Misc Flashcards
clinical trials - phase 0
subjects: humans
microdosing for safety
clinical trials - phase 1
subjects: healthy volunteers
safety, s/e, pharmacokinets and dynamics
clinical trials - phase 2
subjects: target patients
IIA dosing
IIb efficacy
clinical trails - phase 3
subjects: larger groups of paitents
Effectivenss vs gold standard (RCTS)
clinical trials - phase 4
subjects: target group
post-marketing survelliance and yellow card scheme
visual standards group 1 entitlement - VA
Best corrected VA in good lighting sufficient to read a vehicle registration plate at
20 metres (where the figures are 5cm wide)
The equivalent of this is approximately 6/9 and 6/12 Snellen VA
visual standards group 1 entitlement - binocular field
There should be no major binocular field defect: no more than 3 contiguous points
missed in
At least 120 degrees on the horizontal scale
And within 20 degrees above and below fixation in the vertical
The Esterman protocol is commonly used for binocular testing: uses a target
equivalent to the white Goldmann III4e setting
visual standards group 1 entitlement - diplopia
New diplopia is a contraindication
Diplopia must be controlled and the patient must have adapted
when to inform DVLA
The DVLA should be informed about significant visual loss in one eye even if the
other meets the standard for driving
visual standards group 2 entitlement
Best corrected VA at least 6/9 in the stronger eye
Best corrected VA no worse than 6/12 in the other eye
Uncorrected visual acuity must be at least 3/60 in both eyes
NB: one eye with VA less than 3/60 is a contraindication to driving lorries,
buses
Normal binocular field of vision
New onset diplopia is a contraindication
Diplopia must be controlled with prisms only (not with patching) and the
patient must have adapted
blind registration
Best corrected visual acuity is less than 3/60; or,
Best corrected visual acuity is between 6/60 and 3/60 with field constriction; or,
Best corrected visual acuity is between 6/18 and 6/60 with severe field constriction
pelli-robson test purpose
Measures contrast sensitivity
o Method: Uses a single, large letter size (20/60 optotype).
o Contrast Variation: Across different groups of letters.
pelli-robson test procedure
o Starting Point: Patients read letters starting from the highest contrast.
o Continue until unable to correctly read 2 or 3 letters in a group.
pelli-robson test scoring
o Basis: Based on the contrast of the last group where 2 or 3 letters were correctly read.
o Logarithmic Measure: The score represents the subject’s contrast sensitivity.
o Example: A score of 2 indicates the ability to read at least 2 out of 3 letters at a contrast level of 1%(100% contrast sensitivity or log10 2), signifying normal contrast sensitivity.
pelli-robson test interpretation
o Less than 1.5: Consistent with visual impairment.
o Less than 1.0: Represents visual disability.
photostress recovery testing
- Differentiate between vision loss caused by macular lesion/ ocular ischaemia versus optic neuropathy
- Patient with optic neuropathy have normal photostress recovery time
- The theory behind this is that resythesis of visual pigments is required by
photostress recovery testing abnormal time
o age macular degeneration
o central serous retinopathy
o diabetic retinopathy
o digitalis toxicity
photostress recovery testing method
o test the eye monocularly
o patient gazes into bright light 2-3 cm from the eye for 10 seconds
o as soon as light is removed, patient attempts to read the larger Snellen visual acuity line above the line representing the patient’s visual acuity prior to the bright light
o normal photostress recovery time is approximately 30 seconds or more
photostress maculopathy results
severe ocular ischaemia can have recovery times of 90-180 seconds
non-organic visual loss
o Spiraling, Crossing, Stacking of Isoptres on Goldmann Visual Field
o Clover leaf visual field defect on HVF 24-2
tests that do not rely on patients interpretation
o Swinging light test
o Optokinetic nystagmus drum response used to elicit optokinetic nystagmus ( smooth pursuit with refixation saccade)
* Mirror test: when distracting a patient by holding conversation, move a mirror across their field of vision. It is difficult for patient to avoid looking at their own reflection
ishihara plates
screening test for red-green colour deficiency.
o Protan: red
o Deutan: Greeen
sensitivity for ishihara plates
o 95.5% on eight errors
o 97.5% on six errors
o 99% on three errors
which axis does ishahra test
red-green axis
what can test blue axis
Hardy-Rand-Rittler
farnsworth munsell 100
very sensitive as the different in hues between adjacent tablets is divided across a spectrum of subtle shades
* Disadvantages: time consuming, difficult to complete for patient
* Quicker version of Farnsworth-Munsell is the Farnsworth Panel D-15, patients asked to arrange the tablets in sequence according to shades.
relative insenitivty
People with mild degrees of colour deficiency might still be able to function in society practically. Eg: Fail Ishihara plates but pass D-15 can still function practically
confocal microscopy
- Non-invasive technique for in vivo imaging
- Principle of confocal-single point of tissue illuminated by a point source of light; while simultaneously imaged by a camera in the same plane
- Able to produce extremely thin images of the cornea serially and visualise the 5 layers of the cornea
uses of confocal microscopy
o Identify organisms causing infectious keratitis such as Acanthamoeba, fungus, microspores, herpetic eye disease
o Evaluate cornea nerve morphology
o Evaluate cornea endothelial layer
o Differentiate corneal dystrophy
specular microscopy
- Can provide objective measurements of corneal endothelial cells
parameters of specular microscopy
o Density
o Coefficient of variation
o Percentage of hexagonal cells
normal endothelial count in adults
2000/mm2 in adults.
o Average is 2400 to 2500/ mm2.
normal endothelial count in children
3500 cells/mm2 in children
endothelial count <1000/m2
If density < 1000/mm2, the cornea might still be clear.
o However there is a high risk of decompensation following surgery such as phacoemulsification
coefficient varaition in specular mircosopcy
Unitless number , usually less than 0.30. If > 0.40-can signify increase in variation ( also known as polymegethism which can occur in contact lens wearers)
hess chart
investigations of incomitant strabismus ( angle of deviation of squinting eye not the same in all direction).
principles of hess chart
o dissociation through a mirror/ or different coloured image
o foveal projection with normal retinal correspondence ( fovea-to fovea test)
o Hering and Sherrington law of innervation
hess chart set up
angent patterns projected on a black/ grey background
o For dissociations through different coloured images, the fixing target is red and the projected light is green.
o The fixing eye will thus be given a red filter, and the fellow eye will be given a green filter. Alternatively, a mirror can be used to dissociate both eyes instead of the filter method.
distance during hess chart examination
50cm away from the screen to avoid accommodation and convergence.
o Each small square subtends to 5 degrees at 50cm working distance.
interpreting a hess chart results
o Which is the abnormal eye? The chart with the overall smaller field is the abnormal one
o Is it paralytic or restrictive? In restrictive/ mechanical defects, the affected eye shows an overall compressed field with limited muscle sequelae
o Is there a deviation in primary position? If the eye hyper/hypotropic or eso/exotropic?
o Which is the underacting muscle? It is easier to see this on the larger field as this represents greater movement the eye. Negative or inward displacement represents underaction
o Which is the overacting muscle? Positive or outward displacement represents overaction
nasolacrimal synringing
non-physiologic evaluation of nasolacrimal system patency. Therefore, it gives no information on the adequacy of nasolacrimal drainage function under physiological conditions.
results in canalicular obstruction
irrigation would be expected to regurgitate from the punctum being tested.
Reflux from the opposite punctum indicates obstruction at the level of the sac or duct.
casts from nasolacrimal synringing
- Recovery of fluid in the nose after irrigation may be helpful in looking for casts or other debris.
Synotophore
measure all aspects of binocular single vision including simultaneous perception, fusion (including range of fusion) and stereopsis.
* It can also measure the degree of misalignment for horizontal, vertical and torsional misalignments in all directions of gaze.
* It can detect suppression and abnormal retinal correspondence (ARC).
to detect arc
the synoptophore, the objective angle (OA) and subjective angle (SA) are measured, which gives the angle of anomaly (AOA).
o AOA = OA - SAr
results in normal retinal correspondance (NRC
the SA is equal to OA and the AOA will be zero.
unharmonious ARC
, the SA will be less than the OA (but the SA will not be zero)
harmonious ARC
the SA will be zero, so the AOA will be equal to the OA.
definitive TB testing for occular uveitis
o Acid fast smears of mycobacterial culture
o PCR based assays of ocular fluids
* This is usually challenging, with low sensitivity
Presumptive positive for TB
o Positive TB skin test (TST)
o Positive interferon gamma release assay ( IGRA)
o Lesions of imaging of the chest
o Resolution / non-recurrence of uveitis following TB treatment
limitations of TB skin test
o Lack of standardization for test administration and reading
o High false positive rates in patients immunized with BCG vaccine / exposed to nontuberculous mycobacteria
o False negative in severe illness and immunodeficiency
IGRA
o Mechanism: measure interferon gamma response from sensitized T cells produce against Mycobacterium tuberculosis (ESAT 6, CFP 10, TB7.7)
o The proteins above not present in BCG vaccine, won’t get false positive in patient previously given BCG vaccine
Investigations of myasthenia gravis
o Single fibre EMG: Jitters
o Repetitive nerve stimulation test: High specificity (95%)
o Antibody to acetylcholine receptor
o Ice pack test
o CT chest: Thymomas
o Anti-striated muscle antibody
o Tensilon Test
ice pack test for MG
o Ice pack placed on ptotic eyelid/ affected muscle
o 75% sensitivity, but specific for MG
o Cold inhibits action of acetylcholinesterase
antibody testing for MG
Acetylcholine receptor (AChR) antibodies
Present in 90% of systemic MG
50-70% of ocular MG
MuSK protein antibodies positive in 50% of those with -ve AChR antibodies
If positive, less likely to have ocular features, thymoma
Striational antibodies
Found more often in thymoma
Marker for more severe MG
