Sensory causes of diplopia- Aniseikonia

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Sensory causes of diplopia- Aniseikonia

• LIONEL KOWAL
• RVEEH MELBOURNE
• Financial involvement
• Patients paid their bills

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Diplopia

• 2 images, one seen by each eye, are separated
  and the patients motor and sensory fusion are
  inadequate to bring them together
• Usually only consider the motor aspect of
  separation
• Motor fusion impaired by sensory problems - the 2
  images need to be fairly similar to be fused
• Aniseikonia - difference in image size - will
  prevent fusion
• Metamorphopsia
• Field defect
• Often treatable with glasses

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You miss more by not asking than by not knowing
..after John Colvin

• ASK EVERY PATIENT WHOSE DIPLOPIA IS NOT EASILY
  COMPENSATED FOR WITH PRISM
• Is the image seen by the R
• Larger / smaller than the L
• The same shape as L
• Paler / darker than L
• Tilted not aniseikonia torsion

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Materials and methods

• Retrospective chart study
• 11 patients
• Aged 29-86
• MF 83

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Results n11

• 10 vision 6/8 or better in the worse eye
• 10 complained of diplopia
• 1 had wobbling of words

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Results n11

• Anisometropia in 7
• Macular causes in 4
• 2/4 had ERM on macula NO ERM SURGERY
• 1/4 had previous ERM peel with residual or
  recurrent ERM temporal to macula
• 1/4 had macular hole surgery
  anisometropia RESPONDED TO GLASSES FOR
  ANISOMETROPIA

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Measuring aniseikonia

• The least amount of aniseikonia causing
  disruption of fusion was 2
• Largest amount of aniseikonia was 20 which was
  corrected with telescopic lenses (CLs with equal
  in glasses)
• Other techniques
• Synoptophore
• Free space techniques

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AWAYAS NEW ANISEIKONIA TEST
Use R-G glasses. Find the pair of semi- circles
where the difference in sizecompensates for the
patients aniseikonia
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Measuring aniseikonia Free space estimation

• Separate with prism. Which eye sees the bigger /
  smaller image?
• If each bar of the E is 20, how much bigger /
  smaller is the image seen by L? R?
• Check with prism in front of other eye - prisms
  can cause magnification
• CONFOUNDER MEASUREMENT ARTEFACT - each technique
  can give a VERY different answer

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Ask pt to look _at_ both 6/60 E. RE sees the
higher image. Which one is bigger? Does it look
like an E should? Are all parts of it bigger
mmorphopsia? Is the E Tilted? If a bar of
the E is worth 20, how much bigger is it?
Also check with BD prism in front of other eye -
prisms can also cause magnification
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Results n11

• 7 /11 had vertical deviation
• ?vertical fusion is more fragile than horizontal
• 3 /7 also had horizontal deviations
• 2 had exophoria with poor FR

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Results n11

• 5 modified spectacles prisms
• 1 contact lenses
• 1 reduced prescription of near add on one lens

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Results n11

• 1 had telescopic lenses (ve CL and ve spectacle
  lens) FOR 20 ANISEIKONIA
• 2 had surgery for exotropia
• 1 declined treatment

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Results

• In most patients, aniseikonia precipitates small
  angle strabismus due to loss of sensory fusion
  wch in turn impairs motor fusion
• Compensation for the strabismus with prisms along
  with lenses modified to compensate for the
  aniseikonia worked in 5/7 optically corrected
  patients

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Discussion

• Two main clinical causes of Aniseikonia
• Macular causes
• Anisometropia
• 1 of aniseikonia per DS of anisometropia

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A Prospective Study of Binocular Visual Function
before and after Successful Surgery to Remove a
Unilateral Epiretinal MembraneOphthalmology
November 2008

• 2/27 diplopia
• Measured stereo, motor fusion VA.
• Stereo total motor fusion ranges reduced
• After successful surgery, stereo function, VA
  motor fusion improved mainly in those with
  shorter duration of symptoms esp lt 18mo
• Stereo function improved mainly in those with
  better preoperative stereo

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Optical solutions to increase image size

• Increase front base curve
• Increase central thickness
• Decreased vertex distance increases image size in
  lens and decreases in
• increase refractive index
• .often successful
• NOT known to average optometrist / dispenser

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Aniseikonia as a substantial factor in causing
diplopia

• Probably rare
• Always unrecognised by referring doctor or optom
• Need to ask about it - pt always knows but needs
  to be asked the right Q
• Often fixable with prisms and aniseikonic
  modifications
• THANK YOU

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