Predicting Aniseikonia in Anisometropia*

Ryan, Vernon I.

doi:10.1097/00006324-197502000-00003

Cited by 11 publications

(5 citation statements)

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“…Recent studies comparing aniseikonia with spectacles and then contact lenses in the same individual (Arner, 1969;Awaya and Von Noorden, 1971;Ryan, 1975;Flick, 1980) have shown that smaller perceived size differences were found with contact lens corrections. However, axial lengths were not measured in these cases, and the authors concluded that their subjects' anisometropia must have been predominantly refractive in origin.…”

mentioning

confidence: 99%

Reduced aniseikonia in axial anisometropia with contact lens correction§

Winn

Ackerley

Brown

et al. 1988

Ophthalmic Physiologic Optic

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Aniseikonia, although present in isometropia, is associated principally with anisometropia and is widely thought to be the result of differences in the retinal image size presented to each eye. This assumes that equating retinal image size results in congruous cortical images. To test this assumption 1 refractive and 17 axial anisometropic subjects were examined to determine the aniseikonia present when corrected with spectacles and contact lenses. Contrary to many previous predictions, based upon Knapp's Law, the presence of equal retinal images resulted in larger aniseikonias than observed when the eyes were presented with unequal retinal images. This suggests that non-optical components have a significant role in the production of the cortical image, and this therefore requires a shift in the way the management of anisometropia is considered clinically. Contact lens correction maintains the aniseikonia at a minimum level in axial as well as refractive anisometropia and offers the clinician an acceptable practical alternative when prescribing for these patients.

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confidence: 99%

Reduced aniseikonia in axial anisometropia with contact lens correction§

Winn

Ackerley

Brown

et al. 1988

Ophthalmic Physiologic Optic

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“…The difference in images sizes could potentially hinder binocular vision. Currently, estimations [ 29 , 30 ] or empirical calculations [ 31 , 32 ] are used due to presumed difficulties in measuring subjective aniseikonia, especially in children. Estimations and empirical calculations, however, do not take into account the retinal and cortical adaptations that may occur and therefore accurate measurement of subjective aniseikonia is important to determine the amount of image size difference individually experienced.…”

Section: Methodsmentioning

confidence: 99%

Measuring aniseikonia and investigating neuroplasticity and image factors in amblyopia (MAGNIFY): study protocol for a randomised clinical trial

South

Gao

Calderwood

et al. 2022

Trials

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Background Aniseikonia represents a potential barrier to neuroplasticity which may limit visual outcomes in children with anisometropic amblyopia. Full correction of refractive error is the first step in standard amblyopia treatment, which corrects for image focus but neglects image size differences. Methods The MAGNIFY study is a double-masked, randomised clinical trial investigating the effectiveness of aniseikonia correcting lenses in children at first diagnosis of significant anisometropia. We hypothesis that aniseikonia correction lenses will improve image clarity and reduce the retinal size differences producing better visual acuity and stereoacuity improvements after 15 weeks of optical treatment for children with anisometropia. Eligible children will be randomly allocated to the treatment group (aniseikonia-correcting spectacle lenses) or control group (standard spectacle lenses). Visual acuity and binocular functions will be assessed every 5 weeks during the 15-week optical treatment phase according to standard amblyopia treatment protocol. Discussion It is possible that correcting aniseikonia along with anisometropia at first diagnosis will promote binocularity as well as increase spectacle adherence by reducing visual discomfort, improving optical treatment outcomes. This could then reduce the need for additional amblyopia treatment such as patching or atropine, reducing the burden on hospital eye departments and potentially improving visual outcomes for children with amblyopia. Trial registration Australian New Zealand Clinical Trials Registry (ANZCTR) ACTRN12620000061932. Registered on 24 January 2020. Protocol 15th November 2019, version one.

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“…Spectacle magnification can be manipulated by adjusting lens base curves, centre thicknesses and/or refractive indices. The magnification induced by the lens Power Factor, which is determined by back vertex power and vertex distance, usually cannot be easily altered if the refractive error is to be fully corrected. Equation 2: Spectacle magnification equation.

italicSM = M_{p} \times M_{s} = ((), \frac{1}{1 - d {F_{v}}^{'}}) ((), \frac{1}{1 - \frac{t}{n} F_{1}})

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Section: Treatment Of Aniseikoniamentioning

confidence: 99%

Aniseikonia and anisometropia: implications for suppression and amblyopia

South

Gao

Collins

et al. 2019

Clinical and Experimental Optometry

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Aniseikonia is a difference in the perceived size or shape of images between eyes, and can arise from a variety of physiological, neurological, retinal, and optical causes. Aniseikonia is associated with anisometropia, as both anisometropia itself and the optical correction for anisometropia can cause aniseikonia. Image size differences above one to three per cent can be clinically symptomatic. Common symptoms include asthenopia, headache and diplopia in vertical gaze. Size differences of three and more impair binocular visual functions such as binocular summation and stereopsis. Above five per cent of aniseikonia, binocular inhibition or suppression tend to occur to prevent diplopia and confusion. Aniseikonia can be measured using a range of techniques and can be corrected or reduced by prescribing contact lenses or specially designed spectacle lenses. Subjective testing of aniseikonia is the only way to accurately measure the overall perceived amount of aniseikonia. However, currently it is not routinely assessed in most clinical settings. At least two-thirds of patients with amblyopia have anisometropia, thus we may expect aniseikonia to be common in patients with anisometropic amblyopia. However, aniseikonia may not be experienced by the patient under normal binocular viewing conditions if the image from the amblyopic eye is of poor quality or is too strongly suppressed for image size differences to be recognised. This lack of binocular simultaneous perception in amblyopia may also prevent the measurement of aniseikonia, as most common techniques require direct comparisons of images seen by each eye. Current guidelines for the treatment of amblyopia advocate full correction of anisometropia to equalise image clarity, but do not address aniseikonia. Significant image size differences between eyes may lead to suppression and abnormal binocular adaptations. It is possible that correcting anisometropia and aniseikonia simultaneously, particularly at the initial diagnosis of anisometropia, would reduce the need to develop suppression and improve treatment outcomes for anisometropic amblyopia.

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Predicting Aniseikonia in Anisometropia*

Cited by 11 publications

References 0 publications

Reduced aniseikonia in axial anisometropia with contact lens correction§

Reduced aniseikonia in axial anisometropia with contact lens correction§

Measuring aniseikonia and investigating neuroplasticity and image factors in amblyopia (MAGNIFY): study protocol for a randomised clinical trial

Aniseikonia and anisometropia: implications for suppression and amblyopia

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