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Therese Krarup, Ulrik Correll Christensen, Jens Folke Kiilgaard, Morten la Cour; Construction and validation of a novel method to measure tolerance of aniseikonia. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1270.
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No method exists to measure aniseikonia tolerance on stereopsis. The brain can compensate for 2-3% of aniseikonia, (i.e. 2-3 diopters of anisometropia), without affecting stereopsis, however, a significant proportion of anisometropic patients suffer from stereopsis problems due to surgical induced aniseikonia. We hypothesized that an individual difference in tolerances of aniseikonia exists, and set to develop a method to measure endurable aniseikonia without impairing stereopsis.
We included 21 eye-healthy phakic individuals aged above 50 years. All participants were tested with best corrected near and distance visual acuity, cover/uncover test, eye dominance test, optimal stereopsis (TNO-test), slit lamp examination, and ocular coherence tomography. We examined how stereopsis was affected by aniseikonia induced by size glasses from 1-9% larger image on the right (+1 - +9%) eye to 1-9% larger image on the left eye (-1 - -9%). Stereopsis was examined with a blinded TNO-test showed in random order. Aniseikonia Range (AR) was defined as the percentage aniseikonia in which optimal stereopsis is maintained. We retested five patients to examine reproducibility.
We examined 21 individuals, median age 65 (95% CI: 62-66 years), median corrected distance visual acuity 88.5 ETDRS (95% CI: 87-90), median corrected logarithmic near visual acuity 1.05, median spherical equivalent 0.47 ± 2.03, 43% right eye dominant, 57% left eye dominant, 3 (14%) participants with esophoria. Median stereopsis with optimal correction 60“ ± 27.4. We report a large inter-individual differences in AR (Figure 1) with 4 participants with AR of ≤ 1% (19%), 1 with AR 2-4% (4.7%), 1 with AR 5-7% (4.7%), 3 with AR 8-10% (14%), 4 with AR 11-13% (19%) and 8 with AR >13% (38%). In the five participants that were retested the test/retest variance in AR was 0.
We present a novel and reliable method of how to measure AR and the amount of aniseikonia a person can endure without impairing stereopsis. We report large inter-individual differences in tolerance of aniseikonia. Further studies are needed to examine consistency of AR and usefulness in predicting stereopsis problems after refractive surgery with anisometropia.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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