Paediatric optometry - Lecture 4

define stereopsis?

awareness of the relative distances of objects from the observer, by means of binocular vision only and based on retinal disparity

Define stereoacuity?

the ability to detect the smallest difference in depth between 2 objects

What are the requirements for stereopsis?

- ocular alignment

- good VA

What is a normal stereopsis?

60"

40 - 50 seconds of arc

What can poor results in stereopsis indicate?

- Bv issues:

- strabismus

- amblyopia

- monocular vision loss

how to explain stereopsis tests to children

- test to measure 3D vision

- better to hold the test youself

What are some stereopsis tests you can use on children?

- Lang stereotest

- randot stereo test

- frisby test

- TNO stereo test

What is the lang stereo test?

40 cm working distance

- suitable for very young children (18 months to 2 years)

- Lang I = 3 pictures (star 600', cat 1200' and car 550')

- Lang II = 4 pictures (star 200', moon 200', truck 400', elephant 600')

- not suitable for older children as they can see up to 60 seconds of arc , so less sensitive test

How would you interpret a lang stereo test?

- ask patient what they can see

- verbal children can say what shapes they see

- preferential looking can be used in non verbal patients

How do you record for a lang stereo test?

- record what shapes seen or not seen

- 'Lang 400' to 600' (elephant +ve, car -ve)'

What is the randot stereo test?

- vectograph comprising of two similar patterns polarised at rigth angles to each other

- ensure polarising glasses are on before patient sees test

- monocular cues

- animals - 400 to 100

- circles 400 to 20

-supression test

- series of shapes

- circle star and letter e in top half 500

- square, triangle and cross in bottom half 250

What are other variations of the randot stereo test?

- titmus fly test

- random dot e test

- butterfly stereo test

How do you record stereo test?

- record smallest dispairty seen and element used

- 'titmus fly 200' cartoon'

- if patient sees lowest acuity record as ≤ as patient may be able to see better

- 'titmus fly ≤ 40' graded circles'

What is the frisby test?

- MEASURES real depth

- no goggles required

- a contour in the shape of the circle is print on one side of the perspex

- patient identifies which of the 4 has the depth

-start at 50 to 60 cm

What are the different plates available for the frisby test?

- 6mm

- 3mm

- 1mm

How do you record for a frisby test?

- record stereoacuity found

- frisby 30'

- if recording at one distance and the responses were all correct, include '≤'

- "Frsiby ≤ 85' for 40cm"

What is the TNO stereo test?

Random dot test (first 4 plates screen ( gross steropsis , last 3 measure)

- uses red and green goggles

- working distance at 40m

What is TNO test plate I?

- two butterflies

- one is always visible

- other is seen if patient has stereopsis

- ask the patient how many butterflies they can see

What is TNO test plate II?

- 4 discs

- 2 are always visible

- can ask patient 'which is biggest' or 'how many are there'

What is TNO test plate III?

- PATIENT is asked to match the shapes

- practitiner needs to remember where the shapes are

What is TNO test plate IV?

- suppression test

- 'How many circles can you see?'

- 3 = no suppression

- 2 = suppression

What is TNO test plate V to VII?

- 480 to 15'

- 2 dsics for each disparity

- 'where is the piece of cake/ pizza missing'

- important to give the patient time as it can take a while to see image.

How do you record for TNO?

- If plates I to III seen and plates V to VII not then record as 'TNO test, gross stereopsis, plates I to III seen'

- if suppression present record which eye

- Record stereoacuity for plates V to VIII

- 'TNO test, ≤ 30'

recent technology and stereopsis

new computer games are being used to meausre stereoacuity

allows for more intervals to be measured ( more accurate)

potential for better management of amblyopia ( can see exactly how much stereopsis has improved)

What effects can colour vision have?

- education

- future occupations

What is trichromacy?

The idea that color is represented by the relationship of activity in three types of cones:

- L cones

- M cones

- S cones

trichomatism

normal colour vision

anomalous trichromatism

when one of the photoreceptor types out of the three isnt working correctly

anomalous trichromatism types

protanomalous

deuteranomalous

tritanomalous

dichromatism

when one of the colour photoreceptors is absent

dichromatism types

protanopia, deuteranopia, tritanopia

monochromatism

one working photoreceptor - black and white vision / greyscale

What is protanopia?

A form of colour blindness in which you do not see any red.

What is deuteranopia?

lack of functioning green cones

What is tritanopia?

lack of functioning blue cones

What are some colour vision tests?

- isihara

- city colour vision test

- farnsworth d15

- farnsworth munsell 100 hue test

colour vision and genetics

green red

x linked

females usually carriers

males with the x gene will express colour blindness

males always get x gene from mother ( y gene is from father)

lines of confusion

How does testing congenital and acuqired colour vision defect differ?

- congenital: can screen using both eyes, use ishara

- aquired: one eye at atime, city colour vision test or D15 farnsworth test

What is the ishihara test?

- series of pseudochromatic plates

- good for assessing congenital R-G defects

- not so good for acquired defects

- doesn't test for tritanopia

- suitable for children

- 75cm viewing distance, better for practitioner to hold

- present each plate for 3 seconds

- ask patient to read the numbers

What effect does illumination have on the ishihara test?

- colour temperature can have an effect

- needs to be similar to natural daylight conditions

- high colour rendering fluorescent lighting

- patient observes test through kodak wratten #78AA filter with 100 Watt incandescent light source

What is the introduction ishihara plate?

- plate 1

- seen by all

- useful for demonstration

What is the transformation ishihara plate?

- plates 2 to 9

- correct number seen by those with normal vision

- different number seen by those with R - G deficiency

What is the vanishing plate ishihara?

- plates 10 to 17

- number seen = normal colour vision

- number not seen by R-G deficiency

WHta is the hidden digit ishihara plate?

- plate 18 to 21

- normal vision = sees nothing

- R-G deficiency = sees a number

What is the classification isihara plate?

- plates 22 to 25

- classification plate

- only used if screen plates (2-21) identify a deficiency

What is the tracing ishihara plate?

- protans sees the number on the right

- deutans sees the numbers on the left

- people with severe r-g DEFECTS, PARTICULARLY PROTANOPIA, MAY NOT SEE EITHER

How do you record for ishihara test?

- isihara all plates seen, normal colour vision

- ishihara, 3/16 seen, protan, patient and parent counselled regarding future career restrictions

What is the d15 farnsworth test?

- 15 small isochromatic discs

- able to detect moderate to severe colour vision deficiency

- people with nomral or mild colour vision deficiency will pass

What is the Farnsworth munsell 100 hue test?

- more sensitive than the d15

- requires more time (about 15 mins) and concentration

- not suitable for children

- may be suitable for teens

What is the city colour vision test?

- originally derived from d15 test

- good to use if suspecting acquired defect

- not as sensitive to mild RG defects as ishihara

- not a screening test

How should you counsel the patient and parent regarding colour vision?

- impotant to explain the genetics of a congenital colour deficiency to the parent

- no cure for congenital colour deficiency

- need to advise teachers and parents (may confused colour coded school work, coloured writing may be more difficult to see, cryaons/ colour pencils should be amrked, may need help with assignments)

What are the colour vision requirements for the british army?

- requires ishihara pass for army air corps

What are the colour vision requirements for the royal navy?

Patients with impaired colour perceptions may be restricted the branches that are avaiable to them

What are the colour vision requirements for the royal air force?

- can still join but colour deficiencies will limit roles

What are the colour vision requirements for the fire service?

- monochromats and dischromats are not acceptable

- anomalous trichromats require occuptaional testing.

What are the colour vision requirements for the lifeboat crew?

- tested using ishihara

- 3 or more plates failed = fail

What are the colour vision requirements for the police?

- monochromats are not acceptable

- mild anomalous trichromats are acceptable.

- severe anomalous trichromats and dichromats are also acceptable but will need to be instructed in coping strategies

What are the colour vision requirements for the ELECTRICAL ENGINEER?

- Colour vision is important in this profession because colour coding is widely used in electronics and electrical engineering and has significant safety implications

- normall colour vision required

- no more than 2 failed isihara plates

- lantern test required for some roles

What are the colour vision requirements for a civilian pilot?

- need to pass first 15 plates of ishihara without error

- if ishiara failed than further tests required