aniseikonia: a rare cause of diplopia (including after “successful” cataract surgery) logan...

Aniseikonia: A rare cause of diplopia

(Including after “successful” cataract surgery)

Logan Mitchell1, Lionel Kowal1,2

1. Royal Victorian Eye and Ear Hospital, Melbourne2. Private Eye Clinic, Melbourne

RANZCO Congress Adelaide 2010

Barriers to Sensory Fusion

Aniseikonia Torsion Metamorphopsia

Often under-recognised All diagnosable on careful

history-taking


Aniseikonia

Assessment History “20∆ test” New Aniseikonia Test (Awaya)

.


Retinal Causes

Any disruption to foveal photoreceptor distribution ERM DME ARMD Post-RD


Optical Cause - Anisometropia

Refractive Unequal refractive powers (axial

lengths equal)

Axial Unequal axial lengths,

(refractive powers equal)

Distance of corrective lens from anterior surface of eye (mm)

RELATIVE SPECTACLE

MAGNIFICATION

15 10 5 0

High +

High -M

agnificationM

inification

15 10 5 0

High +

High -


Aniseikonia Causing Diplopia

11 cases

Mean age 60 yrs (26-84)

Mean aniseikonia 7.1% (2-13%) Measurement with New Aniseikonia Test (Awaya)

Underlying well-controlled strabismus = 6


0 1 2 3 4 5 6 7 8 9 10 11 120

5

10

15

20

25

30

35

vertical (underlying strab.)horizontal (underlying strab.)vertical (no underlying strab.)horizontal (no underlying strab.)

Case Number

Dev

iatio

n (∆

)


Aniseikonia Causing Diplopia – Retinal Causes

(ERM peel in 1 patient was NOT successful in fixing aniseikonia)

Epiretinal membrane 5

Dry age-related macular degeneration 1

Diabetic macular oedema 1

Previous macula-off retinal detachment 1


Aniseikonia Causing Diplopia – Optical Causes

Axial anisometropia = 1 Case to be discussed

Refractive anisometropia = 2 Iatrogenic in one case

Myopic surprise (3.25 D anisometropia)


A case of aniseikonia due to “sensible cataract surgery”

56 yo male for R phaco/IOL Pre-op refractions (SE)

R -8 D L -2.5 D Post-op refractions (SE)

R +0.25 D (6/8) L -2.5 D (6/6) AND DIPLOPIC

PCT = XT 8 ∆, LHT 8 ∆


Caught “Knapping”?

Axial lengths = R 29.48 mm L 26.75 mm

Knapp's law not considered

13% R macropsia (NAT)

Galilean telescope system (minimising right eye image) has successfully resolved symptoms


Implications for Ophthalmologists

For all: NEED TO ASK / LOOK FOR IT For retinal surgeons:

A (?not uncommon) symptom of macular pathology Usually NOT resolved by retinal surgery

For cataract / refractive surgeons: Beware axial anisometropia (eg. >1 mm difference)

Consider CL trial Emmetropise dominant eye, maintain anisometropia

For strabismologists A barrier to fusion

Thank you


Aniseikonia

Causes Retinal Optical


Eikonometry

New Aniseikonia Test (Awaya)


# Sex Age Aetiology Strabismus Mag Management Outcome

1 M 70 ERM

? axial length

1 ∆ LHT + 2% Tried prism, Galilean telescope

Unsuccessful

2 F 50 ERM 1 ∆ LHT + 10% CL use, then ERM peel

Both unsuccessful

3 M 59 ERM

Intermittent XT

30 ∆ X(T) + 12% Strabismus surgery

Successful

Considering ERM peel

4 F 66 ERM

Divergence insufficiency

14 ∆ E + 9% Gallilean system with prism

Successful

5 M 64 ERM

TED

8 ∆ LHT + 10% Isokeinic prescription

Successful

Retinal Cause = ERM


# Sex Age Aetiology Strabismus Mag. Management Outcome

9 F 26 Inherent refractive anisometropia

(2D)

Intermittent XT

12 ∆ X(T) + 3% CL, BI prism in readers

Improved symptoms

10 M 56 Iatrogenic

Axial anisometropia

Known exophoria

8 ∆ XT

8 ∆ LHT

+ 13% Galilean system Successful

11 M 59 Iatrogenic

Refractive anisometropia (3.25D)

1 ∆ LHT - 5% Isokeinic prescription

Successful

Optical Cause


Tolerance <3% OK 3-5% decreased stereopsis >5% retinal rivalry


No. Sex Age Aetiology Strabismus Mag Management Outcome

7 M 84 Macula-off retinal detachment

2 ∆ XT

5 ∆ RHT

- 4% Isokeinic prescription

N/A

8 F 65 ARMD

Convergence insufficiency

1 ∆ LHT

14 ∆ XT'

4% Isokeinic prescription

N/A

9 F 60 DME, previous laser

0.5 ∆ RHT [20%] Glasses with prism

N/A

Mean horizontal

deviation (∆)

Range of horizontal

deviation (∆)

Mean vertical

deviation (∆)

Range of vertical

deviation (∆)

Known phoria 13 8 - 30 2.8 0 - 8

No known phoria 0.4 2* 1.7 0.5 - 5


Managing aniseikonia

Position refractive correction appropriately Isokeinic lenses Due to retinal causes

Difficult Retinal surgery does not seem of predictable

benefit


Axial Anisometropia

Knapp's Rule

Does not always apply – photoreceptor spacing


Knapp's Rule

Relative Spectacle Magnification (RSM) RSM = equivalent power of reference eye equivalent power of given lens-eye system

where back vertex of lens sits at anterior focal point of eye, and ametropia is axial equivalent power of eye is equal to equivalent power of lens-eye system is equal to equivalent power of reference eye

THUS: RSM = unity KNAPP'S RULE


Relative Spectacle Magnification

RSM = equivalent power of reference eye

equivalent power of given lens-eye system

For axial ametropia delta RSM calculations figures from article


Avoid Iatrogenic Aniseikonia

Be wary of axial anisometropia >1 mm difference in axial lengths

Predict Can simulate with CL Counsel

Avoid Emmetropise dominant eye, keep

anisometropia

aniseikonia: a rare cause of diplopia (including after “successful” cataract surgery) logan...

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