4. Stereoacuity tests Flashcards
List the stereoacuity tests and their method
TNO - Random dot
Lang - Random dot
Frisby - Random dot
Titmus - Polarised light
Randot - Random dot & polarised light
How does TNO introduce disparity?
- Dichoptic images (presenting image separately to each eye)
- Red/Green glasses
How does Lang introduce disparity?
- Dichoptic images (presenting image separately to each eye)
- Cylinders
How does Frisby introduce disparity?
Real depth
How does Titmus introduce disparity?
- Dichoptic images (presenting image separately to each eye)
- Polaroid glasses
How does Randot introduce disparity?
- Dichoptic images (presenting image separately to each eye)
- Polaroid glasses
Describe the Lang 2 pencil test
- Px places vertical pencil on top of a pencil which is held by examiner
- Repeated with one eye occluded
Results:
BSV should have better performance.
If monocular and binocular performance is similar = absent stereopsis
+ves and -ves:
+Simple
- Qualitative
- Performance improves upon repetition
How is random dot stereogram created?
- Create a random dot pattern
- Duplicate it
- Cut a section of the pattern out and shift it (this determines the amount of binocular disparity)
- Once shifted fill in the gap with random dots
- Place the patterns on top of each other
- Dissociate eyes:
1st pattern = red dots
2nd pattern = Green dots
Use red/green goggles. - Where the pattern is shifted, retinal disparity occurs, resulting in 3D image.
Describe the TNO test
- Use of random dot
- Place at 40cm perpendicular to patient
- 3 different types of plates:
Screening plates (1980 sec/arc) = Gross stereoacuity
Suppression plates
Graded plates (480-15 sec/arc) Stereoacuity
+ves and -ves:
+No monocular cues
- Difficult for younger children
- Need to put red and green glasses over prescription glasses
Describe the Lang test
- Random dot images, the images for R/L eyes are separated by a system of fine parallel cylindrical strips.
- Shown Lang 1 : 1200-550 sec/arc
Different shapes:
Cat: 1200 sec/arc
Star: 600 sec/arc
Car: 550 sec/arc - Shown Lang 2 : 600-200 sec/arc
Different shapes:
Elephant: 600 sec/arc
Car: 400 sec/arc
Moon: 200 sec/arc
+ves and -ves:
+ At normal reading distance
+ Small children can observe looking at pictures
Describe the Frisby test
- Plastic plates with real disparities, from 600 to 15 sec/arc.
- 3 different plates
6mm, 3mm, 1mm - Optom places the plate in their lap rested against container, parallel to Px.
- Alter distance and then plate thickness.
Describe the Titmus/ Wirt fly test
- Polarised vectographs placed 40cm from Px.
- Fly plate = 3000 sec/arc
Animal plate = 400 -100 sec/arc
Circles plate = 800 - 40 sec/arc
+ves and -ves:
-Have to wear the polarised glasses
-Affected by monocular cues
Describe the randot test
- Polaroid vectographs ranged between 500-20 sec/arc. Held at 40 cm away from Px
- Ask Px which of the boxes on the vectograph doesn’t have a shape in it.
+ves and -ves:
- Have to put the polaroid glasses on
+No monocular cues
+For children better than TNO test
When can you not test for stereopsis? And how to make it so you can do the tests?
If someone has:
Strabismus
Microtropia
Reduced vision
To overcome make sure they are wearing their corrected glasses.
What are the different types of monocular cues?
Spatial:
1. Linear perspective - looking in the distance, things in the distance look smaller and diminish at vanishing point
2. Overlay of contours
3. Distribution of highlights and shadows - light always from above
4. Retinal image size - larger objects appear closer
5. Size of known objects
Temporal
1. Motion parallax - during movement, closer objects are displaced further than distant objects on retina.
Closer objects move in opposite direction
Distant objects move in same direction
