Sensory causes of diplopia- Aniseikonia

LIONEL KOWALRVEEH 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: SynoptophoreFree space techniques

Use R-G glasses. Find the pair of semi-circles where the difference in sizecompensates for the patient’s aniseikonia

AWAYA’S NEW ANISEIKONIA TEST

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

Also check with BDprism in front of other eye - prisms can alsocause magnification

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?

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

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