Abnormal Retinal Correspondence

Question 1

What does ARC happen in?

Answer 1

• Constant manifest strabismus
• Cortical changes
• Allows correspondence between retinal elements in areas that wouldn’t normally correspond. It’s a sensory adaptation to get some BSV.

Question 2

What’s an extrafoveal area?

Answer 2

It’s the area that ARC allows for of the deviating eye that leads to a psuedofovea. Only when BEO will the cortex regard the psuedofovea of the deviating eye as the fovea. In monocular viewing the anatomical fovea is used.

Question 3

When does ARC occur?

Answer 3

When ARC is <20PD but >20PD would be suppression

Question 4

What’s the most common ARC?

Answer 4

Nasal to the anatomical fovea in Eso & temporal in Exo

Question 5

In an esotropia what becomes the temporal retina?

Answer 5

Becomes the area from the XR (pseudofovea) to the temporal side of the eye (doesn’t stop at the anatomical fovea but continues over to the XR) meaning there is a smaller nasal retina

Question 6

In exotropia what happens to the retina?

Answer 6

The anatomical fovea projects as nasal retina as it goes from medial to the XR which is the new nasal retina and a smaller temporal retina

Question 7

When is ARC most likely to occur?

Answer 7

• Small angle manifest strabismus
• Residual esotropia
• Long duration from a young age
• Stable angle

Question 8

Why does ARC occur?

Answer 8

• Prevents diplopia and confusion
• Prevents suppression
• Subnormal angle

Question 9

What are the drawbacks of ARC?

Answer 9

Not as good as normal BSV but rare to develop in noticeable strabismus as it prevents alignment of the eyes and normal BSV

Question 10

How can a synoptophore show you ARC?

Answer 10

We can look at subjective angle; if it was foveal we would expect this to be zero as testing fovea to pseudofovea. This shows ARC as the synoptophore is BEO. We can also look at objective angle but as this is monocular viewing we’d expect this to be greater than 0 (as fovea to fovea).

Question 11

What is harmonious and unharmonious ARC?

Answer 11

Harmonious is where the objective angle is larger than subjective angle but subjective angle is 0

Unharmonious is where the objective angle is larger than subjective angle but subjective angle is >0

Question 12

What might harmonious and unharmonious ARC be caused by?

Answer 12

Artefact of testing on the synoptophore

Question 13

Should you treat ARC?

Answer 13

We shouldn’t eliminate ARC as it’s not possible to restore normal BSV, there’s no effective treatment and is the next best thing to normal BSV (above suppression and no BSV)

Question 14

What is anomalous diplopia?

Answer 14

The projection diplopia doesn’t fit with the strabismus type (paradoxical diplopia) or the angle of strabismus (incongrous diplopia; as seen in the PCT)
e.g. the ET is heteronymous/crossed (when it should be homonymous/uncrossed)
XT is homonymous/uncrossed which is also opposite to that in normal XT diplopia

Question 15

When does paradoxical diplopia occur?

Answer 15

Paradoxical diplopia is a form of anomalous diplopia

Occurs when residual ET and ARC but ARC fixation point (pseudofovea) doesn’t change or when people with ARC use both foveae (fovea and pseudofovea) are simultaneously stimulated with the synoptophore or after-image testing

Can occur in ET when the image will still hit temporally (as the temporal retina is extended to the XR, pseudofovea, but this becomes PR in projection diagrams to show paradoxical diplopia)

Question 16

What’s incongruous diplopia?

Answer 16

When the separation of diplopic images is less than expected for the deviation size. Can be shown when a patient reports diplopia with fewer prism during Prism Fusion Range than expected as hitting the area of the pseudostrabismus opposed to the anatomical fovea

E.g. PCT showed near 20PD ET
Prism Fusion Range showed near 10PD BO

Incongruous = Increases. Want the image to be at the pseduostrabismus opposed to the anatomical fovea in ARC

Distance between the diplopic images are smaller than we would expect for the deviation size

Question 17

When can incongruous diplopia occur?

Answer 17

Can occur when an ET increases (& presumably when XT decrease)

Question 18

How do we investigate ARC?

Answer 18

• Cover test shows a manifest strabismus without diplopia
• Fovea to Pseudo-Fovea (subjective synoptophore, bagolini, worth’s light, prism fusion range, sterotests, Lang 2-pen test)
• Fovea to Fovea (After-image test, synoptophore - objective equal to subjective is normal ARC but objective larger than subjective is ARC)

Question 19

What would ARC look like on:
- Cover Test
- Bagolini
- Worth’s Lights
- Prism Fusion Range
- Stereotests
- Subjective Synoptophore

Answer 19

• Cover Test (small RE ET without diplopia)
• Bagolini (fusion despite deviation)
• Worth’s Lights (BSV response)
• Prism Fusion Range (lower than normal BSV but still have some range. Can do this at the same time as Bagolini to see at which prism you get a suppression response if not reporting diplopia)
• Stereotests (subnormal e.g. may be unable to do TNO or Frisby but can do Wirt or Lang 2-pen)
• Subjective Synoptophore (as BEO)

Question 20

What’s the After-Image Test?

Answer 20

For testing ARC:
Use synoptophore or hand-held flash. One image to each eye whilst fixing in centre leading to monocular presentation (fovea-fovea) and the patient looks at blank wall for after-image
In normal retinal correspondence (NRC) you see a cross
In abnormal retinal correspondence (ARC) you see a horizontal line and a vertical line with a gap between them

Question 21

What is the Prism Adaptation Test?

Answer 21

PAT. Investigates potential BSV before surgery decisions using Fresnel prisms on glasses (can share prism over both eyes to share the blur) to correct or slightly overcorrect and over time observe the deviation every 1-2 weeks to see new eye positions motor responses and increase as necessary using CT and BSV tests. Increase prism until stable angle achieved.

Question 22

What outcomes can there be from the prism adaptation test?

Answer 22

1) Prism Responder = Residual microtropia with BSV
2) Prism Responder = Visual axes straight with BSV
3) Prism Non-Responder = May have ARC ‘eat up’ the prism and return to their original angle
4) Prism Non-Responder = May suppress or lack BSV so axes remain convergent so can perform surgery for angle previously measured up to the XR (pseudofovea)

Question 23

How can BT/Botox be used for testing ARC?

Answer 23

Eso = BT into MR
Exo = BT into LR
CT and BSV can be used to investigate sensory results.

BT useful if strabismus angle too large for PAT with Fresnel prisms.

It can show ARC, the same way as getting BSV on Bagolini even with a 6PD prism on top to start suppressing

Question 24

Age 7 years old

Previous strabismus surgery, 3 years prior to this report Left medial rectus recession 5.5mm
Left lateral rectus resection 7mm

VA
R 0.00 (6/6)
L 0.00 (6/6) ETDRS

CT
N slight left esotropia
D slight left esotropia

Bagolini glasses
N BSV response
D BSV response

Worth’s lights
N Left suppression
D Left suppression

Lang Negative

Frisby 310” of arc

PCT
N 10Δ BO
D 8Δ BO

Synoptophore
objective angle + 5° (macular slides)
subjective angle 0 (macular slides)
fusion at 0, 5°conv → 3°div (macular slides) stereopsis at 0, gross only

What type of strabismus do they have? What type of retinal correspondence do they have?

Answer 24

Residual Microtropia ET (had a MR recession to loosen, LR resection to tighten) without identity (as a manifest deviation) and with ARC.

Could be a microtropia as <10PD or ET with abnormal BSV so could use a 4D to check foveal suppression but we decided they have a Microtropia has better stereoacuity than ARC so likely microtropia.

Objective > Subjective but the subjective angle is 0 so it’s Harmonious ARC

Question 25

Age 7 years old

Previous strabismus surgery, 3 years prior to this report Left medial rectus recession 5.5mm
Left lateral rectus resection 7mm

VA
R 0.00 (6/6)
L 0.00 (6/6) ETDRS

CT
N slight left esotropia
D slight left esotropia

Bagolini glasses
N BSV response
D BSV response

Worth’s lights
N Left suppression
D Left suppression

Lang Negative

Frisby 310” of arc

PCT
N 10Δ BO
D 8Δ BO

Synoptophore
objective angle + 5° (macular slides)
subjective angle 0 (macular slides)
fusion at 0, 5°conv → 3°div (macular slides) stereopsis at 0, gross only

What other tests could be performed to further clarify your diagnosis of the type of correspondence, and what response would you expect?

Answer 25

After-Image Test and PAT

Other tests include PFR Nr & Dist using Bagolini glasses as control, other stereotests to compare to Frisby, FD2, after image test using the synoptophore

Question 26

Age 7 years old

Previous strabismus surgery, 3 years prior to this report Left medial rectus recession 5.5mm
Left lateral rectus resection 7mm

VA
R 0.00 (6/6)
L 0.00 (6/6) ETDRS

CT
N slight left esotropia
D slight left esotropia

Bagolini glasses
N BSV response
D BSV response

Worth’s lights
N Left suppression
D Left suppression

Lang Negative

Frisby 310” of arc

PCT
N 10Δ BO
D 8Δ BO

Synoptophore
objective angle + 5° (macular slides)
subjective angle 0 (macular slides)
fusion at 0, 5°conv → 3°div (macular slides) stereopsis at 0, gross only

What treatment would you suggest for this patient?

Answer 26

No treatment has binocular vision despite presence of strabismus

Treatment VA –> No amblyopia as equal VA

Deviation –> Slight deviation so want to know if they have BSV or not (our patient does have some evidence of BSV thus have ARC Microtropia so wont treat the ET) and if they have symptoms or not (this patient doesn’t)

Question 27

Age 6 years
Glasses prescription:
R +3.50 L +3.00

VA c gls
R 0.2 (6/9.5)
L 0.0 (6/6) crowded logMAR

CT c gls N slight right esotropia
D slight right esotropia

s gls N moderate right esotropia
D moderate right esotropia

Convergence c gls with reducing deviation to 6cm

Bagolini glasses c gls
N right suppression
D right suppression

PCT c gls
N 20Δ BO
D 15Δ BO

s gls
N 35Δ BO
D 30Δ BO

Synoptophore c gls
objective angle + 10°
subjective angle +10° (10 ET)
fusion at subjective angle +6° → -4°
stereopsis present at subjective angle (gross slides only)

Clarify this strabismus and what type of BSV and correspondence do they have?

Answer 27

Primary Constant Right ET with an Accommodative Element
Hypermetropic
Amblyopic (2 line difference) – have they previously had amblyopia treatment and this is where they’ve gotten to?

Potential for BSV so need to line them up fovea-fovea for BSV thus need to

Normal retinal correspondence because Synoptophore says gross stereopsis subjectively but as this is the same as the objective it is lined up fovea – fovea at the subjective angle and they get gross stereoacuity at this level so have normal ARC

Question 28

Age 6 years
Glasses prescription:
R +3.50 L +3.00

VA c gls
R 0.2 (6/9.5)
L 0.0 (6/6) crowded logMAR

CT c gls N slight right esotropia
D slight right esotropia

s gls N moderate right esotropia
D moderate right esotropia

Convergence c gls with reducing deviation to 6cm

Bagolini glasses c gls
N right suppression
D right suppression

PCT c gls
N 20Δ BO
D 15Δ BO

s gls
N 35Δ BO
D 30Δ BO

What do the findings on examination suggest about the onset of the strabismus?

Answer 28

Age of onset – the fact they have potential BSV suggests that they would have previously had straight eyes to get BSV development earlier in life so suggests it is later onset. If they were early onset (<6mo) they would have very poor BSV or just no BSV at all.

The onset is likely to be after 2 years of age (late-normosensorial type) because demonstrates potential for BSV.

Question 29

Age 6 years
Glasses prescription:
R +3.50 L +3.00

VA c gls
R 0.2 (6/9.5)
L 0.0 (6/6) crowded logMAR

CT c gls N slight right esotropia
D slight right esotropia

s gls N moderate right esotropia
D moderate right esotropia

Convergence c gls with reducing deviation to 6cm

Bagolini glasses c gls
N right suppression
D right suppression

PCT c gls
N 20Δ BO
D 15Δ BO

s gls
N 35Δ BO
D 30Δ BO

What is the management plan for this patient?

Answer 29

Amblyopia Treatment – Patch or atropine over the better eye. Discuss issues occluding 6yo as assessing density of suppression and critical period

Hypermetropic Treatment – Refractive adaptation period

Deviation Treatment as has potential for BSV – Give parents option to have them as slight ET with their glasses on as asymptomatic but consider prisms (like doing a PAT test) to get them back to being binocular or surgery to get them back to being binocular.