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Duke Elder > 01 Basic Science, Investigations & Lasers > Flashcards

01 Basic Science, Investigations & Lasers Flashcards

1
Q

What are the four germ layers of the eye?

A

Surface ectoderm

Neuroectoderm

Neural crest

Mesoderm

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2
Q

Which ocular structures make up the surface ectoderm?

A

Conjunctival and corneal epithelium Nasolacrimal duct
Lens
Lacrimal gland
Eyelids

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3
Q

Which ocular structures make up the neuroectoderm?

A

Neurosensory retina
Pigment epithelium of the retina, iris and ciliary body
Pupillary sphincter and dilator muscles
Optic nerve

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4
Q

Which ocular structures make up the neural crest?

A 
Corneal endothelium
Trabecular meshwork
Stroma of cornea, iris and ciliary body
Ciliary muscle
Choroid
Sclera
Orbital cartilage and bone
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5
Q

Which ocular structures make up the mesoderm?

A

Extraocular muscles
Blood vessels
Schlemm’s canal endothelium
Sclera (temporal portion)

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6
Q

Name some autosomal dominant (AD) conditions - ocular and systemic

A 
Congenital cataracts 
Best disease
Fuchs’ corneal dystrophy (also sporadic) 
Granular and lattice corneal dystrophies
Marfan syndrome
Neurofibromatosis
Retinitis pigmentosa (also AR or XLR) Retinoblastoma (most commonly sporadic) Stickler syndrome
Tuberous sclerosis
Von Hippel-Lindau (VHL)
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7
Q

Name some autosomal recessive (AD) conditions - ocular and systemic

A

Congenital glaucoma (most commonly sporadic)
Oculocutaneous albinism
Stargardt disease
Retinitis pigmentosa-like conditions

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8
Q

Name some x-linked recessive (XLR) conditions - ocular and systemic

A

Fabry disease
Lowe syndrome
Ocular albinism
Retinoschisis

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9
Q

Name an x-linked dominant (XLD) condition

A

Alport syndrome (also AR)

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10
Q

Name some mitochondrial diseases

A

Kearns-Sayre syndrome

Leber hereditary optic neuropathy

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11
Q

What is considered to be normal intraocular pressure (IOP)?

A

Within ± 2 standard deviations of the mean IOP, which ranges between 10 and 21 mmHg.

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12
Q

How does IOP change with age and over the day?

A

IOP increases with age

IOP follows a circadian rhythm, with the highest IOP recorded in the morning.

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13
Q

What is meant by diurnal fluctuation and what is the average IOP diurnal fluctuation in normal individuals vs glaucoma patients?

A

Diurnal fluctuation is the change in IOP over the day.

Normal individuals: 2 to 6 mmHg

Glaucoma patients: > 10 mmHg

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14
Q

Name 3 IOP-raising agents

A
  1. Steroids
  2. Tropicamide (close-angle glaucoma)
  3. Ketamine
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15
Q

Name the common IOP-lowering agents used in glaucoma

A
  1. Beta-blockers (e.g. timolol)
  2. Prostaglandin analogue (e.g. latanoprost)
  3. Alpha-2 agonists (e.g. apraclonidine)
  4. Tropical carbonic anhydrase inhibitors (e.g. dorzolamide)
  5. Systemic carbonic anhydrase inhibitors (e.g. acetazolamide)
  6. Miotics (e.g. pilocarpine)
  7. Osmotic agents (e.g. mannitol)
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16
Q

Name some uncommon IOP-lowering drugs

A

a) cannabinoids - short-lasting effects, and tachyphylaxis (reduced response to drug over time)
b) alcohol - transient effect on IOP

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17
Q

How do beta-blockers lower IOP?

A

Decrease aqueous production

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18
Q

How to prostaglandin analogues lower IOP?

A

Increase aqueous drainage via uveoscleral outflow

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19
Q

How to alpha-2 agonists lower IOP?

A

Decrease aqueous production and increase uveoscleral outflow

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20
Q

How do topical carbonic anhydrase inhibitors lower IOP?

A

Decrease aqueous production

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21
Q

How do systemic topical carbonic anhydrase inhibitors lower IOP?

A

Decrease aqueous production

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22
Q

How do miotics lower IOP?

A

Parasympathomimetics that increase aqueous drainage via trabecular meshwork by causing contraction of ciliary muscles

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23
Q

How do osmotic agents lower IOP?

A

Decrease vitreous volume

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24
Q

Name some agents which cause lens opacification and cataracts

A 
Steroids
Amiodarone
Allopurinol
Chlorpromazine
Tobacco smoke
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25
Q

Which drugs are known for causing cystoid macular oedema?

A

Latanoprost
Epinephrine
Rosiglitazone
Nicotinic acid

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26
Q

Which drugs are known for causing Bull’s eye maculopathy?

A

Hydroxychloroquine

Chloroquine

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27
Q

Which drug can cause crystalline maculopathy?

28
Q

Which drugs have the potential to cause optic nerve damage (optic neuropathy)?

A 
Ethambutol
Chloramphenicol
Amiodarone
Vigabatrin (causes binasal visual field defects)
Isoniazid
29
Q

What is vortex keratopathy (corneal verticillata)?

A

Deposition of asymptomatic grey opacities in a vortex pattern on the corneal epithelium

30
Q

Which drugs cause vortex keratopathy?

A

Amiodarone
Chloroquines
Indomethacin
Phenothiazines

31
Q

What is Fabry disease?

A

An XLR condition characterised by a deficiency of alpha-galactosidase A.

  • vortex keratopathy
  • burning pain in extremities
  • angiokeratomas
  • renal failure
  • posterior subcapsular cataracts
32
Q

Name 3 types of investigations to be done on the cornea

A
  1. Keratometry
  2. Corneal topography
  3. Ultrasonic pachymetry
33
Q

What does keratometry do?

A

Measures the anterior corneal surface curvature

34
Q

Describe corneal topography

What it is, how it works, indications

A

Measures and quantifies the curvature of the whole cornea and provides information on its shape.
Uses placido-disc systems which project concentric rings of light on the anterior corneal surface.

Indications - keratoconus, astigmatism, laser eye surgery, contact lens fitting.

35
Q

What is ultrasonic pachymetry?

A

Measures central corneal thickness (CCT) using an ultrasonic probe.

Normal CCT is between 530 and 545 μm.

36
Q

Name 5 investigations that can be used on the retina.

A
  1. Ocular coherence tomography (OCT)
  2. Fluorescence angiography (FA)
  3. Indocyanine green angiography
  4. Fundus autofluorescence
  5. Electrodiagnostic tests
37
Q

Describe OCT

A

Uses near-infrared waves through the pupil to the retina to produce a cross-sectional and three-dimensional image of the retina.

Main indication - diagnose and monitor progression of macular and optic diseases

38
Q

Describe fluorescence angiography (FA)

A

Sodium fluorescence dye is injected into a peripheral vein to circulate to the eye. Passes through the short posterior ciliary artery into the choriocapillaris 8-12 seconds after injection, then enters the retinal circulation 1 second later.

Dye absorbs blue light and emits a yellow-green light. A fundus camera with cobalt blue excitation and yellow-green barrier filters is used to capture images of the retina to detect vascular abnormalities.

39
Q

Describe indocyanine green angiography

A

Uses near-infrared light to visualised the choroid vasculature.

Indocyanine green is 98% bound to albumin in the plasma and has little leakage while passing through the choroid.

40
Q

Describe fundus autofluorescence

A

Detects lipofuscin already present within the retinal pigment epithelium (RPE).

41
Q

Describe electrodiagnostic tests that can be done on the retina.

A

Electroretinogram (ERG) - tests electrical activity of the retina in response to a light stimulus

Electro-oculogram (EOG) - reflects activity of photoreceptors and RPE
—> retinal diseases proximal to the photoreceptors give normal EOG readings

42
Q

What should be done in the investigation of glaucoma to differentiate the type of glaucoma?

A 
Measure IOP
Assess iridocorneal angle
Measure CCT
Evaluate optic nerve head
Assess visual fields
43
Q

What is tonometry?

A

Procedure to measure the IOP.
Follows the Imbert-Fick law to establish the amount of force required to flatten a corneal area of 3.06mm diameter assuming a CCT of 520 μm.

44
Q

What can lead to errors in tonometry?

A

A) Excessive fluorescein - overestimates IOP
B) Low or high CCT - underestimates or overestimates IOP, respectively
C) Astigmatism
D) Calibration errors

45
Q

What is gonioscopy?

A

Determines whether the iridocorneal angle is open or closed.

Visualisation of all structures indicates a wide-open angle.

Inability to visualise any structures indicates a closed angle.

46
Q

Which structures should be visualised in gonioscopy? (anterior - posterior)

A
  • Schwalbe line
  • Non-pigmented trabecular meshwork
  • Pigmented trabecular meshwork (not present at birth, increases with age)
  • Scleral spur (anterior protrusion of sclera that marks the attachments of the ciliary body’s longitudinal fibres)
  • Ciliary body
47
Q

What is perimetry?

A

Detects visual field defects and is commonly used in glaucoma and neuro-ophthalmic conditions.

E.g. Humphrey visual field analysis, Goldmann visual field testing

48
Q

Give examples of glaucomatous field defects.

A
  • Nasal step
  • Paracentral depressions (most commonly superonasally)
  • Arcuate defects (combination of paracentral depressions)
  • Ring scotoma (superior and inferior arcuate defects)
  • Tunnel vision with a temporal sparing of visual field
49
Q

Which investigations can be used in neuro-ophthalmology and for the orbit?

A

Magnetic resonance imaging (MRI)

Computerised tomography (CT)

50
Q

What is MRI?

A

Scans produced by the alignment of the hydrogen atoms to the magnetic field around the patient.

Useful in aiding the diagnosis of intracranial lesions affecting the visual pathway

51
Q

What is CT?

A

Series of x-ray beams which form a detailed image of the body with the aid of a computer.
Common indications:
- orbital fractures
- orbital cellulitis
- thyroid eye disease
- cerebral haemorrhages
- investigate for subarachnoid haemorrhages and intracranial aneurysms, for example, in cases of 3rd nerve palsy

52
Q

Where is melanin mainly found?

A

RPE and choroid

- absorbs most of the visible spectrum and infrared wavelengths

53
Q

Where is xanthophyll found?

A

Macula.

Absorbs blue light.

54
Q

Which light wavelengths does haemoglobin absorb?

A

Absorbs blue, green (495-570nm) and yellow light (570-590nm)

55
Q

What is photovaporisation?

A

Vaporisation of water from tissues which occurs in lasers such as CO2 lasers, as they raise the temperature above 100°C

56
Q

What is photocoagulation?

A

Absorption of laser emissions by tissues causes a rise in temperature, leading to protein denaturation.

E.g. panretinal photocoagulation (PRP) used in diabetic retinopathy

57
Q

What are photochemical lasers?

A

Work by using ultraviolet light to break chemical bonds that hold tissue together in a process called photoablation.
Important uses in refractive surgery.

  • Photorefractive keratectomy (PRK): corneal epithelium is first removed then laser ablation is used to reshape the cornea.
  • Laser-assisted in situ keratomileusis (LASIK): corneal flap is created, stroma is then ablated to reshape cornea, then flap is replaced.
  • Laser epithelial keratomileusis (LASEK): corneal epithelium is peeled using 20% ethanol, laser ablation is performed and epithelium is replaced.
58
Q

What are photo-ionising lasers?

A

Laser causing destruction of tissues by altering the stable state between photons and electrons.

E.g. used in peripheral iridotomy for managing angle-closure glaucoma.

59
Q

Define sight impairment in terms of visual acuity (VA) and visual fields (VF).
[3 different variations]

A

A) VA 3/30 - 3/60, with full VF

B) VA 6/60 - 6/24, with moderate VF reduction

C) VA ≥6/18 with significant VF reduction (e.g. homonymous hemianopia)

60
Q

Define severe sight impairment (blindness) in terms of visual acuity (VA) and visual fields (VF).
[3 different variations]

A

A) VA < 3/60

B) VA 3/60 - 6/60 with VF reduction

C) VA >6/60 with significantly reduced VF (e.g. inferior altitudinal defects or bitemporal hemianopia)

61
Q

Which cases must be notified to the DVLA?

A

Diplopia (may resume driving after diplopia is controlled)

VF defects —> retinitis pigmentosa, bilateral glaucoma, bi-temporal hemianopia

Nyctalopia

Blepharospasm (even if treated)

62
Q

What is the minimum visual acuity for drivers according to the DVLA?

A

6/12 with both eyes open, or one eye if monocular.

63
Q

Which sutures are absorbable?

A

Polyglactin 910 (VICRYL)

Polyglycolic acid (DEXON)

64
Q

What are some non-absorbable sutures?

A

Silk
Nylon
Polypropylene

65
Q

Which 5 conditions were in the objectives for Vision 2020 (established by the International Agency of the Prevention of Blindness)?

A

Cataract - most common cause of worldwide blindness

Trachoma - most common cause of infectious blindness

Onchocerciasis - 2nd most common cause of infectious blindness

Refractive errors - most common cause of visual impairment

Childhood blindness due to: vit. A deficiency, measles, retinopathy of prematurity (ROP), cataract

Duke Elder (16 decks)

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