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OPTOM > OPTOM 216B > Flashcards

OPTOM 216B Flashcards

1
Q

What is a slit lamp

A

It is a telemicroscope that is Derived from a simple microscope with a large objective lens and low power

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2
Q

What does the large objective lens and low power do

A

Gathers more light

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3
Q

What does a slit lamp do

A

For anterior eye exams using magnification and illumination to see details in transparent and internal structures

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4
Q

What is a slit lamp made of

A

Microscope and a Galilean telescope

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5
Q

What does the telescope do

A

Allow variation in magnification

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6
Q

Is the slit lamp telescope afocal?

A

Yes

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7
Q

How do we solve the afocal problem

A

Adding a positive lens

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8
Q

What is the effect of the positive lens

A

It reversed and inverts the image

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9
Q

How do we fix this reversal and inversion of the image

A

Using 2 vertical and 2 Horizontal pro-prisms

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10
Q

What are the characteristics of Porro-prisms

A

Has 4 45 degree reflecting surfaces

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11
Q

Name the two types of slit lamps and their characteristics

A

Haag-Streit and Zeiss

Haag-Striet has light from above, can also attach accessories and decouple

Zeiss has light from below

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12
Q

Characteristic of Slit Lamps

A

The Light and optical system are focussed at the same point above the centre of rotation

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13
Q

Preparations for the SLE

A

SL has bright lights and have things close to their eyes so turn off lights when not using or aim light away from eye

Sound certain and check the SL operation, focus eye piece and set PD when px comes in

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14
Q

What is an important step during the SLE

A

Pull back base and lock it when not using to prevernt contact with the px

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15
Q

2 techniques for SL

A

Direct and Indirect illumination

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16
Q

What is direct

A

Light shone directlyh onto observed object

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17
Q

What is indirect

A

Light reflects from a surface in the eye to the object being observed

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18
Q

How is indirect done

A

Decoupled

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19
Q

Direct techniques

A

Diffuse, Parallelpiped, Optic section, Specular reflection and Tyndall cone

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20
Q

Diffuse

A

uniform illumination but no info on the object

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21
Q

Parallelpiped

A

0.5mm beam for depth, size and position. Cornea is 0,5mm so this gives true thickness

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22
Q

Optic section

A

Narrow beam from an angle, used with high magnification

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23
Q

Specular reflection

A

Material dependent, reflection is seen if the surface is uneven
IN the cornea this corneal endothelium is the site of reflection.

Done with parallelpiped and high magnification

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24
Q

Specular reflection on anterior lens

A

focus on iris and slowly push in until orange reflex seen

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25
Q

Tyndall effect

A

Narrow beam through the AH, the effect is seen if there are debris in the AH

Uses 2x2mm beam within the pupil from an angle. Can use NaFl to see convection current is AH has cells

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26
Q

What do cells in the AH indicate

A

Inflammation

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27
Q

What is always on during SL

A

IR filter

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28
Q

What does the ND filter do in SL

A

Reduces transmission of all wavelengths which can dim bright light

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29
Q

What does Red-free illumination do

A

More blue to light up the eye making vessels appear more black

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30
Q

What can we use Red-Free illumination for

A

Used to identify between similar but difference conditions.
Can be used both posterior and anterior eye

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31
Q

What are dyes used for

A

Check for abnormalities in the eye when the eye looks normal in normal lighting

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32
Q

How does the fluorescence occur

A

An absorbed photon at a wavelength that is spontaenously emitted at a different wavelength. The energy level goes back to its ground state

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33
Q

What is NaFl used for

A

intraocular injuries, corneal injuries, contact lens fitting and lacrimal drainage tests

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34
Q

What light gives max excitation to NaFl

A

Blue light

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35
Q

Characteristics of NaFl

A

Water soluble so it is broken up in the corneal epithelium, It easily washes away with tears, The brightness is proportional to the tear film thickness

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36
Q

What filter is used to ensure more brightness of the NaFl

A

Blue cobalt filter

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37
Q

How to make NaFl more visible

A

Use yellow wratten filter over the objective lens

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38
Q

Why are potholes in the cornea easier to see with NaFl

A

Dye more concentrated in the cracks

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39
Q

Rose Bengal

A

Stains cells not protected by tear film pink and shows the dead cells.

Dye is toxic and stings on application

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40
Q

Lissamine Green

A

Stains both dead and dying cells green

Sting is miminised by still toxic. The dye is seen easier with red barrier filter

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41
Q

Where to apply Lissamine Green

A

for conjunctival staining where NaFl cant get to easily

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42
Q

what is Lid Wiper Epitheliopathy

A

Disruption of surface epithelium of marginal conjuctiva of both upper and lower eye lids

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43
Q

What stains are used to view LWE

A

Both NaFl and Lissamine Green

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44
Q

What does the VH technique do

A

Gives the anterior chamber angle and corneal thickness as a ratio

Use to screen before dilation

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45
Q

What is the gold standard to view the angle

A

Gonioscopy

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46
Q

The angle closure grade scale

A

Angle closure = Ratio of 0
Angle closer likely = Grade 1 and less than 0.25 ratio
Narrow angle = Grade 2 and 0.25-0.50 ratio
Open angle = Grade 3 = 0.5-1 ratio
Grade 4 of ratio 1 is normal

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47
Q

Set up for Van Hericks

A

Narrow White light at 10-16x mag of 60 degree illumination

Light should be perpendicular to the corneal limbus

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48
Q

Errors in VH

A

Incorrect setup and Not all corneas have constant thickness

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49
Q

Corneal Zones

A

Central zone = 3mm from fixation point for HD vision

Paracentral Zone = 3-4mm wide, flattens progressively

Pericentral Zone = 3-4mm wide and is flatter here

Limbal zone = smallest zone about 1mm thick, this is where the limbus is where cornea turns into sclera

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50
Q

What corneal zones is the contact lens fit based on

A

Central and Paracentral Zone

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51
Q

What is Corneal topography

A

Non-invasive, Non-contact method to give shape of cornea using reflection principle.

1st purkinje image gives radius of curvature of cornea and converted to dioptric power using the standard keratometric index of 1.3375

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52
Q

When does the keratometric index work

A

In normal corneas and less accurate in distorted corneas

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53
Q

What is the reflection principle

A

Relation between image and object size gives radius of curvature of the cornea

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54
Q

What is Keratometry

A

Uses topography principle but is an ellipitcal image is formed then astigmatism exists

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55
Q

What does Keratometry assume

A

This is accurate and reproducible in normal cornea as it assumes perfect cylindrical surface

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56
Q

What information does Keratometry provide

A

Power and Curvature of the central cornea and not the periphery

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57
Q

What does optical doubling do

A

Counter eye movements by duplication images where the distance between the images is the amount of astigmatism

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58
Q

Two types of Keratometers

A

Javal Shiotz and the Bausch and Lomb

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59
Q

Javal Shiotz Keratometer

A

Px in machine and images are random and blurry. Images adjusted until middle of view, we line up the images to get axis power and this is repeated for the other axis

DIfference in power is the amount of astigmatism

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60
Q

Bausch and Lomb

A

Objects are fixed and images are adjusted by us. Object is centred until clear, the circles are adjusted where minus lines up and positives overlap giving power of both axis

BL does not need to rotate to find other axis

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61
Q

What is Keratoscopy

A

Uses Placido discs as objects, it covers more area on the cornea and extends to more meridians

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62
Q

What is photokeratoscopy

A

Uses 12 rings, covers 70% cornea and image is taken and compared to standard images

Accurate but time consuming

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63
Q

Video Keratoscopy

A

More rings and covers 95% cornea.

Too many rings in periphery causing ring jam

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64
Q

How to solve ring jam

A

Use coloured rings

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65
Q

How to increase contrast in rings

A

Use black and white rings

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66
Q

What does a stretched horizontal plane mean

A

Against the rule astigmatism

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67
Q

What does distorted rings indicate

A

Astigmatism

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68
Q

What is Corneal tomography

A

Cross-section of cornea showing both posterior and anterior surface. It uses 2D images to give a 3D corneal construction

Measurements using height is more accurate than slope. This is good as it does not need the refractive index to get corneal radius

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69
Q

Advantage of Corneal tomography

A

Power of posterior and anterior cornea is also given

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70
Q

What principle does Corneal Tomography use

A

Projection principle where image is viewed on the cornea instead of the reflection

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71
Q

Slit Scanning technique

A

Projection based, slit images projected across the cornea.
40 slits projected at 45 degrees, 20 left and 20 right. Slits overlap in central 5mm on cornea

Uses ray tracing to give 3D construction. But also time consuming

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72
Q

Scheimpflug principle

A

Image plane manipulated from top to bottom

Flaring occurs in periphery so information here is bad

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73
Q

How does the scheimplug camera capture information

A

Rotating the camera gives 3D construction.

SIngle camera system gives 50 meridians of 12500-2500 data points.

Dual camera system opposite to each other gives 122000 data points

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74
Q

Advantage of dual camera system

A

Minimises decentration error

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75
Q

What is OCT

A

Is a low coherence interferometry using light to image

Delay and intensity of IR wave gives 3D construction from depth information

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76
Q

What can the scans mentioned before do

A

Used for keratoconus, monitor disease progression and treatment.

Look at corneal ectasias like pellucid degeneration and Keratoconus

Also used before and after LASIK and for CL fitting

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77
Q

What is digital retinal photography

A

Uses camera with low power microscope

This is objective and Non-ambiguous

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78
Q

What is digital retinal photography used for

A

Monitor disease and treatment as for patient education

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79
Q

Traditional fundus camera

A

Uses white light to image fundus and needs dilation

Standard image is 30-50 degrees and 75 degrees for the periphery

Overlapping images can make montages but cataracts can decrease image quality

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80
Q

What is a Non-Mydriatic camera

A

Uses IR to focus image and a flash of white light to capture the fundus

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81
Q

Why is IR used

A

Invisible to px and does not need pupil dilation and does not produce LCA

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82
Q

Wide and Ultrawide field designs

A

Scanning laser ophthalmoscopy, Contact camera system and trans-scleral illumination

Pupil dilation depends on model used

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83
Q

Drawback of wider field imaging

A

Image distortion and flase colour representation

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84
Q

RetCam

A

Handheld contact wide field imaging system for babies

Needs dilation and has interchaneable lens for magnification and contrast

Requires topical anesthetic and coupling gel

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85
Q

Panorent camera

A

Wide field imaging, no dilation needed, light is separated from camera and gives 130 degree coverage

Needs topical anaesthetic and not commerically available due to eye injury risks

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86
Q

CLARUS by Zeiss

A

Latest non-contact ultrawide imaging system of 133 degrees for single image, 200 degrees ultrawide with 2 images and 267 degrees using 6 image montage

No dilation, uses RGB LEDs and IR laser to focus

Gives true to colour photos if white light used

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87
Q

Scanning Laser Ophthalmoscopy

A

Uses one or multiple coloured lasers, Non-contact ultrawide imaging system for 200 degrees single image, or 220 degrees for montage

No dilation needed and produced an optomap

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88
Q

What is an optomap

A

A dual wavelength of green and red, different colour images different layers of the retina.

Images can be photographed separately or merged together producing pseudocoloured images

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89
Q

What layer does Green laser target

A

Retina to the RPE

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90
Q

What layer does Red laser target

A

RPE to Choroid

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91
Q

What can IR image

A

Deeper layers to see choroid structures and it is a longer wavelength

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92
Q

What is stereoimaging

A

Fusing of 2 images of different angles giving 3D image to see any elevation and depression in the retina

Done sequentially and simultaneously

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93
Q

Simultaneous stereoimaging

A

Uses 2 cameras or a single camera with a double lens

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94
Q

Sequential stereoimaging

A

Single camera taking 2 different photos

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95
Q

How is fusing done in stereoimaging

A

Done by stereo viewing or free viewing technique

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96
Q

Fluorescien angiography

A

Uses fundus camera and invasive diagnostic procedure. NaFl injected to see retinal circulation and the BRB integrity

Blue excitation filter and a yellow-green barrier filter used.

Timelapse of NaFl done to see NaFl flow, can see hypo and hyperfluorescence

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97
Q

ICG angiography

A

Uses Indoctanine green, for choroidal circulation and administered with NaFl, also timelapsed after injection.

Uses Near IR excitation filter and a Near IR barrier filter.

Also gives hypo and hyperfluorescence

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98
Q

Funus Autofluorescence

A

Another angiography without use of dye, It detects flurophores when assessing RPE

Flurophore is A2-E compound in RPE lipofuscin

Uses Blue excitation filter and a yellow-green barrier filter

Timelapse not needed, image is taken to see fluorescence level there hyperfluorescence means lots of lipofuscin

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99
Q

What is OCT

A

Non-invasive and Non-contact using IR and Near IR light interference that gives a high-resolution 3D image

Uses ultrasound principle where visuals of tissue structure is seen wihtout histology

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100
Q

OCT principles

A

Uses low coherence interferometry, uses superposition of light beams where the IR light source is split into two paths, the reference and sample arm

Reflected beam gives interference pattern and time delay and intensity information is measured in the sample beam

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101
Q

How is OCT image construction done

A

A, B and C scans

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102
Q

A scans

A

1D depth

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103
Q

B scans

A

2D slice using Multiple A scans

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104
Q

C scans

A

3D data volume from multiple B scans

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105
Q

Time-Domain OCT

A

1st generation OCT using A scans collected over time by moving a reference mirror

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106
Q

Fourier Domain OCT

A

2nd Gen OCT and A-scans are simultaneously acquired, interference patterns record 45-100x faster with better sensitivity

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107
Q

Spectral domain OCT

A

1st variant of FD OCT and interference pattern is deconstructed giving spectral information

Detector is replaced with a spectrometer using a diffraction grating and a line scan camera. A scans here are computed via Fourier Transform

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108
Q

Swept Source OCT

A

2nd variant of FD OCT, uses visible light source that is decontructed giving spectral information, a laser is used here and A scans are computed via the Fourier transform

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109
Q

OCT application

A

Retina diagnosis, Management, Disease/treatment monitoring and give early intervention

ALso used for glaucoma diagnosis and management as it detects RGC loss

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110
Q

OCT pros and cons compared to FFA and ICG-A

A

Non-Invasive and used for diagnostic and management. But training is needed for analysis and has small FoV so motion artefacts can hinder quality

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111
Q

What is Ultrasonography

A

Old, most common and well known.
It collects echoes of high frequency sound waves forming an image via ultrasound

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112
Q

How does ultrasound work

A

Uses transducer with piezoelectric crystals converting electrical to mechanical energy but also required a gel medium

Image made from A and B scans. A scans for measurement and B scans for diagnosis

B scans are greyscale

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113
Q

A-Scans in Ultrasound

A

Transducer in contact with cornea, topical anaesthetic is needed but gel not needed

114
Q

B-Scans in Ultrasound

A

Transducer in contact with closed eyelid and needs gel but not topical anaesthetic

115
Q

What are the scans used for

A

Used in conjuction with light-based techniques if they are not sufficent due to cataracts or miotic pupils

116
Q

What is A-scan biometry

A

Give anatomical dimensions of the eye and for intraocular lens calculations. Can also identify obsecured pathology like trauma and finding causing of optic nerve swelling

117
Q

What is MRI

A

Non-Invasive and gives 3D image using magnetic properties of protons

118
Q

How does MRI work

A

Protons spin randomly and MRI aligns protons with strong magnetic field which is quickly disrupted using RF

Here protons then amit a. RF energy and re-aligns with magnetic field

Time taken to re-align is tissue dependent and used with contrast agents like Gadolinium

119
Q

T1 relaxation time

A

This is longitudinal and is the time needed to re-align with the magnetic field. A shorter time produces stronger field and image is brighter

120
Q

What does Gadolinium do to T1 time

A

Decreases T1 time of tissues

121
Q

T2 relaxation time

A

This is transverse and is the time needed for proton to spin out of sync with each other. T2 is shorter than T1. A shorter T2 means weaker signal and image appears darker

122
Q

What does Gadolinium do to T2 time

A

redeuces T2 time

123
Q

T1 vs T2 images

A

Inverted colours of each other

124
Q

When is MRI used

A

Supplementary to other methods of imaging

125
Q

MRI pros and cons

A

Resolution of MRI is poor but is has good depth penetration and no image distortion.
Can also assess structures behind the globe like the EOM and Cranial Nerves

126
Q

What is Compupted Tomography

A

This is non-invasive and uses X-rays. Rays pass through the body from different angles and X-rays attenuate when passing through tissue

Many 2D images form a 3D image

127
Q

CT contrast agents

A

Iodine and Barium

128
Q

What is X-ray attenuation proportional to

A

Density and composition of the tissue

129
Q

What does Orbital CT show

A

Bone, soft tissues, Fat. This is fast and easier

130
Q

When to use orbital CT

A

When MRI is not possible

131
Q

Where is VR used

A

Gaming, Entertainment and Healthcare

132
Q

What effect does VR simulate

A

Stereopsis to get depth perception from binocular disparity

133
Q

How does VR work for positioning

A

Uses head and orientation tracking, It also used positional tracking to simulate motion parallax

134
Q

Two categories of VR

A

Inside-out and Outside-In

135
Q

Outside-In VR

A

Tracks location of user via constellation system using IR LEDs on the headset/controller and is tracked by external optical sensors

136
Q

Inside-out VR

A

Has sensors on headset to track movements of user relative to environment via lighthouse system of IR lasers

137
Q

What is SLAM

A

Simultaneous Localisation and Mapping.
This determines where you are in space using multiple sensors to calculate solutions

138
Q

Where is SLAM found

A

Autonomous Vehicles

139
Q

VR design

A

High powerred lens and has reduced weight, thickness and cost using the Fresnel design

Aberrations off axis is like distortion is fixed via software

140
Q

Field of View of VR

A

96-135 degrees

141
Q

What is Vergence-Accomodation System

A

Information is mismatched between vergence and accommodation system

142
Q

How is VAC addressed

A

Using space-multiplexing

143
Q

What is space multiplexing

A

using multiple displays of different depths but has more cost, weight and volume

144
Q

Alternative to space multiplexing and what is it

A

Time multiplexing, where optical system has moveable display but is limited to its response time and range of movement

145
Q

What is light field projection

A

Uses light field tech, sensors record light as XYZ space and projects a physical wavefront similar to the real object to correct depth information and retinal blur

146
Q

Problem with VR visuals

A

Latency, simulator sickness felt at 13ms

147
Q

Latency in VR

A

System needs real world positional data but is limited by the computer and display

148
Q

Normal VR refresh rate

A

90Hz

149
Q

How to address latency

A

Low persistence display

150
Q

What is a low persistence display

A

Screen is lit for a fraction of the time of a frame

151
Q

Requirements for low persistence display

A

Pixels need a fast response time to ensure brightness is maintained at higher refresh rates

151
Q

What is Asynchronous timewarp

A

Maintains smoothness of VR when the system is not rendering images at target frame rate

152
Q

VR health concerns

A

Ocular strain like myopia, blue light damage and a visual-vestibular disconnect aka simulator sickness, Physical danger and mental well-being like addiction

152
Q

How does Asynchronous timewarp work

A

Uses positional data to predict what the next frame should be ; It samples current position to render an image and then it resamples the position and warps the rendered image and displays it to reduce latency and judder

152
Q

What succeeds asycnhronous spacewarp

A

Asynchronous timewarp for 3D features

153
Q

VR health benefits

A

Myopia prevention control, vision therapy for BV and visual function assessment

Also for short term pain relief and psychological therapy for phobias

154
Q

What is an optometer and what principle does it use

A

Measures refractive state of eye using Scheiners principle using pinholes/LEDs

It is subjective or objective

155
Q

Subjective optometers

A

Badal Optometer

156
Q

How does Badal Optometer work

A

Use plus lens +8-+10D and an object at eyes far point. This simulates real life conditions and uses visible light

157
Q

Objective optometers

A

Autorefractors which are automated and based on the Scheiner, Retinoscopic principles and image quality analysis

158
Q

Scheiner Autorefractor

A

Most common, Pinholes replaced by IR LEDs which are moved back and fourth until single which gives power

This is measured in three meridians by rotating LED pairs or using multiple pairs of LEDs

Can also give astigmatism correction

159
Q

Scheiner Autorefractor Cons

A

Unreliable on irregular corneas since alignment is important

160
Q

Retinoscopic autorefractor

A

Analyses photos of light reflex from the eye which can be co-axial/eccentric or Size and shape that gives the power.

Video analysis of reflex also is used where the streak of light is rotated and a sensor records records the movement of the reflex like direction and speed of the reflex giving its power

161
Q

Image quality analysis

A

Known as grating focus auto refraction, not used much today. Luminous gratings are projected onto the retina and a detector measured light levels of the retinal image. Low light level = blurry image.

We match the retinal image brightness to the target giving its power and measured in at least 3 meridians

162
Q

Drawback of looking through optical instruments

A

Over accommodation

163
Q

How to solve over accommodation

A

By using cyclopegia or fogging lenses

164
Q

What happens if over accommodation is not accounted for in autorefraction

A

An over minus correction which over diagnoses myopia

165
Q

Auorefractor drawbacks

A

Tend to give a greater prescription compared to an optometrist So subjectve refraction is more comfortable than open field autorefractor

166
Q

Examples of low order aberrations

A

Myopia, Hyperopia and Astigmsatism

167
Q

Examples of higher order aberrations

A

Coma and Spherical aberrations

168
Q

How do higher order aberrations occur

A

With age and corrected using CLs, Glx and LASIK

169
Q

What is an Aberrometer

A

It measures high and low order aberrations, gives objective measure on retinal image quality

170
Q

How do aberrometers work

A

Light projected into eye and light deviates from the predicted path and the reflection is analysed. The distance between the inpit and output is the aberration

171
Q

Cons of aberrometers

A

More expensive then autorefractors but not liekly to replace them

172
Q

What is a Hartman-Shack aberrometer

A

Uses IR and has alot of microlenses to give multiple beams, the wavefront goes through each lenslet and the beams are focussed onto a photon sensor

Beam displacement gives aberration measure

173
Q

Topographical wavefront map

A

Shows aberrations and shape of the wavefront is measured at the exit pupil which is used to get PSF

174
Q

What does a flat wavefront mean

A

No aberrations

175
Q

How is wavefront error decomposed

A

Using Zernike, Talor and Fourier system

176
Q

What does the wavefront guided laser ablation do

A

It minises laser induced aberrations, corrects higher order aberratins and is accurate to 0.01D precision

177
Q

What is Ophthalmoscopy and how does it work

A

Viewing the fundus directly, but can also be done indirectly. The positive lens focusses light at a mirror and directs light to the px pupil onto the px retina

178
Q

What is the illumination area proportional to

A

The amount of retina that can be seen. Closer to px also increases ilumination area

179
Q

What does a compensating lens do

A

Corrects light vergence in the px that has a refractive error and also corrects the ametropia in the optometrist

180
Q

How to calculate the nominal magnification

A

F/4

181
Q

What is nominal magnification proportional to

A

The FoV. The meridian with the most power will be minified more

182
Q

Requirements to perform ophthalmoscopy

A

Requires undiluted pipils in dim lighting, also tell px instructions. Dont get to close to the px

183
Q

What can the ophthalmoscope measure

A

Refractive error, assess optic cup depth and also can measure lesion size

The optic cup is nasal

184
Q

How to perform posterior pole exm

A

Start with optic nerve and assess all positions of gaze

185
Q

What are the distance units on a fundus

A

Disc diameters

186
Q

What is optic neuropathy

A

Optic nerve damage of any cause

187
Q

How to assess optic disc and cup

A

Look for size, shape, depth, pigmentation and margins like the neovascularisation

188
Q

What to look for in the Neuroretinal rim

A

Its hue and thickness

189
Q

What does optic disc size tell us

A

Elevated optic disc may appear blurry and due to swelling

190
Q

What does an oblique optic disc indicate

A

Astigmatism

191
Q

What is PPA

A

Peripapillary atrophy, It is found around the alpha and beta zone of the optic cup

192
Q

Alpha zone

A

furthest from optic nerve

193
Q

Beta zone

A

most adjacent to optic nerve

194
Q

Who likely has PPA

A

Glaucoma px

195
Q

How is the optic cup size shown

A

As a C/D ratio and measured both vertically and horizontally

196
Q

What is a normal C/D ratio

A

0.3

197
Q

What does a large C/D ratio indicate

A

irreversible loss of nerve fibres and blood vessels

198
Q

What does glaucoma do to the cup

A

Increase depth of the optic cup and the cup border is the contour and not the pallor

199
Q

Healthy Neoretinal Rim Characteristics

A

Orange/pink and obeys ISNT rule

200
Q

What is the ISNT rule

A

Inferior>Superior>Nasal>Temporal for the thicknest at the inferior

201
Q

What goes glaucoma do to the Neoretinal rim

A

NRR thinning and does not obey ISNT rule

202
Q

What also indicates glaucoma

A

Notching in the inferior and superior of the NRR even if ISNT rule is obeyed

203
Q

Retinal vasculature abnormalities

A

Microaneurysms, Artery-Vein anastomosis and Neovascularisation

204
Q

What is Tortuosity

A

Blood vessels become twisted and looks convoluted giving poor blood flow

205
Q

What is copper wiring

A

Blood vessels become opaque in a reddish/brown colour from narrowing vessels

206
Q

What is silver wiring

A

When copper wiring gets worse and the vessels become silver

207
Q

What is Sheathing/Cuffing

A

Vessels have white spots due to deposits in the vessel wall from inflammation

208
Q

What are ghost vessels

A

From narrowing vessels and appear pale, and thin due to ischemia or vessel damage

209
Q

What is A/V ratio

A

Ratio between artery and venous lumen diameter

Healthy eyes have smaller ratio due to arteries having smaller lumens

210
Q

What causes vessel dilation that affects A/V ratio

A

Microvascular dysfunction

211
Q

When to do the Macula assessment

A

Done last to avoid bleaching, a reduced aperture size and a red free filter is used

212
Q

What to look for in Macula assessment

A

For fluid, atrophy, brightness and other deposits are made here

213
Q

What does laser stand for

A

Light amplification by stimulated emission of radiation

214
Q

Properties of Lasers

A

Coherent, monochromatic, unidirectional, bright light and can be polarised

215
Q

How can lasers be used

A

Pulsed or continuous

216
Q

How does emission work

A

Atom absorbs photon causing electrons to go from ground to excited state and spontaneously emits energy as a photon in a random direction/phase/wavelength

One photon is emitted at a time

217
Q

What type of emission is Laser

A

Stimulated emission

218
Q

How does stimulated emission work

A

Excitation of atoms occur but two photons of the same direction, phase and wavelength are emitted instead of one. The laser has a laser medium of solid, liquid and gas, an excitation system and an Optical resonator

219
Q

How many energy levels does the lasing medium have

A

at least 3

220
Q

Types of excitation systems

A

Optical, Electrical or Chemical

221
Q

What is a Laser

A

Standing waves, light intensity increased by using two mirrors to amplify light

222
Q

How do lasers get transmitted out of its system

A

One mirror is more transparent than the other allowing the transmission

223
Q

What does an energy pump do

A

Excites electrons from ground to higher state energy level. Which after spontaneously emits energy triggering stimulated emission

224
Q

How does the stimulated emission increase in energy

A

Photons emitted triggers more stimulated emission which each cycle emitting more photons

225
Q

What is population inversion

A

When some electrons to go to level 1 giving enough electrons in level 2 to produce stimulated emission for the laser to work

226
Q

What is point of population inversion

A

To produce enough electrons to be in an excited state compared to ground state

227
Q

How does laser induce tissue damage

A

Its wavelength, irradiance and exposure time

228
Q

What is a photochemical LASER and its application

A

Used for Photoradiation and Photoablation

229
Q

What is photoradiation

A

Photosensitising agent catalyses cytotoxicity

230
Q

What is photoablation

A

breaks down long chain tissue polymers, here the wavelength is suited to the target photosensitiser like rhodopsin
When matched, a reaction happens

231
Q

What is a photothermal LASER and its application

A

Used for Photocoagulation, Photovapourisation and Photocabonisation

232
Q

What is photocoagulation

A

This denatures protein and colagen at 60-100 degrees

233
Q

What is photovapourisation

A

When intra/extracellular water is vapourises at 100 degrees

234
Q

What is photocabonisation

A

When local store of water is vapourised at more than 100 degrees

Here the lasers wavelenfth depends on the target chromophore and the interactions are non-selective and non-specific

235
Q

What is a photomechanical LASER and its application

A

These are non-thermal, high energy and only used for short time intervals. One type is photodisruption

236
Q

What is photodisruption

A

Tissue is split by indirect mechanical forces and is reduced to plasma using IR pulses

237
Q

Characteristics of Nd:YAG Laser

A

Solid state laser, rare earth metals for lasing medium. Uses IR and is frequency doubled to get a green laser and absorbed by melanin and Hb. Can be used both pulsed and continous for photothermal and photodisruptive effects

238
Q

Characteristics of Excimer Laser

A

Noble gas halides mixed with either argon, krypton or Xenon with addition of Fluorine or chlorine as the halide. Wavelength depends on gas used in the UV range and operates in pulsed mode of 100Hz. Used for photoablation on corneal tissue

239
Q

Characteristics of Femtosecond Laser

A

Used in a range of lasing media in Near IR. Uses ultra short pulse in femtosecond for photodisruption and photoionisation effects on the cornea. Short pulse reduces collateral damage and a more modern corneal laser

240
Q

Characteristics of Gas Laser

A

Argon laser uses argon gas as lasing medium and emits more than 35 wavelengths mainly in green, blue and UV regions. Strongest emission at green and the colour laser is chosen by turning prism of diffraction grating. This is used pusled or continous and used for photocoagulation

241
Q

Application of Nd:YA

A

Laser peripheral iridotomy to put hole in iris for AH outflow pathway and in Selective laser Trabeculoplasty

242
Q

Application of Excimer

A

Used for LASIK, here the epithelial flap is opened, the laser reshapes the stroma and the flap is put back to heal

243
Q

Why is LASIK better than PRK

A

PRK has to regrow entire corneal epitherlial layer.

244
Q

LASIK complications

A

Flap may be torn off

245
Q

Application of Femtosecond

A

3rd gen known as SMILE. Laser performs the area of cornea on the stroma you wanna remove. Small incision is made to extract the performed structure and then applied onto the cornea.
This doe snot need a flap like the Excimer LASIK

246
Q

Application of Gas Lasers

A

For diabetic macular oedema., Can shoot laser at blood vessels that are leaking to seal them. Can also seal holes in retina to stop VH from entering retinal layer to prevent retinal detachment

247
Q

What can lasers damage

A

More damage done on the eye than outside the eye and is absorbed in melanin in the RPE causing painless burns on the retina

IR also does not elicit blinking

248
Q

AI flow pathway for information

A

Lots of input and have a summed output of information. The inputs are not weighted the same

249
Q

What do modern AI layers include

A

Input and Output layer with more layers in between for information filtering

250
Q

AI vs Human errror rate

A

AI has lower error rate

251
Q

Name 3 types of AI

A

Deep learning, Machine learning and Artifical intelligence

252
Q

What is machine learning

A

Learns data without human input by giving it alot of data to learn from that are pre-labelled and identifies patterns from data and learns from this

253
Q

What is deep learning

A

A subset of machine learning with multiple layers in its neural network. Here it can self learn without human labelling of data

254
Q

How do large language models work

A

Uses alot of data to learn to make human like text. Data like books, articles and webpages. It uses probability to create sentences known as Natural Language processing

255
Q

How to text to image models work

A

Makes images from text that uses labelled data that describes the image. This is done by diffusion and denoising

256
Q

What is diffusion and denoising

A

It destructs the data by adding noise and making a new image by denoising

257
Q

What is deepfake

A

A combination of deep learning discriminative and generative image models

It changes media to make near real content and learns from hours of data from speech and face patterns

258
Q

Name all 3 generative AI

A

Deepfake, Text to image and Language models

259
Q

What AI is Siri

A

Discriminative AI, it analyses patterns to predict things but it is not creative.

260
Q

How is AI used in healthcare

A

Can be used if the disease is categorisable for diagnosis, used for risk prediction and progression analysis.

Faster and more accurate than humans

261
Q

Advantages of AI in health

A

Reduces cost and better px outcomes

262
Q

Drawback of AI in health

A

Needs alot of data of quantity and quality and a lack of information for rare diseases

263
Q

Ethical considerations for AI

A

Data security and privacy. If AI makes a mistake, who is at fault?

BUT it can give all px an equal playing field

264
Q

What is eye tracking used for

A

Records positions of gaze, for cognitive behaviour and measures the visual field

265
Q

Methods to eye track

A

Assumed gaze, Manual methods, Electro-oculography, Video-based IR tracking and Deep Learning

266
Q

What is Assumed Gaze

A

For blind spot monitoring for VF testing. Can also compare retinal sensitivities in the central and peripheral retina and to also check responses to changes in brightness

267
Q

Manual Methods

A

Looking at px smooth pursuits and saccades, this is innacurate and makes it difficult if they have strabismus. BUT minimal tools needed

268
Q

What is preferential looking

A

Px looks at centre and then suddenly showing them twopictures and seeing which one they look at first

269
Q

What is electro-oculography

A

This is gold standard and uses magnetic field electric currents.

Retina has alot of electrical activity compared to cornea and electrodes can detect this on either side of eye. Any change to EM field duirng eye movements are measured for different directions and also works when the eye is closed.

270
Q

Drawback of Electro-oculography

A

Hard to setup, noisy data from EOMs and Facial muscles, recalibration needed since electrodes slip or contact lens decentering

271
Q

What is Video IR Tracking

A

This is non-contact, popular and can be fixed, mobile or werable.

Uses pupil centre corneal reflection to know how far the tracker is from the screen.

Works with both dark or bright pupils and can be head fixed or head free to move.

Glx and dark irises can make the tracking inconsistent

Dark pupil mode has the system looking for dark circular spot Vice Versa

272
Q

What does eye tracking use now and how reliable is it

A

Uses deep learning and only as reliable as the database it is learning from

273
Q

Where is Eye tracking used

A

Gaming, Marketing and assistive technology, in clinics for disease/diagnosis

274
Q

How is eye tracking used in sports

A

Track reaction time and peripheral awareness

275
Q

How does eye tracking work with gratings

A

Moving grating shown, the spatial frequency that triggers the OKN is the VA for the visual system

276
Q
A
277
Q
A
277
Q
A

OPTOM (8 decks)

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