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
