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Aniseikonia: A rare cause of diplopia (Including after “successful” cataract surgery)

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Aniseikonia: A rare cause of diplopia (Including after “successful” cataract surgery)

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  1. 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 RANZCO Congress Adelaide 2010

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

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

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

  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 RANZCO Congress Adelaide 2010

  7. RANZCO Congress Adelaide 2010

  8. Aniseikonia Causing Diplopia – Retinal Causes • (ERM peel in 1 patient was NOT successful in fixing aniseikonia) RANZCO Congress Adelaide 2010

  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) RANZCO Congress Adelaide 2010

  10. A case of aniseikonia due to “sensible cataract surgery” • 56 yo male for R phaco/IOL • Pre-op refractions (SE) • R -8 DL -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

  11. 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

  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 RANZCO Congress Adelaide 2010

  13. Thank you

  14. Aniseikonia • Causes • Retinal • Optical A A RANZCO Congress Adelaide 2010

  15. Eikonometry • New Aniseikonia Test (Awaya) RANZCO Congress Adelaide 2010

  16. Retinal Cause = ERM RANZCO Congress Adelaide 2010

  17. Optical Cause RANZCO Congress Adelaide 2010

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

  19. RANZCO Congress Adelaide 2010

  20. 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

  21. RANZCO Congress Adelaide 2010

  22. Axial Anisometropia • Knapp's Rule • Does not always apply – photoreceptor spacing RANZCO Congress Adelaide 2010

  23. RANZCO Congress Adelaide 2010

  24. RANZCO Congress Adelaide 2010

  25. 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

  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 RANZCO Congress Adelaide 2010

  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 RANZCO Congress Adelaide 2010