Aniseikonia:
A rare cause of diplopia
(Including after “successful” cataract surgery)
Logan Mitchell1, Lionel Kowal1,2
1.
2.
Royal Victorian Eye and Ear Hospital, Melbourne
Private Eye Clinic, Melbourne
Barriers to Sensory Fusion





Aniseikonia
Torsion
Metamorphopsia
Often under-recognised
All diagnosable on careful
history-taking
RANZCO Congress Adelaide 2010
Aniseikonia

Assessment



History
“20∆ test”
New Aniseikonia Test (Awaya)
.
RANZCO Congress Adelaide 2010
Retinal Causes

Any disruption to
foveal
photoreceptor
distribution




ERM
DME
ARMD
Post-RD
RANZCO Congress Adelaide 2010
Optical Cause - Anisometropia

Refractive


Unequal refractive powers (axial
lengths equal)
Axial

Unequal axial lengths,
(refractive powers equal)
Magnification
Minification
RELATIVE
SPECTACLE
MAGNIFICATION
15
10
5
0
15
10
5
Distance of corrective lens from anterior surface of eye (mm)
RANZCO Congress Adelaide 2010
0
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
RANZCO Congress Adelaide 2010
35
30
25
Deviation (∆)
20
vertical (underlying strab.)
horizontal (underlying strab.)
vertical (no underlying strab.)
horizontal (no underlying
strab.)
15
10
5
0
0
1
2
3
4
5
6
7
8
9
Case Number
RANZCO Congress Adelaide 2010
10
11
12
Aniseikonia Causing Diplopia –
Retinal Causes

Epiretinal membrane
5
Dry age-related macular degeneration
1
Diabetic macular oedema
1
Previous macula-off retinal detachment
1
(ERM peel in 1 patient was NOT successful
in fixing aniseikonia)
RANZCO Congress Adelaide 2010
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)
RANZCO Congress Adelaide 2010
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 ∆
RANZCO Congress Adelaide 2010
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
RANZCO Congress Adelaide 2010
Implications for Ophthalmologists


For all: NEED TO ASK / LOOK FOR IT
For retinal surgeons:

A (?not uncommon) symptom of macular pathology


For cataract / refractive surgeons:

Beware axial anisometropia (eg. >1 mm difference)



Usually NOT resolved by retinal surgery
Consider CL trial
Emmetropise dominant eye, maintain anisometropia
For strabismologists

A barrier to fusion
RANZCO Congress Adelaide 2010
Thank you
Aniseikonia

Causes


Retinal
Optical
RANZCO Congress Adelaide 2010
Eikonometry

New Aniseikonia Test (Awaya)
RANZCO Congress Adelaide 2010
Retinal Cause = ERM
#
Sex Age
Aetiology
Strabismus
Mag
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 Successful
with prism
5
M
64
ERM
TED
8 ∆ LHT
+ 10%
Isokeinic
prescription
RANZCO Congress Adelaide 2010
Management
Outcome
Successful
Optical Cause
#
Sex Age
Aetiology
Strabismus
Mag.
Management Outcome
CL, BI prism in
readers
F
26
Inherent refractive
anisometropia
(2D)
Intermittent XT
12 ∆ X(T)
+ 3%
10 M
56
Iatrogenic
Axial anisometropia
Known exophoria
8 ∆ XT
8 ∆ LHT
+ 13% Galilean system Successful
11
59
Iatrogenic
Refractive
anisometropia
(3.25D)
1 ∆ LHT
- 5%
9
M
RANZCO Congress Adelaide 2010
Isokeinic
prescription
Improved
symptoms
Successful

Tolerance



<3% OK
3-5% decreased stereopsis
>5% retinal rivalry
RANZCO Congress Adelaide 2010
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
Range of
Mean
Range of
horizontal
horizontal
vertical
vertical
deviation (∆) deviation (∆) deviation (∆) deviation (∆)
Known
phoria
13
No known
phoria
0.4
8 - 30
2.8
0-8
2*
1.7
0.5 - 5
RANZCO Congress Adelaide 2010
Managing aniseikonia



Position refractive correction appropriately
Isokeinic lenses
Due to retinal causes


Difficult
Retinal surgery does not seem of predictable
benefit
RANZCO Congress Adelaide 2010
RANZCO Congress Adelaide 2010
Axial Anisometropia

Knapp's Rule

Does not always apply – photoreceptor spacing
RANZCO Congress Adelaide 2010
RANZCO Congress Adelaide 2010
RANZCO Congress Adelaide 2010
Knapp's Rule

Relative Spectacle Magnification (RSM)

RSM =


where back vertex of lens sits at anterior focal point
of eye, and ametropia is axial




equivalent power of reference eye
equivalent power of given lens-eye system
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
RANZCO Congress Adelaide 2010
Relative Spectacle Magnification

RSM =

reference eye
equivalent power of given lenseye system

equivalent power of
For axial ametropia
 delta RSM calculations
 figures from article
RANZCO Congress Adelaide 2010
Avoid Iatrogenic Aniseikonia

Be wary of axial anisometropia


Predict



>1 mm difference in axial lengths
Can simulate with CL
Counsel
Avoid

Emmetropise dominant eye, keep
anisometropia
RANZCO Congress Adelaide 2010