Sensory causes of diplopia- Aniseikonia LIONEL KOWAL RVEEH MELBOURNE Financial involvement: Patients paid their bills

Diplopia 2 images, one seen by each eye, are separated and the patient’s 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

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]

Materials and methods Retrospective chart study 11 patients Aged 29-86 M:F 8:3

Results n=11 10 vision 6/8 or better in the worse eye 10 complained of diplopia 1 had wobbling of words

Results n=11 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

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

AWAYA’S NEW ANISEIKONIA TEST Use R-G glasses. Find the pair of semi- circles where the difference in size compensates for the patient’s aniseikonia

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

Ask pt to look @ 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 [m’morphopsia]? 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

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

Results n=11 5 modified spectacles + prisms 1 contact lenses 1 reduced prescription of near add on one lens

Results n=11 1 had telescopic lenses (+ve CL and –ve spectacle lens) FOR 20% ANISEIKONIA 2 had surgery for exotropia 1 declined treatment

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

Discussion Two main clinical causes of Aniseikonia Macular causes Anisometropia ~ 1% of aniseikonia per DS of anisometropia

Measured stereo, motor fusion & VA. A Prospective Study of Binocular Visual Function before and after Successful Surgery to Remove a Unilateral Epiretinal Membrane Ophthalmology 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 < 18mo] Stereo function improved mainly in those with better preoperative stereo

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

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

Discussion