • Because it is avascular!!

-> therefore, it only obtains its nutrition from aqueous and vitreous humor and is surrounded by it
(+ due to lack of blood vessels, is less able to re-absorb fluid from the eye -> lens opacification)

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11
Q

What are the functions of the Tear film?

A
  • Keeps cornea moist: prevents drying
  • Washes away any particulate foreign bodies
  • Has antibodies and lysozymes to kill microbes
  • Smooths outer surface of Cornea -> provides smooth surface for refraction
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12
Q

What is the structure of the Tear film?

A
  • 3 layers*
  • Layer 3: oily layer (most superficial)
  • Layer 2: aqueous layer (lies over mucinous layer)
  • Layer 1: mucinous layer (overlies corneal epithelium)
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13
Q

What allows you to clinically “see” the Tear film?

A

With a Fluorescein dye

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14
Q

Which nerve is responsible for the secretion of tears?

A
  • Cranial Nerve VII (Facial Nerve)

- > autonomic innervation to the Lacrimal gland

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15
Q

What stimulates blinking?

A
  • During blink: the sharp lower border of the upper eyelid distributes the tear film evenly
  • When eyelids open, the aqueous layer (layer 2) of tears begins to evaporate -> oily layer (layer 3) comes into contact with mucinous layer (layer 1)
  • The tear film breaks up (point of ocular discomfort) when these 2 layers touch -> stimulates further blinking
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16
Q

What is refraction?

A
  • Bending of light when it passes from one optical medium (an object) to another
  • > light rays bend to form a sharp image on the retina
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17
Q

How does the eye allow for Refraction?

A

Cornea, AH, Lens, VH are all transparent to allow light to fall on Retina

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18
Q

What is meant by Accomodation?

A

Accommodation is the adjustment of the optics of the eye to keep an object in focus on the retina as the object’s distance from the eye varies

ie. a closer-up object requires more bending power than a further-away object to bring the object into focus, so therefore the lens becomes thicker and hence more powerful, and a clear image is formed on the retina again

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19
Q

What are the ways in which the eyes change to accommodate for different objects?

A
  • The Lens changes shape
  • > becomes thicker and more speherical
  • Pupils constrict
  • Eyes converge
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20
Q

What muscles causes the Lens to change shape when accommodating for closer up objects?

A
  • Ciliary body muscle contraction
  • Parasympathetic via CN III)
  • Suspensory ligaments become lax
  • Lens becomes thicker and more spherical
  • Thicker lens is more powerful -> can focus more on close objects
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21
Q

What muscle causes Pupillary constriction when accommodating for closer up objects?

A
  • Sphinctor Pupillae contraction
  • > concentric muscle in the iris of the eye, at the border of the pupil
  • Parasympathetic via CN III
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22
Q

What muscle causes Eye convergence when accommodating for closer up objects?

A
  • Medial rectus muscle contraction

- via CN III

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23
Q

What causes refractive errors?

A

Occurs when there is a mismatch between how much we bend light rays

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24
Q

What is Myopia?

A

Short-sightedness

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25
Q

What causes Myopia?

A

Eyeball is too long or too big

  • > (eyeball is a wee bit squished already)
  • > therefore, cornea and lens bend the rays of light when it falls on the retina, + the image forms in front of the retina -> far off objects not clearly seen
  • > eyeball is a bit squished, so naturally is more able to see closer up objects effectively
  • > alternatively: “bending power” of cornea and lens is too much for the eyeball and can only see closer up objects clearly
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26
Q

Which parts of the eye are responsible for refraction?

A
  • Cornea
  • > (most powerful “bender” of light (45D))
  • Lens
  • > (has the capacity to change its “bending power” (15D))
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27
Q

What are the symptoms of Myopia?

A
  • Headaches
  • Complain of not being able to see blackboard/distant objects
  • Infants and preverbal children: divergent squint
  • > (eyes diverge when trying to look at further away objects)
  • Toddlers: loss of interest in sports/people, more interest in books, pictures
  • Teachers may notice child losing interest in class
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28
Q

How do you correct Myopia?

A
  • Bending power needs to be decreased
  • Biconcave lenses:
    -> spectacles
    -> contact lenses
    -> laser eye surgery
    (flattens the lens -> can get more light rays in and can see more further away)
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29
Q

What is Hyperopia?

A

Farsightedness

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30
Q

What causes Hyperopia?

A
  • Eyeball too short

(eyeball is a wee bit elongated)

or

  • Cornea + Lens too flat
  • > The image of the distant object is formed behind the retina
  • > person uses accommodative powers to make lens thicker to form image on the retina
  • > they are using accommodative powers to see further away things when they shouldn’t need them
  • > therefore, when viewing closer objects, they are unable to use accommodation to view them as power is all used up on distant objects
  • > hence, long-sightedness (can’t see nearby objects)
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31
Q

What is Emmetropia?

A
  • Just the right length to allow light to reach the retina for clear vision
  • 20/20 vision
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32
Q

What are the symptoms of Hyperopia?

A
  • Eyestrain after reading/ working on the computer (young people)
  • Convergent squint in children toddlers
    (eyes converge when trying to see closer up things!)
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33
Q

How do you correct Hyperopia?

A
  • Convergent squint in children: needs immediate correction with glasses/lenses to preserve vision in both eyes to prevent “lazy eye:
  • Biconvex glasses
  • > (spherical lens)
  • > rests accommodative power without actually affecting the lens
  • > allows u to see closer up things more clearly
  • Contact lenses
  • Laser eye surgery
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34
Q

What is Presbyopia?

A

Long-sightedness of old age

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35
Q

What causes Presbyopia?

A
  • With age the lens becomes less mobile/elastic
  • Therefore, when ciliary muscle contracts, it is less able to change the shape of the lens -> loss of accommodative powers
  • Therefore, seeing nearby objects/reading newspapers becomes more difficult without glasses
  • Usually starts in the 5th decade of life
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36
Q

How do you correct Presbyopia?

A

By using Biconvex “reading” glasses!!!

  • > (spherical lens)
  • > rests accommodative power without actually affecting the lens
  • > allows u to see closer up things more clearly
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37
Q

What is Astigmatism?

A
  • > Astigmatism means your eye is shaped more like a rugby ball than a football
  • > Surface has different curvatures with different meridians (mismatched curves of the eye)
  • > Therefore, light is focused at more than 1 place in the eye (and not on the fovea!) -> this causes the image formed to be always hazy, no matter the distance of the object
38
Q

How do you correct Astigmatism?

A
  • Cylindrical glasses (special glasses
  • > curved only in one axis
  • > allows light to focus only in one point of the eye
  • Toric lenses (special contact lenses)
  • Laser eye surgery
39
Q

What is phototransduction?

A
  • The process whereby light energy is converted to an electrochemical response by the photoreceptors (rods + cones)
  • The phototransduced rods + cones need to activate optic nerve cells to generate an AP
40
Q

What is the function of rods?

A

Rods are responsible for vision at low light

41
Q

What is the function of cones?

A

Cones are responsible for colour vision and vision at bright light

42
Q

Summarise the phototransduction cascade

A
  • Photoreceptor cells (rods) at rest (in the dark) are kept in a depolarised state by open Na+ and Ca2+ channels
  • Photon of light activates Rhodopsin
  • activated Rhodopsin converts Transducin-GDP to Transducin GTP
  • Transducin GTP activates Phosphodiesterase (PDE)
  • Activated PDE converts cGMP to GMP
  • GMP closes Na+ channels -> RELATIVE HYPERPOLARISATION OF PHOTORECEPTOR CELL
  • Hyperpolarisation is transmitted by a flux of Ca2+ ions into the cell to the synapse with bipolar cell
  • Ultimately reaches retinal cell (optic nerve)
43
Q

What is the the role of Vitamin A in phototransduction?

A
  • Vitamin A (retinol) turns into Retinal in the Pigment Epithelial cell
  • Retinal then combines with Opsin in Photoreceptor cells to form Rhodopsin
    (therefore: Vit A is a precursor of Rhodopsin, which is required for phototransduction!)
44
Q

What does Vit A deficiency cause in the eye?

A
  • Night-blindness
  • > required for vision
  • Also abnormal conjunctivae and cornea
  • > (bc Vit A is responsible for normal epithelium)
45
Q

What are the clinical signs of Vit A deficiency in the eye?

A
  • Bitot’s spots
  • Corneal ulceration
  • Corneal melting
  • Opacification of Cornea
  • > due to healing by fibrosis of corneal melting
46
Q

In which conditions can Vit A deficiency occur?

A
  • Malnutrition
  • Malabsorption syndrome:
    ie. Coeliac disease, Sprue
47
Q

What would occur if Right Optic nerve is damaged?

A

Blindness in Left eye

48
Q

What would occur if Optic Chiasm is damaged?

A

Bitemporal Hemianopia

  • > loss of temporal half of both visual fields (“tunnel vision”)
  • > as this is where nasal fibres cross over (responsible for viewing the temporal sides of both visual fields)
49
Q

What would occur if Right Optic Tract is damaged?

A

Left Homonymous Hemianopia

-> damage to left visual field of both eyes

50
Q

What would occur if Optic Radiation is damaged?

A

Left Homonymous Hemianopia

-> damage to left visual field of both eyes

51
Q

What occurs at the Optic Chiasm?

A
  • Where optic nerves come back from the eyes and meet on the inferior
    surface of the brain → sits just superior to the Pituitary Fossa in the Sphenoid bone
  • This is also where nasal fibres cross over (view TEMPORAL half of both visual fields)
52
Q

What occurs at the Optic Tract?

A

Contains fibres from the (lateral) temporal half of the ipsilateral eye and the crossed-over nasal fibres from the contralateral eye (corresponds to all fibres from the opposite half of the visual field)

53
Q

What occurs at the LGB (Thalamus) ?

A

Where fibres from the Optic tract synapse

54
Q

Where is the Primary Visual Cortex?

What occurs there?

A
  • Occipital Lobe (Area 17)
  • Fibres reach here from the Optic radiation, which passes from the LGB (Thalamus), behind the Internal capsule (retro-lentiform fibres)
55
Q

What is Strabismus?

What are the different types of Strabismus?

A
  • Misalignment of the eyes (typically due to a problem with the eye muscles)
  • Esotropia = convergent squint
  • Exotropia = divergent squint
56
Q

What are the functional consequences of Strabismus?

A
  • Amblyopia (“lazy eye”)
  • > where brain suppresses the image of one eye leading to poor vision in that eye without any pathology (correctable in the early years using eye patches to stimulate the “lazy” eye to work)
  • Diplopia (double vision)
  • > usually occurs in squints occurring as a result of nerve palsies
57
Q

What are the intrinsic muscles of the eye?

A
  • Ciliaris muscle -> in ciliary body
  • Constrictor pupillae -> in iris at pupillary border
  • Dilator pupillae -> radially running muscle in iris
58
Q

What is the innervation to the intrinsic muscles of the eye?

A
  • Ciliaris muscle and Constrictor pupillae = parasympathetic via CN III
  • Dilator pupillae = sympathetic (plexus around blood vessels)
59
Q

What is the pupillary reaction to light?

A
  • Increased illumination -> parasympathetic -> both pupils constrict
  • Decreased illumination -> sympathetic -> pupils dilate
60
Q

How do you elicit the pupillary light reflex?

A
  • Start in dimly lit room (pupils dilated)
  • Shine pen torch in one of the eyes -> check that BOTH pupils are constricting
  • Swing light to the other eye and BOTH eyes should remain constricted
61
Q

Why are both eyes constricted in the pupillary light reflex?

A
  • When light falls on retina -> goes through optic nerve to optic chiasm to optic tract
  • Fibres destined for the pupillary light reflex do not go to the LGB, but instead go to the EWN (where CN III nucleus is situated -> in the midbrain)
  • The fibres go to the EWN of BOTH sides -> then goes through preganglionic fibres going to the ciliary ganglion of both eyes -> then post-ganglionic fibres from the ciliary ganglion go to constrictor pupillae of both sides -> constrictor pupillae contracts -> pupillary constriction of both sides
62
Q

What are the most common pupillary abnormalities?

A
  • Aniscoria: pupils of different sizes (ie. in Horner’s syndrome)
  • Abnormal light reflex: pupils may look normal but react abnormally to light
63
Q

What are some common causes of absent/abnormal Pupillary Reflex?

A
  • Diseases of the retina
  • > detachment/degenerations or dystrophies
  • Diseases of the optic nerve: ie. optic neuritis (MS)
  • Diseases of CN III (efferent limb), ie. diabetes, cerebral artery aneurysm
64
Q

How to tell the difference between Diabetes and Cerebral Artery Aneurysm when a pt. presents with a CN III palsy?

A
  • Check pupillary reflex!
  • Diabetes spares parasympathetic fibres, whereas CAA does not!
  • Therefore, if you suspect a CN III palsy and pupillary reflex is absent -> MEDICAL EMERGENCY!!!
65
Q

What causes Aniscoria in Horner’s syndrome?

What other features are present alongside it?

A
  • Damage to the sympathetic innervation to the eye (ie. cannot dilate pupil)
    -> ie. due to a Pancoast tumour
    (excessive constriction of pupil = Miosis)
  • You may also see: Ptosis (drooping of eyelid) and Anhidrosis (loss of sweating on the affected side)
66
Q

What is Cataracts?

A
  • Lens opacification

- Most common cause of blindness worldwide

67
Q

What are the different types of Cataracts?

A
  • Congenital cataracts ie. sutural, zonular cataracts (bilateral)
  • Steroid-induced Cataracts
  • Traumatic Cataracts
  • Nuclear Sclerotic Cataracts
68
Q

What is the management of Cataracts?

A
  • Eye drops do not treat Cataracts (!!!)

- Surgery: (day case) PCIOL (Posterior Chamber Intra-Ocular Lens) -> lens implant after cataract surgery

69
Q

What fluid is present in the Anterior vs. Posterior segment of the eye?

A
  • Anterior Segment (includes anterior + posterior chamber) = Aqueous humour
  • Posterior Segment = Vitreous humour
70
Q

What is Glaucoma?

A

A group of eye conditions that damage the optic nerve

71
Q

What is the leading cause of blindness worldwide?

What is second?

A
  • Cataracts

- Glaucoma

72
Q

What is the most common type of Glaucoma?

A

Primary Open-Angle Glaucoma (POAG)

73
Q

What is the cause of Glaucoma?

A

Raised Intra-Ocular Pressure (IOP)

74
Q

What are the clinical features of Glaucoma?

A

Triad

  • Raised IOP
  • > puts pressure on nerve fibres on the surface of the retina, causes them to die out
  • Visual field defects
  • > changes to optic disc may result in blindness
  • Optic disc changes on Ophthalmoscopy
  • > optic disc appears pale, cupped due to raised IOP (as nerve fibres are dying out)
75
Q

What is the management of Glaucoma?

A
  • Eye drops to decrease IOP
  • > prostaglandin analogues
  • > beta blockers
  • > carbonic anhydrase inhibitors
  • Laser trabeculoplasty
  • Trabeculectomy surgery
  • basically all aim to drain aqueous humour from the eye/ reduce aqueous humour production*
76
Q

What are the clinical features of Angle-Closure Glaucoma?

A
  • Sudden onset, painful, vision lost/blurred, headaches (!!!) (often confused with migraine)
  • Red eye, cornea often opaque as raised IOP drives fluid into the Cornea
  • Slit-lamp: shallow Anterior Chamber, angle is closed
  • Pupil mid-dilated
  • IOP severely raised
77
Q

What is the mechanism of Angle Closure Glaucoma?

A
  • Functional block in a small eye -> large lens
  • Mid-dilated pupil -> periphery of iris crowds around the angle and outflow is obstructed
  • Iris sticks to pupillary border (synechia) which prevents fluid from reaching the anterior chamber -> iris balloons anteriorly and obstructs angle
78
Q

What is the management of Angle Closure Glaucoma?

A

MEDICAL EMERGENCY

(initial)

  • Decrease IOP:
  • > IV Acetazolamide (carbonic anhydrase inhibitor
  • > Topical pilocarpine (constricts pupils)
  • > Beta-blockers
  • > Steroids

(then consider)

  • Iridotomy (laser):
  • > BOTH eyes
  • > to bypass the blockage
79
Q

What is the difference between Open-angle and Angle-closure glaucoma?

A
  • In open-angle glaucoma or POAG): the drainage through the trabecular meshwork is partially blocked (in most cases) -> this leads to a gradual (!!!) painless build-up of IOP
  • > In angle-closure glaucoma: some events on a predisposed eye lead to the peripheral iris blocking the angle, therefore aqueous humour can’t drain (AT ALL) -> so the increase in IOP is sudden and leads to a red eye and severe pain -> pt. is usually treated as an emergency
80
Q

What are the most common inflammatory and non-inflammatory causes of cornea disorders?

A
  • Inflammatory = corneal ulcers

- Non-inflammatory = corneal dystrophies

81
Q

What is the most common treatment of corneal disorders?

A
  • Laser: Phototherapeutic Keratectomy (re-shapes the cornea, removes scar tissue)
  • Keratoplasty! (corneal transplant) -> nb. “immune-privileged” site!
  • remember: corneal damage heals by fibrosis -> leads to opacification of the cornea (= no bueno!!) -> need to remove it with keratectomy or keratoplasty*
82
Q

What are the most common causes of corneal ulcers?

A
  • Infectious (!!!): viral, bacterial, fungal infection of cornea
  • Non-Infectious: trauma, corneal degenerations or dystrophy
83
Q

What are Corneal dystrophies/ degenerations?

A

A group of diseases affecting the cornea which are:

  • Bilateral
  • Opacifying
  • Non-inflammatory
  • Mostly genetically determined
  • Sometimes due to the accumulation of substances (ie. Lipids) in the cornea
84
Q

What is the clinical presentation of Corneal dystrophies/ degenerations?

A
  • 1st-4th decade
  • Most commonly: decreased vision
  • Start in one of the layers of the cornea and spread to the others
85
Q

What are the types of Uveitis?

A
  • Vascular layer of the Eye = Uvea*
  • Anterior Uveitis: iris with or without ciliary body inflamed
  • Intermediate Uveitis: ciliary body inflamed
  • Posterior Uveitis: choroid inflamed
86
Q

What forms the vascular layer of the eye? (Uvea)

A
  • Choroid
  • Ciliary body
  • Iris
87
Q

What are the causes of Uveitis?

A
  • Isolated illness
  • Non-infectious auto-immune causes: presence of HLA-B27 predisposes to anterior uveitis (ankylosing spondylitis)
  • Infectious causes: chronic diseases ie. TB
  • Associated with systemic disease: (ie. ankylosing spondylitis)
88
Q

What is Conjunctivitis?

A

Self-limiting bacterial or viral infection of the conjunctiva

89
Q

What are the clinical features of Conjunctivitis?

A
  • Red, watering eyes + discharge

- no loss of vision if it does not spread to the cornea

90
Q

What is the treatment of Conjunctivitis?

A
  • Most require no treatment

- abx eye drops (if likely to be bacterial)

91
Q

What causes a Stye (Hordeolum)?

A

Blockage of either the…

  • Sebaceous glands of the eyelash (external)
  • Meibomian glands (internal)
92
Q

What is the treatment of styes/hordeolums?

A
  • Warm compress
  • Eyelid hygiene
  • May need surgical excision and curettage (if severe)

H+N and Dermatology (16 decks)

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