Meridional aniseikonia-causes, symptoms, and therapies.

BACKGROUND: The term aniseikonia refers to the two eyes' appreciating different image sizes when viewing the same object. Meridional aniseikonia can occasionally cause significant distortion of the binocular spatial sense in perceptive patients. METHODS: The medical records of 3 adult patients who complained of binocular spatial distortion consistent with meridional aniseikonia were reviewed retrospectively. Detailed descriptions of symptoms, ocular findings, and management are reported. RESULTS: Each patient had undergone a refraction-altering surgical procedure, and each complained of binocular spatial distortion characterized by a trapezoidal view of square or rectangular shapes. Each patient improved following management of the astigmatic correction. CONCLUSIONS: Patients requiring a new astigmatic correction following cataract or corneal surgery may complain of binocular spatial distortion caused by meridional aniseikonia.

Effects of simulated anisometropia and aniseikonia on stereopsis.

PURPOSE: Stereopsis depends on horizontally disparate retinal images but otherwise concordance between eyes. Here we investigate the effect of spherical and meridional simulated anisometropia and aniseikonia on stereopsis thresholds. The aims were to determine effects of meridian, magnitude and the relative effects of the two conditions. METHODS: Ten participants with normal binocular vision viewed McGill modified random dot stereograms through synchronised shutter glasses. Stereoacuities were determined using a four-alternative forced-choice procedure. To induce anisometropia, trial lenses of varying power and axes were placed in front of right eyes. Seventeen combinations were used: zero (no lens) and both positive and negative, 1 and 2 D powers, at 45, 90 and 180 axes; spherical lenses were also tested. To induce aniseikonia 17 magnification power and axis combinations were used. This included zero (no lens), and 3%, 6%, 9% and 12% at axes 45, 90 and 180; overall magnifications were also tested. RESULTS: For induced anisometropia, stereopsis loss increased as cylindrical axis rotated from 180° to 90°, at which the loss was similar to that for spherical blur. For example, for 2 D meridional anisometropia threshold increased from 1.53 log sec arc (i.e. 34 sec arc) for x 180 to 1.89 log sec arc (78 sec arc) for x 90. Anisometropia induced with either positive or negative lenses had similar detrimental effects on stereopsis. Unlike anisometropia, the stereopsis loss with induced meridional aniseikonia was not affected by axis and was about 64% of that for overall aniseikonia of the same amount. Approximately, each 1 D of induced anisometropia had the same effect on threshold as did each 6% of induced aniseikonia. CONCLUSION: The axes of meridional anisometropia but not aniseikonia affected stereopsis. This suggests differences in the way that monocular blur (anisometropia) and interocular shape differences (aniseikonia) are processed during the production of stereopsis.

Changes in aniseikonia of an axial anisometrope at various stages of orthokeratology lens wear.

PURPOSE: To report a case of reduced aniseikonia in a myopic axial anisometrope during orthokeratology (OK) lens wear. CASE REPORT: A 19-year-old female university student with myopic anisometropia presented for an OK lens fitting consultation. At baseline, perceptual interocular image size difference or aniseikonia of 1.45% was found, with a smaller image seen by the right eye compared to the left eye. The patient was fitted with a pair of OK lenses and interocular image size differences, subjective refraction and corneal topography were measured after 7, 14 and 47 days of overnight lens wear. Hyperopic shifts in central refraction and corresponding flattening of the central cornea was measured during OK treatment. Aniseikonia reduced after OK wear with the most significant change measured from baseline to day 7. Aniseikonia recorded after 7, 14 and 47 nights of lens wear was 0.05%, 0.35% and 0.85%, respectively. Although minimum differences in refractive error between eyes was reached after 47 days of OK, aniseikonia was greater than that measured after 7 and 14 days of OK. CONCLUSION: This case report demonstrates reduction in aniseikonia with OK lens wear in a myopic patient with axial anisometropia, although this effect was not sustained beyond 1 week of lens wear. As the impact of corneal curvature changes on aniseikonia is not well understood, future studies on the impact of OK on aniseikonia and associated asthenopia is required.

Tratamento da aniseiconia induzida na correção óptica de anisometropia em escolares do ensino fundamental / Treatment of aniseikonia induced by optical correction of anisometropia in elementary school children

Resumo Objetivos: Comparar a aniseiconia e a estereopsia em escolares anisometropes do primeiro ano do ensino fundamental corrigidos com lentes oftálmicas de estoque com curvas-base selecionadas para minimizar a diferença de tamanho interocular das imagens retínicas e com lentes iseicônicas sugeridas pelo software Aniseikonia Inspector 3 e verificar a preferência dos escolares por uma destas formas de correção. Métodos: Dezenove escolares com anisometropia ≥ 1,5 D em meridianos correspondentes no uso de óculos com lentes oftálmicas de estoque e com lentes iseicônicas foram avaliados para aniseiconia (software Aniseikonia Inspector 3) e estereopsia (teste Stereo Fly test com símbolos LEA. A preferência por uma das formas de correção foi verificada após 40-50 dias de uso dos óculos. Resultados: As médias e os desvios-padrão das aniseiconias vertical e horizontal no uso de óculos com lentes oftálmicas de estoque e com lentes iseicônicas foram, respectivamente, -1,05% ± 2,20% e -1,37% ± 2,36% (p=0,82739) e -0,895% ± 2,23% e -1,16% ± 2,03% (p=0,77018). 31,6% dos escolares corrigidos com lentes iseicônicas e 21,1% dos escolares corrigidos com lentes oftálmicas de estoque identificaram os optotipos que sugerem estereopsia < 100 segundos de arco (p= 0,475). Em relação à preferência, 4/15 (26,7%) escolheram os óculos com lentes iseicônicas, 2/15 (13,3%) escolheram os óculos com lentes oftálmicas de estoque e para 9/15 (60%) a escolha foi indiferente. Conclusão: A aniseiconia induzida nos escolares anisometropes corrigidos com lentes iseicônicas sugeridas pelo software Aniseikonia Inspector 3 foi similar ao obtido na correção com lentes oftálmicas de estoque com curvas-base selecionadas para minimizar a diferença de tamanho interocular das imagens retínicas.

Abstract Objectives: To compare the aniseikonia and the stereopsis in school children anisometropes of the first-year of elementary school corrected with stock ophthalmic lenses with base curve selected to minimize the interocular size difference of retinal images and with size lenses suggested by the software Aniseikonia Inspector 3, and to check the preference of them for one of these forms of correction. Methods: Nineteen school children with anisometropia ≥ 1.5 D in corresponding meridians, in the use of glasses with stock ophthalmic lenses and with size lenses were evaluated for aniseikonia (software Aniseikonia Inspector 3) and stereopsis (Stereo Fly test with LEA symbols). The preference for one of the forms of correction was verified after 40-50 days of wearing glasses. Results: The mean and standard deviations of the vertical and horizontal aniseikonia in the use of glasses with stock ophthalmic lenses and with size lenses were, respectively, -1.05% ± 2.20% and-1.37% ± 2.36% (p = 0,82739) and -0.895% ± 2.23% and -1.16% ± 2.03% (p = 0,77018). 31.6% of the school children corrected with size lenses and 21.1% of the students corrected with stock ophthalmic lenses identified the optotypes that suggest stereopsis less than 100 seconds of arc (p = 0.475). Regarding the preference, 4/15 (26.7%) of the students chose the glasses with size lenses, 2/15 (13.3%) chose the glasses with stock ophthalmic lenses, and for 9/15 (60%) the choice was indifferent. Conclusion: The induced aniseikonia in school children with anisometropia corrected with size lenses suggested by the software Aniseikonia Inspector 3 was similar to that obtained in the correction with stock ophthalmic lenses with base curves selected to minimize the difference of interocular size of retinal images.

Aniseikonia: A 21st Century Look.

Purpose: Aniseikonia, an appreciation of image size differences between the eyes, can produce symptoms in patients, ranging from headaches to loss of fusion. The purpose of this research was to take a 21st century look at aniseikonia. Methods: Kellogg Eye Center patient records were evaluated for measurable aniseikonia in patients tested with the Aniseikonia Helper, a tablet-based application. Anaglyph slides for the synoptophore were developed to test the limits of induced aniseikonia on stereopsis and fusion. A survey was developed to determine how frequently members of the American Association of Certified Orthoptists (AACO) examine and treat patients with aniseikonia.Results: The prevalence of measurable aniseikonia in this cohort was 7.8%. Moderate amounts of induced aniseikonia, 4% induced image size disparity, disrupt fusion and can cause a loss of stereopsis. Eighty percent of responding AACO members see patients with aniseikonia and among those, 25% see them on a monthly basis. Treatment options, other than wearing contact lenses, are limited to occlusion or fogging techniques. Conclusions: Aniseikonia remains a frequent complaint among patients. The ophthalmologic community needs to use the best methods for measuring aniseikonia and to develop better methods for treating aniseikonia.

Aniseikonia and anisometropia: implications for suppression and amblyopia.

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.

Partial correction of irregular aniseikonia secondary to retinal traction.

PURPOSE: This case report presents the management of symptomatic retinally induced aniseikonia and a short review of the literature pertaining to two clinical tests used in the measurement and management of aniseikonia. The clinician is also provided a review of how to design eikonic lenses. CASE REPORT: A 30-year-old white male presented with symptoms of perceived image size difference after scleral buckle repair for retinal detachment in the right eye. Three measures of aniseikonia resulted in markedly different values, but all indicated larger perceived left eye image. Stereopsis was measured before and after placing an afocal magnifying lens over the right eye. Stereopsis improved immediately upon placement of the afocal lens, with further improvement after 20 minutes, and stereopsis decreased upon removal. The patient reported improved visual comfort for near work with the afocal lens. Eikonic glasses were designed, and the patient reported improved comfort for near work that has remained for over 1 year of wear. Studies evaluating the validity and reliability of the New Aniseikonia Test and the Aniseikonia Inspector are reviewed. Most studies report that induced aniseikonia is underestimated. This case report illustrates that despite the problem with underestimation, these tests are useful clinical tools to identify whether aniseikonia exists and which eye has the larger perceived image. Results can be used as a starting point when making clinical decisions about managing aniseikonia. The Aniseikonia Inspector also assists in the design of eikonic glasses. CONCLUSIONS: Even when aniseikonia is substantial, variable in magnitude, and irregular due to retinal disease, reducing the overall aniseikonia can improve binocularity and patient's comfort noticeably for the long term. The underestimation of induced aniseikonia in clinical tests does not preclude their use as a tool in the management of symptomatic aniseikonia.

[Pitfalls in the determination of distance glasses]. / Fallstricke bei der Bestimmung von Fernbrillen.

The correct determination of distance glasses depends on a correct objective refraction and a subject determination of power and axis of a possible astigmatism in both a coarse and fine manner. In suitable cases a binocular fine refraction under polarized conditions with a red-green test should be performed. Special considerations have to be taken into account in cases of high unilateral congenital or acquired astigmatism as well as in case of congenital or acquired anisometropia or aniseiconia.

The evaluation of two new computer-based tests for measurement of Aniseikonia.

PURPOSE: To evaluate the accuracy and repeatability of size lens induced aniseikonia measurement with the Aniseikonia Inspector Version 1 and a newer customized version of the Aniseikonia Inspector, Version 2. METHODS: Aniseikonia was measured on 27 subjects with both versions of the Aniseikonia Inspector in normal room illumination. Measurements of induced aniseikonia were made using size lenses in a randomized order. Twenty-five subjects were further tested in the dark using target sizes of equal visual angle for both tests. Repeatability of the intrinsic aniseikonia measurement was assessed on five subjects using randomized testing order for instrument and light and dark measurements. RESULTS: In normal illumination, the mean slopes for plots of induced aniseikonia vs. size lens magnification for Version 1 were 0.883 and 0.838 for the vertical and horizontal meridians, respectively. For Version 2, the corresponding slopes were 1.162 and 1.043. In the dark and using targets of the same size for both tests, the slopes for Version 1 were 1.038 in the vertical meridian and 0.866 in the horizontal meridian whereas for Version 2, the slopes were 1.195 in the vertical meridian and 1.127 in the horizontal meridian. The amount of underestimation or overestimation within any given testing condition showed considerable intersubject variation. Version 1 was more repeatable than 2, particularly in the vertical meridian. CONCLUSIONS: On average, the most accurate and repeatable measurement of aniseikonia was found with Version 1 in the vertical meridian in the dark. Measurement of aniseikonia in the horizontal meridian appears to be less reliable. Version 2 overestimates size lens-induced aniseikonia under all testing conditions. Intersubject variation in slopes of induced aniseikonia vs. size lens magnification should be further addressed.

Orthoptic indications for contact lens wear.

Orthoptic anomalies are prevalent: they are encountered in at least 5% of patients seen in a typical primary eyecare practice. Several cases are reviewed that highlight the role of contact lenses in treating orthoptic anomalies. In particular, contact lenses are the preferred optical approach to the correction of anisometropia, and it is often argued that anisometropia should be corrected as young as possible. However, fitting contact lenses to patients, particularly children, with anisometropic amblyopia has been problematic because there is no immediate binocular acuity improvement when the contact lenses are inserted which reduces patient motivation. Continuous wear with silicone hydrogels represents a breakthrough for these cases and some illustrative case studies are given. The visual deficit in amblyopia can be reduced in some cases solely by fitting contact lenses, without the need for occlusion therapy. Other orthoptic uses of contact lenses are reviewed including: correcting motor deviations, occlusion, and infantile onset nystagmus. It is concluded that there are orthoptic anomalies where contact lenses are the preferred mode of correction. It is in patients' best interest for practitioners to discuss contact lenses in these cases.

Compensation of aniseikonia in astigmatic pseudophakic eyes.

PURPOSE: A recently published manuscript addressed the problem of compensating for aniseikonia between pseudophakic astigmatic eyes using a least-squares calculation scheme. The purpose of this paper is to revisit this topic with the specific aim of providing explicit formulae for the determination of the intra-ocular lens required to produce a specified transverse image size at the plane of the retina and the characteristics of the contact or spectacle lens required to realize some desired refractive outcome. METHODS: The 4 x 4 ray transference is central to the development of all formulae presented in this paper. Specifically, the formula for the determination of the power of the intra-ocular lens required to achieve some transverse image size at the retina is derived directly from the disjugacy of the pseudophakic eye. RESULTS: The formula is applicable to both stigmatic and astigmatic systems without restriction. A detailed numerical example for an unusual eye is provided. CONCLUSION: A formula for the determination of the intra-ocular lens required to produce any given transverse image size at the retina is derived. This approach does not require the application of the Moore-Penrose pseudo-inverse and one is able to work rather with the properties of the optical system directly without further modification.

Contact lens management of aniseikonia and photophobia induced by trauma.

PURPOSE: To describe a case of a contact lens fitting to relieve aniseikonia and photophobia resulting from trauma. METHODS: A 61-year-old man suffered a blunt injury to his left eye resulting in glaucoma and a traumatic cataract with a fixed pupil and iris defects. A vitrectomy, lensectomy, and iris repair were performed leaving him with significant anisometropia. RESULTS: The patient was fitted with a prosthetic contact lens. CONCLUSIONS: Contact lenses can provide significant visual improvement in cases of aniseikonia and photophobia.

Compensation of aniseikonia with toric intraocular lenses and spherocylindrical spectacles.

BACKGROUND AND PURPOSE: Magnification disparity between the two eyes (aniseikonia) is one of the major unresolved problems in modern cataract surgery, potentially degrading binocular visual function or causing diplopia. The purpose of this study is to describe a paraxial computing scheme using 4x4 system matrices to simulate a corrected pseudophakic 'optical system eye' with a meridional magnification that matches the magnification of a given contralateral eye. METHODS: Based on the definition of a centred optical system in the paraxial Gaussian space containing astigmatic surfaces using 4x4 refraction and translation matrices, we derived a methodology for calculating the refractive power and axis of toric intraocular lenses and spherocylindrical spectacle corrections for (i) fully correcting the optical system eye and (ii) realizing an arbitrary meridional magnification by solving a linear equation system. RESULTS: The capabilities of this computing scheme are demonstrated with two examples. In example 1 we calculate a toric lens and a spherocylindrical spectacle correction for compensation of a corneal astigmatism to realize a predefined iso-meridional magnification. In example 2 we first determine the meridional magnification of the contralateral eye, which has been treated with cataract surgery and toric lens implantation, and then we compute the appropriate combination of a fully correcting toric lens and spherocylindrical spectacle refraction, which exactly matches the meridional magnification of the contralateral eye. CONCLUSION: We presented an en bloc matrix based strategy for the calculation of an optical system eye containing an astigmatic cornea, a toric lens implant and a spherocylindrical spectacle correction, where the toric lens and the spherocylindrical spectacle correction are determined to fully correct the system and to realize an arbitrary meridional magnification i.e. to eliminate aniseikonia.