Effects of induced aniseikonia on binocular visual acuity.

CLINICAL RELEVANCE: Binocular visual acuity is an important index of functional performance. Optometrists need to know how binocular visual acuity is affected by aniseikonia, and whether reduced binocular visual acuity is a marker for aniseikonia. BACKGROUND: Aniseikonia, the perception of unequal image sizes between the eyes, can occur spontaneously or can be induced after different types of eye surgery, or trauma. It is known to affect binocular vision, but there are no prior studies about how it affects visual acuity. METHODS: Visual acuity was measured for 10 healthy well-corrected participants aged 18-21 years of age. Aniseikonia of up to 20% was induced in one of two ways: (1) size lenses, which provided minification of field of view in one eye of each participant and (2) polaroid filters, which allowed vectographic viewing of optotypes on a 3D computer monitor. The best corrected acuity was measured on conventional logarithmic progression format vision charts and isolated optotypes, under both induced aniseikonia conditions. RESULTS: Induced aniseikonia caused binocular visual acuity thresholds to increase by small but statistically significant amounts, with the largest deficit being 0.06 logMAR for 20% size differences between the eyes. Binocular visual acuity was worse than monocular visual acuity for aniseikonia of 9% and greater. Acuity measured with the vectographic presentation gave slightly higher thresholds (by 0.01 logMAR) than for those viewed with size lenses. Acuity measured with charts gave slightly higher thresholds (by 0.02 logMAR) than with isolated letters. CONCLUSION: An acuity change of 0.06 logMAR is small and may be missed in a clinical examination. Therefore, visual acuity cannot be used as a marker of aniseikonia in clinical settings. Even with very marked induced aniseikonia, binocular visual acuity remained well within standards for licen*c*sing of drivers.

Prediction of ocular magnification and aniseikonia after cataract surgery.

BACKGROUND: Ocular magnification and aniseikonia after cataract surgery has been widely ignored in modern cataract surgery. The purpose of this study was to analyse ocular magnification and inter-individual differences in a normal cataract population with a focus on monovision. METHODS: From a large dataset containing biometric measurements (IOLMaster 700) of both eyes of 9734 patients prior to cataract surgery, eyes were indexed randomly as primary (P) and secondary (S). Intraocular lens power (IOLP) was derived for the HofferQ, Haigis and Castrop formulae for emmetropia for P and emmetropia or myopia (-0.5 to -2 dpt) for S to simulate monovision. Based on the pseudophakic eye model in addition to these formulae, ocular magnification was extracted using matrix algebra (refraction and translation matrices and a system matrix describing the optical property of the entire spectacle corrected or uncorrected eye). RESULTS: With emmetropia for P and S the IOLP differences (S-P) showed a standard deviation of 0.162/0.156/0.157 dpt and ocular magnification differences yielded a standard deviation of 0.0414/0.0405/0.0408 mm/mrad for the HofferQ/Haigis/Castrop setting. Simulating monovision, the myopic eye (S) showed a systematically smaller mean absolute spectacle corrected ocular magnification than the emmetropic eye (-0.0351/-0.0340/-0.0336, respectively, relative magnification around 2%). If myopia in the S eye remains uncorrected, the reduction of ocular magnification is much smaller (around 0.2-0.3%). CONCLUSION: Vergence formulae for IOLP calculation sometimes implicitly define a pseudophakic eye model which can be directly used to predict ocular magnification after cataract surgery. Despite a strong similarity of both eyes, ocular magnification does not fully match between eyes and the prediction of ocular magnification and aniseikonia might be relevant to avoid eikonic problems in the pseudophakic eye.

Aniseikonia and visual functions with optical correction and after refractive surgery in axial anisometropia.

PURPOSE: To evaluate differences in the subjective aniseikonia and stereoacuity in patients with axial anisometropia after full correction of the refractive error with spectacles, contact lenses, and refractive surgery. METHODS: A prospective study was performed in Cairo University Hospitals on 20 patients with axial anisometropia caused by unilateral myopia > 5 D with > 4 D inter-ocular difference in spherical equivalent who were suitable candidates for excimer laser ablation (LASIK) or implantable collamer lens implantation (ICL). All patients had measurement of best-corrected visual acuity (BCVA), fusion, stereoacuity, and magnitude of aniseikonia with spectacles, contact lenses, and after surgery. RESULTS: The mean age at time of surgery was 25.7 ± 3.1 years. There were no statistically significant differences in the BCVA or stereoacuity with spectacles, contact lenses, or after refractive surgery. Microkonia < 5%) was perceived with spectacles in 8 patients (40%) and remained unchanged in 7 of these 8 patients with contact lenses. Following LASIK (n = 11), there was an induced macrokonia < 2% in 4 patients (36%), persistent microkonia of 3% in 1 patient (9%), and no change in image size in 6 (55%) patients. Following ICL implantation (n = 9), there was a perceived macrokonia of 2% in 4 patients (44%), disappearance of microkonia in 1 patient (11%) and no change in 4 patients (44%). CONCLUSIONS: Differences in BCVA, stereoacuity, and aniseikonia after correction of anisometropia by glasses, contact lens and surgery are both clinically and statistically insignificant. Retinal or neural adaptation might have a role in correction for differences in image size.

Comparative analysis of metamorphopsia and aniseikonia after vitrectomy for epiretinal membrane, macular hole, or rhegmatogenous retinal detachment.

This study investigated postoperative changes in metamorphopsia and aniseikonia in eyes that underwent vitrectomy for epiretinal membrane (ERM), macular hole (MH), or rhegmatogenous retinal detachment (RRD). In total, 166 eyes were included from 166 patients with ERM, MH, or RRD who underwent primary vitrectomy. Metamorphopsia and aniseikonia were quantified by M-CHARTS and the New Aniseikonia Test (NAT). Best-corrected visual acuity (BCVA), M-CHARTS, NAT assessments, and OCT examination were performed at 1, 3, and 6 months postoperatively. Of the 166 eyes, 65 had ERM, 21 had MH, 42 had macula-off RRD, and 38 had macula-on RRD. BCVA improved significantly between 1 and 6 months postoperatively in eyes with ERM, MH, and macula-off RRD (P = 0.0057, P = 0.0065, and P = 0.0021, respectively). M-CHARTS scores at 1 month postoperatively significantly decreased in eyes with ERM (P = 0.0034) and tended to decrease in eyes with MH (P = 0.068). NAT scores did not change between baseline and 1 month postoperatively in eyes with ERM or MH. Between 1 and 6 months postoperatively, M-CHARTS and NAT scores significantly decreased in eyes with macula-off RRD (P = 0.0064 and P = 0.0009, respectively), but not in eyes with ERM, MH, or macula-on RRD. At 6 months postoperatively, significant metamorphopsia was evident in 33.3% of eyes with ERM, 29.2% of eyes with MH, and 35.7% of eyes with macula-off RRD; 61.5% of eyes with ERM showed macropsia and 52.3% of eyes with macula-off RRD showed micropsia. In eyes with ERM, more central retinal thickness (CRT) correlated with postoperative BCVA, and deep retinal folds on enface OCT image correlated with postoperative metamorphopsia. In eyes with macula-off RRD, less CRT correlated with postoperative BCVA, and tended to correlate with postoperative micropsia. Macular morphologies could contribute to differences in postoperative visual acuity, metamorphopsia, and aniseikonia.

CORRELATION BETWEEN MACULAR MICROSTRUCTURES AND ANISEIKONIA AFTER IDIOPATHIC EPIRETINAL MEMBRANE REMOVAL.

PURPOSE: To analyze the correlation between preoperative measurements of macular microstructures and aniseikonia after epiretinal membrane removal. METHODS: This retrospective study included 32 eyes of 32 patients who underwent epiretinal membrane surgery and were followed up for 12 months. Spectral-domain optical coherence tomography was used to measure the thicknesses of the ganglion cell layer-inner plexiform layer, inner nuclear layer (INL), and outer retinal layer in macular microstructures. The new aniseikonia test was used to measure vertical and horizontal aniseikonia scores. RESULTS: There was a significant decrease in central macular thickness and ganglion cell layer-inner plexiform layer thickness at 6 and 12 months postoperatively (all P < 0.001). Vertical aniseikonia scores, horizontal aniseikonia scores, and INL and outer retinal layer thicknesses did not show significant changes. Vertical aniseikonia scores and horizontal aniseikonia scores were significantly associated with INL thicknesses of each meridian at each follow-up time point (all P < 0.05). Preoperative vertical and horizontal INL thicknesses were correlated with vertical aniseikonia scores and horizontal aniseikonia scores at 12 months postoperatively (P = 0.014 and P = 0.002, respectively). CONCLUSION: Aniseikonia values did not change after epiretinal membrane removal and were associated with INL thickness before and after surgery. Thus, preoperative INL thickness could be used as a predictor of surgical prognosis in epiretinal membrane patients.

Topical Review: Retinally Induced Aniseikonia.

SIGNIFICANCE: We review retinally induced aniseikonia, an underrecognized condition resulting from common retinal conditions that has a significant effect on quality of life. Optometrists can influence the timing of surgical intervention to mitigate the damage from delaying surgical intervention in patients whose other findings do not meet a surgeon's treatment threshold.Aniseikonia due to optical differences between the eyes occurs in 1 to 3.5% of the population and can hinder the quality of binocular vision. The less noted retinally induced aniseikonia is due to mechanical distortion and displacement of the retinal photoreceptors and occurs with disorders such as epiretinal membrane, reattached retinal detachment, macular hole, and macular edema. Despite that it was first reported in 1950 and its incidence continues to rise in the aging population, many eye care practitioners are unaware of this condition, which can persist or even be exacerbated after treatment as a contributing cause of binocular vision symptoms. The purpose of this report is to allow more eye care practitioners to become familiar with retinally induced aniseikonia. The review of the literature includes demographics and epidemiology, etiology, pathogenesis, diagnosis, results of treatment, prognosis, and case examples.

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.

Relationship between the morphology of the foveal avascular zone and the degree of aniseikonia before and after vitrectomy in patients with unilateral epiretinal membrane.

PURPOSE: Persistent metamorphopsia, particularly aniseikonia, is a troublesome problem which may occur after epiretinal membrane (ERM) surgery. To clarify if the preoperative foveal avascular zone (FAZ) morphology can be used as a predictor of postoperative residual aniseikonia, the morphological changes in the FAZ and the degree of aniseikonia between before and 12 months after vitrectomy for epiretinal membrane (ERM) were measured and analyzed. METHODS: Thirty patients, each with a unilateral idiopathic ERM, who underwent treatment between September 2016 and March 2017 were enrolled for this prospective case series study. Best-corrected visual acuity (BCVA), the degree of aniseikonia, central foveal thickness (CFT), FAZ area (FAZa), perimeter (FAZp), and circularity in ERM eyes were examined before and 1, 3, 6 and 12 months after surgery. The fellow eye without an ERM was also examined and used as the control. The interocular ratios of the CFT, FAZa, and FAZp in ERM eyes with those in control eyes were also calculated. Multiple regression analysis was performed on preoperative parameters that were found to be significantly correlated with the 12-month aniseikonia in univariate analyses. RESULTS: The BCVA in the ERM eyes was significantly improved at 1 month after surgery (P < .0001) The degree of aniseikonia was significantly reduced only after 12 months (P = .004). The CFT had decreased significantly by 3 months after the surgery and continued decreasing thereafter (P < .0001). Both FAZa and FAZp were significantly smaller in the ERM eyes than in the control eyes throughout the study period (P < .0001 and P < .0001, respectively), with no change in either parameter over the study period. Correlation analyses revealed that the degree of aniseikonia was significantly correlated with pre- and postoperative CFT, CFT ratio, FAZa, FAZa ratio, FAZp, and FAZp ratio. Within preoperative OCT parameters, FAZa ratio remained significant after multiple regression analysis was performed (P < .0001). CONCLUSIONS: Aniseikonia changed little over the long term following ERM surgery. Preoperative FAZ area ratio was identified as a significant predictor of postoperative aniseikonia.

Associations of aniseikonia with metamorphopsia and retinal displacements after epiretinal membrane surgery.

PurposeTo determine the correlation of the degree of aniseikonia with the retinal displacements and metamorphopsia in patients that have undergone successful epiretinal membrane (ERM) surgery.MethodsSubjects were 28 eyes with an ERM in 28 patients. The New Aniseikonia Test (NAT) and M-CHARTS were used to quantify the degree of preoperative and postoperative aniseikonia and metamorphopsia. We also evaluated the distance between the intersections of 2 sets of retinal vessels situated vertically or horizontally by using spectral-domain optical coherence tomography (SD-OCT) images in 28 patients.ResultsThe vertical score of M-CHARTS (MV) was not significantly improved, but the horizontal score of M-CHARTS (MH) was significantly improved at 1 week, 1 month, and 3 months postoperatively. The preoperative NAT score was significantly correlated with the preoperative MH. The NAT score at 3 months was significantly correlated with the MH at 3 months and the MV at 3 months. The preoperative NAT score was significantly correlated with the ratio of the vertical retinal displacement at 1 month and at 3 months after surgery. However, the NAT scores did not improve significantly at any postoperative times.ConclusionsThe degree of aniseikonia was significantly correlated with the degree of metamorphopsia and the tangential displacement of the retina after ERM surgery. Aniseikonia is difficult to improve and metamorphopsia may be a more sensitive parameter to detect the functional recovery after successful ERM surgery.

POSTOPERATIVE CHANGES AND PROGNOSTIC FACTORS OF VISUAL ACUITY, METAMORPHOPSIA, AND ANISEIKONIA AFTER VITRECTOMY FOR EPIRETINAL MEMBRANE.

PURPOSE: To investigate postoperative changes and prognostic factors of visual impairment after vitrectomy for unilateral epiretinal membrane. METHODS: A prospective observational study on 45 eyes from 45 patients with unilateral idiopathic epiretinal membrane who underwent vitrectomy. Visual parameters (best-corrected visual acuity, metamorphopsia using M-CHARTS, and aniseikonia using the New Aniseikonia Test) and spectral domain optical coherence tomography parameters (macular retinal layer thickness and microstructure of the outer retina) were measured preoperatively and 6 and 12 months postoperatively. Statistical analyses included linear mixed-effects models for the longitudinal changes and prognostic factors of visual parameters. RESULTS: Best-corrected visual acuity and horizontal metamorphopsia improved significantly from 6 months after surgery (P < 0.001), whereas aniseikonia decreased significantly only at 12 months (P = 0.015). Vertical metamorphopsia remained unchanged. Preoperative inner nuclear layer thickness was significantly correlated with preoperative metamorphopsia. Besides baseline values, best-corrected visual acuity had no significant prognostic factors, but preoperative ellipsoid zone disruption had a negative direction of association with postoperative metamorphopsia (coefficients: -0.37 and -0.62, P = 0.015 and 0.006 for horizontal and vertical metamorphopsia, respectively), and preoperative horizontal metamorphopsia had a positive direction of association with postoperative aniseikonia (coefficient: 1.77, P = 0.002). CONCLUSION: After vitrectomy, postoperative changes and prognostic factors for unilateral epiretinal membrane differed for best-corrected visual acuity, metamorphopsia, and aniseikonia.

Aniseikonia and Foveal Microstructure in Patients with Idiopathic Macular Hole.

PURPOSE: To quantify the severity of aniseikonia in patients undergoing vitrectomy for idiopathic macular hole (MH) and to examine any relationship between aniseikonia and the foveal microstructure. DESIGN: Prospective, consecutive, interventional case series. PARTICIPANTS: We included 56 eyes of 56 patients who underwent vitrectomy to treat idiopathic MH. METHODS: We examined visual acuity, aniseikonia using the New Aniseikonia Test, and foveal structure using optical coherence tomography (OCT) before and 3, 6, and 12 months after surgery. Based on OCT images, minimum and base diameters of MH, height of MH, and defect lengths of the external limiting membrane (ELM), ellipsoid zone, and interdigitation zone were assessed. MAIN OUTCOME MEASURES: Degree of aniseikonia before and after surgery. RESULTS: The mean aniseikonia was -3.2±4.6%, ranging from -15.5% to +5.0%. Of the patients, 55% had micropsia, 7% had macropsia, and 38% had no aniseikonia. The mean absolute value of aniseikonia improved significantly from 3.8±4.1% before surgery to 1.0±1.5% at 12 months after surgery (P < 0.0001). The preoperative mean absolute value of aniseikonia showed a significant correlation with minimum diameters of MH (P < 0.01), base diameters of MH (P < 0.01), and the defect length of ELM (P < 0.05). In multivariate analysis, preoperative aniseikonia showed a significant correlation with the defect length of ELM (P < 0.05). In contrast, postoperative aniseikonia was not associated with any of the parameters. CONCLUSIONS: Approximately half of MH patients had micropsia. Vitrectomy for MH improved aniseikonia. Preoperative aniseikonia was associated with MH size and the defect length of ELM.

Relationship Between Vertical and Horizontal Aniseikonia Scores and Vertical and Horizontal OCT Images in Idiopathic Epiretinal Membrane.

PURPOSE: The purpose of this study was to identify the relationship between aniseikonia scores in the vertical and horizontal meridians and the foveal microstructure on vertical and horizontal spectral-domain optical coherence tomography (SD-OCT) in patients with idiopathic epiretinal membrane (ERM). METHODS: All patients (n = 65) with unilateral ERM were examined, and the aniseikonia scores in the vertical (VAS) and horizontal (HAS) meridians were determined using the New Aniseikonia Test. Vertical and horizontal images passing through the fovea were obtained by axial SD-OCT in both eyes. The thicknesses of the ganglion cell layer + inner plexiform layer, inner nuclear layer (INL), and outer retinal layer were measured on the SD-OCT images, and color histograms were analyzed using Photoshop software. RESULTS: Of the 65 ERM patients, 81.5% (53 patients) had macropsia. The VAS and HAS were equal in 52.8% (28 patients). Multiple regression analysis revealed significant correlations between the VAS and vertical INL thickness (R = 0.388, P = 0.001) and between the HAS and horizontal INL thickness (R = 0.349, P = 0.001). The difference between VAS and HAS was proportional to the ratio of the vertical INL thickness to horizontal INL thicknesses (R = 0.370, P < 0.001). CONCLUSIONS: Eyes with ERM mostly presented macropsia. The aniseikonia scores in the vertical and horizontal meridians correlate well with INL thickness on the vertical and horizontal directions of SD-OCT images, respectively. Aniseikonia induced by ERM may be related to the INL thickening detected with SD-OCT.

Aniseikonia induced by cataract surgery and its effect on binocular vision.

PURPOSE: This study measured aniseikonia before and after the first and second cataract surgeries in ametropic adults. The relationship of aniseikonia to anisometropia and its effect on stereopsis, ocular alignment, and clinical symptoms were determined. METHODS: Seventeen patients scheduled to have bilateral cataract surgery with 2 diopters or more ametropia participated. Patients were evaluated before cataract surgery and 4 weeks (±1 week) after the first and second surgery. Visual acuity, refractive error, aniseikonia, stereopsis, ocular alignment, and visual symptoms were determined at each visit. RESULTS: Aniseikonia increased after the first cataract surgery. The increase in aniseikonia occurred in concert with increased anisometropia and resulted in poorer stereopsis overall. Aniseikonia and anisometropia 1 month (±1 week) after the second cataract surgery returned to near baseline and were associated with better stereopsis. The amount of aniseikonia showed substantial variance and could not be predicted by the amount of induced anisometropia. Changes in ocular alignment were minimal. Statistically significant changes in patient symptoms between study visits were infrequent. CONCLUSIONS: Aniseikonia induced by cataract surgery may not be a substantial problem for ametropic adults with normal binocular vision, at least in the short term.

Aniseikonia following pneumatic retinopexy for rhegmatogenous retinal detachment.

PURPOSE: To evaluate the characteristics of aniseikonia in patients with rhegmatogenous retinal detachment (RD) after pneumatic retinopexy. DESIGN: Prospective, interventional case series study. METHODS: Thirty patients who had undergone pneumatic retinopexy as the initial procedure for rhegmatogenous retinal detachment were selected for this study. The principal outcomes included visual acuity, postoperative aniseikonia measured by the New Aniseikonia Test, anatomical success, and measurement of central retinal thickness using optical coherence topography (OCT). These outcomes were measured postoperatively at 3, 6, and 12 months. RESULTS: The median patient age was 37 years (range, 13-57 years), with 17 cases of macula-off RD and 13 cases of macula-on RD. All of these patients achieved anatomical success, proven by OCT after surgical repair. Three months after pneumatic retinopexy, 18 patients (60.0%) developed micropsic aniseikonia and aniseikonia was diagnosed in 15 patients (88.2%) in the macula-off RD group, leaving 2 patients (11.8%) unaffected. In the macula-on RD group, 3 patients (23.1%) were found to have aniseikonia, while 10 patients (76.9%) were unaffected. The presence of aniseikonia was strongly linked to the difference in central retinal thickness, between the operated eye and the fellow eye, measured at 12 months postoperatively. CONCLUSION: Aniseikonia after pneumatic retinopexy for rhegmatogenous RD may be related to the preoperative macular status. Macula-off RD patients had a higher incidence of aniseikonia, compared to macula-on RD patients, following retina reattachment. There was a moderate to high correlation between the grading of aniseikonia and the difference in central retinal thickness.

Retinally induced aniseikonia: a case series.

PURPOSE: To report the clinical findings for patients with binocular vision difficulties attributed to retinally induced aniseikonia. METHODS: Clinical records of patients referred to the author and diagnosed with retinally induced aniseikonia from 2006 to 2012 were retrospectively reviewed. RESULTS: Twelve patients with retinally induced aniseikonia attributed to epiretinal membrane, retinal detachment surgical repair, or age-related macular degeneration are reported. Eleven patients were male. The age range was 44 to 76 years. Diplopia occurred in 10 patients, and prism lenses were prescribed for seven patients by their referring practitioner. The amount of aniseikonia measured using either the computerized Aniseikonia Inspector (visual field angle, approximately 14.5 degrees) or the new Aniseikonia test (visual field angle, approximately 5.7 degrees) ranged from 1.7 to 11.3% and from 1.5 to 13.3% in the vertical and horizontal meridians, respectively. At other visual field angles, the amount of aniseikonia might have been different. Five patients perceived macropsia and seven patients perceived micropsia in the affected eye. Seven patients had measurable stereopsis. Use of Bangerter filters was the most frequent treatment modality. Detailed case reports on three patients are included. CONCLUSIONS: Retinally induced aniseikonia is an increasingly important cause of binocular vision symptoms in the aging population. Long-term studies on its incidence, clinical course, and effect of treatment are needed.

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.

[Anisometropia and aniseikonia--unsolved problems of cataract surgery]. / Anisometropie und Aniseikonie--ungelöste Probleme der Kataraktchirurgie.

BACKGROUND AND PURPOSE: Aniseikonia is one of the relevant unsolved problems of modern cataract surgery and may cause severe functional problems such as deteriorated binocular vision, diplopia or headaches. The aim of the present study is to assist the clinician as to how to estimate lateral magnification in a pseudophakic eye and how to reduce or eliminate aniseikonia. METHODS: Based on the characterisation of a centred optical system in the paraxial space, the optical system eye is modelled with 2 x 2 matrices and the lateral magnification is extracted. This method is applied on the "thin lens model" as well as the "thick lens model" and illustrated in detail with 4 working examples. Additionally, we demonstrate how a predefined lateral magnification (e. g., from the contralateral eye) can be realised during cataract surgery by calculating an appropriate combination of an IOL and a spectacle correction. WORKING EXAMPLES: In example 1 the lateral magnification of the reference eye following cataract surgery is determined. In example 2 we estimate the lateral magnification behaviour that is expected after cataract surgery using the same IOL as in example 1. Example 3 gives an overview of how the magnification varies if the IOL position in the eye, the geometry of the lens or the central thickness is changed. Example 4 shows how to calculate an appropriate combination of an IOL and spectacle correction to realise an eikonic imaging of both eyes. CONCLUSION: The present study should sensitise ophthalmic surgeons for the still unsolved problem of aniseikonia after cataract surgery and should give them a simple mathematical tool to help determine object-image magnification and show how to reduce or eliminate aniseikonia during cataract surgery.

Retinally-induced aniseikonia.

PURPOSE: To show that retinally-induced aniseikonia may vary as a function of visual field angle (i.e., field-dependent aniseikonia), how this could be explained, and what implications this has for managing the aniseikonia. DESIGN: Observational case series. METHOD: Self-administration using software that can be assumed the predecessor of the Aniseikonia Inspector version 2. Aniseikonia was tested in the vertical nd horizontal direction. In each direction aniseikonia was tested for visual field angles of 0.5 to 8 degrees. PATIENTS: Three patients with different retinal conditions: an epiretinal membrane (ERM), a retinal detachment (RD), and a retinoschisis. RESULTS: All patients had field- dependent aniseikonia, with aniseikonia variations of up to 20% over the measured visual field. The aniseikonia for the ERM patient was similar in the vertical and horizontal direction, while this was not the case for the RD patient and the retinoschisis patient. The retinoschisis patient even had negative aniseikonia in one direction and positive aniseikonia in the other direction. CONCLUSIONS: When reporting the aniseikonia of patients with retinal conditions, one cannot speak of 'the' aniseikonia(i.e., a single value or a single value for each direction), because it is most likely field-dependent. It is also important to use a test that only measures static aniseikonia (direct comparison tests with long viewing times may be less suitable). Correction of field- dependent aniseikonia is relatively difficult, because an optical correction is field-independent. Nevertheless, optically correcting the aniseikonia for part of the visual filed often improves the vision comfort considerably. If necessary, an optical correction could be augmented with a unilateral partial transparency occlusion or a unilateral partial field occlusion for more vision comfort.

Field-dependent aniseikonia associated with an epiretinal membrane a case study.

PURPOSE: Aniseikonia is a binocular anomaly in which the two eyes perceive images of different sizes and/or shapes. It is usually assumed to be constant as a function of visual field angle (VFA) (i.e., angular distance from the line of sight). This is correct for optically induced aniseikonia, such as the aniseikonia that is associated with anisometropia and probably also pseudophakia. The purpose of this article is to show that if the aniseikonia is of retinal origin, then the aniseikonia may no longer be constant as a function of VFA (i.e., field-dependent aniseikonia). DESIGN: Case report, with the patient having a unilateral epiretinal membrane. METHODS: The aniseikonia was measured in vertical and horizontal directions with a customized version of the Aniseikonia Inspector software. The VFA was made variable by changing the dimensions of the comparison targets in the direct comparison procedure. MAIN OUTCOME MEASURE: Aniseikonia as a function of VFA. RESULTS: The patient exhibited good repeatable aniseikonia, ranging from 23% to 2.5% for VFAs ranging from 0.36 degrees to 5.7 degrees . Higher angles had lower aniseikonia. A control subject did not show this field-dependent aniseikonia. CONCLUSIONS: Aniseikonia may vary with VFA due to a retinal cause such as an epiretinal membrane. The problem with field-dependent aniseikonia is that it cannot be corrected fully with conventional optics, which exhibit an approximately constant magnification as a function of VFA. Nevertheless, by correcting 5% to 10% aniseikonia, which showed up in the VFA measurement range at 2 degrees to 3 degrees , our patient had improved visual comfort, especially for reading.