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Strabismus 106 > Stereotests for Stereoacuity > Flashcards

Stereotests for Stereoacuity Flashcards

1
Q

What is stereoacuity measured in?

A

Seconds of arc “

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2
Q

What is gross stereoacuity and fine stereoacuity in minutes of arc?

A

3,000” (gross) and 10” (fine)

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3
Q

What are the qualitative tests for stereoacuity?

A

Lang 2-pen test & synoptophore slides

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4
Q

What are the quantitative tests for steroacuity?

A
  • Random Dot Tests (TNO, Randot, Randor Pre-School Steroacuity, Distance Stero Randot and Lang I & II)
  • Polarised Contoured Vectograph (Wirt)
  • Real-Depth Tests (Frisby Near, FNS and Frisby Davis Distance, FD2)
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5
Q

What are random dot tests?

A

Include TNO, Randot, Randor Pre-School, Distance Stereo Randot and Lang I & II

Dots which form the stereo-shape are duplicated and shifted horizontally to create a disparity. The fusion of dots creates a stereo-effect and tests for global stereopsis and is less susceptible to monocular cues.

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6
Q

What are real-depth tests of stereoacuity?

A

Frisby Near and Frisby-Davis Distance
They’re truer to life but monocular cues can be an issue if care isn’t taken when presenting

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7
Q

What distance are the near sterotests?

A

40cm or 16 inches

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8
Q

What must you be aware of when presenting sterotests?

A
  • Near at 40cm/16 inches
  • Correct plane to the eyes and in good illumination, either in primary position, perpendicular or at reading
  • No leading questions
  • Inconclusive or unusual results warrants another test
  • To be aware of not presenting monocular cues by head movements or moving the test
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9
Q

What are the benefits of using stereograms for stereotests?

A
  • Less monocular cues
  • Often need to have glasses on (not Lang)
  • Cue conflict can affect blur
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10
Q

What are the benefits of using real-depth tests for stereotests?

A
  • ‘Real life’
  • Monocular cues
  • No glasses needed
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11
Q

What must you consider for choosing stereotests?

A
  • Monocular Cues
  • Disparity Range
  • Presentation
  • Fine vs. Coarse Texture
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12
Q

How do monocular cues affect stereotests?

A
  • Aid recognition (enhance BSV)
  • TNO contoured butterfly is more readily seen even with abnormal BSV
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13
Q

How does disparity range affect stereotests?

A

Tests vary as to the range of stereoacuities that they assess; normal stereogram disparity is approximately 60” and real objects are approximately 10”
Wirt fly is really good for patients with poor stereoacuity as it measures gross stereopsis

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14
Q

How does presentation affect stereotests?

A

The ease and repeatability of presentation is important and you can’t learn FNS and FD2 but things like the Lang are quick and portable.

The understanding and age is important to picking stereotests. FNS and FD2 both have monocular cues that you can use to teach the task.
Randot, Lang and Wirt have animals that children like

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15
Q

How does Fine vs. Coarse Texture affect stereotests?

A

Stereotests can help identify poor VA; the Frisby (FNS) has a chunky texture. TNO has fine textures so some can’t appreciate the stereo effect as unable to resolve the texture (dots) BUT passing the test is a good indicator of normal visual system and so is considered the ‘gold standard’

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16
Q

What’s the gold standard sterotest?

A

TNO

17
Q

What glasses do you wear for TNO?

A

Red-Green

18
Q

What does the Randot look like?

A

Had a bunch of circles; 3 within a crowding bar and then has cartoon images below on the left side. Then on the right-side is a random dot task. Has a way of checking suppression on the R-L. Answers are on the back. Can sometimes see a shape is distorted without having stereoacuity. Wear polarised glasses

19
Q

What test has a way of checking suppression?

A

Randot

20
Q

What does the Randot Pre-School Stereoacuity test look like?

A

There are 3 books, start with book 1 and then, if able to pass this go on to book 2 but if fail then move on to book 3.
It’s a case of matching which of the squares on the right are shown with the key on the Left

21
Q

What does the Distance Randot Stereotest look like?

A

This is conducted at 3m but some will do it 4m for a distance test.
Has the seconds or arc (“) under each image and is a pure random dot test
Have to use polaroid glasses
Must hold straight on as if tilted = doesn’t work

22
Q

What does the Lang I & II look like?

A
  • Random dots using cylinders for dissociation
  • Good for children as only has 3 pictures and thus 3 levels of stereoacuity
  • Portable
  • Can use on individuals as pre-verbal
  • II is harder than I; read the lowest number disparity for each image as this shows the hardest level
23
Q

What does the Lang Stereopad look like?

A

Designed to have movement of the images so that the individual cannot learn via rote learning what they should be expected to see.

24
Q

What does the Wirt Stereotest look like?

A

It’s polaroid contoured vectograph with polaroid glasses and doesn’t rely on dissociation of random dots
There is a latency for getting the fly further out from the page. Helpful for someone with abnormal BSV as it gives the contours and they know how a fly looks.
It’s an easy-to-use test
However, as not random dot abnormal BSV can see the distortion and there are some monocular cues so have to ensure they’re seeing depth and not just something that looks “different”
On the left are dot and cartoon animal pictures

25
Q

How do you do the Frisby Near Stereotest (FNS)?

A
  • Can hold it either way so that the circle is either protruding (normal) or inverse
  • Can move the plate so they cannot rote learn
  • Orthoptist can tell where the the correct is based on the bobbles or on sharp edges
  • Present at eye-level, straight on and with some distance to the white background
  • Don’t allow the patient to move their head because of motion parallax which is a monocular cue
  • Can move the plate around to show them the circle through motion parallax if they don’t know what they’re looking for
26
Q

What’s the Frisby Davis Distance Stereotest (FD2)?

A

Designed to be tested at 6m but there is a conversion for 3m or 4m if there is not enough distance. The equation is on the back.
Had 3 shapes that are flat against the background and then one shape that’s pushed further out. The rods show how far out the rod is in terms of seconds of arc.
Maximum acuity is 50” of arc but adults should get around 20”.

27
Q

What are the different ways of presenting images in stereotests to each eye?

A
  • Naturally
  • Stereoscope Mirrors/Lenses
  • Red-Green Anaglyphs
  • Crossed Polaroids
  • Shutter Glasses
  • Lenticular Lenses

(1 and 2 solve the problems of cross-talk)

28
Q

How do crossed polaroid glasses work?

A

Images to each eye have light with different (crossed) polarisation. They allow light through in one direction

29
Q

How do shutter glasses work?

A

They come in front of the eyes alternating very quickly so still allow you to fuse as past the critical fusion frequency

30
Q

What are lenticular lenses?

A

Same principle as a concertina sliding door. Lang stereotest has this.

31
Q

Which of the stereotests have suppression plates?

A

Suppression plates on stereotests (TNO, Wirt & Randot)

32
Q

What is the mean stereoacuity for a 3, 5 and 7+ year old?

A

3 years = 100”
5 years = 60”
7 years = 40”

33
Q

What’s the mean stereoacuity for real objects?

A

10”

34
Q

What is the minimum FD2 and what’s what you expect from adults?

A

Minimum 50” but most adults get down to 20”

35
Q

How is Frisby Nr real depth?

A

No dissociation
See whole test
Plate thickness changes

36
Q

What’s the difference between stereoacuity and stereopsis?

A

Stereopsis = Gross
Stereoacuity = Exact measurement

37
Q

What is a threshold measurement?

A

The point of the best stereoacuity of the patient

Strabismus 106 (35 decks)

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