Sensory fusion

Question 1

What is simultaneous perception

Answer 1

ability to use both eyes at same time

Question 2

Name the two forms of fusion

Answer 2

sensory fusion

motor fusion

Question 3

what is stereopsis

Answer 3

the use of BSV to see in 3D

Question 4

which worth’s 3 grades is needed to achieve the best BV/binocular function

Answer 4

1. simultaneous perception
2. Fusion (sensory & motor)
3. steriopsis

Question 5

what is sensory fusion

Answer 5

integration of two similar images, one formed on each retina into one image within the brain
images must be similar in brightness, size and form

Question 6

when do you assess sensory fusion

Answer 6

in patients with a strabismus e.g. a tropia

Question 7

what type of patient do we assess sensory fusion on

Answer 7

1. confusion
2. pathological diplopia
3. suppression
4. abnormal retinal correspondence

Question 8

why must we know which condition a patient has before we assess their sensory fusion

Answer 8

because management for each condition is different

Question 9

in what circumstance will you assess a patients sensory fusion without checking the type of condition

Answer 9

those with hetereophoria to confirm they have normal BSV

Question 10

after what age does a patient get confusion and double vision

Answer 10

after 8 years old

Question 11

name and explain the two types of confusion

Answer 11

1. esotropia (SOT)
   cyclopean eye sees superimposed e.g. tree and house
   is uncommon e.g. right esotropia means nasal retina looks at tree and house and tree over laps
2. exotropia (XOT)
   cyclopean eye sees superimposed tree and house
   is uncommon

Question 12

after what age does pathological diplopia occur

Answer 12

8 years old

Question 13

name and explain the two types of pathological diplopia

Answer 13

1. esotropia (SOT)
   strabismic eye - fixation object imaged on nasal retina which is projected temporally causes uncrossed diplopia, is more common than confusion
2. exotropia (XOT)
   strabismic eye - fixation object imaged on temporal retina which is projected nasally causes crossed diplopia, is more common than confusion

Question 14

at what age can someone get pathological suppression

Answer 14

begins under age of 8

Question 15

what is constant suppression

Answer 15

one blind eye
constant manifest strabismus
complete suppression of non dominant/non fixating eye
can have right eye or left eye or alternating suppression
e.g. if the right eye has esotropia the nasal retina projects temporally and px should get double vision but suppression switches the 2nd image off in the brain so px can only see one image

Question 16

what is partial suppression

Answer 16

suppression in only a part of the image in one eye e.g. macula suppression with peripheral BSV e.g. small part of image is suppressed

Question 17

what is intermittent suppression

Answer 17

suppression in some circumstances only e.g. in the distance and normal BSV or double vision at intermediate

Question 18

how do you investigate suppression

Answer 18

1. diagnose the presence of suppression
2. measure the size and position of the scooter (important for surgery)
   it can be central suppression with peripheral fusion
   can measure size of scooter with prisms
3. measure the density of suppression which can vary

Question 19

what do you measure the size and position of a scotoma with

Answer 19

prisms

Question 20

what do you measure the density of suppression with

Answer 20

sbisa bar - red filter
or
NDF bar

Question 21

what is area suppression also termed as

Answer 21

suppression scotoma

Question 22

how do you use prisms to measure suppression scotoma

Answer 22

prism is placed before the deviated eye
prism increased until patient notes diplopia (which is out of the area of suppression)
record for base out, base in, base up and base down

Question 23

how do you measure the density of suppression with a sbisa bar

Answer 23

• graded bar of varying density of red filters
• placed infront of the fixating eye
• px requested to view light and asked what colour which will be red as viewed by fixing eye
• filters slowly increased in strength/darkness until px cannot see through the filter
  three outcomes shows the density of suppression:
• patient informs examiner when the light changes from red to white as they have to use their suppressed eye in order to see
• or examiner will see fixation swap between eyes
• or px reports diplopia
• record the density
• less than 10 = suppression weak
• danger of intractable diplopia if do this test

Question 24

what is the risk of measuring the density of suppression

Answer 24

danger of intractable diplopia

Question 25

what is intractable diplopia

Answer 25

taking suppression away from the px which will then experience diplopia

Question 26

when does abnormal (anomalies) retinal correspondence begin

Answer 26

in children under 8 years old

Question 27

what happens in abnormal retinal correspondence

Answer 27

fovea of one eye learns to correspond to a non-foveal area in the other eye (pseudo fovea) and then all the retinal correspondence in the periphery also shifts

Question 28

what do patients with ARC have

Answer 28

``` abnormal BSV (ABSV) for some targets but generally BSV slightly weaker than normal ```

Question 29

what can a test for sensory fusion be achieved by

Answer 29

total dissociation or partial dissociation

Question 30

what is total dissociation

Answer 30

different targets/images to each eye | each eye has a different viewing tube

Question 31

what is partial dissociation

Answer 31

a single target/same image is seen by both eyes but each eye sees a different part of the image e.g. a part is seen by the right eye only and not the left

Question 32

name three types of partial dissociation tests

Answer 32

1. worth's lights - red/green 2. bagolini lenses - diffraction 3. mallett unit - polarisation

Question 33

describe the worth's lights 4 dot test

Answer 33

- four lights, usually round but can be different shapes 2 green 1 red 1 white - view through red and green goggles red filter before R eye green filter before L eye green is not transmitted through a red filter red is not transmitted through a green filter white is transmitted equally through both filters both eyes see white light, appears red through red filter and appears green through green filter

Question 34

what is the normal BSV response for the worth's lights 4 dot test

Answer 34

1 red light (control) 2 green lights (control) the fused white light appears to be a mixture of red and green/alternates but stays a single image

Question 35

what sizes is the worth's lights 4 dot test available in

Answer 35

use at 6M, 1M and 1/3rdM viewing distances

Question 36

how can you manage esotropia

Answer 36

- maximum plus/minimum minus as plus relaxes accommodation so good for moving eye out - base out prisms (fresnel or incorporated) - exercises stereograms, lens prism bar - refer HES - surgery or second opinion

Question 37

how can you manage exotropia

Answer 37

- maximum minus/minimum plus stimulates accommodation for both eyes so good for bringing eye in - base in prism (fresnel or incorporated) - exercises stereograms, lens prism bar - refer HES - surgery or second opinion

Question 38

how do you manage constant suppression

Answer 38

- leave alone as no symptoms (lenses can cause double vision) - cosmetic surgery (only reason for treatment)

Question 39

how do you manage central suppression

Answer 39

- microtropia - usually no treatment needed except for amblyopia - beware as BSV slightly inferior to normal

Question 40

what does a px with ARC see with the worth's lights 4 dot test

Answer 40

exactly the same as a person with normal BSV despite the fact they have a manifest deviation

Question 41

how do you manage ARC

Answer 41

- do not treat | - be aware that BSV slightly inferior therefore monitor

Question 42

explain striated lens partial dissociation/bagolini lenses

Answer 42

- striations form a partial dissociation (control) - spot light seen by both eyes - striations are orientated in different directions for each eye - the streak of light is seen separately by either eye

Question 43

with bagolini lenses, which orientation does the patient report to see the streak of light in comparison to the striations on the lens seen by the optometrist

Answer 43

perpendicular | e.g. if px sees light at 45 degrees, optometrist sees striations at 135 degrees

Question 44

describe the bagolini glasses test

Answer 44

- fixate a spot light (near or distance fixation and easiest with a bright pen torch) - striations before the R eye placed perpendicular to striations before the L eye (normally 135 and 45 degrees) - ask patient to report on how many lights they see - ask them to draw the pattern they see - are there any gaps in the centre near light

Question 45

what happens in the bagolini test with right eye esotropia

Answer 45

- image hits nasal retina which projects temporarily - px will see two lights - one to the right which is seen by right eye - uncrossed diplopia

Question 46

what happens in the bagolini test with right eye exotropia

Answer 46

- image hits temporal retina which projects nasally - px will see two lights - light at right eye will be moved to the left - crossed diplopia

Question 47

what happens in the bagolini test with right eye suppression

Answer 47

will see light on the left only

Question 48

what happens in the bagolini test with central/foveal suppression of right eye

Answer 48

streaks will be superimposed, but right streak will have a gap in the middle from suppression

Question 49

what happens in the bagolini test with ARC

Answer 49

px will see exactly the same as a person with normal BSV despite the fact they have a manifest deviation

Question 50

in the worth's lights test, if a patient has suppression of their left eye, how many and which lights will they see

Answer 50

two red lights, vertical (the green horizontal lights will be missing as cannot see out of that eye)

Question 51

in the worth's light test, if a patient has suppression of their right eye, how many and which lights will they see

Answer 51

two green lights. horizontal (the red vertical lights will be missing as cannot see out of that eye)