Aniseikonia: A rare cause of diplopia (Including after

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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

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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

• Axial
• Unequal axial lengths, (refractive powers equal)

• Refractive
• Unequal refractive powers (axial lengths equal)

RELATIVE SPECTACLE MAGNIFICATION
Distance of corrective lens from anterior surface
of eye (mm)
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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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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)

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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. gt1 mm difference)
• Consider CL trial
• Emmetropise dominant eye, maintain anisometropia
• For strabismologists
• A barrier to fusion

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Thank you
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Aniseikonia

• Causes
• Retinal
• Optical

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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 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
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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 M 59 Iatrogenic Refractive anisometropia (3.25D) 1 ? LHT - 5 Isokeinic prescription Successful
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• Tolerance
• lt3 OK
• 3-5 decreased stereopsis
• gt5 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
• gt1 mm difference in axial lengths
• Predict
• Can simulate with CL
• Counsel
• Avoid
• Emmetropise dominant eye, keep anisometropia