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Duke Elder Exam Prep > Investigations > Flashcards

Investigations Flashcards

1
Q

What is keratometry used for?

A

Measured the anterior corneal surface curvature

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2
Q

What is corneal topography?

A

Measures and quantifies the curvature of the entire cornea and provides info on its shape.

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3
Q

How does corneal topography work?

A

Uses placido-disc systems which project concentric rings of light on the anterior corneal surface.

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4
Q

When would corneal topography be indicated as an appropriate investigation?

A

Keratoconus
Astigmatism
Laser eye surgery
Contact lens fitting

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5
Q

What is ultrasonic pachymetry?

A

This is used to measure central corneal thickness using an ultrasonic probe.

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6
Q

What is a normal central corneal thickness?

A

530-545 micrometres. (um)

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7
Q

What investigation is used to diagnose and monitor macular and optic disease progression?

A

Ocular coherence tomography

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8
Q

How does ocular coherence tomography work/

A

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

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9
Q

When is fluorescence angiography used?

A

When looking to detect vascular abnormalities or problems.

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10
Q

How does fluorescence angiography work?

A

Sodium fluorescence dye is injected into the peripheral vein to e circulate to the eye - it passes through the short ciliary artery and into the choriocapillaris in about 8-12s post injection, then enters the retinal circulation moments after.

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11
Q

What are some side effects of fluorescence angiography?

A 
Discolouration of the urine
Nausea
Vasovagal syncope
Anaphylaxis
DO not give in shellfish allergy
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12
Q

How does sodium fluorescence dye work?

A

It absorbs blue light and emits yellow green light which is detected by a fundus camera with cobalt blue excitation and yellow green barrier filters

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13
Q

What type of retina imaging does not use dye but instead detects the already present lipofuscin on the retinal pigmented epithelium?

A

Fundus auto fluorescence

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14
Q

When is fundus auto-fluorescence the most appropriate investigation?

A

Best disease

Monitoring geographic atrophy

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15
Q

What is indocyanine green?

A

This is a dye which is 98% bound to albumin in the plasma and barely leaks when passing through the choroid.

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16
Q

What does Indocyanine green angiography use?

A

Infrared light

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17
Q

What is indocyanine green angiography used for?

A

Better at visualising the choroid vasculature.

18
Q

When is indocyanine contraindicated?

A

Pregnancy
Seafood allergy
Iodine allergy

19
Q

What investigation is used to measure the intraocular pressure?

A

Tonometry

20
Q

What does an electroretinogram test?

A

Electrical activity of the retina in response to a light stimulus

21
Q

How does an electrooculogram work?

A

it reflects the activity of the photoreceptors and retinal pigmented endothelium.
Useful in aiding diagnosis of Best disease and retinitis pigmentosa

22
Q

What investigations would be appropriate when differentiating between different types of glaucoma?

A

IOP
Iridocorneal angle
central corneal thickness
examine optic nerve head and visual field

23
Q

What is gonioscope?

A

This investigation is used to measure whether the iridocorneal angle is open or closed.

24
Q

How do you differentiate between an open and closed angle?

A

If you can visualise all the structures of the angle then it is open, if you cannot visualise any structures the angle is closed.

25
Q

What are the structures of the iridocorneal angle (anterior to posterior)

A 
Schwalbe line
Non pigmented trabecular meshwork
pigmented trabecular meshwork (pigment not present at birth, increases with age.)
Scleral spur
ciliary body
26
Q

What is the scleral spur?

A

This is an anterior protrusion of the sclera which marks the attachment of the ciliary body’s longitudinal fibres.

27
Q

What is used to test visual field defect, and is commonly used in glaucoma and neuro-ophthalmic conditions?

A

Perimetry e.g. Humphrey visual field testing

28
Q

List the visual field defects associated with glaucoma:

A 
Nasal step
Paracentral depressions 
Arcuate defects
Ring scotoma 
tunnel vision with central vision sparing
29
Q

When might MRI be useful?

A

When determining if there are any intracranial lesions affecting the visual pathway

30
Q

What would be reasonable indications for CT investigations?

A 
Cerebral and subarachnoid haemorrhage
Orbital fracture
Orbital cellulitis
Thyroid eye disease
Third nerve palsy (could be intracranial lesion/aneurysms)
31
Q

What are the 3 fundamental properties of lasers?

A

Monochromaticity
coherency
Collimation

32
Q

How does melanin respond to lasers?

A

Absorbs most of the light on the visible spectrum and infrared wavelengths
Found mainly in the RPE and choroid

33
Q

How does xanthophyll react to lasers:

A

(Found in the macula of the eye)

Absorbs blue light wavelengths

34
Q

How does Haemoglobin respond to lasers?

A

Absorbs green and yellow light

35
Q

How does a photochemical laser work?

A

Breaks down the chemical bonds which hold the tissue together by using UV light.
This process is called photoablation.
Has important uses in refractive surgery

36
Q

How does a photoionizing laser work?

A

This type of laser causes the destruction of tissues by altering the stable state between photons and electrons.

37
Q

When is photo-ionizing laser’s used?

A

Treats posterior capsule opacification

Peripheral iridotomy used in managing closed angle glaucoma.

38
Q

How do photothermal laser’s work?

A

Two forms:
Photovapourisation - Carbon dioxide lasers cause water to evaporate from the tissues by heating it to over 100 degrees.
Photocoagulation: Tissues absorb the laser emissions, causing a rise in temperature which in turn leads to protein denaturation and causes coagulation.

39
Q

When is photocoagulation laser therapy used?

A

Diabetic retinopathy

40
Q

Give some examples of photocoagulation lasers and what might absorb them:

A

Argon blue green - not used on macula as absorbed by melanin, haemoglobin and xanthophyll
Krypton red - absorbed by melanin
Frequency doubled Nd:YAG - absorbed by Hg and melanin
Diode - absorbed by melanin

Duke Elder Exam Prep (18 decks)

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