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

Barriers to Sensory Fusion Aniseikonia Torsion Metamorphopsia Often under-recognised All diagnosable on careful history-taking A A RANZCO Congress Adelaide 2010

RANZCO Congress Adelaide 2010 Aniseikonia A Assessment History “20∆ test” New Aniseikonia Test (Awaya) . RANZCO Congress Adelaide 2010

RANZCO Congress Adelaide 2010 Retinal Causes Any disruption to foveal photoreceptor distribution ERM DME ARMD Post-RD RANZCO Congress Adelaide 2010

Optical Cause - Anisometropia Axial Unequal axial lengths, (refractive powers equal) Refractive Unequal refractive powers (axial lengths equal) 15 10 5 0 High + High - Magnification Minification 15 10 5 0 RELATIVE SPECTACLE MAGNIFICATION Distance of corrective lens from anterior surface of eye (mm) RANZCO Congress Adelaide 2010

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

RANZCO Congress Adelaide 2010

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) 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

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 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 RANZCO Congress Adelaide 2010

Thank you

RANZCO Congress Adelaide 2010 Aniseikonia Causes Retinal Optical A A RANZCO Congress Adelaide 2010

RANZCO Congress Adelaide 2010 Eikonometry New Aniseikonia Test (Awaya) RANZCO Congress Adelaide 2010

RANZCO Congress Adelaide 2010 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 RANZCO Congress Adelaide 2010

RANZCO Congress Adelaide 2010 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 RANZCO Congress Adelaide 2010

RANZCO Congress Adelaide 2010 Tolerance <3% OK 3-5% decreased stereopsis >5% retinal rivalry RANZCO Congress Adelaide 2010

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 0.5 - 5 RANZCO Congress Adelaide 2010

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

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

RANZCO Congress Adelaide 2010 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 RANZCO Congress Adelaide 2010

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 RANZCO Congress Adelaide 2010

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 RANZCO Congress Adelaide 2010