Assessment interocular symmetry of peripapillary vessel density in young myopes with optical coherence tomographic angiography.

PURPOSE: The purpose of our study was to evaluate the interocular symmetry and distribution of peripapillary vessel density in young myopic eyes. METHODS: A cross-sectional observational study was designed. A total of 174 eyes of 87 young myopic patients were recruited in this study. According to spherical equivalent (SE), 48 eyes were classified as mild myopia with a mean SE of - 2.12D (SD 0.66D), 66 as moderate myopia with a mean SE of - 4.50D (SD 0.87D), and 60 as high myopia with a mean SE of - 7.39D (SD 1.30D). Optical coherence tomography angiography (OCTA) was used to measure the vessel density. The distribution and interocular symmetry of peripapillary vessel densities were analyzed. RESULTS: The vessel densities in the whole image, peripapillary, superior and inferior sectors were significantly lower in the high myopia group than in the mild or moderate myopia group (All P < 0.001), and the density in the nasal sector was significantly lower in the high myopia group than in the mild group. And most interesting, the vessel densities in the inside disc and temporal sector showed no difference among the three myopic groups (All P > 0.05). By Pearson correlation analysis, the vessel densities in the whole image, peripapillary, superior, inferior and nasal sectors were negatively correlated with axial length (AL) and SE (All P < 0.001), but vessel densities in the inside disc and temporal sector did not show this correlation (All P > 0.05). Interocular symmetry was observed in all the vascular parameters through paired-samples t-tests (All P > 0.05), intraclass correlation coefficient (ICC) and Pearson correlation analysis (All P < 0.001). CONCLUSION: The density of radial peripapillary capillaries decreased in the myopic eye with axial elongation, and optical vascular parameters showed significant interocular symmetry among young myopic eyes.

Interocular biometric parameters comparison measured with swept-source technology.

PURPOSE: In the event that any ocular parameter involved in the calculation of intraocular lens power could not be properly measured in one eye, it is important to know whether clinically relevant differences between both eyes can be expected. The aim of this work is to evaluate the symmetry of interocular biometric parameters. METHODS: This was a prospective, cross-sectional study involving 4090 subjects. Patients underwent consecutive swept-source optical biometry performed with an IOLMaster 700 (Carl Zeiss Meditec AG, Jena, Germany). The biometric parameters that were evaluated were: axial length (AL), mean anterior curvature (Rm), anterior chamber depth (ACD), crystalline lens thickness (LT), central corneal thickness (CCT) and white-to-white (WTW). The Chang-Waring chord distance (CWC-D) and the Chang-Waring chord angle (CWC-A) were also evaluated. RESULTS: There is an excellent correlation between both eyes for almost all the biometric parameters under study, with the exception of the CWC. Agreement for AL was better for eyes shorter than 24 mm. The linearity of the OD-vs-OS relationship can be correctly assumed for all parameters (Cusum test: p > 0.05 in all cases). CONCLUSION: There are no clinically significant interocular differences for the biometric parameters under study, although for all of them, except the LT, statistically significant differences did arise. In the case of AL, moderate differences can be expected in eyes larger than 24 mm.

Interobserver reproducibility and interocular symmetry of the macular ganglion cell complex: assessment in healthy children using optical coherence tomography.

BACKGROUND: Assessment of interobserver reproducibility and interocular symmetry using optical coherence tomography (OCT)-based measurements of the macular ganglion cell complex (GCC) in healthy children facilitates interpretation of OCT data. We assessed the interobserver reproducibility and interocular symmetry of GCC and evaluated candidate determinants. METHODS: This was a cross-sectional study performed in a primary and tertiary health-care setting. A total of 126 healthy participants aged 5 to 18 years were eligible. GCC scans were performed by 4 operators using the Topcon 3D OCT-2000 device. Intraclass correlation coefficients (ICCs) were used to estimate reproducibility and symmetry. Cut-off points for symmetry were defined as the 95th percentile of the absolute interocular difference for 6 GCC parameters. Percentile distributions of interocular difference were generated based on age and difference in absolute interocular spherical equivalent (SE). RESULTS: The reproducibility ICC ranged from 0.96 to 0.98 for all 6 GCC parameters. Cut-off points for interocular symmetry of the superior and inferior quadrants and total macular retinal nerve fibre layer thickness (mRNFL) and macular ganglion cell layer-inner plexiform layer thickness were 3.5, 4.5, 3.0, 3.0, 2.5, and 2.5 µm respectively. A positive association was observed between the absolute interocular difference of SE and superior and total mRNFL symmetry values (p = 0.047 and p = 0.040, respectively). CONCLUSIONS: OCT measurements of GCC in healthy children show excellent reproducibility. Interocular differences in SE should be assessed when mRNFL differences exceed the 95% cut-off. These findings can contribute to establish reference values for interocular symmetry in paediatric GCC parameters.

Optic Nerve Head Parameters Measured with Spectral-Domain Optical Coherence Tomography in Healthy Turkish Children: Normal Values, Repeatability, and Interocular Symmetry.

To determine normal values, repeatability, and interocular symmetry of optic nerve head measurements, three spectral-domain optical coherence tomography (SD-OCT) scans were obtained from 128 healthy Turkish children aged 5-17 years consecutively and prospectively. The mean disc area, rim area, cup volume, cup to disc area ratio, and vertical and horizontal cup to disc ratios were 2.30 ± 0.42 mm2, 1.84 ± 0.45 mm2, 0.09 ± 0.10 mm3, 0.20 ± 0.13, 0.37 ± 0.17, and 0.45 ± 0.20, respectively. The intraclass correlation coefficients were >0.9 for repeatability and >0.75 for interocular correlation. Interocular differences were not statistically significant (p > 0.05). Normal paediatric SD-OCT measurements of the optic nerve head are presented, which showed excellent repeatability and no interocular difference.

The short-term accommodation response to aniso-accommodative stimuli in isometropia.

PURPOSE: There have been only a limited number of studies examining the accommodative response that occurs when the two eyes are provided with disparate accommodative stimuli, and the results from these studies to date have been equivocal. In this study, we therefore aimed to examine the capacity of the visual system to aniso-accommodate by objectively measuring the interocular difference in the accommodation response between fellow dominant and non-dominant eyes under controlled monocular and binocular viewing conditions during short-term exposure to aniso-accommodative stimuli. METHODS: The accommodative response of each eye of 16 young isometropic adults (mean age 22 ± 2 years) with normal binocular vision was measured using an open-field autorefractor during a range of testing conditions; monocularly (accommodative demands ranging from 1.97 to 2.90 D) and binocularly while altering the accommodation demand for each eye (aniso-accommodative stimuli ranging from 0.08 to 0.53 D) [Corrected]. RESULTS: Under monocular viewing conditions, the dominant and non-dominant eyes displayed a highly symmetric accommodative response; mean interocular difference in spherical equivalent 0.01 ± 0.06 D (relative) and 0.22 ± 0.06 D (absolute) (p > 0.05). During binocular viewing, the dominant eye displayed a greater accommodative response (0.11 ± 0.34 D relative and 0.24 ± 0.26 D absolute) irrespective of whether the demand of the dominant or non-dominant eye was altered (p = 0.01). Astigmatic power vectors J0 and J45 did not vary between eyes or with increasing accommodation demands under monocular or binocular viewing conditions (p > 0.05). CONCLUSION: The dominant and non-dominant eyes of young isometropic individuals display a similar consensual lag of accommodation under both monocular and binocular viewing conditions, with the dominant eye showing a small but significantly greater (by 0.12-0.25 D) accommodative response. Evidence of short-term aniso-accommodation in response to asymmetric accommodation demands was not observed.

Interocular Symmetry of Choroidal Parameters in Patients with Diabetic Retinopathy with and without Diabetic Macular Edema.

This study focuses on the interocular comparison of choroidal parameters in diabetic patients with diabetic retinopathy (DR) with and without diabetic macular edema (DME), as well as in patients with unilateral DME (present in only one eye). The aim of this study was to determine the symmetry in order to obtain better insights into the pathophysiology of diabetic choroidopathy. This retrospective single-center cross-sectional study included 170 eyes from 85 patients (61 with DR and 24 controls), divided into subgroups depending on the presence of DME. The patients underwent fluorescein angiography and spectral domain optical coherence tomography examination, and the analysis included various choroidal parameters: choroidal thickness, volume, and the choroidal vascularity index (CVI). In terms of the choroidal thickness, one eye of a patient with DR, regardless of the presence, absence, or unilaterality of DME, may be treated as representative for that patient. CVI proved symmetrical for controls and patients with DR without DME. However, there was some asymmetry of CVI in patients with bilateral or unilateral DME. There was no straightforward relationship between choroidopathy and DME. Other mechanisms were also involved in the pathogenesis.

Interocular Symmetry in Retinal Nerve Fiber Layer Thickness in Children: The Hong Kong Children Eye Study.

INTRODUCTION: The aim of this work is to determine the interocular differences in peripapillary retinal nerve fiber layer (p-RNFL) thickness and its associations among school children in Hong Kong. METHODS: We conducted a population-based study including 4034 children aged 6-8 years from the Hong Kong Children Eye Study (HKCES). All participants received comprehensive ocular examinations where p-RNFL thickness was measured using spectral-domain optical coherence tomography (SD-OCT). The degree of symmetry between both eyes was analyzed and represented by intraclass correlation coefficient (ICC) values. Multivariable linear regression analysis was used to investigate the associations between ocular and systemic factors with p-RNFL thickness difference. RESULTS: The study included 4034 children with a mean age of 7.61 ± 0.98 years. The mean global p-RNFL thickness was 106.60 ± 9.41 µm in right eyes and 105.99 ± 9.30 µm in left eyes. The ICC for global p-RNFL difference was 0.866 (95% CI 0.858-0.873, p < 0.001). The symmetry displayed the largest values in nasal inferior quadrant with the ICC value of 0.736 (95% CI 0.721-0.749); and the smallest degree of symmetry was found to be in the superior temporal quadrant with the ICC value of 0.567 (95% CI 0.546-0.588). Axial length (AL) difference was found to have more pronounced correlation to interocular symmetry in p-RNFL thickness with the coefficient of 0.514 (p < 0.001). CONCLUSIONS: Normal variation in interocular symmetry exists in children. Our results can contribute to the establishment of a standard reference for interocular differences in OCT parameters in children. The interocular differences in AL should be considered in the interpretation of RNFL symmetry, in terms of identifying children at risk of developing glaucoma or other ocular disorders.

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.

Interocular Symmetry and Repeatability of Central Corneal Thickness and Corneal Endothelial Cell Morphology and Density in Healthy Eyes of Congolese.

PURPOSE: To determine the limits of normal interocular symmetry and the repeatability of central corneal thickness (CCT) and endothelial cell morphology and density. METHODS: Two hundred and seventy-eight subjects (age: 10.9-80.7 years) with healthy eyes were studied. CCT as well as endothelial cell morphology and density were measured by non-contact specular microscopy. Three measurements were obtained per eye per participant. Upper and lower tolerance limits of normal interocular symmetry were defined as the 2.5th and 97.5th percentiles of the interocular differences in CCT, endothelial cell density (CECD), coefficient of variation (CoV), hexagonality, and cell size. Repeatability was determined using the intraclass coefficient correlation (ICC), the coefficient of variation (CV), and the test-retest variability standard deviation (TRTSD). RESULTS: The mean interocular differences were -1.05 ± 17.5 µm (p = .32) for CCT and 0.5 ± 90.8 cells/mm2 (p = .76) for CECD. The 2.5th and 97.5th percentiles of the interocular differences were -13.9 and 15.4 µm for CCT and -177.4 cells/mm2 to 182.0 cells/mm2 for CECD. Only interocular difference in CoV correlated weakly with age (r = -0.22, P < .001). ICCs were 0.93 (95% CI: 0.89-0.96, P < .001) for CCT and 0.95 (0.94-0.96, P < .001) for CECD. CV and TRTSD were 1.2% ± 5.3% and 4.4 ± 3.4 µm for CCT and 2.4% ± 3.9% and 17.7 ± 7.7 cells/mm2 for CECD, respectively. CONCLUSIONS: CCT and CECD showed good repeatability and interocular symmetry in normal Congolese subjects. Absolute interocular differences in CCT and CECD exceeding 15.5 µm and 182 cells/mm2, respectively, should be considered suspicious and investigated. When comparing two intrasession measurements from the same eye, a difference of approximately 4.5 µm in CCT and 18 cells/mm2 or greater may be considered statistically significant.

Evaluating Distribution of Foveal Avascular Zone Parameters Corrected by Lateral Magnification and Their Associations with Retinal Thickness.

Purpose: To examine the distribution of foveal avascular zone (FAZ) parameters, with and without correction for lateral magnification, in a large cohort of healthy young adults. Design: Cross-sectional, observational cohort study. Participants: A total of 504 healthy adults, 27 to 30 years of age. Methods: Participants underwent a comprehensive ophthalmic examination including axial length measurement and OCT angiography (OCTA) imaging of the macula. OCT angiography images of combined superficial and deep retinal vessel plexuses were processed via a custom software to extract foveal avascular zone area (FAZA) and foveal density-300 (FD-300), the vessel density in a 300-µm wide annulus surrounding the FAZ, with and without correction for lateral magnification. Bland-Altman analyses were performed to examine the effect of lateral magnification on FAZA and FD-300, as well as to evaluate the interocular agreement in both parameters. Linear mixed-effects models were used to examine the relationship between retinal thicknesses and OCTA parameters. Main Outcome Measures: The FAZA and FD-300, corrected for lateral magnification. Results: The mean (standard deviation [SD]) of laterally corrected FAZA and FD-300 was 0.22 mm2 (0.10 mm2) and 51.9% (3.2%), respectively. Relative to uncorrected data, 55.6% of corrected FAZA showed a relative change > 5%, whereas all FD-300 changes were within 5%. There was good interocular symmetry (mean right eye-left eye difference, 95% limits of agreement [LoA]) in both FAZA (0.006 mm2, -0.05 mm2, to 0.07 mm2) and FD-300 (-0.05%, -5.39%, to 5.30%). There were significant negative associations between central retinal thickness and FAZA (ß = -0.0029), as well as between central retinal thickness and FD-300 (ß = -0.044), with the relationships driven by inner, not outer, retina. Conclusions: We reported lateral magnification adjusted normative values for FAZA and FD-300 in a large cohort of young, healthy eyes. Clinicians should strongly consider accounting for lateral magnification when evaluating FAZA. Good interocular agreement in FAZA and FD-300 suggests the contralateral eye can be used as control data.

Wide-Field Swept-Source OCT Analysis of Interocular Symmetry of Choroidal Thickness in Subjects with Uncomplicated Pachychoroid.

BACKGROUND: We aimed to study the bilateral choroidal thickness (CT) symmetry and difference in uncomplicated pachychoroid subjects using wide-field swept-source optical coherence tomography (SS-OCT). METHODS: All subjects underwent a wide-field 16-mm one-line scan using SS-OCT. Bilateral CT was measured at, and compared among, the following 12 points: three points at 900-µm intervals from the nasal optic disc margin (nasal peripapillary area), one point at the subfovea, six points at 900-µm intervals from the fovea to the nasal and temporal areas (macular area), and two peripheral points 5400 and 8100 µm from the fovea (peripheral area). RESULTS: There were no statistically significant differences in CT between the right and left eyes in any area (all p > 0.05); they all showed significant positive correlations (all p < 0.01). However, the correlation coefficients (ρ) were smaller for the nasal peripapillary and peripheral areas compared to the macular area. CONCLUSIONS: The CTs in each region were bilaterally symmetrical in subjects with uncomplicated pachychoroid. However, interocular difference in CT increased from the center to the periphery, indicating that the anatomical variation of the nasal peripapillary and peripheral choroid was greater than that of the macula.

Interocular Symmetry Analysis of Corneal Elevation Using the Fellow Eye as the Reference Surface and Machine Learning.

Unilateral corneal indices and topography maps are routinely used in practice, however, although there is consensus that fellow-eye asymmetry can be clinically significant, symmetry studies are limited to local curvature and single-point thickness or elevation measures. To improve our current practices, there is a need to devise algorithms for generating symmetry colormaps, study and categorize their patterns, and develop reference ranges for new global discriminative indices for identifying abnormal corneas. In this work, we test the feasibility of using the fellow eye as the reference surface for studying elevation symmetry throughout the entire corneal surface using 9230 raw Pentacam files from a population-based cohort of 4613 middle-aged adults. The 140 × 140 matrix of anterior elevation data in these files were handled with Python to subtract matrices, create color-coded maps, and engineer features for machine learning. The most common pattern was a monochrome circle ("flat") denoting excellent mirror symmetry. Other discernible patterns were named "tilt", "cone", and "four-leaf". Clustering was done with different combinations of features and various algorithms using Waikato Environment for Knowledge Analysis (WEKA). Our proposed approach can identify cases that may appear normal in each eye individually but need further testing. This work will be enhanced by including data of posterior elevation, thickness, and common diagnostic indices.

Interocular Symmetry of Foveal Cone Topography in Congenital Achromatopsia.

Purpose: To determine the interocular symmetry of foveal cone topography in achromatopsia (ACHM) using non-confocal split-detection adaptive optics scanning light ophthalmoscopy (AOSLO). Methods: Split-detector AOSLO images of the foveal cone mosaic were acquired from both eyes of 26 subjects (mean age 24.3 years; range 8-44 years, 14 females) with genetically confirmed CNGA3- or CNGB3-associated ACHM. Cones were identified within a manually delineated rod-free zone. Peak cone density (PCD) was determined using an 80 × 80 µm sampling window within the rod-free zone. The mean and standard deviation (SD) of inter-cell distance (ICD) were calculated to derive the coefficient of variation (CV). Cone density difference maps were generated to compare cone topography between eyes. Results: PCD (mean ± SD) was 17,530 ± 9,614 cones/mm2 and 17,638 ± 9,753 cones/mm2 for right and left eyes, respectively (p = .677, Wilcoxon test). The mean (± SD) for ICD was 9.05 ± 2.55 µm and 9.24 ± 2.55 µm for right and left eyes, respectively (p = .410, paired t-test). The mean (± SD) for CV of ICD was 0.16 ± 0.03 µm and 0.16 ± 0.04 µm for right and left eyes, respectively (p = .562, paired t-test). Cone density maps demonstrated that cone topography of the ACHM fovea is non-uniform with local variations in cone density between eyes. Conclusions: These results demonstrate the interocular symmetry of the foveal cone mosaic (both density and packing) in ACHM. As cone topography can differ between eyes of a subject, PCD does not completely describe the foveal cone mosaic in ACHM. Nonetheless, these findings are of value in longitudinal monitoring of patients during treatment trials and further suggest that both eyes of a given subject may have similar therapeutic potential and non-study eye can be used as a control.

Interocular symmetry of the foveal avascular zone area in healthy eyes: a swept-source optical coherence tomography angiography study.

PURPOSE: To determine the presence or absence of interocular differences in the foveal avascular zone (FAZ) area in healthy eyes. STUDY DESIGN: Cross-sectional study. METHODS: We examined 236 healthy eyes of 118 consecutive subjects (mean age, 39.1 ± 18.9 years). We used swept-source optical coherence tomography angiography (OCTA) images of the FAZ to measure its area from both the superficial capillary plexus (SCP-FAZ) and the whole retinal capillary plexus (WCP-FAZ). We also investigated the relationship between interocular differences in SCP-FAZ and other factors such as: axial length, spherical equivalent, central retinal thickness, and retinal vascular density. RESULTS: There was no significant difference in the FAZ area between the right and left eyes in either the SCP-FAZ (P = 0.61) or WCP-FAZ (P = 0.80), and the FAZ areas of both eyes showed significant positive correlations (SCP-FAZ; P < 0.001, R2 = 0.884, WCP-FAZ; P < 0.001, R2 = 0.856). Bland-Altman plots showed that the mean interocular difference in SCP-FAZ area was 0.002 ± 0.037 mm2 (95% confidence interval, -0.072-0.075 mm2), and in the WCP-FAZ area, 0.050 ± 0.044 mm2 (95% confidence interval, -0.036-0.137 mm2). Multivariate regression analysis showed that none of the investigated factors were significantly associated with interocular differences in SCP-FAZ (P = 0.61, R2 = 0.138). CONCLUSIONS: There was no significant interocular difference in SCP- and WCP-FAZ areas in healthy eyes. The normal range of values for interocular difference in SCP-FAZ area was 0.002 ± 0.037 mm2 and in the WCP-FAZ area, 0.050 ± 0.044 mm2.

Interocular Symmetry of Fixation, Optic Disc, and Corneal Astigmatism in Bilateral High Myopia: The Shanghai High Myopia Study.

PURPOSE: We investigate the interocular symmetry of fixation, optic disc, and corneal astigmatism in bilateral high myopia, and evaluate the predictive relationships between them. METHODS: We enrolled 202 cases with bilateral high myopia. Fixation, in terms of the bivariate contour ellipse area (BCEA), was evaluated with the Macular Integrity Assessment microperimetry. Optic disc features, including orientation, tilt, and rotation, were evaluated with ultrawide-field retinal photographs. Corneal topography was performed with Pentacam. Interocular symmetry of fixation, optic disc, and corneal astigmatism was assessed, and the predictive relationships between these parameters were investigated. RESULTS: Axial length differences between the two eyes were: ≥0 to ≤1 mm, 67.8%; 1 to ≤2 mm, 20.3%; 2 to ≤3 mm, 9.4%; and >3 mm, 2.5%. Axial length, 95% BCEA, and magnitude of corneal astigmatism showed good interocular symmetry, whereas the optic disc tilt, rotation, and axis of corneal astigmatism (mirror axes) showed less symmetry (all P < 0.05). No interocular symmetry was observed in the direction of the fixation ellipse. In both eyes, the corneal steep meridian more often was consistent with the optic disc orientation than inconsistent (right eye [OD], P < 0.001; left eye [OS], P = 0.029). CONCLUSIONS: As different parameters presented different degrees of symmetry, cautions are needed when including both eyes or only one lateral eye in cases of bilateral high myopia for clinical investigations. The optic disc orientation, to some extent, may indicate the steep meridian of the cornea. TRANSLATIONAL RELEVANCE: Our study provided evidences for selection of eye laterality in clinical investigations of highly myopic eyes.

Lateral thinking - Interocular symmetry and asymmetry in neurovascular patterning, in health and disease.

No biological system or structure is likely to be perfectly symmetrical, or have identical right and left forms. This review explores the evidence for eye and visual pathway asymmetry, in health and in disease, and attempts to provide guidance for those studying the structure and function of the visual system, where recognition of symmetry or asymmetry may be essential. The principal question with regards to asymmetry is not 'are the eyes the same?', for some degree of asymmetry is pervasive, but 'when are they importantly different?'. Knowing if right and left eyes are 'importantly different' could have significant consequences for deciding whether right or left eyes are included in an analysis or for examining the association between a phenotype and ocular parameter. The presence of significant asymmetry would also have important implications for the design of normative databases of retinal and optic nerve metrics. In this review, we highlight not only the universal presence of asymmetry, but provide evidence that some elements of the visual system are inherently more asymmetric than others, pointing to the need for improved normative data to explain sources of asymmetry and their impact on determining associations with genetic, environmental or health-related factors and ultimately in clinical practice.

Interocular symmetry in retinal and optic nerve parameters in children as measured by spectral domain optical coherence tomography.

BACKGROUND/AIMS: To report interocular differences in retinal nerve fibre layer (RNFL), optic nerve head and macular parameters in children using spectral domain optical coherence tomography (SD-OCT). METHODS: This was an observational cross-sectional study including 108 healthy children aged 6-17 years with no ocular abnormality except refractive error. After a comprehensive eye exam and axial length measurement, RNFL, optic nerve and macular thickness measurements were performed using the Cirrus OCT machine. Right and left eyes were compared and interocular differences were computed. Subjects were also divided into two groups based on age (under or over 10 years of age). Main outcome measures were interocular differences and their correlations with age and gender. RESULTS: The study included 108 children, mean age 10.7 ± 3.1 years; significant interocular differences were observed in both macular and RNFL parameters. The macular thickness analysis revealed interocular differences in the outer nasal and outer inferior quadrants, with left eyes displaying larger values. With respect to RNFL parameters, right eyes displayed thicker nasal and temporal quadrants, and inferior clock hours; left eyes had a thicker superior quadrant. The older age group (>10 years) had more pronounced variation in interocular differences compared with the younger group with less mature visual systems. CONCLUSIONS: Normal variation in interocular symmetry exists. Our results can contribute to establishing a standard reference for interocular differences in OCT parameters in children aged 6-17 years using the Cirrus device.