Asymmetries of the retinal nerve fibre layer thickness in normal eyes

Biphasic change in retinal nerve fibre layer thickness from 30 to 60 weeks postmenstrual age in preterm infants

BACKGROUND/AIMS

The optic nerve development during the critical postnatal weeks of preterm infants is unclear. We aimed to investigate the change of retinal nerve fibre layer (RNFL) in preterm infants.

METHODS

We used an investigational handheld optical coherence tomography (OCT) system to serially image awake preterm infants between 30 and 60 weeks postmenstrual age (PMA) at the bedside. We assessed RNFL thickness in the papillomacular bundle and nasal macular ganglion cell layer+inner plexiform layer (GCL+IPL) thickness. We applied a segmented mixed model to analyse the change in the thickness of RNFL and GCL+IPL as a function of PMA.

RESULTS

From 631 OCT imaging sessions of 101 infants (201 eyes), RNFL thickness followed a biphasic model between 30 and 60 weeks, with an estimated transition at 37.8 weeks PMA (95% CI: 37.0 to 38.6). RNFL thickness increased at 1.8 μm/week (95% CI: 1.6 to 2.1) before 37.8 weeks and decreased at -0.3 μm/week (95% CI: -0.5 to -0.2) afterwards. GCL+IPL thickness followed a similar biphasic model, in which the thickness increased at 2.9 μm/week (95% CI: 2.5 to 3.2) before 39.5 weeks PMA (95% CI: 38.8 to 40.1) and then decreased at -0.8 μm/week (95% CI: -0.9 to -0.6).

CONCLUSION

We demonstrate the feasibility of monitoring RNFL and GCL+IPL thickness from OCT during the postnatal weeks of preterm infants. Thicknesses follow a biphasic model with a transition age at 37.8 and 39.5 weeks PMA, respectively. These findings may shed light on optic nerve development in preterm infants and assist future study designs.

Birth Weight Is a Significant Predictor of Retinal Nerve Fiber Layer Thickness at 36 Weeks Postmenstrual Age in Preterm Infants

PURPOSE

To assess retinal nerve fiber layer (RNFL) thickness in preterm infants.

DESIGN

Prospective observational study.

METHODS

We imaged 83 awake infants (159 eyes) at 36 ± 1 weeks postmenstrual age (defined as the time elapsed between the first day of the last maternal menstrual period and the time at imaging) using a handheld optical coherence tomography (OCT) system at the bedside. Blinded graders semi-automatically segmented RNFL in the papillomacular bundle (-15 to +15° relative to the fovea-optic nerve axis). We correlated RNFL thickness and 7 characteristics of interest (sex, race, ethnicity, gestational age, birth weight, stage of retinopathy at prematurity, and presence of pre-plus or plus disease) via univariable and multivariable regressions.

RESULTS

RNFL was 3.4 μm thicker in the right eyes than in the left eyes (P < .001). Among 7 characteristics, birth weight was the only independent predictor of RNFL thickness (P < .001). A 250-g increase in birth weight was associated with 5.2 μm (95% confidence interval: 3.3-7.0) increase in RNFL thickness. Compared with very preterm infants, extremely preterm infants had thinner RNFL (58.0 ± 10.7 μm vs 63.4 ± 10.7 μm, P = .03), but the statistical significance disappeared after adjustment for birth weight (P = .25). RNFL thickness was 11.2 μm thinner in extremely low birth weight infants than in very low birth weight infants (55.5 ± 8.3 μm vs. 66.7 ± 10.2 μm; P < .001). The difference remained statistically significant after adjustment for gestational age.

CONCLUSION

Birth weight is a significant independent predictor of RNFL thickness near birth, implying that the retinal ganglion cells reserve is affected by intrauterine processes that affect birth weight.

Evaluation of Asymmetry in Right and Left Eyes of Normal Individuals Using Extracted Features from Optical Coherence Tomography and Fundus Images

BACKGROUND

Asymmetry analysis of retinal layers in right and left eyes can be a valuable tool for early diagnoses of retinal diseases. To determine the limits of the normal interocular asymmetry in retinal layers around macula, thickness measurements are obtained with optical coherence tomography (OCT).

METHODS

For this purpose, after segmentation of intraretinal layer in threedimensional OCT data and calculating the midmacular point, the TM of each layer is obtained in 9 sectors in concentric circles around the macula. To compare corresponding sectors in the right and left eyes, the TMs of the left and right images are registered by alignment of retinal raphe (i.e. diskfovea axes). Since the retinal raphe of macular OCTs is not calculable due to limited region size, the TMs are registered by first aligning corresponding retinal raphe of fundus images and then registration of the OCTs to aligned fundus images. To analyze the asymmetry in each retinal layer, the mean and standard deviation of thickness in 9 sectors of 11 layers are calculated in 50 normal individuals.

RESULTS

The results demonstrate that some sectors of retinal layers have signifcant asymmetry with P < 0.05 in normal population. In this base, the tolerance limits for normal individuals are calculated.

CONCLUSION

This article shows that normal population does not have identical retinal information in both eyes, and without considering this reality, normal asymmetry in information gathered from both eyes might be interpreted as retinal disorders.

Peripapillary Retinal Nerve Fiber Layer Profile in Relation to Refractive Error and Axial Length: Results From the Gutenberg Health Study

Purpose

To investigate the retinal nerve fiber layer profile measured by optical coherence tomography and its relation to refractive error and axial length.

Methods

The Gutenberg Health Study is a population-based study in Mainz, Germany. At the five-year follow-up examination, participants underwent optical coherence tomography, objective refraction and biometry. Peripapillary retinal nerve fiber layer (pRNFL) was segmented using proprietary software. The pRNFL profiles were compared between different refraction groups and the angle between the maxima, i.e., the peaks of pRNFL thickness in the upper and lower hemisphere (angle between the maxima of pRNFL thickness [AMR]) was computed. Multivariable linear regression analysis was carried out to determine associations of pRNFL profile (AMR) including age, sex, optic disc size, and axial length in model 1 and spherical equivalent in model 2.

Results

A total of 5387 participants were included. AMR was 145.3° ± 23.4° in right eyes and 151.8° ± 26.7° in left eyes and the pRNFL profile was significant different in the upper hemisphere. The AMR decreased with increasing axial length by −5.86°/mm (95% confidence interval [CI]: [−6.44; −5.29], P < 0.001), female sex (−7.61°; 95% CI: [−8.71; −6.51], P < 0.001) and increased with higher age (0.08°/year; 95% CI: [0.03; 0.14], P = 0.002) and larger optic disc size (2.29°/mm²; 95% CI: [1.18; 3.41], P < 0.001). In phakic eyes, AMR increased with hyperopic refractive error by 2.60°/diopters (dpt) (95% CI: [2.33; 2.88], P < 0.001).

Conclusions

The pRNFL profiles are related to individual ocular and systemic parameters.

Translational Relevance

Biometric parameters should be considered when pRNFL profiles are interpreted in diagnostics, i.e., in glaucoma.

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 retinal nerve fiber layer thickness difference in normal adults

Purpose

To determine the interocular retinal nerve fiber layer (RNFL) thickness difference of normal subjects.

Methods

Both eyes of 230 normal adults received peripapillary RNFL thickness measurements using OCT. The effect of ocular cyclotorsion on the RNFL thickness profile was mathematically corrected. The fractional and absolute interocular RNFL thickness differences at 256 points of peripapillary area were calculated. We divided the subjects into 3 groups according to the locations of superior and inferior peak thickness, respectively, and compared the interocular RNFL thickness differences between the subgroups.

Results

The fractional interocular RNFL thickness difference exhibited smaller regional variations than the absolute interocular difference. The means of fractional interocular differences were 0.100 ± 0.077 in the temporal half area and 0.146 ± 0.105 in the nasal half area, and the tolerance limits for the 95th and 99th distributions were about 0.246 and 0.344 in the temporal half area and 0.293 and 0.408 in the nasal half area, respectively. The fractional interocular differences of subgroups classified by the locations of superior and inferior peak RNFL thickness showed difference at smaller areas than the absolute interocular differences (19 and 8 points versus 49 and 23 points, respectively).

Conclusion

Glaucoma can be strongly suspected, if interocular fractional RNFL thickness difference is over 25% at 5 consecutive points or over 35% at 3 consecutive points in the temporal half area. The fractional interocular comparison is a better diagnostic approach because the fractional interocular RNFL thickness difference is less influenced by the locations of peak RNFL thickness.

Macular ganglion cell imaging study: interocular symmetry of ganglion cell-inner plexiform layer thickness in normal healthy eyes

PURPOSE

To determine cutoffs for interocular differences in ganglion cell-inner plexiform layer thickness in normal healthy eyes and to evaluate the diagnostic performance of these values for differentiating between normal subjects and glaucoma patients.

DESIGN

Observational, cross-sectional study.

METHODS

Macular and optic disc scanning were performed in 275 normal subjects, 58 glaucoma patients, and 58 normal controls by high-definition optical coherence tomography. The ganglion cell-inner plexiform layer thickness was calculated, and the normal ranges of the interocular differences were determined as 2.5th and 97.5th percentiles. The signed and absolute interocular differences were compared between normal subjects and glaucoma patients.

RESULTS

The mean ± standard deviation interocular difference in the average ganglion cell-inner plexiform layer thickness thickness was 0.10 ± 2.31 μm, which was not statistically significant (P = .466). The 2.5th and 97.5th percentiles of the interocular difference were -4.10 μm and +5.00 μm, respectively. On multiple regression analysis, the interocular difference in axial length was correlated with the interocular difference in average ganglion cell-inner plexiform layer thickness thickness (β = 2.044, P = .003). The signed and absolute interocular differences in ganglion cell-inner plexiform layer thickness were higher in glaucoma patients than in normal subjects (all P < .001). Sensitivity and specificity of absolute interocular differences ranged from 25.9% to 51.7% and from 93.1% to 100.0%, respectively.

CONCLUSIONS

Ganglion cell-inner plexiform layer thickness shows significant interocular symmetry in normal subjects. An absolute interocular difference exceeding normal limits may be indicative of glaucoma.

Retinal asymmetry in children measured with optical coherence tomography

PURPOSE

To determinate the physiological asymmetry of retinal measurements in the pediatric population with Fourier-domain optical coherence tomography (Cirrus HD-OCT).

DESIGN

Prospective cross-sectional study.

METHODS

Three hundred and fifty-seven healthy children were recruited. All subjects underwent a comprehensive ophthalmologic examination and an evaluation of the retinal nerve fiber layer (RNFL), optic nerve head, and macula with Cirrus OCT. Differences between right and left eyes were calculated and values were compared by means of a paired t test. Normal ranges of interocular differences were established as the 2.5th and the 97.5th percentiles. The correlations between right and left eyes were assessed by the intraclass correlation coefficients.

RESULTS

Mean best-corrected visual acuity (logMAR) was -0.01. Differences in the average RNFL between right and left eyes were not statistically significant. The RNFL in the right eyes was thicker in the temporal and nasal quadrants, whereas the left eyes showed thicker RNFL in the superior quadrant. The interocular difference tolerance limits for average RNFL and macular thicknesses were 13.00 μm and 23.20 μm, respectively. There was a strong correlation for all the parameters between the right and the left eyes.

CONCLUSIONS

The asymmetry of retinal parameters might be more valuable than the absolute values in assessing certain early diseases. The interocular differences in average RNFL and macular thickness of normal individuals should not exceed 13 μm and 23 μm, respectively, if measured with Cirrus HD-OCT.

African descent and glaucoma evaluation study: asymmetry of structural measures in normal participants

PURPOSE

The purpose of the study is to determine the degree of intereye asymmetry of optic disc topography and retinal nerve fiber layer (RNFL) thickness in healthy individuals of African descent (AD) and European descent (ED).

DESIGN

Observational, clinical study.

METHODS

Five hundred nineteen healthy individuals (AD, n=262, mean age=44.9 years; ED, n=257, mean age=47.1 years) from the African Descent and Glaucoma Evaluation Study and Diagnostic Innovations in Glaucoma Study were tested using Heidelberg retina romograph (HRT), GDx variable corneal compensation (GDx-VCC), and standard, automated perimetry within 6 months of one another. HRT-II measurements included cup area, cup volume, rim area, and rim volume. GDx-VCC measurements included average RNFL thickness. Intereye asymmetry was calculated as the absolute value of the differences in measurements between the right and left eye.

RESULTS

AD participants showed significantly higher median asymmetry in cup volume and rim volume (P<0.001 and 0.033, respectively) compared with ED participants. The effect of race lost significance after adjustment for mean disc area and disc area asymmetry in multivariable models. Axial length asymmetry was not correlated with increased asymmetry in any of this study's asymmetry parameters. Normal ranges of asymmetry for the HRT-II measurements of cup area (up to 0.39 mm), cup volume (up to 0.15 mm), rim area (up to 0.45 mm), and rim volume (up to 0.22 mm) were derived, as were asymmetry ranges for GDx-VCC-measured average RNFL thickness (up to 6.25 μm).

CONCLUSIONS

The effect of race was no longer significant after adjustment for mean disc area and disc area asymmetry. Individuals with asymmetries with magnitudes greater than those of the normal ranges could be considered as suspicious for glaucoma.

Interocular symmetry in peripapillary retinal nerve fiber layer thickness measured with the Cirrus HD-OCT in healthy eyes

PURPOSE

To determine the cutoffs for the interocular difference in retinal nerve fiber layer (RNFL) thickness measured with Cirrus HD-OCT (Carl Zeiss Meditec, Inc) in normal eyes.

DESIGN

Observational, clinical study.

METHODS

Scans were acquired at 7 academic glaucoma clinics from both eyes of 284 normal subjects using the Optic Disc Cube 200 × 200 protocol. The interocular differences in RNFL thickness were calculated, and normal ranges of interocular differences were determined as the 2.5th and 97.5th percentiles.

RESULTS

The average RNFL in the right eye was 0.52 μm thicker than in the left eye; the difference was marginally significant (P = .049). The temporal, nasal, and inferior quadrants had significantly thicker RNFL in the right eye, whereas the left eye showed thicker RNFL in the superior quadrant. The 2.5th and 97.5th percentile interocular difference tolerance limits for average RNFL thickness were -7.9 μm and 8.8 μm, respectively. Although the difference in average RNFL thickness correlated with differences in axial length, disc area, cup-to-disc ratio, and vertical cup-to-disc ratio, only differences in axial length (β = -0.21; P < .001) and disc area (β = 0.17; P < .001) were associated with an interocular difference of average RNFL thickness after adjustment for each other. The interocular difference remained stable despite significant decrease in RNFL thickness with aging.

CONCLUSIONS

An interocular difference in average RNFL thickness exceeding 9 μm when measured with the Cirrus HD-OCT in normal eyes may be considered statistically significant asymmetry and may be indicative of early glaucomatous damage.

Peripapillary retinal nerve fiber layer thickness analysis with scanning laser polarimetry (GDx VCC) in normal children

PURPOSE

To assess the use of scanning laser polarimeter with variable corneal compensation (GDx VCC) in children; to compare GDx VCC parameters between normal children and adults; and, to evaluate peripapillary retinal nerve fiber layer thickness variation with age in normals.

PATIENTS AND METHODS

Ninety-eight normal children (mean age 8.5+/-2.8 y; range: 3 to 17) and 96 normal adults (mean age of 47.0+/-20.4 y; range: 18 to 87) underwent GDx VCC testing. Eyes with small or large optic discs were excluded. The "extended parameter table" parameters and mean thickness values of the 4 quadrants and 64 sectors were considered. Differences between age groups, retinal thickness comparisons and age effect were assessed using unpaired t test, analysis of variance, and regression analysis.

RESULTS

GDx VCC parameters in children and adults showed wide intersubject variability. All parameters, excluding Symmetry, were significantly greater in children (P<0.05). TSNIT (temporal, superior, nasal, inferior, temporal) average, superior average and inferior average parameters showed a significant age-related thinning (P<0.01), at a rate of 0.043, 0.057, and 0.121 microm/y, respectively.

CONCLUSIONS

A significant age-related superior and inferior retinal nerve fiber layer thinning was found using GDx VCC. Considering the significant differences between children and adults for most GDx VCC parameters, the built-in adult normative database cannot be applied in children.

Asymmetry analysis of the retinal nerve fiber layer thickness in normal eyes using optical coherence tomography

PURPOSE

To investigate the asymmetry of the retinal nerve fiber layer thickness (RNFLT) with respect to the horizontal and vertical meridian and between the right and left eye in normal subjects.

METHODS

The RNFLT was measured in 121 normal volunteers by optical coherence tomography (OCT). The RNFLT was analyzed by dividing the circle scanning area (diameter 3.4 mm) around the optic disc into 4 quadrants and 12 sectors.

RESULTS

There was a significant difference between the RNFLT of the nasal and temporal quadrant in individual eyes. There was a significant difference between the RNFLT of corresponding sectors with respect to the vertical or horizontal meridian in individual eyes. The nasal and temporal RNFLTs were asymmetrical between the right and left eye in the quadrant and sector analysis. The RNFLT of the nasal and temporal quadrant was thicker in the right eye. The nasal and inferior RNFLT measured by OCT had a significant correlation with degree of refractive error.

CONCLUSIONS

In normal subjects without significant anisometropia, there was significant asymmetry of the RNFLT for each eye as well as between the right and left eye.

Differences by quadrant of retinal nerve fiber layer thickness in healthy eyes

PURPOSE

The purpose of this study was to determine the distribution of retinal nerve fiber layer thickness by quadrant in healthy eyes.

PATIENTS AND METHODS

Forty subjects with healthy eyes were included in the study. A complete ophthalmic examination was performed, including determination of visual fields by automated perimetry. The subjects had no family history of retinal disease or glaucoma. Forty right eyes and 40 left eyes were measured. Retinal nerve fiber layer thickness was measured using simultaneous stereophotographs with stereophotogrammetry at the disc margin. For the total disc and four quadrants, absolute retinal nerve fiber layer thickness and optic disc area was determined using a magnification correction formula.

RESULTS

Comparison of the quadrants showed that the retinal nerve fiber layer thicknesses of the superior, inferior, and nasal quadrants were significantly thicker than the temporal quadrant (P = 0.00006 for right and left eyes). No significant differences were observed between the superior, inferior, and nasal quadrants in the right eye. In the left eye, the superior retinal nerve fiber layer thickness was significantly greater than the inferior (P = 0.028) and nasal retinal nerve fiber layer thicknesses (P = 0.00006), while the inferior was not significantly different from the nasal. No significant difference in quadrant retinal nerve fiber layer thickness was noted between eyes.

CONCLUSIONS

Measurements of retinal nerve fiber layer thickness in healthy eyes show the thinnest quadrant to be the temporal, with the other three quadrants having similar thicknesses. This pattern corresponds to the histologic measurements of retinal nerve fiber layer thickness.