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
