Unit 3 Ocular Examination Flashcards
why/when do we test colour vision
Careers – Police, Armed Forces, Pilots, Electrical engineers
Educational – Chemistry, Geography, History
Safety – Traffic Light, Electrical Wiring, Electronic PCBs
Acquired CVDs
- Around 8% of the male population have a red-green CVD i.e. 1 in 12
- Around 4% of the female population have a red-green CVD i.e. 1 in 200
what is the genetic of a red green CVD
The gene which causes inherited red/green defects is only found on the X chromosome
Red/green CVDS = X-linked recessive
o Males XY= one altered copy is sufficient to cause CVD
o Females XX = mutation must occur on both copies of the gene
o This is why males are affected by X-linked recessive disorders much more frequently
o There is no male-male transmission (mother must be at least a carrier)
o 8% male’s vs 1 in 200 women
o Colour blind father & mother not a carrier = no colour-blind sons & 100% daughters’ carriers
o Normal father & carrier mother = 50% colour blind son & 50% daughter carrier
o Colour blind father & carrier mother = 50% colour blind son & 50% daughter carrier/50% daughter colour blind
o Normal father & mother colour blind = 100% sons colour blind & 50% daughters’ carriers
tritan congenital defects
Blue/yellow defects (tritan) CVD has an autosomal dominant inheritance
o One mutated copy of the gene is sufficient to cause CVD
o Encoded on chromosome 7
o Are not sex linked – affect men & women equally
RARE
Monochromacy
monochromats = typically totally colour blind, single functioning cone
o Rod monochromat (rare 1 in 30,000) – truly colour blind, no functioning cones VA ~6/60
* Reduced VA
* Photophobia
* Nystagmus
o Cone monochromat (rare 1 in 100,000) – only 1 functioning cone, VA ~6/9
Anomalous trichromacy
anomalous trichromats = have all 3 cone pigments, however one cone pigment is anomalous having a shifted peak sensitivity
Trichromacy / trichromats
normal CV
Protan CVD - red = long = 700nm
o Protanopia – L wavelength cone missing
o Protanomaly – L wavelength cone is anomalous/reduced sensitivity
Deutan CVD - Green = medium = 540nm
o Deuteranopia – M wavelength cone missing
o Deuteranomaly – M wavelength cone is anomalous/reduced sensitivity
Tritan – blue = short = 490nm
o Tritanopia = S wavelength cone missing
o Tritanomaly = S wavelength cone is anomalous/reduced sensitivity
how should acquired CVD be tested
City should be used as it is sensitive to blue-yellow defects
Monocular testing – may be unilateral or bilateral/asymmetrical
Secondary to pathology both ocular and systemic disease
Associated with loss of VA and VF
types of CVD acquired
- Type 1 (similar to protan) – Red/Green – found in macular
dystrophy/hydroxychloroquine retinal toxicity (rheumatoid arthritis) - Type 2 (similar to deutran) – Red/Green – found in retrobulbar optic neuritis
(common with ON defect) - Type 3 (similar to tritan) – Blue found in many central and peripheral retinal
lesions and lesions of the visual pathway – POAGlaucoma, AMD, DR, cataract
how should ishihara be used
A Confusion test used to screen for protan and deutan (R-G) CVDs
o No blue/yellow plates
38 or 24 plate version, does not grade severity – pass or fail basis
38 – three fails = pass
24 – two fails = pass
Should be used @ 30- 75cm (at WD)
Plates should be illuminated by daylight/artificial daylight, illuminant C or D65 luminance in the range 250-600 lux
4 seconds per plate
Px must have a VA of at least 6/24
Colour normal will make immediate decisions, CVD takes time to use brightness cues
classification plates
o Used to differentiate protan from deutan and employ a vanishing design set on a neutral background
o 2 digits one made up in reddish dots – lies on protan isochromatic confusion line, one in purple which lies on deutan isochromatic confusion line
City CV test
Three editions – edition 3 in practice
This is useful for acquired CVD and to grade the severity of a congenital defect
Confusion test – used for classification
Subjects select the peripheral colour that looks closest to the central spot
o 3 peripheral colours are isochromatic confusions with central spot, the fourth colour is the next colour in the D15 sequence
4 screening plates
6 detection plates
Classification based on number of errors
o Includes 4 screening plates, but screening efficiency not known and probably not good – of px sees 10/10 or 9/10 different colour spots then it is normal
o 6 classification/grading plates – only 4 plates are equivalent to the 2nd edition
Advantages = available in book form, not available online so px can’t practice
Disadvantages = px can give mixed response (go for the majority), protan classification poor due to brightness cues, different pages have different classification efficacies.
Use @50cm
Farnsworth D15
15 loose caps, on fixed cap/reference cap in the box
Colour confusion test (based on isochromatic confusion lines)
Caps have approx. equal hue differences, colours lie on isochromatic confusion lines
Not a screening test
Pass and fail criteria varies;
o 1 minor error (transposition of adjacent caps permitted
o 1 major error (isochromatic confusion) permitted
o 2 major errors (isochromatic confusion) permitted
Farnsworth 100 hue
Colour matching / hue discrimination test
Developed for vocational use
CVD classified from position of errors, does not reliably identify mild CVDs
TES is calculated, perfect observer error score = 0
HRR cvd TEST
Out of print now
Pseudoisochromatic plates, similar to ishihara
Uses shapes, can be useful in children
CAD CVD TEST
Computer-based test
New approach to CV assessment, by isolating the use of colour signals in the eye
Detects acquired & congenital; protan/deutan/tritan – provides automatic classification
100% sensitivity & specificity – picks up on very low levels of colour deficient
Provides automatic outcome report based on CAA / FAA reports
Anomaloscope
Based on a colour match
Two different light sources must be matched to the same colour
Vocational standards CVD
Police Scotland
o Monochromats rejected
o Mild anomalous trichromats acceptable and treated as normal
o Severe anomalous trichromats and dichromats also acceptable and are to be instructed in coping strategies
o Applicants who show lowered discrimination for blue colours are to be referred to an ophthalmologist for further assessment. This must include a measure of their dark adaptation performance.
Army/RAF/Navy
o Ishihara normal
Fire services
o Minimum standard – pass Farnsworth D15
o Monochromats & dichromats = not accepted
o Anomalous trichromats = occupational testing
Electrical engineers
o No more than two incorrect plates with ishihara
o Holmes-Wright or Giles-archer lantern test
o CAM lantern
Pilots
o Ishihara – 24 plate, must pass first 16 plates
o Ishihara fail
▪ Anomaloscope – Nagel or equivalent
▪ Colour assessment and diagnosis i.e. CAD test: pass if threshold is < 6 SU deutans / <12 SU for protan
City CVD procedure edition 1 and 2
Procedure
* Testing distance: 35cm 2nd edition
* Viewing time: 6 seconds per page
* Complete score sheet for section 1 (out of 6) and section 2 (out of 4)
* Fail if more than 2 mistakes
mode of action anaesthetic
Blocks the initiation and propagation of action potentials by preventing
the voltage dependent increase in Na+ via blocking Na+ channels on the nerve cell
membrane. Cationic portion of the Topical Anaesthetic binds causing a physical occlusion
and preventing an axon depolarisation.
uses of anaesthetic
- Anaesthesia prior to contact tonometry
Þ Goldmann’s or Perkins - Anaesthesia prior to foreign body removal
Þ In either cornea or sub-tarsus - Anaesthesia prior to punctual plug insertion or removal
- Anaesthesia prior to eye impressions
Þ Scleral Contact Lenses
Þ Ocular Prosthetics - Anaesthesia prior to diagnostic procedures
Þ Gonioscopy
Þ Schirmer test
Þ Pachymetry - Irrigation of the eye
Þ Foreign body removal
Þ Burns
Þ Chemical Injuries
Contraindications for Anaesthetics
- Known hypersensitivity
- Premature babies (don’t have the enzymes to metabolise amides especially)
- Global penetrating injuries
- Pregnancy & Breastfeeding
- Where wound healing would be compromised
perkins calibration
Calibration
1. Take off battery pack
2. Place instrument on its back, with black disc under head of the instrument
3. Place 2g or 5g weight on the probe
4. The probe should lift at 2 and 5.
5. If it does not, compensate by removing/adding the difference. As long as the difference is
equal between the 2 and 5g weight, then the instrument can be used.
goldmann calibration
- Place metal rod into the side of the probe
- The probe should rock at 2g and 6g (first line and second line)
- Make sure biprism probe is horizontal
- Slit-lamp should be cobalt blue and wratten 32
errors of contact tonometry
- Calibration
- Incorrect alignment
- lids touching the probe
- Quantity/quality of tears,
- high astigmatism (distorted mires)
- Repeated measurements: reduce IOP – 2-4mmhHg
why is only one reading required for applanation tonometry
Goldman/Perkins takes ocular pulse into account, so the reading is an average = only 1 required
errors of perkins - high cyls what would be done
If astigmatism exceeds 3DC: needs to be compensated for as cornea is elliptical
Causes misreading if this is not compensated for
In this instance, the axis of the prism must be set to 43 degrees to the flattest meridian to ensure an area of 7.354mm2 is applanated
This is achieved by aligning the minus cyl axis with the red mark on the cone holder (Goldman) / align with A (Perkins)
advise after anaesthetic
Drops take 60 secs to work
May last for up to 25 mins
Do not rub eyes for at least 30 mins
Avoid getting dust/grit in eyes
Do not reinsert CLs until at least 30 mins post drops instillation
If experience any unusual symptoms (pain/blurred vision), contact practice or seek medical advice
Give leaflet
principle of NCT
Produces applanation using controlled air puff that impinges cornea
Interval of time required for air pulse to produce applanation is proportional to IOP
Requires at least 3 readings to take an average so ocular pulse is accounted for
IOPs Factors affecting accuracy
Diurnal variation of up to 5mmHg; lowest in morning, increases throughout day
The fluctuation of IOP with the heart rate, being equal to the difference between systolic and diastolic IOP is the ocular pulse amplitude (OPA)
Stress / apprehension / eye squeezing (increase)
Exercise (increase by up to 50%)
Unstable tear film
Accommodation can decrease IOP by 2-3mmHg
SIGN Referral guidelines IOPS
IOP > 25mmHg – irrespective of CCT
IOP between 21-25– when CCT is <555 (thin) & px 65 or under
IOP < 26 & CCT > or equal to 555 (thick) – MONITOR
NICE guidelines
IOP >24mmHg, asymmetry of 5mmHg
Risks of anaesthetic
Px may have adverse reaction (RARE)
Ocular
- Delayed healing & tear flow
- Lowering IOP
- Increase permeability & compromise integrity of cornea
- Desquamation/corneal melt risk if repeated drops instilled (VA suddenly reduces but recovers with artificial tears)
Systemic
- Light headedness
- Tinnitus
- Occasional fainting
Px may have allergic response (in form of blepharoconjunctivitis)
which group of anaesthetics does lidocaine belong to
amide
what are included in esters
proxymetacaine
oxybuprocaine
tetracaine
normal VF
Superior 60 degrees
Inferior 70 degrees
Nasally 60 degrees
Temporally 100 degrees
Blind spot = 15 degrees temporally
differnece between supra and full threshold VFs
Supra-Threshold: Tests at a threshold assumed achievable based on px age.
* Full-Threshold: Measures the patients threshold, by increasing the brightness
until the patient reports that they have seen the stimulus
why confrontation with a red target
It may be beneficial to perform the confrontation test with a red target.
In chiasmal lesions due to pituitary tumours, colour desaturation occurs across the
vertical midline
Cecocentral scotomas
Cecocentral scotomas can be caused by damage to the optic nerve or certain areas of the brain, and can be a symptom of a number of conditions, including:
Glaucoma
Optic neuritis
Stroke
Tumors
adjustments for VFs when VA <6/18
larger target for confrontation, chart 2 for amsler, diamond for Humphrey.
pituitary tumour causes which VF defect
bitemporal hemianopia
different types of VF test types eg sita fast
24-2
o 24 degrees from fixation (in 3 directions, 30 degrees nasally)
o 58 locations over central 25 degrees, extends 30 degrees nasally, pts are 3 degrees apart
o 2 = at each side of horizontal, no points on horizontal midline
o Slightly quicker than 30-2 (reduces test time by 25%)
30-2
o 30 degrees from fixation (in 4 directions)
o 76 locations over central 30 degrees, pts are 6 degrees apart
o Glaucoma, cataract, neurological
10-2
o 10 degrees from fixation
o 69 points, 2 degrees apart
o Useful for macular investigation
C40
o Central 40 points
visual field plot information givne - what does it mean
Reliable: <20% Fixation losses, <20% False Postives and False Negatives
Sensitivity Plot – visual threshold level for each tested point measured in Decibel (db) (higher number= more sensitive to dimmer light)
Greyscale – visual representation of reduced sensitivity
(light colour= high sensitivity and vice versa)
- & 5. Compares normative data with a person of similar age
- & 7. looks at focal losses after taking into account general loss due to cataracts etc
- Anayses symmetry of 5 predefined areas in Superior and Inferior VFs
- VFI – reflects the Ganglion Cell Loss as a %, 100%= NORMAL
- Self explanatory
what is MD and PSD in VFs
MD (mean deviation) = mean difference in decibels between the normal expected hill of vision and the patients hill of vision
o If deviation out with norm a p value will be given
PSD (Pattern standard deviation) = takes into account generalised loss i.e., overall depression
This indicates a deviation in the shape of the hill of vision. It has a positive sign. A low value indicates a normal shape of the hill of vision, whereas a higher value indicates an irregular hill of visio
kinetic vs static VFs
Static
o Measures the sensivity of retinal points
o Stimulus is stationary, luminance changes
o 3D hill of vision
Kinetic
o Measures the extent of the VF by plotting isopters
o Stimulus moves from a non-seeing to seeing area
o 2D measurement of hill of vision
o Only done with a Goldmann visual field
false negative meaning VFs
- False Negative: Patient doesn’t respond to a brighter stimulus, even though they
had already responded to a duller one in the same spot.
what does -2 mean in VFs, like in 24-2
“-2” presents the points 2-3 degrees away from the midline, so that the practitioner can
more easily discern if the defect respects the horizontal midline.
(Right/Left) (Superior/Inferior) Homonymous quadrantanopia types
o Pie in the sky - Meyer’s loop, temporal lobe
o Pie on the floor - Baum’s loop, parietal lobe
Cause:
* Vascular, such as a stroke
Binasal Defect causes
Causes:
* Compression of temporal nerve fibres
* Vigabatrin for Epilepsy
* Atheroma of the Internal Carotid Artery
What does the G chart on OCT tell us?
G chart represents normative data comparison for Ganglion Cell Complex (GCC). This comprises of the inner most retinal layers (ILM, RNFL, GCL, IPL, INL). The GCC is clinically proven to be the only layers of the retina affected by GLAUCOMA.
The S/I shows the comparison between superior and inferior GCC. This plot shows up altitudinal defects and early glaucomatous changes
what percentage of dry needs to be used when flashes or floaters
College guidelines state MUST use 1% solution when investigating new onset flashes and floaters.
generally how long does anaesthetic last and how long does it take
produces anaesthesia within 1 minute
last 15-30mins
what is an amide
lidocaine
contradindication of tetracaine
not for children
if px on sulphonamides (antibacterial type of drug) then cannot use
which is the only anaesthetic that could be used for pregnant and lactating
lidocaine and NaFl, have been used for many yrs without apparent ill effects
proxymetacaine use cautiously in who
known allergy
cardiac disease
hyperthyroidism
(because of increased risk of sensitivity)
ocular side effects of anaesthetic drops
transient stinging (all)
transient burning (all)
punctate keratitis (all)
conjunctival hyperaemia (proxy,tetra)
pupillary dilation or cycloplegic effects rarely (proxy)
proxy/tetra:
severe, immediate type, hyperallergic corneal reactions occur rarely (acute, intense diffuse epithelial keratitis, a grey ground glass appearance, sloughing of large areas of necrotic epithelium)
Oxy, lido:
hypersensitivity may occur rarely, (allergic conjunctivitis, peri orbital oedema)
general side effects of anaethetic
proxy, oxy ,lido - none reported
tetra - systemic toxicity mainly involves CNS, systemic effects unlikely with topical application (topical here mean skin)
storage of anaesthetics
somewhere dark
oxy, tetra, lido - store in <25 degrees
Proxy - once opened 2-8 degrees ( in fridge)
if kept in room temp then store <25 degrees for up to 1 month
before using anaesthetics ask about what
pregnancy and lactating
contact lenses (cannot wear for minimum 30mins after)
GH and meds
(proxy hyperthyroid, cardiac - use cautiously)
(tetra - cannot be used if on sulphonamides)
which anaesthetic has the least antibacterial action
proxy - good for taking swabs
what are the 2 ways to dilate the pupil
- sphincter pupillae relaxation (tropicamide, cyclopentolate), antimuscarinic
sphincter muscle has the biggest effect on pupil size - dilator pupillae contraction (phenylephrine 2.5/10%) sympathomimetic
topical anaesthetics mode of action
Mode of Action - Blocks the initiation and propagation of action potentials by preventing the
voltage dependent increase in Na+ by blocking Na+ channels on the nerve cell membrane.
Cationic portion of the Topical Anaesthetic binds causing a physical occlusion and preventing an
axon depolarisation
typical guidance for percentage of cyclo
child 3 months to 11 yrs - 1%
12-17 yrs - 0.5%
atropine poisioning systemic effects
blind as a bat - accommodation paralysis
dry as a bone - inhibition of sweat and salivary glands
red as a beetroot - dilation of BVs
mad as a hatter - CNS effects
advise after dilation drops (tropicamide)
Advice:
* Cannot Drive 4-6 hours after dilation
* Sx of AACG and action required
* Dilation leaflet
o Practical risk in driving and operating heavy machinery post dilation.
o Advise sunglasses due to glare.
o concern of inducing an ACG attack (1/5000) but often the risks of not dilating outweigh risks of dilating (VH and IOP).
ACG is most likely to occur during the recovery phase of dilation whereby the mid dilated pupil in close apposition to anterior surface of the lens can impeded aqueous outflow
systemic effects after cyclo
dry mouth
dry skin
flushing
increased body temp
increased heart rate
HAs
CNS effects - drowsy, hallucinations, drowsiness
(young kids and elderly more likely to get side effects)
phenylephrine contraindications
GH: aneuryms, thyrotoxicois, caridovascular diseases
MEDS: MAOIs, (anti depressants), beta blockers
PX age: 10% should not be used in kids or elderly
Children & over 65 as increased risk of systemic toxicity
* Neonates
Cautions: asthma,
side effects of phenylephrine
Ocular Side Effects of Phenylephrine
* Transient pain (but not as stingy as tropicamide)
* Lacrimation
* Keratitis
* Pigmented aqueous floaters
* Rebound miosis
* Rebound conjunctival congestion
* Conjunctival hypoxia
Systemic Side Effects of Phenylephrine
* Systemic hypertension
* Occipital headache
* Subarachnoid haemorrhage
* Ventricular arrythmia
* Tachycardia
* Reflex bradycardia
* Blanching of skin
