Ocular Imaging and Tests

Question 1

Importance of ocular imaging?

Answer 1

1. It allows findings from clinical ocular examination to be recorded in an objective, reproducible, transmissible and durable manner.
2. It also facilitates identification of anatomical and disease features that are not readily visible with standard examination techniques, and enables sophisticated quantitative analyses.

Question 2

Common ocular imaging tests?

Answer 2

1. Optical coherence tomography
2. Ultrasonography
3. Retinal imaging (Fundus photography)
4. Fluorescein angiography
5. Indocyanine green angiography
6. CT scan and MRI

Question 3

What is optical coherence tomography?

Answer 3

OCT provides a cross sectional image of the anterior eye and retina in-vivo with a high resolution, similar to a histological section.

Question 4

Uses of OCT?

Answer 4

OCT allows assessment of retinal disease, understanding of pathology and correlations between structure and function

Question 5

How OCT works?

Answer 5

Uses light instead of ultrasound to form an image.

Question 6

OCT allows detection and measurement of?

Answer 6

1. Morphological changes in retina
2. Retinal thickness
3. Retinal volume
4. Retinal nerve fiber layer thickness (RNFL)
5. Various parameters of the optic nerve head (ONH)

Question 7

What is ultrasonography?

Answer 7

Ultrasound is acoustic energy with frequencies above the audible limit.

Question 8

Types of ultrasonography?

Answer 8

1. A scan
2. B scan
3. Ultrasound biomicroscopy (UBM)
4. Colour flow mapping and spectra dopler technique

Question 9

Describe an ocular and orbital ultrasound?

Answer 9

Very high frequencies, low energy and short duration ultrasonic pulses are transmitted into the ocular and orbital structures from a probe via a coupling agent
- In time interval between pulse transimissions, reflections from tissues are received by same probe and signals can be used to produce of images.

Question 10

What is an A scan?

Answer 10

A-scan(short for Amplitudescan), is routine type of diagnostic testusedin optometry or ophthalmology
- The A-scanprovides data on the length of the eye, which is a major determinant in common sight disorders
- Produces a graphical output echo amplitude vs distance in the eye

Question 11

Indications for A scan?

Answer 11

1. Anterior chamber depth
2. Axial length of the eye

Question 12

What is a B scan?

Answer 12

B-scan Ultrasonography, often called justB-scanor Brightnessscan, offers two-dimensional cross-sectional view of the eye as well as the orbit
- AB-scanis used on the outside of the closed eyelid to view the eye.
- Produces cross-sectional images of the orbital and ocular tissues

Question 13

Indicatiosn for B scan?

Answer 13

1. Retinal detachments
2. Orbital tumors(choroidal melanoma)
3. Dense cataracts
4. Intraocular foreign bodies

Question 14

Features of an A scan?

Answer 14

1. amplitude modulation scan
2. frequency of ultrasound is 8 mhertz
3. one dimensional image of spikes of varying amplitudes along baseline
4. emits unfocused beam
5. provides quantitative information’s
6. is a basis of ocular biometry

Question 15

Features of a B scan?

Answer 15

1. brightness modulation scan
2. frequency of ultrasound is 10 mhertz
3. 2 dimensional imaging of series of dots and lines that form the ecogram
4. emits focused beam
5. provides topographic information’s
6. allows real time evaluation of any ocular pathology

Question 16

What is retinal imagining/fundus photography?

Answer 16

• Acquires color photographs of the retina
• Specialized low power microscope with an attached camera
• Images can be kept in a computer and therefore allows long term patient monitoring
  E.g. As part of diabetic screening programmes

Question 17

What does retinal imaging view?

Answer 17

views optic nerve head and the retina

Question 18

What is fluorescein angiography?

Answer 18

• Fluorescein angiography (FA) is a diagnostic technique that uses intravenous fluorescein dye to allow the sequential visualization of the blood flow simultaneously through retinal, choroidal and iris tissue.
• Enables assessment of choroidal and retinal vessels
• Uses IV contrast dye (fluorescein fluoride) to enable assessment of choroidal and retinal vessels

Question 19

Indications for fluorescein angiography?

Answer 19

1. Diabetic retinopathy
2. Choroidal neovascularization
3. Macular diseases
4. Planning laser procedures

Question 20

Contraindications of fluorescein angiography?

Answer 20

1. Allergic to fluorescein
2. Renal impairment

Question 21

What is fluorescein?

Answer 21

Sodium Fluorescein is a water-soluble dye of an orange-red crystalline hydrocarbon

Question 22

Describe fluorescein distribution and metabolism?

Answer 22

• When injected intravenously, remains largely intravascular and circulates in the blood stream.
• 80% of fluorescein molecules bind to serum proteins(albumin), the residue remaining unbound. Only the unbound molecules are available for fluorescence.
• It undergoes both renal and hepatic metabolism and is excreted in the urine over 24–48 hours.

Question 23

Absolute contraindications of fluorescein?

Answer 23

Fluorescein allergy

Question 24

Relative contraindications of fluorescein angiography?

Answer 24

1. History of a severe reaction to any allergen is a strong relative contraindication.
2. Renal failure (lower the fluorescein dose if angiography is necessary)
3. Pregnancy: Although no reported birth defects.
4. Moderate-severe asthma
5. Significant cardiac disease

Question 25

Describe the procedure of fluorescein angiography?

Answer 25

1. Both pupils are dilated 2. The patient is seated at the camera and IV cannula is inserted in antecubital fossa. 3. Coloured funds photos, red-free photos +/- autofluorescence images are taken. 4. Sodium fluorescein is injected 5 ml of 10% solution, or 2.5 ml of 25% solution (15mg/kg). 5. Images are taken

Question 26

What are the images order in fluorescein angiography?

Answer 26

1. Early rapid-sequence photographs (1 second intervals for 25–30 seconds). 2. Less rapid sequences between 5 and 10 min. 3. Late images at 10–20 minutes

Question 27

Indications of fluorescein angiography?

Answer 27

1. Diabetic retinopathy 2. Age related macular degeneration 3. Subretinal neovascular membrane from other causes (myopia, histoplasmosis, etc.) 4. Central retinal vein occlusion 5. Branch retinal vein occlusion 6. Central serous chorioretinopathy 7. Cystoid macular edema 8. Hypertensive retinopathy 9. Central retinal artery occlusion 10. Branch retinal artery occlusion 11. Retinal arterial macroaneurysms

Question 28

What is indocyanine green angiography?

Answer 28

Uses the same principle as Fluorecsein angiography but uses indocyanine green instead of fluorescein sodium.

Question 29

Why is indocyanine green angiography better than fluorescein angiography?

Answer 29

- With fluorescein angiography, the retinal pigment epithelium dampens transmission of choroidal fluorescence (melanin acts as a curtain) - Thus it gives a less clear resolution of the choroidal circulation/choroidal lesions - Indocyanine green gives a better resolution of the choroidal circulation

Question 30

Indications of indocyanine green angiography?

Answer 30

1. Age-related macular degeneration 2. Choroidal polypoidal vasculopathy 3. Retinal Angiomatous Proliferation 4. Choroidal tumours 5. Chorioretinal Inflammatory Diseases

Question 31

What is computed tomography scane?

Answer 31

It employs X rays which pass through body and reach a detector , image is reconstructed using a computer.

Question 32

Indications for CT scan?

Answer 32

1. Suspected trauma. 2. Intraocular Foreign body. 3. Evaluation of orbital infections/abscesses. 4. Evaluation of extraocular muscles. Note: Not so useful in optic nerve disease/ demyelinations. - Visualises calcified bony lesions and orbits better

Question 33

Reading CT scans?

Answer 33

- Fluid filled structures like globe , fat are dark - dense structures like bone are light

Question 34

Cautions with CT?

Answer 34

1. CT is associated with radiation - There is a small increased risk of cancer with repeated CT examination. 2. A CT head delivers 2-3 mSv of radiation dose 3. Repeated CTs are also associated with rising incidence of cataract

Question 35

What is magnetic resonance imaging?

Answer 35

MRI employs a powerful magnet , radio waves and movement of protons inside our body to produce images - High soft tissue resolution.

Question 36

Uses of MRI?

Answer 36

1. MRI is used in particular useful in optic nerve pathology, demyelination and cranial nerve assessment. 2. Less useful in trauma as bony details (e.g., fractures) is not well depicted.

Question 37

Caution with MRI?

Answer 37

1. MRI should not be done in a patient suspected of metallic foreign body without doing CT - if a ferromagnetic particle is present , it can have missile effect and damage orbital structures. 2. Should be cautious while doing MRI in patients with pacemakers , protruding metallic objects.

Question 38

Reading MRI images?

Answer 38

1. T2 sequence - globe shows bright appearance, fuzzy appearance 2. T1 sequence - glove is dark, fat is bright

Question 39

Indication for MRI?

Answer 39

1. Intracranial aneurysm 2. Optic nerve disease 3. Retrobulbar neuritis

Question 40

What is retrobulbar neuritis?

Answer 40

- Retrobulbar neuritis is a form of optic neuritis in which the optic nerve, which is at the back of the eye, becomes inflamed - The inflamed area is between the back of the eye and the brain - The optic nerve contains fibers that carry visual information from the nerve cells in the retina to the nerve cells in the brain.

Question 41

Ophthalmic diagnostic tests?

Answer 41

1. Tonometry 2. Perimetry 3. Gonioscopy 4. Pachymetry

Question 42

What is tonometry?