1. Logan Mitchell1, Lionel Kowal1,2
Aniseikonia: A rare cause of diplopia (Including after “successful” cataract surgery)
Logan Mitchell1, Lionel Kowal1,2
Royal Victorian Eye and Ear Hospital, Melbourne
Private Eye Clinic, Melbourne

2. Barriers to Sensory Fusion
Aniseikonia
Torsion
Metamorphopsia
Often under-recognised
All diagnosable on careful history-taking A A
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Aniseikonia A
Assessment
History
“20∆ test”
New Aniseikonia Test (Awaya) .
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Retinal Causes
Any disruption to foveal photoreceptor distribution
ERM
DME
ARMD
Post-RD
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5. Optical Cause - Anisometropia
Axial
Unequal axial lengths, (refractive powers equal)
Refractive
Unequal refractive powers (axial lengths equal)
High +
High -
Magnification
Minification
RELATIVE SPECTACLE MAGNIFICATION
Distance of corrective lens from anterior surface of eye (mm)
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6. 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
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8. Aniseikonia Causing Diplopia – Retinal Causes
Epiretinal membrane 5
Dry age-related macular degeneration 1
Diabetic macular oedema
Previous macula-off retinal detachment
(ERM peel in 1 patient was NOT successful in fixing aniseikonia)
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9. 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)
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10. 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 D (6/8) L -2.5 D (6/6)
AND DIPLOPIC
PCT = XT 8 ∆, LHT 8 ∆
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Caught “Knapping”?
Axial lengths = R mm L mm
Knapp's law not considered
13% R macropsia (NAT)
Galilean telescope system (minimising right eye image) has successfully resolved symptoms
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12. 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
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13. Thank you

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Aniseikonia
Causes
Retinal
Optical A A
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Eikonometry
New Aniseikonia Test (Awaya)
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Retinal Cause = ERM #
Sex
Age
Aetiology
Strabismus
Mag
Management
Outcome 1 M 70
ERM
? axial length
1 ∆ LHT
+ 2%
Tried prism, Galilean telescope
Unsuccessful 2 F 50
+ 10%
CL use, then ERM peel
Both unsuccessful 3 59
Intermittent XT
30 ∆ X(T)
+ 12%
Strabismus surgery
Successful
Considering ERM peel 4 66
Divergence insufficiency
14 ∆ E
+ 9%
Gallilean system with prism 5 64
TED
8 ∆ LHT
Isokeinic prescription
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Optical Cause #
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 59
Refractive anisometropia (3.25D)
1 ∆ LHT
- 5%
Isokeinic prescription
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Tolerance
<3% OK
3-5% decreased stereopsis
>5% retinal rivalry
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19. 13 8 - 30 2.8 0 - 8 0.4 2* 1.7 0.5 - 5 Mean horizontal deviation (∆)
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% 9 60
DME, previous laser
0.5 ∆ RHT
[20%]
Glasses with prism
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
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Managing aniseikonia
Position refractive correction appropriately
Isokeinic lenses
Due to retinal causes
Difficult
Retinal surgery does not seem of predictable benefit
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Axial Anisometropia
Knapp's Rule
Does not always apply – photoreceptor spacing
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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
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26. 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
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27. 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
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