Purpose: The purpose of this study was to predict the base curve of the spectacle correction of patients in order to minimize their aniseikonia. We hypothesized that in order to correct the patient’s aniseikonia, we can manipulate the base curve of the subject’s prescription to change the magnification, without ultimately altering the prescription.
Methods: Ten female adults with spherical equivalent of ≥ 1 D anisometropia, and visual acuity of 20/25 or greater corrected vision, were studied. The participants were evaluated for anisometropia while wearing their habitual spectacles (i.e. non-size lens) and reassessed 4 weeks later (± 2 weeks). A-scan ultrasound biometry and keratometry measurement were determined at first visit. Ocular history, visual acuity, refraction, stereopsis at near, and aniseikonia subjective symptoms was evaluated at each visit. Aniseikonia amount was measured by the Brecher test and Aniseikonia Inspector Software test for both spectacles and with contact lenses. Size lens spectacles were prescribed according to the findings of the first visit with new frames using two base curves: 2 D (the flattest base curve) and 6 D (steepest base curve) for the subjects to be used full time.
Results: Seven subjects were classified as axial anisometropes and three had the mixed type. Anisometropia spherical equivalent of ≥ 1 D caused aniseikonia of at least 1 %. A good model of predication about the relationship between the axial length and anisometropic SE difference between the two eyes was shown. Visual acuity improved ((P < 0.05) one line with size lens spectacles. Stereopsis was not affected (P > 0.05) for all subjects except one, who showed improvement. Aniesikonia decreased with size lens spectacles by 57.5 % from the first visit (P < 0.05). Aniseikonia improved more when the subjective phoria was compensated by loose prism, as needed, to 95 percent (P < 0.05), regardless of the subject’s anisometropia type. There were no statistically significant (P > 0.05), differences of the symptoms between habitual spectacles, contact lenses and size lens spectacles, but there was a clinically significant change of headache, asthenopia, photophobia and reading difficulity with size lens spectacles compared to habitual spectacles and contact lenses. The mean average of the two aniseikonia tests was 0.7845 percent per one diopter of anisometropia spherical equivalent.
Conclusions: Manipulation of the size lens spectacle base curve helps to correct aniseikonia. Prism is one of the option to treat aniseikonia but further study is necessary to show the relation between aniseikonia and prism.
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