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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
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Barriers to Sensory Fusion
Aniseikonia Torsion Metamorphopsia
Often under-recognised All diagnosable on careful
history-taking
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Aniseikonia
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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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 -
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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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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 (∆
)
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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
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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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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 ∆
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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
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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
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Aniseikonia
Causes Retinal Optical
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Eikonometry
New Aniseikonia Test (Awaya)
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# 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
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# 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
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Tolerance <3% OK 3-5% decreased stereopsis >5% retinal rivalry
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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
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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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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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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