NPC, W4D, Stereo

Question 1

Define near point of convergence (NPC).

Answer 1

Measuring the maximum vergence response
Amplitude of vergence

Question 2

How do we measure NPC?

Answer 2

Advance a target towards the patient until either
They report diplopia (subj)
You see one eye turn out (obj)

Question 3

What is the NPC measured when testing?

Answer 3

Distance from target to the patient when diplopia/eye turn out

Question 4

What is the expected break value for NPC?

Answer 4

5cm/ 20MA / 120prism (assume PD=60) from outer canthus (center of rotation of the eye)

Question 5

What is the expected recovery for NPC?

Answer 5

7cm from outer canthus

Question 6

How is NPC recorded?

Answer 6

4cm/6cm + diplopia
8cm/11cm; OS turns out
TTN

Question 7

What kind of effect does age have on NPC?

Answer 7

NPC DOES NOT decline significantly with age (unlike accommodation)

Question 8

What does the Worth 4 Dot Test test?

Answer 8

Binocular vision
How well our eyes work together

Question 9

What does a recording of Grade 1 for W4D indicate?

Answer 9

Simultaneous perception
See out of both eyes at the same time (binocular)
Without this we have no binocular vision at all

Question 10

What does Grade 2 indicate for W4D?

Answer 10

Flat fusion

Pt has grade 1 and can fuse image
No double vision

Question 11

What does grade 3 indicated for W4D?

Answer 11

Stereopsis

Grade 1 and 2 and can see in depth

Only can be indicated with a Stereopsis test, if patient has grade 3 you do not need to test for grade 1 and 2

Question 12

What color filters are placed on the patient for W4D? What are the images for each eye?

Answer 12

Red filter OD, green filter OS
OD sees 2 lights (red and white one as red)
OS sees 3 lights (2 green and white one as green)

Patient may see 2-5 lights in total

Question 13

What does it mean if the patient sees 4 lights?

Answer 13

Patient has at least flat fusion

Binocular and fusing the white dot (appears as red, green or flickering depending on eye dominance and retinal rivalry)

Question 14

What does it mean if the patient sees 3 lights?

Answer 14

Patient is suppressing their right eye
Images from left eye

Question 15

What does it mean if the patient only sees 2 lights?

Answer 15

Patient is suppressing left eye
Right eye images

Question 16

What does a response of 5 lights mean?

Answer 16

Patient has simultaneous perception (grade 1)
Seeing out of both eyes, NOT fusing the white dot

Question 17

How can an exo or eso deviation be determined from W4D?

Answer 17

Ask patient where the red dots are relative to the green

Red dots on left= exo
Red dots on right= eso

Question 18

What is the diagnosis if the red dots are higher then the left?

Answer 18

Left hyperopia

Question 19

What distances is W4D performed at? What about the handheld device?

Answer 19

6m (20ft), 3m (10ft), 40cm (16in)

Small handheld unit- 3m and 40cm

Question 20

Define stereopsis.

Answer 20

Binocular perception of depth based on retinal disparity (correspondence)

Question 21

What must be true regarding the correspondence of reinstall points during stereopsis?

Answer 21

Images must be imaged on non-corresponding retinal points with the disparity not exceeding Panum’s fusional area

Question 22

What is Panum’s fusional area?

Answer 22

Point on retina away from corresponding point (not necessarily the fovea) where the image will still be single

How much we can under or over converge and still see a single image

Question 23

Define corresponding retinal points.

Answer 23

Same visual direction

Question 24

How large is PFA typically when corresponding point is the fovea?

Answer 24

6 to 10 minutes of arc on the retina (does not apply to periphery)
Image will be single within this range

Question 25

What are monocular depth cues?

Answer 25

Shadow, perspective, overlap, texture, size constancy provide a lot of depth information

Question 26

How do patients without Stereopsis (one-eyed patients) still see in 3D?

Answer 26

Monocular depth cues Stereopsis only provides a high level of depth perception

Question 27

Define stereo-threshold.

Answer 27

The smallest separation between the two objects when the observer can reliably state that one object is in front of the other

Question 28

Describe the three needle test.

Answer 28

Middle needle is moved Observer must determine if center needle is in front, behind, or next to the outside of the two needles

Question 29

What is the Howard-Dolman test?

Answer 29

Same as three needle but only has 2 needle Observer must determine which is closer to them

Question 30

What is the frisby test?

Answer 30

Patient must determine which square includes a circle that appears depressed Circle is painted on the back of the plastic sheet, everything else is on front Thinner sheets needed for lower stereo-thresholds (better)

Question 31

Define stereoacuity.

Answer 31

The difference between 2 vergence demands (2 different objects, how much total vergence they require in degrees) Unit is seconds of arc

Question 32

What is the average stereoacuity in patients with normal binocular vision?

Answer 32

20 seconds of arc with standard deviation of 10 96% of the normal adult population should have stereoacuity of at least 40 seconds of arc

Question 33

Why do we have to test for stereopsis?

Answer 33

Assessment of binocular function (highest level) Screening test in young children (amblyopia, anisometropia, heterotropia) Job demands

Question 34

What condition may affect stereopsis in a patient?

Answer 34

Amblyopia, strabismus, unequal refractive error

Question 35

Do we have to perform W4D if patient has good stereopsis?

Answer 35

No

Question 36

Is Stereopsis more important for near or distance vision?

Answer 36

Near

Question 37

What do clinical Stereopsis tests use?

Answer 37

Polarization to present disparate images to each eye Produces impression of depth

Question 38

What are some examples of clinical stereopsis tests?

Answer 38

Stereo fly test Wirt Circles (circles overlap to create 3D effect, imaged at non corresponding point within PFA, circles become more closely overlapped as the test continues (less 3D effect), images are closer to fovea, stereoacuity decreases)

Question 39

What does turning the wirt circle book upside or upside down polarized sunglasses do to the image?

Answer 39

Fused images are now seen behind the book (going into book) Uncrossed instead of crossed

Question 40

What is the lowest recording value for Randot? How can we test for higher levels of stereopsis?

Answer 40

20 seconds of arc (average level of stereoacuity for patient with normal binocular vision) Changing the working distance to 80cm (halves the angles)

Question 41

What can be observed regarding the wirt circles when glasses are removed?

Answer 41

They have monocular cues

Question 42

Do RDS’s have any monocular cues?

Answer 42

No

Question 43

Describe the magic eye test.

Answer 43

To see charts in 3D requires accommodation in the plane of the picture (for clarity) with relative divergence that the eye are converged to a point behind the plane of the picture (NRV) Can also be PRV, the image will be behind the plane of the page rather then in front of it

Question 44

What happens to PFA as we move away from the fovea?

Answer 44

Increases Always measured from the fovea (think of eccentricity of retina)