Investigations

Question 1

What is keratometry used for?

Answer 1

Measured the anterior corneal surface curvature

Question 2

What is corneal topography?

Answer 2

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

Question 3

How does corneal topography work?

Answer 3

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

Question 4

When would corneal topography be indicated as an appropriate investigation?

Answer 4

Keratoconus
Astigmatism
Laser eye surgery
Contact lens fitting

Question 5

What is ultrasonic pachymetry?

Answer 5

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

Question 6

What is a normal central corneal thickness?

Answer 6

530-545 micrometres. (um)

Question 7

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

Answer 7

Ocular coherence tomography

Question 8

How does ocular coherence tomography work/

Answer 8

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

Question 9

When is fluorescence angiography used?

Answer 9

When looking to detect vascular abnormalities or problems.

Question 10

How does fluorescence angiography work?

Answer 10

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.

Question 11

What are some side effects of fluorescence angiography?

Answer 11

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

Question 12

How does sodium fluorescence dye work?

Answer 12

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

Question 13

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

Answer 13

Fundus auto fluorescence

Question 14

When is fundus auto-fluorescence the most appropriate investigation?

Answer 14

Best disease

Monitoring geographic atrophy

Question 15

What is indocyanine green?

Answer 15

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

Question 16

What does Indocyanine green angiography use?

Answer 16

Infrared light

Question 17

What is indocyanine green angiography used for?

Answer 17

Better at visualising the choroid vasculature.

Question 18

When is indocyanine contraindicated?

Answer 18

Pregnancy
Seafood allergy
Iodine allergy

Question 19

What investigation is used to measure the intraocular pressure?

Answer 19

Tonometry

Question 20

What does an electroretinogram test?

Answer 20

Electrical activity of the retina in response to a light stimulus

Question 21

How does an electrooculogram work?

Answer 21

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

Question 22

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

Answer 22

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

Question 23

What is gonioscope?

Answer 23

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

Question 24

How do you differentiate between an open and closed angle?

Answer 24

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

Question 25

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

Answer 25

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

Question 26

What is the scleral spur?

Answer 26

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

Question 27

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

Answer 27

Perimetry e.g. Humphrey visual field testing

Question 28

List the visual field defects associated with glaucoma:

Answer 28

``` Nasal step Paracentral depressions Arcuate defects Ring scotoma tunnel vision with central vision sparing ```

Question 29

When might MRI be useful?

Answer 29

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

Question 30

What would be reasonable indications for CT investigations?

Answer 30

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

Question 31

What are the 3 fundamental properties of lasers?

Answer 31

Monochromaticity coherency Collimation

Question 32

How does melanin respond to lasers?

Answer 32

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

Question 33

How does xanthophyll react to lasers:

Answer 33

(Found in the macula of the eye) | Absorbs blue light wavelengths

Question 34

How does Haemoglobin respond to lasers?

Answer 34

Absorbs green and yellow light

Question 35

How does a photochemical laser work?

Answer 35

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

Question 36

How does a photoionizing laser work?

Answer 36

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

Question 37

When is photo-ionizing laser's used?

Answer 37

Treats posterior capsule opacification | Peripheral iridotomy used in managing closed angle glaucoma.

Question 38

How do photothermal laser's work?

Answer 38

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.

Question 39

When is photocoagulation laser therapy used?

Answer 39

Diabetic retinopathy

Question 40

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

Answer 40

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