OPTOM 216B Flashcards
What is a slit lamp
It is a telemicroscope that is Derived from a simple microscope with a large objective lens and low power
What does the large objective lens and low power do
Gathers more light
What does a slit lamp do
For anterior eye exams using magnification and illumination to see details in transparent and internal structures
What is a slit lamp made of
Microscope and a Galilean telescope
What does the telescope do
Allow variation in magnification
Is the slit lamp telescope afocal?
Yes
How do we solve the afocal problem
Adding a positive lens
What is the effect of the positive lens
It reversed and inverts the image
How do we fix this reversal and inversion of the image
Using 2 vertical and 2 Horizontal pro-prisms
What are the characteristics of Porro-prisms
Has 4 45 degree reflecting surfaces
Name the two types of slit lamps and their characteristics
Haag-Streit and Zeiss
Haag-Striet has light from above, can also attach accessories and decouple
Zeiss has light from below
Characteristic of Slit Lamps
The Light and optical system are focussed at the same point above the centre of rotation
Preparations for the SLE
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
What is an important step during the SLE
Pull back base and lock it when not using to prevernt contact with the px
2 techniques for SL
Direct and Indirect illumination
What is direct
Light shone directlyh onto observed object
What is indirect
Light reflects from a surface in the eye to the object being observed
How is indirect done
Decoupled
Direct techniques
Diffuse, Parallelpiped, Optic section, Specular reflection and Tyndall cone
Diffuse
uniform illumination but no info on the object
Parallelpiped
0.5mm beam for depth, size and position. Cornea is 0,5mm so this gives true thickness
Optic section
Narrow beam from an angle, used with high magnification
Specular reflection
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
Specular reflection on anterior lens
focus on iris and slowly push in until orange reflex seen
Tyndall effect
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
What do cells in the AH indicate
Inflammation
What is always on during SL
IR filter
What does the ND filter do in SL
Reduces transmission of all wavelengths which can dim bright light
What does Red-free illumination do
More blue to light up the eye making vessels appear more black
What can we use Red-Free illumination for
Used to identify between similar but difference conditions.
Can be used both posterior and anterior eye
What are dyes used for
Check for abnormalities in the eye when the eye looks normal in normal lighting
How does the fluorescence occur
An absorbed photon at a wavelength that is spontaenously emitted at a different wavelength. The energy level goes back to its ground state
What is NaFl used for
intraocular injuries, corneal injuries, contact lens fitting and lacrimal drainage tests
What light gives max excitation to NaFl
Blue light
Characteristics of NaFl
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
What filter is used to ensure more brightness of the NaFl
Blue cobalt filter
How to make NaFl more visible
Use yellow wratten filter over the objective lens
Why are potholes in the cornea easier to see with NaFl
Dye more concentrated in the cracks
Rose Bengal
Stains cells not protected by tear film pink and shows the dead cells.
Dye is toxic and stings on application
Lissamine Green
Stains both dead and dying cells green
Sting is miminised by still toxic. The dye is seen easier with red barrier filter
Where to apply Lissamine Green
for conjunctival staining where NaFl cant get to easily
what is Lid Wiper Epitheliopathy
Disruption of surface epithelium of marginal conjuctiva of both upper and lower eye lids
What stains are used to view LWE
Both NaFl and Lissamine Green
What does the VH technique do
Gives the anterior chamber angle and corneal thickness as a ratio
Use to screen before dilation
What is the gold standard to view the angle
Gonioscopy
The angle closure grade scale
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
Set up for Van Hericks
Narrow White light at 10-16x mag of 60 degree illumination
Light should be perpendicular to the corneal limbus
Errors in VH
Incorrect setup and Not all corneas have constant thickness
Corneal Zones
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
What corneal zones is the contact lens fit based on
Central and Paracentral Zone
What is Corneal topography
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
When does the keratometric index work
In normal corneas and less accurate in distorted corneas
What is the reflection principle
Relation between image and object size gives radius of curvature of the cornea
What is Keratometry
Uses topography principle but is an ellipitcal image is formed then astigmatism exists
What does Keratometry assume
This is accurate and reproducible in normal cornea as it assumes perfect cylindrical surface
What information does Keratometry provide
Power and Curvature of the central cornea and not the periphery
What does optical doubling do
Counter eye movements by duplication images where the distance between the images is the amount of astigmatism
Two types of Keratometers
Javal Shiotz and the Bausch and Lomb
Javal Shiotz Keratometer
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
Bausch and Lomb
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
What is Keratoscopy
Uses Placido discs as objects, it covers more area on the cornea and extends to more meridians
What is photokeratoscopy
Uses 12 rings, covers 70% cornea and image is taken and compared to standard images
Accurate but time consuming
Video Keratoscopy
More rings and covers 95% cornea.
Too many rings in periphery causing ring jam
How to solve ring jam
Use coloured rings
How to increase contrast in rings
Use black and white rings
What does a stretched horizontal plane mean
Against the rule astigmatism
What does distorted rings indicate
Astigmatism
What is Corneal tomography
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
Advantage of Corneal tomography
Power of posterior and anterior cornea is also given
What principle does Corneal Tomography use
Projection principle where image is viewed on the cornea instead of the reflection
Slit Scanning technique
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
Scheimpflug principle
Image plane manipulated from top to bottom
Flaring occurs in periphery so information here is bad
How does the scheimplug camera capture information
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
Advantage of dual camera system
Minimises decentration error
What is OCT
Is a low coherence interferometry using light to image
Delay and intensity of IR wave gives 3D construction from depth information
What can the scans mentioned before do
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
What is digital retinal photography
Uses camera with low power microscope
This is objective and Non-ambiguous
What is digital retinal photography used for
Monitor disease and treatment as for patient education
Traditional fundus camera
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
What is a Non-Mydriatic camera
Uses IR to focus image and a flash of white light to capture the fundus
Why is IR used
Invisible to px and does not need pupil dilation and does not produce LCA
Wide and Ultrawide field designs
Scanning laser ophthalmoscopy, Contact camera system and trans-scleral illumination
Pupil dilation depends on model used
Drawback of wider field imaging
Image distortion and flase colour representation
RetCam
Handheld contact wide field imaging system for babies
Needs dilation and has interchaneable lens for magnification and contrast
Requires topical anesthetic and coupling gel
Panorent camera
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
CLARUS by Zeiss
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
Scanning Laser Ophthalmoscopy
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
What is an optomap
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
What layer does Green laser target
Retina to the RPE
What layer does Red laser target
RPE to Choroid
What can IR image
Deeper layers to see choroid structures and it is a longer wavelength
What is stereoimaging
Fusing of 2 images of different angles giving 3D image to see any elevation and depression in the retina
Done sequentially and simultaneously
Simultaneous stereoimaging
Uses 2 cameras or a single camera with a double lens
Sequential stereoimaging
Single camera taking 2 different photos
How is fusing done in stereoimaging
Done by stereo viewing or free viewing technique
Fluorescien angiography
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
ICG angiography
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
Funus Autofluorescence
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
What is OCT
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
OCT principles
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
How is OCT image construction done
A, B and C scans
A scans
1D depth
B scans
2D slice using Multiple A scans
C scans
3D data volume from multiple B scans
Time-Domain OCT
1st generation OCT using A scans collected over time by moving a reference mirror
Fourier Domain OCT
2nd Gen OCT and A-scans are simultaneously acquired, interference patterns record 45-100x faster with better sensitivity
Spectral domain OCT
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
Swept Source OCT
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
OCT application
Retina diagnosis, Management, Disease/treatment monitoring and give early intervention
ALso used for glaucoma diagnosis and management as it detects RGC loss
OCT pros and cons compared to FFA and ICG-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
What is Ultrasonography
Old, most common and well known.
It collects echoes of high frequency sound waves forming an image via ultrasound
How does ultrasound work
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
A-Scans in Ultrasound
Transducer in contact with cornea, topical anaesthetic is needed but gel not needed
B-Scans in Ultrasound
Transducer in contact with closed eyelid and needs gel but not topical anaesthetic
What are the scans used for
Used in conjuction with light-based techniques if they are not sufficent due to cataracts or miotic pupils
What is A-scan biometry
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
What is MRI
Non-Invasive and gives 3D image using magnetic properties of protons
How does MRI work
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
T1 relaxation time
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
What does Gadolinium do to T1 time
Decreases T1 time of tissues
T2 relaxation time
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
What does Gadolinium do to T2 time
redeuces T2 time
T1 vs T2 images
Inverted colours of each other
When is MRI used
Supplementary to other methods of imaging
MRI pros and cons
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
What is Compupted Tomography
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
CT contrast agents
Iodine and Barium
What is X-ray attenuation proportional to
Density and composition of the tissue
What does Orbital CT show
Bone, soft tissues, Fat. This is fast and easier
When to use orbital CT
When MRI is not possible
Where is VR used
Gaming, Entertainment and Healthcare
What effect does VR simulate
Stereopsis to get depth perception from binocular disparity
How does VR work for positioning
Uses head and orientation tracking, It also used positional tracking to simulate motion parallax
Two categories of VR
Inside-out and Outside-In
Outside-In VR
Tracks location of user via constellation system using IR LEDs on the headset/controller and is tracked by external optical sensors
Inside-out VR
Has sensors on headset to track movements of user relative to environment via lighthouse system of IR lasers
What is SLAM
Simultaneous Localisation and Mapping.
This determines where you are in space using multiple sensors to calculate solutions
Where is SLAM found
Autonomous Vehicles
VR design
High powerred lens and has reduced weight, thickness and cost using the Fresnel design
Aberrations off axis is like distortion is fixed via software
Field of View of VR
96-135 degrees
What is Vergence-Accomodation System
Information is mismatched between vergence and accommodation system
How is VAC addressed
Using space-multiplexing
What is space multiplexing
using multiple displays of different depths but has more cost, weight and volume
Alternative to space multiplexing and what is it
Time multiplexing, where optical system has moveable display but is limited to its response time and range of movement
What is light field projection
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
Problem with VR visuals
Latency, simulator sickness felt at 13ms
Latency in VR
System needs real world positional data but is limited by the computer and display
Normal VR refresh rate
90Hz
How to address latency
Low persistence display
What is a low persistence display
Screen is lit for a fraction of the time of a frame
Requirements for low persistence display
Pixels need a fast response time to ensure brightness is maintained at higher refresh rates
What is Asynchronous timewarp
Maintains smoothness of VR when the system is not rendering images at target frame rate
VR health concerns
Ocular strain like myopia, blue light damage and a visual-vestibular disconnect aka simulator sickness, Physical danger and mental well-being like addiction
How does Asynchronous timewarp work
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
What succeeds asycnhronous spacewarp
Asynchronous timewarp for 3D features
VR health benefits
Myopia prevention control, vision therapy for BV and visual function assessment
Also for short term pain relief and psychological therapy for phobias
What is an optometer and what principle does it use
Measures refractive state of eye using Scheiners principle using pinholes/LEDs
It is subjective or objective
Subjective optometers
Badal Optometer
How does Badal Optometer work
Use plus lens +8-+10D and an object at eyes far point. This simulates real life conditions and uses visible light
Objective optometers
Autorefractors which are automated and based on the Scheiner, Retinoscopic principles and image quality analysis
Scheiner Autorefractor
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
Scheiner Autorefractor Cons
Unreliable on irregular corneas since alignment is important
Retinoscopic autorefractor
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
Image quality analysis
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
Drawback of looking through optical instruments
Over accommodation
How to solve over accommodation
By using cyclopegia or fogging lenses
What happens if over accommodation is not accounted for in autorefraction
An over minus correction which over diagnoses myopia
Auorefractor drawbacks
Tend to give a greater prescription compared to an optometrist So subjectve refraction is more comfortable than open field autorefractor
Examples of low order aberrations
Myopia, Hyperopia and Astigmsatism
Examples of higher order aberrations
Coma and Spherical aberrations
How do higher order aberrations occur
With age and corrected using CLs, Glx and LASIK
What is an Aberrometer
It measures high and low order aberrations, gives objective measure on retinal image quality
How do aberrometers work
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
Cons of aberrometers
More expensive then autorefractors but not liekly to replace them
What is a Hartman-Shack aberrometer
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
Topographical wavefront map
Shows aberrations and shape of the wavefront is measured at the exit pupil which is used to get PSF
What does a flat wavefront mean
No aberrations
How is wavefront error decomposed
Using Zernike, Talor and Fourier system
What does the wavefront guided laser ablation do
It minises laser induced aberrations, corrects higher order aberratins and is accurate to 0.01D precision
What is Ophthalmoscopy and how does it work
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
What is the illumination area proportional to
The amount of retina that can be seen. Closer to px also increases ilumination area
What does a compensating lens do
Corrects light vergence in the px that has a refractive error and also corrects the ametropia in the optometrist
How to calculate the nominal magnification
F/4
What is nominal magnification proportional to
The FoV. The meridian with the most power will be minified more
Requirements to perform ophthalmoscopy
Requires undiluted pipils in dim lighting, also tell px instructions. Dont get to close to the px
What can the ophthalmoscope measure
Refractive error, assess optic cup depth and also can measure lesion size
The optic cup is nasal
How to perform posterior pole exm
Start with optic nerve and assess all positions of gaze
What are the distance units on a fundus
Disc diameters
What is optic neuropathy
Optic nerve damage of any cause
How to assess optic disc and cup
Look for size, shape, depth, pigmentation and margins like the neovascularisation
What to look for in the Neuroretinal rim
Its hue and thickness
What does optic disc size tell us
Elevated optic disc may appear blurry and due to swelling
What does an oblique optic disc indicate
Astigmatism
What is PPA
Peripapillary atrophy, It is found around the alpha and beta zone of the optic cup
Alpha zone
furthest from optic nerve
Beta zone
most adjacent to optic nerve
Who likely has PPA
Glaucoma px
How is the optic cup size shown
As a C/D ratio and measured both vertically and horizontally
What is a normal C/D ratio
0.3
What does a large C/D ratio indicate
irreversible loss of nerve fibres and blood vessels
What does glaucoma do to the cup
Increase depth of the optic cup and the cup border is the contour and not the pallor
Healthy Neoretinal Rim Characteristics
Orange/pink and obeys ISNT rule
What is the ISNT rule
Inferior>Superior>Nasal>Temporal for the thicknest at the inferior
What goes glaucoma do to the Neoretinal rim
NRR thinning and does not obey ISNT rule
What also indicates glaucoma
Notching in the inferior and superior of the NRR even if ISNT rule is obeyed
Retinal vasculature abnormalities
Microaneurysms, Artery-Vein anastomosis and Neovascularisation
What is Tortuosity
Blood vessels become twisted and looks convoluted giving poor blood flow
What is copper wiring
Blood vessels become opaque in a reddish/brown colour from narrowing vessels
What is silver wiring
When copper wiring gets worse and the vessels become silver
What is Sheathing/Cuffing
Vessels have white spots due to deposits in the vessel wall from inflammation
What are ghost vessels
From narrowing vessels and appear pale, and thin due to ischemia or vessel damage
What is A/V ratio
Ratio between artery and venous lumen diameter
Healthy eyes have smaller ratio due to arteries having smaller lumens
What causes vessel dilation that affects A/V ratio
Microvascular dysfunction
When to do the Macula assessment
Done last to avoid bleaching, a reduced aperture size and a red free filter is used
What to look for in Macula assessment
For fluid, atrophy, brightness and other deposits are made here
What does laser stand for
Light amplification by stimulated emission of radiation
Properties of Lasers
Coherent, monochromatic, unidirectional, bright light and can be polarised
How can lasers be used
Pulsed or continuous
How does emission work
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
What type of emission is Laser
Stimulated emission
How does stimulated emission work
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
How many energy levels does the lasing medium have
at least 3
Types of excitation systems
Optical, Electrical or Chemical
What is a Laser
Standing waves, light intensity increased by using two mirrors to amplify light
How do lasers get transmitted out of its system
One mirror is more transparent than the other allowing the transmission
What does an energy pump do
Excites electrons from ground to higher state energy level. Which after spontaneously emits energy triggering stimulated emission
How does the stimulated emission increase in energy
Photons emitted triggers more stimulated emission which each cycle emitting more photons
What is population inversion
When some electrons to go to level 1 giving enough electrons in level 2 to produce stimulated emission for the laser to work
What is point of population inversion
To produce enough electrons to be in an excited state compared to ground state
How does laser induce tissue damage
Its wavelength, irradiance and exposure time
What is a photochemical LASER and its application
Used for Photoradiation and Photoablation
What is photoradiation
Photosensitising agent catalyses cytotoxicity
What is photoablation
breaks down long chain tissue polymers, here the wavelength is suited to the target photosensitiser like rhodopsin
When matched, a reaction happens
What is a photothermal LASER and its application
Used for Photocoagulation, Photovapourisation and Photocabonisation
What is photocoagulation
This denatures protein and colagen at 60-100 degrees
What is photovapourisation
When intra/extracellular water is vapourises at 100 degrees
What is photocabonisation
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
What is a photomechanical LASER and its application
These are non-thermal, high energy and only used for short time intervals. One type is photodisruption
What is photodisruption
Tissue is split by indirect mechanical forces and is reduced to plasma using IR pulses
Characteristics of Nd:YAG Laser
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
Characteristics of Excimer Laser
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
Characteristics of Femtosecond Laser
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
Characteristics of Gas Laser
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
Application of Nd:YA
Laser peripheral iridotomy to put hole in iris for AH outflow pathway and in Selective laser Trabeculoplasty
Application of Excimer
Used for LASIK, here the epithelial flap is opened, the laser reshapes the stroma and the flap is put back to heal
Why is LASIK better than PRK
PRK has to regrow entire corneal epitherlial layer.
LASIK complications
Flap may be torn off
Application of Femtosecond
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
Application of Gas Lasers
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
What can lasers damage
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
AI flow pathway for information
Lots of input and have a summed output of information. The inputs are not weighted the same
What do modern AI layers include
Input and Output layer with more layers in between for information filtering
AI vs Human errror rate
AI has lower error rate
Name 3 types of AI
Deep learning, Machine learning and Artifical intelligence
What is machine learning
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
What is deep learning
A subset of machine learning with multiple layers in its neural network. Here it can self learn without human labelling of data
How do large language models work
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
How to text to image models work
Makes images from text that uses labelled data that describes the image. This is done by diffusion and denoising
What is diffusion and denoising
It destructs the data by adding noise and making a new image by denoising
What is deepfake
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
Name all 3 generative AI
Deepfake, Text to image and Language models
What AI is Siri
Discriminative AI, it analyses patterns to predict things but it is not creative.
How is AI used in healthcare
Can be used if the disease is categorisable for diagnosis, used for risk prediction and progression analysis.
Faster and more accurate than humans
Advantages of AI in health
Reduces cost and better px outcomes
Drawback of AI in health
Needs alot of data of quantity and quality and a lack of information for rare diseases
Ethical considerations for AI
Data security and privacy. If AI makes a mistake, who is at fault?
BUT it can give all px an equal playing field
What is eye tracking used for
Records positions of gaze, for cognitive behaviour and measures the visual field
Methods to eye track
Assumed gaze, Manual methods, Electro-oculography, Video-based IR tracking and Deep Learning
What is Assumed Gaze
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
Manual Methods
Looking at px smooth pursuits and saccades, this is innacurate and makes it difficult if they have strabismus. BUT minimal tools needed
What is preferential looking
Px looks at centre and then suddenly showing them twopictures and seeing which one they look at first
What is electro-oculography
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.
Drawback of Electro-oculography
Hard to setup, noisy data from EOMs and Facial muscles, recalibration needed since electrodes slip or contact lens decentering
What is Video IR Tracking
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
What does eye tracking use now and how reliable is it
Uses deep learning and only as reliable as the database it is learning from
Where is Eye tracking used
Gaming, Marketing and assistive technology, in clinics for disease/diagnosis
How is eye tracking used in sports
Track reaction time and peripheral awareness
How does eye tracking work with gratings
Moving grating shown, the spatial frequency that triggers the OKN is the VA for the visual system
