W4: Measurement of Stereopsis and Colour Vision

WATCH LECTURE

Define:

• Stereopsis

• Stereoacuity

• SO:

  • Awareness of relative dists of objects from the observer, by means of BV only + based on retinal disparity. Req’s:

    • Ocular alignment

    • Good VA

• SA:

  • Ability to detect the smallest diff in depth btwn 2 objects

How is stereopsis interpreted and tested in practice?

• Normal threshold: Around 60“, though often better

• Poor stereopsis may indicate BV issues:

  • Strabismus

  • Amblyopia

  • Monocular vision loss

• Communication tip: Say, “I’m going to do a test to measure your 3-D vision.”

• Tip: Hold the test yourself

Give examples of stereopsis tests

• Lang stereotest

• Randot Stereo Test

• Frisby Test

• TNO stereo test

What are the features and differences between Lang I and Lang II Stereo Tests?

WD=40cm

Suitable for v young children : 18mo-2 years

Lang I: 3 pictures

• Star: 600”

• Cat: 1200”

• Car: 550”

Lang II: 4 pictures

• Star: 200” (always visible; attracts attention)

• Moon: 200”

• Truck: 400”

• Elephant: 600”

Record stereopsis tests appropriately.

How is the Lang Stereo Test performed, interpreted, and recorded?

• Procedure: Ask child what shapes they see

  • Verbal children: name the shapes

  • Non-verbal children: use preferential looking

• Recording: Note which shapes were seen or not

  • Example: “Lang 400–600” (Elephant +, Car –)

What is the Randot Stereo Test and how is it set up?

• Vectograph comprising of 2 similar patterns polarized at right angles to each other.

• Polarising glasses

  • Ensure glasses are on before patient sees test. 

  • Monocular cues

• Animals: 400” to 100”

• Circles: 400” to 20”

  • 20” Doesn’t matter as long as they can see 60”

• Includes a suppression test

How are the Randot Stereo Test shapes structured and graded?

• Top half: Circle, star, letter E → 500”

• Bottom half: Square, triangle, cross → 250”

Series of shapes

Other variants of stereopsis tests

• Titmus Fly test

• Random Dot E test

• Butterfly Stereo test

Discuss how to use measures of stereoacuity commonly found in practice.

How should results be recorded for a stereoacuity test?

• Record smallest disparity seen + element used

  • Example: “Titmus fly, 200”, “cartoon”

• If pt sees the lowest acuity, record as “≤” as pt may be able to see better

  • Example: “Titmus fly, ≤ 40” (graded circles)

What is the Frisby Stereo Test and what is its main advantage?

• Measures real depth

• No goggles req’d

• Plates: 6/3/1 mm thickness

Discuss how to use measures of stereoacuity commonly found in practice.

How is the Frisby Stereo Test performed and how are results recorded?

• Circle-shaped contour printed on one side of Perspex; pt identifies which of four targets shows depth

• Correct answer: flat button, others are round

• Recording:

  • Note stereoacuity found, e.g., “Frisby, 30”

  • If all responses correct at one distance, use “≤”, e.g., “Frisby, ≤ 85” (for 40 cm)

Discuss how to use measures of stereoacuity commonly found in practice.

What is the TNO Stereo Test and how is it set up?

• Random-dot stereopsis test

  • First 4 plates screen, last 3 measure stereoacuity

• Uses R+G goggles

• WD: 40 cm

How are the TNO Test plates I–IV performed?

• Plate I: Two butterflies

  • One always visible, the other only if stereopsis present

  • Ask: “How many butterflies can you see?”

• Plate II: 4 discs, two always visible

  • Ask: “Which is biggest?” or “How many are there?”

• Plate III: Pt matches shapes; practitioner must remember shape locations

• Plate IV: Suppression test

  • Ask: “How many circles can you see?”

  • 3 = no suppression, 2 = suppression

• Plate V-VII: 480-15’

  • 2 discs for each disparity “where is the piece of cake/pizza missing?”

  • Give pt time- can take a while to see whole image

Record stereopsis tests appropriately.

How are TNO Stereo Test results recorded?

• If Plates I-III seen and Plates V-VII not

  • Record “TNO test, Gross Stereopsis, Plates I-III seen”

• If suppression present record which eye.

• Record Stereoacuity for Plates V-VII

  • “TNO test, ≤ 30”

Discuss recent developments in stereopsis assessment

How is recent technology used to assess and manage stereoacuity?

• Computer game tests are now being employed as measure of stereoacuity (Portela- Camino et al., 2021).

• Allows for more intervals to be measured.

• Potential for better management of Amblyopia

Discuss the educational and occupational factors affecting colour vision

Why is it important to test colour vision in children?

Can have effects on education/future occupations

If father has it may affect female child-could be a carrier

How do we see colours?

Trichromacy

3 diff photopigments w/ overlapping absorption spectra

• L cones

• M cones

• S cones

CIE 1931 Chromaticity Diagram

Discuss how different colour vision conditions can affect the patient.

What colour confusions occur in Protanopia?

• Black with many shades of red

• Dark brown with dark green, dark orange and dark red

• Some blues with some reds, purples and dark pinks

• Mid-greens with some orange

R-G related

Discuss how different colour vision conditions can affect the patient.

What colour confusions occur in Deuteranopia?

• Mid-reds with mid-greens

• Blue-greens with grey and mid-pinks

• Bright greens with yellows 

• Pale pinks with light grey

• Mid-reds with mid-brown 

• Light blues with lilac

Won’t mix up blue + red if deuteranomalous but will if protanomalous 

Discuss how different colour vision conditions can affect the patient.

What colour confusions occur in Tritanopia?

• Light blues with greys

• Dark purples with black

• Mid-greens with blues

• Oranges with reds.

Affects Blues/yellows-orientation flipped

What do CV tests like Ishihara primarily take into account?

• Based on which lines will be mixed up when looking at Ishihara for congenital defects

• Primarily takes into account lines of confusion of protanopia + deuteranopia

• Not good for tritanopes because it doesn’t take into account lines of confusion

  • But City CV test will

How do Ishihara and City CV tests differ in detail and application?

• City CV test doesn’t go into as much detail as Ishihara for lines of confusion for deuteranopia + protanopia

• Can tell a moderate defect well but milder defects it isn’t as good at

• If congenital → HAS to be Ishihara

• Acquired → Ishihara is NO good because it doesn’t test for tritanopia

• Use Farnsworth or City CV for acquired defects

Discuss the tests used to assess colour vision and determine which are appropriate for paediatric testing.

Give examples of colour vision tests

• Ishihara

• City Colour Vision Test

• Farnsworth D-15

• Farnsworth-Munsell 100 hue test

What are the key clinical indicators of retrobulbar neuritis, and which colour vision test is useful?

• Good for detecting when there is a swollen optic disc that can’t be seen on fundoscopy

• Based on case history findings

  • Hurts more when moving eyes as ON affected

• Will present with a blue–yellow (tritan) CV deficiency

• City Colour Vision Test =useful

How do congenital and acquired colour vision defects differ in testing approach?

C:

• Can screen using BE. 

• Ishihara Test

A:

• One eye at a time.

• City Colour Vision Test 

• D-15 Farnsworth

What are the key features and uses of the Ishihara Test (1907)?

• Series of pseudoisochromatic plates 

• Good for assessing congenital R-G defects

  • Not so good for acquired defects.

  • Doesn’t test for Tritanopia

• Suitable for children.

What illumination conditions are required for the Ishihara Test?

• Colour temp needs to be similar to natural daylight conditions

  • High Colour rendering fluorescent lighting (>5000 K)

  • Pt observes test through Kodak Wratten #78AA filter with 100-W incandescent light source

How is the Ishihara Test performed?

• Viewing dist=75 cm.

  • Better for practitioner to hold.

• Present each plate for 3s

  • Recommended but doesn’t appear to make a difference (Long et al., 1985).

• Ask pt to read the numbers.

What are the different Ishihara plate types and their purposes (Plates 1–9)?

• Plate 1: Introduction plate - seen by all, useful for :

  • demonstration

  • malingerers

• Plates 2–9: Transformation plates

  • Normal vision: correct no seen

  • R–G deficiency: Diff no seen (e.g., 70 instead of 29)

What are the different Ishihara plate types and their purposes (Plates 10–25)?

• Plates 10–17: Vanishing plates

  • Seen by normal vision, not seen by R–G deficiency

• Plates 18–21: Hidden digit plates

  • Normal vision: sees nothing

  • R–G deficiency: sees a no (e.g., 45)

• Plates 22–25: Classification plates

  • Used only if screening plates (2–21) indicate a CV deficiency

What are tracing plates in the Ishihara Test and who are they used for?

• Found toward the end of the test

  • Designed for pts not no literate

• Protans: See numbers on the right (e.g., 2)

• Deutans: See numbers on the left (e.g., 4)

• Those w/ severe R-G defects (esp protanopia) may not see either

Record stereopsis tests appropriately.

How are Ishihara Test results interpreted and recorded?

• If 3+ plates wrong, proceed to classification plates

• Recording e.g:

  • “Ishihara, all plates seen – normal colour vision.”

  • Ishihara, 3/16 seen, protan – pt + parent counselled regarding future career restrictions.

What are the key features and purpose of the Farnsworth D-15 test (1947)?

• 15 small isochromatic discs, each of a different hue

• Detects moderate to severe CV  deficiencies

• Not a screening test

  • ppl w/ normal or mild CV defs will pass

Farnsworth D-15

Normal or Near Normal

Farnsworth D-15

Strong Protan

• Protan+deutan close tog as they share similar lines of confusion .Tritans on diff orientation.

SEE PIC

Farnsworth D-15

• Strong deutan

• Medium deutan

• Near normal or mild deutan

  • Mix up first few then get along fine for rest of test

Farnsworth D-15

Tritan

What are the features and clinical considerations of the Farnsworth-Munsell 100 Hue test?

• More sensitive than the D-15.

• Req’s more time (about 15 min) + concentration.

• Not suitable for children.

  • May be suitable for teenager

What are the key features and uses of the City Colour Vision Test?

• Orig derived from D-15 test.

• Good to use if suspecting acquired defect.

• Not as sensitive to mild R-G defects as Ishihara

  • Not a screening test

How should patients and parents be counselled regarding congenital colour deficiency?

• Explain genetics of a congenital colour deficiency to parent

• No cure for congenital colour deficiency

What advice should be given to schools and parents for children with colour vision defects?

• Need to advise teachers + parents.

  • May confuse colour coded schoolwork.

  • Coloured writing may be more diffic to see

    • Partic on a colour background.

• Crayons / Colour pencils should be marked.

• May need help w/ assignments 

  • E.g., Colour coding a pie chart etc.

Discuss the educational and occupational factors affecting colour vision

How does colour vision testing vary for different occupations?

• British Army

  • Req’s Ishihara Pass for Army Air Corps

• Royal Navy

  • Pt’s w/ impaired colour perception may be restricted the branches that are available to them.

• Royal Air Force

  • Can still join but colour deficiencies will limit roles.

Discuss the educational and occupational factors affecting colour vision

What are the colour vision requirements for the fire service?

Discuss the educational and occupational factors affecting colour vision

What are the colour vision requirements for lifeboat crew members?

• Tested using Ishihara.

• 3+ plates failed = Fail

Discuss the educational and occupational factors affecting colour vision

What are the colour vision requirements for police officers?

• Monochromats: not acceptable

• Mild anomalous trichromats: acceptable

• Severe anomalous trichromats + dichromats: acceptable but must be trained in coping strategies

Discuss the educational and occupational factors affecting colour vision

What are the colour vision requirements for electrical engineers?

• Normal CV req’d due to extensive colour coding in electronics + safety implications

• No more than 2 failed Ishihara plates

• Lantern test may be req’d for some roles

Discuss the educational and occupational factors affecting colour vision

What are the colour vision requirements for civilian pilots?

• Must pass first 15 Ishihara plates w/o error

• If Ishihara failed, further testing req’d:

  • Anomaloscopy (Nagel or equiv)

  • Colour Assessment + Diagnosis Test