Examination Techniques Flashcards
What is distance visual acuity directly related to?
The minimum
angle of separation (subtended at the nodal point of the eye)
between two objects that allow them to be perceived as distinct.
What is normal monocular VA
Equates to 6/6 (metric notation; 20/20 in non-metric ‘English’ notation) on Snellen testing.
Normal corrected VA in young adults is often superior to 6/6.
What is Best corrected VA
denotes the level achieved with
optimal refractive correction.
What is pinhole VA
pinhole (PH) aperture compensates for the
effect of refractive error, and consists of an opaque occluder
perforated by one or more holes of about 1 mm diameter
PH acuity in patients with macular disease and
posterior lens opacities may be worse than with spectacle cor-
rection.
If the VA is less than 6/6 Snellen equivalent, testing is
repeated using a pinhole aperture.
What is Binocular VA
usually superior to the better monocular VA of each eye, at least where both eyes have roughly equal vision.
What does CF vision mean
denotes that the patient is
able to tell how many fingers the examiner is holding up at a
specified distance usually 1 metre.
What is HM vision
the ability to distinguish whether the examiner’s hand is moving when held just in front of the patient.
What is PL vision
the patient can discern only light
(e.g. pen torch), but no shapes or movement. Careful occlusion of the other eye is necessary. If poor vision is due solely to a dense media opacity such as cataract, the patient should readily be able to determine the direction from which the light
is being projected
What is log MAR
an acronym for the base-10 logarithm of the minimum angle of resolution (MAR) and refers to the ability to resolve the elements of an optotype
Thus, if a letter on the
6/6 (20/20) equivalent line subtends 5′ of arc, and each limb of
the letter has an angular width of 1′, a MAR of 1′ is needed for resolution. For the 6/12 (20/40) line, the MAR is 2′, and for the
6/60 (20/200) line it is 10′
What is the value of each letter on the LogMAR chart
0.02
Examples of LogMAR Charts
1) Bailey- Lovie Chart
2) ETDRS chart
3) Computer charts
At what distance is the Bailey Lovie chart read from?
6m
At what distance is the ETDRS chart read from?
4m
Is macula disease better tested with distance or near vision?
Near vision
Which conditions reduce contrast sensitivity but preserve VA
1) Amblyopia
2) Optic Neuropathy
3) Some cataracts
4) Higher order aberrations
What is the Pelli Robson chart
contrast sensitivity letter chart is viewed
at 1 metre and consists of rows of letters of equal size (spatial frequency of 1 cycle per degree) but with decreasing contrast of 0.15 log units for groups of three letters.
The patient
reads down the rows of letters until the lowest-resolvable
group of three is reached.
What is the principle of contrast sensitivity testing?
It is a measure of the ability of the
visual system to distinguish an object against its background.
A light grey
letter will be less well seen against a white background than a
black letter.
Examples of contrast sensitivity tests
1) Pelli-Robson chart
2) Sinusoidal (sine wave) gratings
3) Spaeth Richman Contrast Sensitivity test (SPARCS)
How is sine wave grating contrast sensitivity test performed
require the test subject to
view a sequence of increasingly lower contrast gratings.
How is near VA tested?
A range of near vision charts (including logMAR and ETDRS versions) or a test type book can be used. The book or chart is held at a comfortable reading distance and this is measured and noted. The patient wears any necessary distance correction
together with a presbyopia correction if applicable (usually their own reading spectacles). The smallest type legible is recorded for each eye individually and then using both eyes together
What is the Amsler grid used for?
evaluates the 20° of the visual field centred on
fixation. It is principally useful in screening for and monitoring macular disease, but will also demonstrate central visual field defects originating elsewhere. Patients with a substantial risk
of choroidal neovascularization (CNV) should be provided with an Amsler grid for regular use at home.
How many types of Amsler grid are there?
7
At what distance from the eyes should the Amsler grid be held?
33cm
How to differentiate macula vs optic neuropathy on an Amsler grid?
Patients with macular disease often report
that the lines are wavy whereas those with optic neuropathy tend to remark that some of the lines are missing or faint but not distorted.
Types of Amsler grid charts
1) White grid black background
2) Similar to chart 1 with diagonal lines to aid fixation
3) Similar to chart 1 but with red squares
4) Random dots
5) Horizontal lines detecting metamorphopsia along specific meridians
6) Similar to chart 5 but with a white background and lines closer together
7) Fine central grid each square subtending an angle of half degree
What is the light brightness comparison test used for?
This is a test of optic nerve function, which is usually normal in
early and moderate retinal disease.
What is photostress testing?
a gross test of dark adaptation in which the visual pigments are bleached by light. This causes a temporary state of retinal insensitivity perceived by the patient as a scotoma.
What does the photostress test, test?
detecting maculopathy when ophthalmoscopy is equivocal, as in mild cystoid macular
oedema or central serous retinopathy. It may also differentiate
visual loss caused by macular disease from that caused by an
optic nerve lesion.
What is the blue retinal cone peak sensitivity?
414-424nm
What is the green retinal cone peak sensitivity?
522-539nm
What is the red retinal cone peak sensitivity?
549-570nm
What is protanomaly?
red cone weakness
What is protanopia?
red cone absence
What are people with red-green deficiency called?
Protanomalous- due to abnormality of red sensitive cones
What are people with an abnormality of green sensitive cones called?
Deuteranomalous
What are people with blue green deficiency called?
Tritanomalous
What colour defect does acquired macula disease produce
Blue- yellow defects
What colour defect do optic nerve lesions produce
Red-green defects
What defects does the Ishihara test screen for?
Congenital protan and deuteran defects (red-green) colour vision defect
Examples of colour vision tests?
Ishihara test
City university test
Hardy Rand Rittler test
Farnsworth- Munsell 100 hue test
What is the photostress test?
1) BCVA measured first
2) The patient looks at a light held about 3 cm away from the eye, for about 10 seconds;
3) The photostress recovery time is the time taken to read any three letters of the pre-test acuity line and is normally between 15 and 30 seconds
What is the hill of increasing sensitivity of a visual field
1) 50 deg superiorly
2) 60 deg nasally
3) 70 deg inferiorly
4) 90 deg temporally
What is an isopter?
a line connecting points of the same sensitivity, and on a two-dimensional isopter plot encloses an area within which a stimulus of a given strength is visible. When the field is represented as a hill, isopters resemble the contour lines on a map
What is a scotoma?
an area of reduced (‘relative’) or total (‘absolute’)
loss of vision surrounded by a seeing area.
What is luminance?
intensity or ‘brightness’ of a light stimulus,
measured in apostilbs (asb)
A higher intensity stimulus has a
higher asb value; this is related inversely to sensitivity.
Are rods or cones more sensitive in dim light?
Rods - and the peripheral retina becomes more sensitive in proportion to the central retina so the hill of vision flattens with a central crater rather than a peak at the fovea (As the cones have low sensitivity in scotopic conditions)
How long does it take to adapt from darkness to brightness
5 minutes
How long does it take to adapt from bright sunlight to darkness?
20-30 mins
What is static perimetry?
the location of a stimulus remains fixed, with
intensity increased until it is seen by the subject (threshold is
reached) or decreased until it is no longer detected
What is kinetic (dynamic perimetry)
stimulus of constant
intensity is moved from a non-seeing area to a seeing area at a standardized speed until it is perceived, and the point of perception is recorded on a chart. Points from different meridians are joined to plot an isopter for that stimulus intensity. Stimuli of different intensities are used to produce a contour map of the visual field.
What is manual perimetry?
involves presentation of a stimulus by the
perimetrist, with manual recording of the response. It was
formerly the standard method of field testing but has now largely been superseded by automated methods. It is still used occasionally, particularly in cognitively limited patients unable to interact adequately with an automated system, and for dynamic testing of peripheral fields.
What is standard automated perimetry (SAP)
the method used
routinely in most clinical situations. These predominantly utilize static testing, though software is
available on some machines to perform dynamic assessment.
What is threshold testing algorithm used for?
used for detailed assessment of the hill
of vision by plotting the threshold luminance value at various locations in the visual field and comparing the results with age-matched ‘normal’ values.
A typical automated strategy is to present
a stimulus of higher than expected intensity. If seen, the intensity
is decreased in steps (e.g. 4 dB) until it is no longer seen (‘staircasing’)
Used for monitoring glaucoma
What is suprathreshold testing algorithm used for?
involves testing with stimuli of
luminance above the expected normal threshold levels for an age- matched population to assess whether these are detected.
In other words, testing to check that a subject can see stimuli that would be seen by a normal person of the same age. It enables testing to be carried out rapidly to indicate whether function is grossly normal
or not and is usually reserved for screening.
What are fast testing algorithms used for?
The HFA offers the SITA (Swedish
Interactive Thresholding Algorithm), which uses a database of
normal and glaucomatous fields to estimate threshold values and takes responses during the test into account to arrive at adjusted estimates throughout the test. Full-threshold values are obtained at the start of the test for four points
At what radius from the fixation point do most glaucomatous defects occur?
30 degree radius
What does 24-2 mean?
‘24’ denotes the extent in degrees to which the field is tested on the temporal side (to 30° on the nasal side). The number
after the hyphen (2) describes the pattern of the points
tested. 30-2 is an alternative.
What does 10-2 mean?
used to assess a central area of radius 10°. Glaucomatous defects here may threaten central vision. The 10-2
pattern facilitates more detailed monitoring of the extent of damage, especially in advanced glaucoma where there is
‘split’ fixation.
When is peripheral field testing used?
Patterns that include central and peripheral
points (e.g. FF-120) are typically limited to the assessment of
neurological defects.
When is binocular field testing used?
(e.g. Esterman strategy) is used to
assess statutory driving entitlement in many jurisdictions.
With SITA strategies, what % of false positives/negatives are significant?
> 15%
With full threshold strategy what % fixation losses is significant?
> 20%
With full threshold strategy what % false positives/negatives are significant?
> 33%
What is a fixation loss?
indicate steadiness of gaze during the test.
Methods of assessment include presentation of stimuli to the
blind spot to ensure no response is recorded, and the use of a ‘gaze monitor’.
What are false positives on VF testing?
assessed by decoupling a stimulus
from its accompanying sound. If the sound alone is presented
and the patient still responds, a false positive is recorded.
What are false negatives on VF testing?
registered by presenting a stimulus much brighter than threshold at a location where the threshold has
already been determined. If the patient fails to respond, a false
negative is recorded.
A high false-negative score indicates
inattention, tiredness or malingering, but is occasionally an
indication of disease severity rather than unreliability.
What does the grey scale on the visual field test represent?
decreasing sensitivity is represented by
darker tones – the physiological blind spot is a darker area
in the temporal field typically just below the horizontal axis.
Each change in grey scale tone is equivalent to a 5 dB change in sensitivity at that location.
What does total deviation on the visual field test represent?
Shows the
difference between a test-derived threshold at a given point and the normal sensitivity at that point for the general population, correcting for age. Negative values indicate lower than
normal sensitivity, positive values higher than normal.
What does pattern deviation on the visual field test represent?
derived from total deviation values adjusted for any generalized decrease in sensitivity in the overall field (e.g. lens
opacity), and demonstrates localized defects.
What do the probability value plots on the visual field test represent?
a representation of
the percentage (<5% to <0.5%) of the normal population in
whom the measured defect at each point would be expected.
Darker symbols represent a greater likelihood that a defect is significant.
What do the summary values on the visual field test represent?
These values are principally
used to monitor progression of glaucomatous damage rather than
for initial diagnosis.
What is the visual field index?
a measure of the
patient’s overall visual field function expressed as a percentage,
the normal age-adjusted value being 100%.
What is mean deviation (MD)?
gives an indication of the overall sensitivity of the field. It is derived from averaging the total deviation values.
What is pattern standard deviation (PSD)?
a measure of focal loss or variability within the field and considers any generalized depression in the hill of vision. An increased PSD is
therefore a more specific indicator of glaucomatous damage than MD.
What are probability values?
Abnormal summary values are followed
by a probability value, representing the percentage likelihood
that an abnormal value of this level will occur in a normal
subject. The lower the P value, the more likely the result is
abnormal.
What is the glaucoma hemifield test?
compares corresponding
areas in the superior and inferior hemifields and relates only to
glaucoma.
Does SAP detect early field loss?
detects field damage only after substantial ganglion cell loss is established. Attempts at detecting change at an earlier stage include the adoption of stimuli intended to target specific
ganglion cell types.
What is SWAP
Short-wave automated perimetry (SWAP) uses a blue stimulus on a yellow background. Sensitivity to blue light (mediated
by blue cone photoreceptors) is adversely affected relatively early in glaucoma.
SWAP is more sensitive to early glaucomatous defects but has not been widely adopted because cataract
decreases sensitivity to blue light (the brunescent lens acts as a yellow filter) and patients frequently dislike the lengthy test.
What is microperimetry?
a visual field test that measures retinal
sensitivity and fixation behaviour in patients with macular
disease and focal glaucoma involving the central visual field.
It allows an exact correlation between pathology involving
the macula and the corresponding functional abnormality.
What is scleral scatter illumination used for?
A corneal stromal lesion will become illuminated
because of forward light scatter. This technique is especially useful
to detect subtle stromal haze, or cellular or lipid infiltration.
What is retroillumination used for?
uses reflected light from the iris or fundus after
pupil dilation to illuminate the cornea. This allows the detection of fine epithelial and endothelial changes, such as epithelial cysts, keratic precipitates and small blood vessels.
What is specular reflection used for?
Specular reflection shows abnormalities of the endothelium such as reduced cell density and guttata. Pseudoguttata probably represent reversible endothelial cell oedema and inflammatory cells
beneath the endothelial layer.
With a 60D lens, indirect ophthalmoscopy of the optic disc needs how much correction factor?
0.88-1.00x
With a 90D lens, indirect ophthalmoscopy of the optic disc needs how much correction factor?
1.3x
With a 78D lens, indirect ophthalmoscopy of the optic disc needs how much correction factor?
1.1x
What are the image properties of IO image?
Vertically inverted and laterally reversed
How to calculate magnification factor of a BIO lens eg 20D lens?
60/20
3x magnification
What principle does GAT obey?
Imbert Fick principle. Pressure= Force/Area
Corneal rigidity and capillary attraction cancel each
other out when the flattened area has a diameter of 3.06 mm
What CCT does GAT assume?
520 microns
What is corneal hysteresis?
A measure of how corneal tissue absorbs and dissipates
energy during deformation and return. Corneal hysteresis appears to
provide a measurement of IOP that is less affected by factors such as
previous laser refractive surgery.
Which IOP measuring machine uses the principle of corneal hysteresis?
Reichert ORA
What disinfection regime is recommended for lenses?
A suggested regimen is to soak the lens
in 2% hypochlorite solution for at least 5 minutes followed by
thorough rinsing in sterile saline, then air-drying.
Examples of indentation gonioscopy lenses?
Zeiss
Posner
Sussman
All are 4 mirror gonioprisms
What does indentation gonioscopy help identify?
Indentation is performed by gently pressing the lens pos-
teriorly against the cornea. This forces aqueous into the
angle, pushing the peripheral iris posteriorly.
If the angle is closed only by apposition between the iris
and cornea it will be forced open, allowing visualization of
the angle recess.
If the angle is closed by adhesions between the peripheral
iris and cornea – peripheral anterior synechiae (PAS) – it
will remain closed.
Examples of direct goniolenses?
Koeppe
Barkan
Swan Jacob
What does the Schwalbe line represent?
Peripheral termination of descemet membrane anatomically.
What are pigment deposits anterior to Schwalbe line called?
Sampaolesi line
especially in heavily pigmented angles (e.g. pseudoexfoliation
syndrome)
Anatomically what structure on gonioscopy is the most anterior projection of the sclera?
Scleral spur
Which conditions are peripheral anterior synechiae seen in?
○ Primary angle-closure glaucoma.
○ Anterior uveitis.
○ Iridocorneal endothelial (ICE) syndrome.
Which conditions are angle neovascularization seen in?
○ Neovascular glaucoma.
○ Fuchs heterochromic cyclitis.
○ Chronic anterior uveitis.
Which conditions are angle hyperpigmentation seen in?
○ Physiological variant.
○ Pigment dispersion syndrome.
○ Pseudophakic pigment dispersion.
○ Pseudoexfoliation syndrome.
○ Blunt ocular trauma.
○ Anterior uveitis.
○ Following acute angle-closure glaucoma.
○ Following YAG laser iridotomy.
○ Iris or angle melanoma or naevus.
○ Iris pigment epithelial cysts.
○ Naevus of Ota.
Name some traumatic angle conditions?
○ Angle recession.
○ Trabecular dialysis.
○ Cyclodialysis.
○ Foreign bodies.
What are causes of blood in the Schlemm canal?
○ Physiological variant.
○ Carotid–cavernous fistula and dural shunt.
○ Sturge–Weber syndrome.
○ Obstruction of the superior vena cava.
What is the normal distribution of central corneal thickness (CCT)
540 +/- 30 microns
