Quantification of nerve fiber layer thickness in normal and glaucomatous eyes using optical coherence tomography

Influence of disc-fovea angle and retinal blood vessels on interindividual variability of circumpapillary retinal nerve fibre layer

BACKGROUND

To assess whether intersubject variability of circumpapillary retinal nerve fibre layer (RNFL) thickness in healthy subjects acquired with spectral domain optical coherence tomography (SD-OCT) can be reduced by considering the disc-fovea angle (DFA), either alone or together with a compensation based on retinal blood vessel distribution (RVD).

METHODS

106 healthy volunteers underwent SD-OCT examination centred on the optic disc (OD) and on the macula. OD contours and foveal positions were automatically calculated. RVD at 3.4 mm diameter circle was manually assessed. We made two approaches to reduce interindividual variability in RNFL values using compensation processes; RVD compensation: RNFL thickness values were compensated according to RVD variation (RNFLRVD) and DFA compensation: we shifted the RNFL thickness measurements according to the DFA (RNFLDFA). Coefficient of variance (CoV) was calculated in 12 clock hour sectors for original RNFL (RNFLo), RNFLDFA, RNFLRVD and RNFL with both compensation methods (RNFLDFA-RVD).

RESULTS

Compared with the mean CoV of RNFLO, mean CoV of RNFLDFA, RNFLRVD and RNFLDFA-RVD was changed by -0.71% (p>0.05), -9.51% (p<0.001) and -7.55% (p=0.001), respectively. When compared with RNFLDFA, RNFL DFA-RVD significantly reduced the mean CoV by -6.69% (p=0.001), while compared with RNFLRVD, RNFL DFA-RVD did not significantly increase the mean CoV (+2.20%), (p>0.05).

CONCLUSIONS

Although reaching an improvement in some sectors, rotation of RNFL measurements according to the DFA on average does not reduce intersubject variability of RNFL. However, adjusting for RVD reduced the variance significantly. The results reinforce our work in assessing RVD as an important anatomical factor responsible for intersubject variability in RNFL measurements.

Correlation between optic disc perfusion and glaucomatous severity in patients with open-angle glaucoma: an optical coherence tomography angiography study

PURPOSE

To explore how optic disc perfusion varies in patients with open-angle glaucoma (OAG) and how this correlates with glaucoma severity.

METHODS

We performed a prospective and cross-sectional observational study that included 62 eyes from 62 patients with OAG, divided into three groups according to their visual field (VF) results, and 20 eyes from 20 normal control subjects. Optic disc perfusion was studied using optical coherence tomography angiography (angio-OCT), and flow index and vessel density were determined. The VF, mean deviation (MD), pattern standard deviation (PSD), retinal nerve fiber layer (RNFL) thickness, and ganglion cell complex (GCC) thickness were also recorded. The potential associations between disc perfusion and VF defects or structural loss were analyzed.

RESULTS

In OAG patients, the disc flow index and vessel density were significantly lower than in normal controls (all p<0.001) and were correlated with the severity of glaucoma. In OAG eyes, the flow index and vessel density were significantly correlated with MD, RNFL, and GCC thickness (all p<0.01), but were not in the normal controls. The receiver operating characteristic (ROC) curve analysis also revealed that disc flow index and vessel density had the power to differentiate normal eyes from eyes with OAG (under the ROC curves: 0.82 and 0.80, respectively).

CONCLUSIONS

Angiograms demonstrated a reduced disc flow index and vessel density in glaucoma, and this reduction was closely related to GCC thickness. This indicated that measurement of disc perfusion by angio-OCT might be important for the monitoring of glaucoma.

Optical Coherence Tomography in Alzheimer's Disease: A Meta-Analysis

Background

Alzheimer’s disease (AD) is a neurodegenerative disorder, which is likely to start as mild cognitive impairment (MCI) several years before the its full-blown clinical manifestation. Optical coherence tomography (OCT) has been used to detect a loss in peripapillary retina nerve fiber layer (RNFL) and a reduction in macular thickness and volume of people affected by MCI or AD. Here, we performed an aggregate meta-analysis combining results from different studies.

Methods and Findings

Data sources were case-control studies published between January 2001 and August 2014 (identified through PubMed and Google Scholar databases) that examined the RNFL thickness by means of OCT in AD and MCI patients compared with cognitively healthy controls.

Results

11 studies were identified, including 380 patients with AD, 68 with MCI and 293 healthy controls (HC). The studies suggest that the mean RNFL thickness is reduced in MCI (weighted mean differences in μm, WMD = -13.39, 95% CI: -17.34 to -9.45, p = 0.031) and, even more so, in AD (WMD = -15.95, 95% CI: -21.65 to -10.21, p<0.0001) patients compared to HC. RNFL in the 4 quadrants were all significantly thinner in AD superior (superior WMD = -24.0, 95% CI: -34.9 to -13.1, p<0.0001; inferior WMD = -20.8, 95% CI: -32.0 to -9.7, p<0.0001; nasal WMD = -14.7, 95% CI: -23.9 to -5.5, p<0.0001; and temporal WMD = -10.7, 95% CI: -19.9 to -1.4, p<0.0001); the same significant reduction in quadrant RNFL was observed in MCI patients compared with HC (Inferior WMD = -20.22, 95% CI: -30.41 to -10.03, p = 0.0001; nasal WMD = -7.4, 95% CI: -10.08 to -4.7, p = 0.0000; and temporal WMD = -6.88, 95% CI: -12.62 to -1.13, p = 0.01), with the exception of superior quadrant (WMD = -19.45, 95% CI: -40.23 to 1.32, p = 0.06).

Conclusion

Results from the meta-analysis support the important role of OCT for RNFL analysis in monitoring the progression of AD and in assessing the effectiveness of purported AD treatments.

Evaluation of the effect of elevated intraocular pressure and reduced ocular perfusion pressure on retinal capillary bed filling and total retinal blood flow in rats by OMAG/OCT

PURPOSE

To determine if retinal capillary filling is preserved in the face of acutely elevated intraocular pressure (IOP) in anesthetized rats, despite a reduction in total retinal blood flow (RBF), using optical microangiography/optical coherence tomography (OMAG/OCT).

METHODS

OMAG provided the capability of depth-resolved imaging of the retinal microvasculature down to the capillary level. Doppler OCT was applied to measure the total RBF using an enface integration approach. The microvascular pattern, capillary density, and total RBF were monitored in vivo as the IOP was increased from 10 to 100mmHg in 10mmHg intervals and returned back to 10mmHg.

RESULTS

In animals with mean arterial pressure (MAP) of 102±4mmHg (n=10), when IOP was increased from 0 to 100mmHg, the capillary density remained at or above 80% of baseline for the IOP up to 60mmHg [or ocular perfusion pressure (OPP) at 40mmHg]. This was then decreased, achieving 60% of baseline at IOP 70mmHg and OPP of 30mmHg. Total RBF was unaffected by moderate increases in IOP up to 30mmHg, beyond which total RBF decreased linearly, reaching 50% of baseline at IOP 60mmHg and OPP 40mmHg. Both capillary density and total RBF were totally extinguished at 100mmHg, but fully recovered when IOP returned to baseline. By comparison, a separate group of animals with lower MAP (mean=75±6mmHg, n=7) demonstrated comparable decreases in both capillary filling and total RBF at IOPs that were 20mmHg lower than in the initial group. Both were totally extinguished at 80mmHg, but fully recovered when IOP returned to baseline. Relationships of both parameters to OPP were unchanged.

CONCLUSION

Retinal capillary filling and total RBF responses to IOP elevation can be monitored non-invasively by OMAG/OCT and both are influenced by OPP. Retinal capillary filling was relatively preserved down to a perfusion pressure of 40mmHg, despite a linear reduction in total RBF.

Interocular symmetry of retinal nerve fibre layer thickness in healthy eyes: a spectral-domain optical coherence tomographic study

PURPOSE

This study was performed to investigate the interocular symmetry of peripapillary retinal nerve fibre layer (RNFL) thickness, as measured by Cirrus high-definition spectral-domain optical coherence tomography (OCT), in healthy eyes. A wide range of subject ages and refractive errors was examined.

METHODS

The retinal nerve fibre layer thickness was measured in 1,234 healthy eyes from 617 subjects using OCT. Interocular differences (right eye minus left eye) in global area and quadrant nerve fibre layer thicknesses were measured. The effect of age and refractive error on interocular nerve fibre layer thickness difference was also examined.

RESULTS

Means (and standard deviations) of subjects' ages and average subject refractive errors were 36.4 ± 19.8 years (range: five to 80 years) and -2.67 ± 2.91 D (range: -14.13 to +5.75 D), respectively. Cutoff limits for normal interocular nerve fibre layer thickness differences (2.5th and 97.5th percentiles of normative data) in the global area and in the superior, nasal, inferior and temporal quadrants were 9.5, 23.0, 15.6, 20.0 and 22.6 μm, respectively. Mean interocular retinal nerve fibre layer thickness differences in global area and in superior, nasal, inferior and temporal quadrants were 0.7 (p < 0.001), -3.9 (p < 0.001), 2.6 (p < 0.001), 1.1 (p = 0.007) and 3.0 (p < 0.001) μm, respectively. Interocular nerve fibre layer thickness differences were not significantly correlated with age or refractive error (average of right and left eyes, both p > 0.05).

CONCLUSIONS

Significant interocular differences in peripapillary retinal nerve fibre layer thickness exist in healthy eyes, particularly in the superior quadrant. This finding should be considered when comparing retinal nerve fibre layer thickness between right and left eyes.

Peripapillary retinal nerve fiber layer and optic nerve head characteristics in eyes with situs inversus of the optic disc

PURPOSE

This study was performed to investigate the peripapillary retinal nerve fiber layer (RNFL) and optic nerve head (ONH) characteristics, as determined using a spectral-domain optical coherence tomography (OCT), in eyes with situs inversus of the optic disc.

METHODS

The peripapillary RNFL and the ONH were assessed in 12 eyes belonging to 6 subjects with situs inversus of the optic disc (situs inversus group) and 24 eyes in 12 age-matched, sex-matched, and refractive error-matched healthy subjects (control group) by using OCT. The average, quadrant, and clock-hour RNFL thicknesses (clock-hour 9 on the scan represented the temporal side of the optic disc in both eyes), the superior/inferior RNFL peak locations, and ONH characteristics such as disc area, rim area, cup-to-disc ratio, vertical cup-to-disc ratio, and cup volume were obtained. The differences in RNFL and ONH characteristics between the 2 groups were analyzed.

RESULTS

The situs inversus group had a thicker RNFL in the clock-hour sectors 3 and 4, a thinner RNFL in the clock-hour sectors 7, 8, and 11, and more nasally located superior and inferior RNFL peak locations than the control group (P≤0.001). The situs inversus group had a smaller cup-to-disc area ratio, smaller vertical cup-to-disc ratio, and a lesser cup volume than the control group (P<0.01).

CONCLUSIONS

Eyes with situs inversus of the optic disc showed different peripapillary RNFL and ONH characteristics from those without this abnormality. These findings should be considered when assessing eyes with situs inversus of the optic disc.

In vivo imaging methods to assess glaucomatous optic neuropathy

The goal of this review is to summarize the most common imaging methods currently applied for in vivo assessment of ocular structure in animal models of experimental glaucoma with an emphasis on translational relevance to clinical studies of the human disease. The most common techniques in current use include optical coherence tomography and scanning laser ophthalmoscopy. In reviewing the application of these and other imaging modalities to study glaucomatous optic neuropathy, this article is organized into three major sections: 1) imaging the optic nerve head, 2) imaging the retinal nerve fiber layer and 3) imaging retinal ganglion cell soma and dendrites. The article concludes with a brief section on possible future directions.

The Correlation of Retinal Nerve Fiber Layer Thickness With Blood Pressure in a Chinese Hypertensive Population

To investigate the association between retinal nerve fiber layer (RNFL) thickness and blood pressure (BP) in subjects with systemic hypertension. Subjects with systemic hypertension on anti-hypertensive medications were screened by fundus photography and referred for glaucoma work-up if there was enlarged vertical cup-to-disc (VCDR) ratio ≥0.6, VCDR asymmetry ≥0.2, or optic disc hemorrhage. Workup included a complete ophthalmological examination, Humphrey visual field test, and RNFL thickness measurement by optical coherence tomography. The intraocular pressure (IOP) and RNFL thicknesses (global and quadrant) were averaged from both eyes and the means were correlated with: the systolic BP (SBP), diastolic BP (DBP), and mean arterial pressure (MAP) using Pearson correlation. Among 4000 screened hypertensive subjects, 133 were referred for glaucoma workup and 110 completed the workup. Of the 4000 screened subjects, 1.3% had glaucoma (0.9% had normal tension glaucoma [NTG], 0.2% had primary open angle glaucoma, and 0.2% had primary angle closure glaucoma), whereas 0.3% were NTG suspects. The SBP was negatively correlated with the mean superior RNFL thickness (P = 0.01). The DBP was negatively correlated with the mean global (P = 0.03), superior (P = 0.02), and nasal (P = 0.003) RNFL thickness. The MAP was negatively correlated with the mean global (P = 0.01), superior (P = 0.002), and nasal (P = 0.004) RNFL thickness while positively correlated with the mean IOP (P = 0.02). In medically treated hypertensive subjects, glaucoma was present in 1.3%, with NTG being most prevalent. MAP control may help with IOP lowering and RNFL preservation, although future prospective studies will be needed.

Treatment with citicoline eye drops enhances retinal function and neural conduction along the visual pathways in open angle glaucoma

PURPOSE

To evaluate the retinal function and the neural conduction along the visual pathways after treatment with citicoline eye drops in patients with open angle glaucoma (OAG).

METHODS

Fifty-six OAG patients (mean age 52.4 ± 4.72 years, IOP <18 mmHg with beta-blocker monotherapy only) were enrolled. Of these, 47 eyes completed the study: 24 OAG eyes were treated with topical citicoline (OMK1®, Omikron Italia, 3 drops/day) (GC eyes) over a 4-month period (month 4) followed by a 2-month period of citicoline wash-out (month 6), and another 23 OAG eyes were only treated with beta-blocker monotherapy (GP eyes). In GC and GP eyes, pattern electroretinogram (PERG) and visual evoked potentials (VEP) were assessed at baseline and at months 4 and 6 in both groups.

RESULTS

At baseline, similar (ANOVA, p > 0.01) PERG and VEP values in GC and GP eyes were observed. After treatment with topical citicoline, a significant (p < 0.01) increase of PERG P50-N95 and VEP N75-P100 amplitudes, and a significant (p < 0.01) shortening of VEP P100 implicit times were found. In GC eyes, the shortening of VEP P100 implicit times was correlated significantly (p < 0.01) with the increase of PERG P50-N95 amplitudes. After a 2-month period of topical Citicoline wash-out, PERG and VEP values were similar (p > 0.01) to baseline ones. GP eyes showed not significant changes of PERG and VEP values during the entire follow-up.

CONCLUSIONS

Topical treatment with citicoline in OAG eyes induces an enhancement of the retinal bioelectrical responses (increase of PERG amplitude) with a consequent improvement of the bioelectrical activity of the visual cortex (shortening and increase of VEP implicit time and amplitude, respectively).

Protective effect of high concentration of BN52021 on retinal contusion in cat eyes

Background

Blunt injuries/contusion on eyes might cause retina blunt trauma. This study is to evaluate the protective function of BN52021 against retinal trauma.

Methods

A total of 70 cats, 6 months old, were divided into six groups: Group A to E (n = 12) and normal control (N) group (n = 10). The right eyes in Group A to E were contused. All experiments were performed under general anesthetization. Retrobulbar injections of medication in right eyes were performed. Cats were administrated with 0.5 mL of normal saline (NS), dimethyl sulphoxide, 0.2 g/L BN52021, 1 g/L BN52021 and 5 g/L BN52021, respectively. Cats in Group N were administrated with 0.5 mL of NS. Intraocular pressure (IOP), flash electroretinogram (ERG), and retinal nerve fiber layer (RNFL) thickness were measured. Hematoxylin and eosin (HE) staining and transmission electron microscope (TEM) were detected.

Results

No significant difference was observed in IOP levels among groups. Comparing with cats in Group N, those in Group A to E showed significant lower amplitudes of rod a- and b-waves (P < 0.05). Amplitudes of rod a- and b-waves were increased by administration of high concentration of BN52021 (≥1 g/L). Moreover, high concentration of BN52021 decreased the RNFL thickness increased by contusion. Axons in RNFL in Group E arranged neatly at 7 days after modeling.

Conclusions

The degenerated axons caused by contusion were repaired by BN52021. The administration of high concentration of (≥1 g/L) BN52021 could partially repair retinal function in contused cat eyes.

Reproducibility of spectral-domain optical coherence tomography RNFL map for glaucomatous and fellow normal eyes in unilateral glaucoma

PURPOSE

To compare the reproducibility of the optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) thickness map between glaucomatous and fellow normal eyes of unilateral glaucoma patients.

METHODS

In this prospective case-control study, Cirrus HD-OCT was performed for 79 unilateral glaucoma patients 3 times on the first visit and on 3 subsequent visits within a 2-month period. Test-retest standard deviation (TRT-SD) and tolerance limit based on the 1.645×√2×TRT-SD formula were derived for RNFL thicknesses at the respective superpixels of the RNFL thickness map.

RESULTS

The TRT-SDs and tolerance limits of the glaucomatous eyes (TRT-SD: 2.75 to 20.25 μm; tolerance limits: 6.40 and 47.11 μm) were significantly smaller than those of the fellow normal eyes (TRT-SD: 2.73 to 26.49 μm; tolerance limits: 6.35 and 61.63 μm) in the superotemporal, inferotemporal, and superonasal areas (P <0.05). The TRT-SDs in most areas showed a significant positive correlation with the RNFL thicknesses (P<0.05).

CONCLUSIONS

The test-retest variabilities of the Cirrus HD-OCT RNFL thickness map of the glaucomatous eyes were lower than those of the fellow normal eyes, especially in areas of high diagnostic importance. Moreover, variability was positively correlated with the baseline RNFL thicknesses. Therefore, adjusting the tolerance limits on the basis of the baseline RNFL thickness values might help improve the ability to recognize progression. Further prospective studies on this issue are warranted.

Applications of optical coherence tomography in pediatric clinical neuroscience

For nearly two centuries, the ophthalmoscope has permitted examination of the retina and optic nerve-the only axons directly visualized by the physician. The retinal ganglion cells project their axons, which travel along the innermost retina to form the optic nerve, marking the beginning of the anterior visual pathway. Both the structure and function of the visual pathway are essential components of the neurologic examination as it can be involved in numerous acquired, congenital and genetic central nervous system conditions. The development of optical coherence tomography now permits the pediatric neuroscientist to visualize and quantify the optic nerve and retinal layers with unprecedented resolution. As optical coherence tomography becomes more accessible and integrated into research and clinical care, the pediatric neuroscientist may have the opportunity to utilize and/or interpret results from this device. This review describes the basic technical features of optical coherence tomography and highlights its potential clinical and research applications in pediatric clinical neuroscience including optic nerve swelling, optic neuritis, tumors of the visual pathway, vigabatrin toxicity, nystagmus, and neurodegenerative conditions.

Assessment of retinal nerve fiber layer thickness in healthy, full-term neonates

PURPOSE

To measure average retinal nerve fiber layer (RNFL) thicknesses in healthy, full-term neonates.

DESIGN

Descriptive research to develop normative data.

METHODS

Healthy infants born between 37 and 42 weeks postmenstrual age were imaged with hand-held spectral-domain optical coherence tomography. A custom script segmented the RNFL; the fovea and optic nerve center were manually selected. A second script measured the average RNFL thickness along the papillomacular bundle, defined as the arc from -15 degrees to +15 degrees on the axis from the optic nerve to fovea, with radii of 1.1, 1.3, 1.5, and 1.7 mm from the center of the optic disc. Shapiro-Wilk W tests assessed these measurements for normality to determine the age-appropriate radial distance for subsequent analyses. Average RNFL thicknesses for four temporal 45-degree sectors (superior temporal, temporal superior, temporal inferior, and inferior temporal) and the temporal quadrant were calculated and compared to demographic parameters for all infants.

RESULTS

Fifty full-term infants were adequately imaged for RNFL analysis. RNFL thicknesses at 1.5 mm radial distance from the optic nerve were the most normally distributed. While there was a trend toward greater mean superior temporal RNFL thickness for both black and Hispanic vs white infants (128 ± 27 μm, 124 ± 30 μm, and 100 ± 19 μm, respectively, P = .04 for both comparisons), there were no other significant differences noted in RNFL thicknesses by race, sex, gestational age, or birth weight.

CONCLUSIONS

We present RNFL thickness measurements for healthy, full-term infants that may serve as normative data for future analyses.

In vivo optical microscopy of peripheral nerve myelination with polarization sensitive-optical coherence tomography

Assessing nerve integrity and myelination after injury is necessary to provide insight for treatment strategies aimed at restoring neuromuscular function. Currently, this is largely done with electrical analysis, which lacks direct quantitative information. In vivo optical imaging with sufficient imaging depth and resolution could be used to assess the nerve microarchitecture. In this study, we examine the use of polarization sensitive-optical coherence tomography (PS-OCT) to quantitatively assess the sciatic nerve microenvironment through measurements of birefringence after applying a nerve crush injury in a rat model. Initial loss of function and subsequent recovery were demonstrated by calculating the sciatic function index (SFI). We found that the PS-OCT phase retardation slope, which is proportional to birefringence, increased monotonically with the SFI. Additionally, histomorphometric analysis of the myelin thickness and g-ratio shows that the PS-OCT slope is a good indicator of myelin health and recovery after injury. These results demonstrate that PS-OCT is capable of providing nondestructive and quantitative assessment of nerve health after injury and shows promise for continued use both clinically and experimentally in neuroscience.

Compensation for retinal vessel density reduces the variation of circumpapillary RNFL in healthy subjects

This work intends to assess circumpapillary retinal vessel density (RVD) at a 3.46 mm diameter circle and correlate it with circumpapillary retinal nerve fiber layer (RNFL) thickness measured with Fourier-Domain Optical Coherence Tomography. Furthermore, it aims to evaluate the reduction of intersubject variability of RNFL when considering RVD as a source of information for RNFL distribution. For that, 106 healthy subjects underwent circumpapillary RNFL measurement. Using the scanning laser ophthalmoscope fundus image, thickness and position of retinal vessels were assessed and integrated in a 256-sector RVD profile. The relationship between local RVD value and local RNFL thickness was modeled by linear regression. RNFL was then compensated for RVD variation by regression formulas. A strong statistically significant intrasubject correlation was found for all subjects between RVD and RNFL profiles (mean R = 0.769). In the intersubject regression analysis, 247 of 256 RNFL sectors showed a statistically significant positive correlation with RVD (mean R = 0.423). RVD compensation of RNFL resulted in a relative reduction of up to 20% of the intersubject variance. In conclusion, RVD in a 3.46 mm circle has a clinically relevant influence on the RNFL distribution. RVD may be used to develop more individualized normative values for RNFL measurement, which might improve early diagnosis of glaucoma.

The Effect of Peripapillary Detachment on Retinal Nerve Fiber Layer Measurement by Spectral Domain Optical Coherence Tomography in High Myopia

Purpose: The aim of this study was to investigate the repercussions of peripapillary detachment on retinal nerve fiber layer (RNFL) measurements in patients with highly myopic eyes. Methods: A total of 244 highly myopic eyes underwent a complete ophthalmologic examination that included optical coherence tomography (OCT) to analyze the peripapillary retina and RNFL thickness. Based on the OCT findings, patients were grouped as follows: group A: eyes with a peripapillary intrachoroidal cavitation (PIC); group B: eyes with a peripapillary neurosensory retinal detachment (PNRD), and group C: eyes without a peripapillary detachment. Results: The OCT scans identified a peripapillary detachment in 42 eyes (17.21%). Out of these 42 eyes, 22 showed PIC (52.38%; group A) and 20 had a PNRD (47.62%; group B). The average overall RNFL thickness in groups A, B and C was 74.11 ± 10.88, 88.26 ± 25.72 and 72.75 ± 16.24 μm, respectively (ANOVA test, p = 0.00). Conclusion: Eyes with a PNRD had a significantly greater average RFNL thickness than those without peripapillary detachment in pathologic myopia due to a misidentification of the outer profile of the RFNL. This fact makes the interpretation of RNFL thickness in highly myopic eyes more challenging.

Retinal nerve fiber bundle tracing and analysis in human eye by polarization sensitive OCT

We present a new semi-automatic processing method for retinal nerve fiber bundle tracing based on polarization sensitive optical coherence tomography (PS-OCT) data sets. The method for tracing is based on a nerve fiber orientation map that covers the fovea and optic nerve head (ONH) regions. In order to generate the orientation map, two types of information are used: optic axis orientation based on polarization data, and complementary information obtained from nerve fiber layer (NFL) local thickness variation to reveal fiber bundle structures around the fovea. The corresponding two orientation maps are fused into a combined fiber orientation map. En face maps of NFL retardation, thickness, and unit-depth-retardation (UDR, equivalent to birefringence) are transformed into "along-trace" maps by using the obtained traces of the nerve fiber bundles. The method is demonstrated in the eyes of healthy volunteers, and as an example of further analyses utilizing this method, maps illustrating the gradients of NFL retardation, thickness, and UDR are demonstrated.

In vivo evaluation of the cornea and conjunctiva of the normal laboratory beagle using time- and Fourier-domain optical coherence tomography and ultrasound pachymetry

OBJECTIVE

To obtain normative data for the canine cornea and conjunctiva using high-resolution time- and Fourier-domain optical coherence tomography (TD-OCT and FD-OCT) and ultrasound pachymetry (USP).

ANIMALS

One hundred sixty-eight eyes of 133 healthy young intact laboratory beagles.

PROCEDURES

The cornea and conjunctiva of 16 eyes of 8 healthy young intact female beagles were imaged using FD-OCT. Corneal thickness was measured with FD-OCT and USP, while corneal epithelial thickness and conjunctival epithelial thickness were measured with FD-OCT. The central corneal thickness (CCT) was determined in 152 eyes of 125 healthy young adult intact female (35) and male (90) beagles using TD-OCT. Mixed effects linear regression was used for statistical analysis.

RESULTS

The CCT was (mean ± standard deviation) 497.54 ± 29.76, 555.49 ± 17.19, and 594.81 ± 33.02 μm as measured by FD-OCT, USP, and TD-OCT, respectively. The central, superior paraxial, superior perilimbal corneal epithelial thickness and superior bulbar conjunctival epithelial thickness were 52.38 ± 7.27, 56.96 ± 6.47, 69.06 ± 8.84 and 42.98 ± 6.17 μm, respectively. When comparing techniques used for measuring CCT (USP vs. FD-OCT and FD-OCT vs. TD-OCT), USP and TD-OCT generated significantly greater values in comparison with FD-OCT (both P < 0.001). For all dogs, CCT increased with increasing age and body weight (both P < 0.001) and was higher in intact males vs. females using TD-OCT (P = 0.034).

CONCLUSION

High-resolution FD-OCT and TD-OCT provide detailed noninvasive evaluation of in vivo canine anterior segment structures. Normative values of the canine cornea and conjunctiva are reported.

Evaluating glaucoma damage: emerging imaging technologies

The use of ocular imaging tools to estimate structural and functional damage in glaucoma has become a common clinical practice and a substantial focus of vision research. The evolution of the imaging technologies through increased scanning speed, penetration depth, image registration and development of multimodal devices has the potential to detect the pathology more reliably and in earlier stages. This review is focused on new ocular imaging modalities used for glaucoma diagnosis.

Optical coherence tomography assisted retinal nerve fibre layer thickness profile in high myopia

INTRODUCTION

To evaluate the association of high myopia with retinal nerve fibre layer (RNFL) thickness by Fourier domain optical coherence tomography (FD OCT).

MATERIALS AND METHODS

Fifty highly myopic eyes (25 patients) and forty emmetropic eyes (20 Normal subject) were randomly selected after excluding concomitant ophthalmic disorder and RNFL thickness measured using the Fourier domain optical coherence tomography (FD OCT).

RESULTS

The overall mean RNFL thickness in the myopic groups and control were 87.89 μm and 111.64 μm respectively. The mean retinal nerve fibre thickness was significantly less in myopic eyes as compared to control group (p =0.0001). Retinal nerve fibre layer thickness shows topographic double hump pattern in both the groups (myopes and emmetropes).

CONCLUSION

Retinal nerve fibre thickness was significantly less in myopic eyes as compared to emmetropic eyes. The retinal nerve fibre layer thinning in high myopes may be confused with open angle glaucoma, a disease also prevalent in high myopes. There is therefore a need to have retinal nerve fibre layer thickness normogram for high myopes of a given population group to avoid wrong interpretation.

Teleglaucoma: ready to go?

Telemedicine technologies and services allow today's ophthalmic clinicians to remotely diagnose, manage and monitor several ophthalmic conditions from a distance. But is this the case for glaucomas? There has been a proliferation of telemedicine friendly devices in recent years that improves the capabilities of the clinician in managing glaucomas. The existing instruments still need to align themselves with accepted industry standards. There are successful programmes running in several areas of the world. The safety and efficacy of these programmes needs further exploration. The inability of a single device or test to diagnose glaucomas satisfactorily has also hampered progress in remotely diagnosing these conditions. There is, however, significant potential for telemedicine-friendly devices to remotely monitor the progress of glaucoma and, thereby, reduce some of the workload on an overstretched health service.

Population-based evaluation of retinal nerve fiber layer, retinal ganglion cell layer, and inner plexiform layer as a diagnostic tool for glaucoma

PURPOSE

We determined the glaucoma screening performance of regional optical coherence tomography (OCT) layer thickness measurements in the peripapillary and macular region, in a population-based setting.

METHODS

Subjects (n = 1224) in the Rotterdam Study underwent visual field testing (Humphrey Field Analyzer) and OCT of the macula and optic nerve head (Topcon 3-D OCT-1000). We determined the mean thicknesses of the retinal nerve fiber layer (RNFL), retinal ganglion cell layer (RGCL), and inner plexiform layer for regions-of-interest; thus, defining a series of OCT parameters, using the Iowa Reference Algorithms. Reference standard was the presence of glaucomatous visual field loss (GVFL); controls were subjects without GVFL, an intraocular pressure (IOP) of 21 mm Hg or less, and no positive family history for glaucoma. We calculated the area under the receiver operating characteristics curve (AUCs) and the sensitivity at 97.5% specificity for each parameter.

RESULTS

After excluding 23 subjects with an IOP > 21 mm Hg and 73 subjects with a positive family history for glaucoma, there were 1087 controls and 41 glaucoma cases. Mean RGCL thickness in the inferior half of the macular region showed the highest AUC (0.85; 95% confidence interval [CI] 0.77-0.92) and sensitivity (53.7%; 95% CI, 38.7-68.0%). The mean thickness of the peripapillary RNFL had an AUC of 0.77 (95% CI, 0.69-0.85) and a sensitivity of 24.4% (95% CI, 13.7-39.5%).

CONCLUSIONS

Macular RGCL loss is at least as common as peripapillary RNFL abnormalities in population-based glaucoma cases. Screening for glaucoma using OCT-derived regional thickness identifies approximately half of those cases of glaucoma as diagnosed by perimetry.

Predictive Values of Optical Coherence Tomography (OCT) Parameters in Assessment of Glaucoma progression

Goal:

the purpose of the current study was to estimate the predictive values of optical coherence tomography parameters in early, developed perimetric and terminal glaucoma.

Methods:

180 eyes of 120 consecutive patients were evaluated in this retrospective cross sectional pilot study. Copernicus Spectral –domain optical coherence tomography with resolution of 3 mm obtained throught the optic nerve head were included. All examined eyes were divided to four groups (healthy,early, developed perimetric glaucoma and terminal glaucoma). The values of the thicknes of the retinal nerve fibre layer, the size of the disk, the volume of the cup, the E/D parameter and the size of the RIM were compared in four study groups.

Results:

The sensitivity of RNFL was 90,0%, specificity 82,0 %, positive predictability 83,3 % and negative predictability was 89,1 %. The total accuracy was 86,0 % and area under curve (AUC) was 0,878 for RNFL indeks compering early to developed glaucoma. The sensitivity for CUP was 78%, the specificity was 80,8 %, the positive predictability 81,2% and the negative predictability was 77,5 %. The total accuracy was 79,3 % and area under curve (AUC) was 0,86 compering early to developed glaucoma. The sensitivity for E/D was 82,0%, the specificity was 82,9 % the positive predictability 83,7 % and the negative predictability was 81,3 %. The total accuracy was 82,5 % and area under curve (AUC) for E/D was 0,89 compering eearly to developed glaucoma. The sensitivity for RIM was 78,0%, the specificity was 76,6 %, the positive predictability was 84,7 and the negative predictability was 67,7 %. The total accuracy was 77,5 % and area under curve (AUC) for the RIM compering the developed to terminal glaucoma was 0,792. The sensitivity of RNFL was 88,0 %, the specificity was 66,7 %, the positive predictability was 81,5% and the negative predictability was 76,9%. The total accuracy was 80,0% and the area under curve (AUC) for RNFL compering developed to terminal glaucoma was 0,815. The incrreasing 0,1 unit RNFL decreases the risk of developing glaucoma from early to another developed stage of glaucoma for 6,95%. The increasing of E/D for only one unit increases the risk to develop another stage of glaucoma for 18,75 times. The increasing of RNFL for only one unit decreases the risk of performing developed glaucoma from initial stage for 7,8%. The increasing for only one unit of CUP increases the risk to develop terminal glaucoma for 8,47 times and increasing for 0,1 unit of the value of RIM decreases the risk developing terminal glaucoma for 9,27%. The increasing for 0,01 unit of the E/D index increases the risk for terminal glaucoma for 23,23 times. The increasing for one unit of RNFL decreasing the risk developing terminal glaucoma for 5,7%.

Comparison of longitudinal in vivo measurements of retinal nerve fiber layer thickness and retinal ganglion cell density after optic nerve transection in rat

Purpose

To determine the relationship between longitudinal in vivo measurements of retinal nerve fiber layer thickness (RNFLT) and retinal ganglion cell (RGC) density after unilateral optic nerve transection (ONT).

Methods

Nineteen adult Brown-Norway rats were studied; N = 10 ONT plus RGC label, N = 3 ONT plus vehicle only (sans label), N = 6 sham ONT plus RGC label. RNFLT was measured by spectral domain optical coherence tomography (SD-OCT) at baseline then weekly for 1 month. RGCs were labeled by retrograde transport of fluorescently conjugated cholera toxin B (CTB) from the superior colliculus 48 hours prior to ONT or sham surgery. RGC density measurements were obtained by confocal scanning laser ophthalmoscopy (CSLO) at baseline and weekly for 1 month. RGC density and reactivity of microglia (anti-Iba1) and astrocytes (anti-GFAP) were determined from post mortem fluorescence microscopy of whole-mount retinae.

Results

RNFLT decreased after ONT by 17% (p<0.05), 30% (p<0.0001) and 36% (p<0.0001) at weeks 2, 3 and 4. RGC density decreased after ONT by 18%, 69%, 85% and 92% at weeks 1, 2, 3 and 4 (p<0.0001 each). RGC density measured in vivo at week 4 and post mortem by microscopy were strongly correlated (R = 0.91, p<0.0001). In vivo measures of RNFLT and RGC density were strongly correlated (R = 0.81, p<0.0001). In ONT- CTB labeled fellow eyes, RNFLT increased by 18%, 52% and 36% at weeks 2, 3 and 4 (p<0.0001), but did not change in fellow ONT-eyes sans CTB. Microgliosis was evident in the RNFL of the ONT-CTB fellow eyes, exceeding that observed in other fellow eyes.

Conclusions

In vivo measurements of RNFLT and RGC density are strongly correlated and can be used to monitor longitudinal changes after optic nerve injury. The strong fellow eye effect observed in eyes contralateral to ONT, only in the presence of CTB label, consisted of a dramatic increase in RNFLT associated with retinal microgliosis.

The cellular origins of the outer retinal bands in optical coherence tomography images

PURPOSE

To test the recently proposed hypothesis that the second outer retinal band, observed in clinical OCT images, originates from the inner segment ellipsoid, by measuring: (1) the thickness of this band within single cone photoreceptors, and (2) its respective distance from the putative external limiting membrane (band 1) and cone outer segment tips (band 3).

METHODS

Adaptive optics-optical coherence tomography images were acquired from four subjects without known retinal disease. Images were obtained at foveal (2°) and perifoveal (5°) locations. Cone photoreceptors (n = 9593) were identified and segmented in three dimensions using custom software. Features corresponding to bands 1, 2, and 3 were automatically identified. The thickness of band 2 was assessed in each cell by fitting the longitudinal reflectance profile of the band with a Gaussian function. Distances between bands 1 and 2, and between 2 and 3, respectively, were also measured in each cell. Two independent calibration techniques were employed to determine the depth scale (physical length per pixel) of the imaging system.

RESULTS

When resolved within single cells, the thickness of band 2 is a factor of three to four times narrower than in corresponding clinical OCT images. The distribution of band 2 thickness across subjects and eccentricities had a modal value of 4.7 μm, with 48% of the cones falling between 4.1 and 5.2 μm. No significant differences were found between cells in the fovea and perifovea. The distance separating bands 1 and 2 was found to be larger than the distance between bands 2 and 3, across subjects and eccentricities, with a significantly larger difference at 5° than 2°.

CONCLUSIONS

On the basis of these findings, we suggest that ascription of the outer retinal band 2 to the inner segment ellipsoid is unjustified, because the ellipsoid is both too thick and proximally located to produce the band.

The relationship between retinal nerve fiber layer thickness and optic nerve head neuroretinal rim tissue in glaucoma

PURPOSE

The purpose of this study was to determine the relationship between optical coherence tomography (OCT) measures of retinal nerve fiber layer (RNFL) and neuroretinal rim (NRR) in a nonhuman primate experimental glaucoma model, and in a population of clinical patients.

METHODS

For nonhuman primates, normative data were collected from 44 healthy monkeys, and nine animals with unilateral experimental glaucoma that were followed longitudinally. Cross-sectional human subjects data were collected from 89 healthy, 74 glaucoma suspects, and 104 glaucoma patients. Individualized transverse scaling for OCT scans was calculated using a schematic eye that incorporated optical ocular biometry. Custom algorithms were used to quantify RNFL thickness with and without vessels removed, scaled minimum rim width (sMRW), and neural rim volume (NRV).

RESULTS

For the experimental glaucoma group, NRR parameters showed the first changes with increased cumulative IOP. The data for both NRR and RNFL measures were best fit by an exponential rise model (NRV, R2=0.79, P<0.01, sMRW, R2=0.74, P<0.01). The major retinal vascular thickness contribution to the RNFL decreased (0.03 μm/μm, P<0.01) with RNFL loss, but the percent vascular contribution increased (-0.1%/μm, P<0.01) with disease progression. Overall, the findings for the cross-sectional human data were similar to those of the experimental model.

CONCLUSIONS

The findings illustrate a nonlinear relationship between NRR and RNFL measures and provide support for the use of multiple OCT scaled morphological measures for the diagnosis and management of primary open angle glaucoma in humans.

Analysis of peripapilary retinal nerve fiber layer thickness of healthy Chinese from northwestern Shanghai using Cirrus HD-OCT

AIM

To investigate peripapillary retinal nerve fiber layer (RNFL) thickness of healthy Chinese individuals from northwestern Shanghai using Cirrus HD-OCT (Carl Zeiss Meditec, Inc. Dublin, CA, USA).

METHODS

The peripapillary RNFL thickness of 720 eyes from 360 healthy Chinese participants were measured using the Optic Disc Cube 200×200 protocol. Each eye was scanned 3 times. Global and each quadrant's RNFL thickness around the optic nerve were compared between genders, and interocular differences were analyzed. The correlation between global RNFL thickness and age were also assessed in this study.

RESULTS

The mean global, superior, nasal, inferior and temporal RNFL thickness of all the eyes were 96.04±7.40 µm, 118.36±13.52 µm, 67.63±8.60 µm, 125.17±13.48 µm, 72.49±10.70 µm, respectively. When analyzing between genders, the mean nasal RNFL thickness of male and female were 68.29±8.44 µm and 66.97±8.70 µm, with statistically significant difference (P=0.038), while the data of global, superior, inferior and temporal quadrant showed no significant difference (all P>0.05). When analyzing interocular differences, the mean RNFL thickness of all the right eyes and all the left eyes were 116.46±13.17 µm and 120.27±13.61 µm in superior quadrant (P<0.001); 68.74±8.80 µm and 66.52±8.25 µm in nasal quadrant (P<0.001); 73.16±10.95 and 71.83±10.41 in temporal quadrant (P<0.001), all having statistically significant differences. There were no statistically significant interocular differences of global and inferior RNFL thickness (both P>0.05). There was a significantly negative correlation (r=-0.618, P<0.001) between the mean global RNFL thickness and the age.

CONCLUSION

In healthy Chinese from northwestern Shanghai, there were no significant differences detected interocular difference and between genders in the mean global RNFL thickness. Nevertheless, significant difference existed in the nasal quadrant between genders, and interocular differences existed in the superior, nasal and temporal quadrants. The RNFL thickness appeared to gradually decrease with age.

In vivo adaptive optics imaging of the temporal raphe and its relationship to the optic disc and fovea in the human retina

PURPOSE

To investigate the anatomy of the temporal raphe and its angular relationship to the optic disc and fovea in the human retina in vivo.

METHODS

Adaptive optics scanning laser ophthalmoscope (AOSLO) was used to image the temporal raphe in 11 young subjects. The raphe's angle relative to a horizontal line and the raphe-fovea-disc angle (angle between the raphe and the line connecting the disc and fovea center) were determined. In addition, to investigate the impact of aging on the raphe, we imaged the raphe at 9° eccentricity in 10 additional older healthy subjects and compared the raphe's anatomy between the two age groups.

RESULTS

The raphe's in vivo appearance was generally in agreement with major findings of ex vivo studies. The raphe angle was -1.67° ± 4.8°, with the ranges from -9° to 6°. It was related to the angle of the foveal depression relative to the disc. The raphe-fovea-disc angle was 170.3° ± 3.6°. The raphe gap, defined as the averaged distance between superior and inferior bundles, was significantly larger in the older subjects than in younger subjects (230.83 ± 113.22 μm vs. 1.93 ± 68.73 μm, P < 0.0001).

CONCLUSIONS

The angle of the raphe in the study was not consistent with classic raphe models. While the angle showed relatively large individual variability, there seems to be a systematic relation between the disc, fovea, and raphe. It may be useful for individualizing retinal measurement strategies with regard to perimetry.

Measurement of retinal nerve fiber layer and macular ganglion cell-inner plexiform layer with spectral-domain optical coherence tomography in patients with optic nerve head drusen

PURPOSE

To evaluate the effect of optic nerve head drusen (ONHD) on the retinal nerve fiber layer (RNFL) and macular ganglion cell-inner plexiform layer (GCIPL) using Cirrus optical coherence tomography (OCT).

METHODS

Fifty-seven eyes of thirty patients with ONHD and thirty-eight eyes of twenty age-matched and sex-matched control subjects underwent circumpapillary and macular scanning using Cirrus OCT. The percentages of eyes with abnormal GCIPL and RNFL values according to the Cirrus normative data were analysed and compared.

RESULTS

Overall, eyes with ONHD showed abnormally reduced values for average and minimum GCIPL thicknesses in 35 % and 45 % of cases compared to 2 % for both values in control eyes (P < 0.001). Average RNFL thickness comparison between eyes with ONHD and normal eyes revealed abnormal thinning in 33 % vs. 0 %, respectively (p = 0.002). The percentage of abnormal thinning increased with higher grades of ONHD for all the parameters evaluated, so that in grade III drusen, values were abnormally reduced in 80 % of eyes in all three analyses. Regarding buried ONHD, 30 % and 4 % of eyes had an abnormally reduced minimum GCIPL and average RNFL thickness, respectively. Furthermore, 26 % of these eyes had abnormal GCIPL exams with a normal or increased RNFL thickness.

CONCLUSIONS

Both RNFL and GCIPL analysis reveal significant thinning in eyes with ONHD directly correlated with drusen severity. In buried ONHD, the abnormality rate was significantly higher with GCIPL compared to RNFL evaluation, suggesting that GCIPL analysis might be an early structural indicator of neuronal loss in the setting of thickened RNFL.

On improving the use of OCT imaging for detecting glaucomatous damage

AIMS

To describe two approaches for improving the detection of glaucomatous damage seen with optical coherence tomography (OCT).

METHODS

The two approaches described were: one, a visual analysis of the high-quality OCT circle scans and two, a comparison of local visual field sensitivity loss to local OCT retinal ganglion cell plus inner plexiform (RGC+) and retinal nerve fibre layer (RNFL) thinning. OCT images were obtained from glaucoma patients and suspects using a spectral domain OCT machine and commercially available scanning protocols. A high-quality peripapillary circle scan (average of 50), a three-dimensional (3D) scan of the optic disc, and a 3D scan of the macula were obtained. RGC+ and RNFL thickness and probability plots were generated from the 3D scans.

RESULTS

A close visual analysis of a high-quality circle scan can help avoid both false positive and false negative errors. Similarly, to avoid these errors, the location of abnormal visual field points should be compared to regions of abnormal RGC+ and RNFL thickness.

CONCLUSIONS

To improve the sensitivity and specificity of OCT imaging, high-quality images should be visually scrutinised and topographical information from visual fields and OCT scans combined.

Multifocal interferometric synthetic aperture microscopy

There is an inherent trade-off between transverse resolution and depth of field (DOF) in optical coherence tomography (OCT) which becomes a limiting factor for certain applications. Multifocal OCT and interferometric synthetic aperture microscopy (ISAM) each provide a distinct solution to the trade-off through modification to the experiment or via post-processing, respectively. In this paper, we have solved the inverse problem of multifocal OCT and present a general algorithm for combining multiple ISAM datasets. Multifocal ISAM (MISAM) uses a regularized combination of the resampled datasets to bring advantages of both multifocal OCT and ISAM to achieve optimal transverse resolution, extended effective DOF and improved signal-to-noise ratio. We present theory, simulation and experimental results.

Handheld optical coherence tomography during sedation in young children with optic pathway gliomas

IMPORTANCE

Monitoring young children with optic pathway gliomas (OPGs) for visual deterioration can be difficult owing to age-related noncompliance. Optical coherence tomography (OCT) measures of retinal nerve fiber layer (RNFL) thickness have been proposed as a surrogate marker of vision but this technique is also limited by patient cooperation.

OBJECTIVE

To determine whether measures of circumpapillary RNFL thickness, acquired with handheld OCT (HH-OCT) during sedation, can differentiate between young children with and without vision loss from OPGs.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional analysis of a prospective observational study was conducted at a tertiary-care children's hospital. Children with an OPG (sporadic or secondary to neurofibromatosis type 1) who were cooperative for visual acuity testing, but required sedation to complete magnetic resonance imaging, underwent HH-OCT imaging of the circumpapillary RNFL while sedated.

MAIN OUTCOMES AND MEASURES

Area under the curve of the receiver operating characteristic, sensitivity, specificity, positive predictive value, and negative predictive value of the average and quadrant-specific RNFL thicknesses.

RESULTS

Thirty-three children (64 eyes) met inclusion criteria (median age, 4.8 years; range, 1.8-12.6 years). In children with vision loss (abnormal visual acuity and/or visual field), RNFL thickness was decreased in all quadrants compared with the normal-vision group (P < .001 for all comparisons). Using abnormal criteria of less than 5% and less than 1%, the area under the curve was highest for the average RNFL thickness (0.96 and 0.97, respectively) compared with specific anatomic quadrants. The highest discrimination and predictive values were demonstrated for participants with 2 or more quadrants meeting less than 5% (sensitivity = 93.3; specificity = 97.9; positive predictive value = 93.3; and negative predictive value = 97.9) and less than 1% (sensitivity = 93.3; specificity = 100; positive predictive value = 100; and negative predictive value = 98.0) criteria.

CONCLUSIONS AND RELEVANCE

Measures of RNFL thickness acquired with HH-OCT during sedation can differentiate between young children with and without vision loss from OPGs. For young children who do not cooperate with vision testing, HH-OCT measures may be a surrogate marker of vision. Longitudinal studies are needed to delineate the temporal relationship between RNFL decline and vision loss.

Correlation of retinal nerve fiber layer thickness and visual fields in glaucoma: a broken stick model

PURPOSE

To determine the retinal nerve fiber layer (RNFL) thickness at which visual field (VF) damage becomes detectable and associated with structural loss.

DESIGN

Retrospective cross-sectional study.

METHODS

Eighty-seven healthy and 108 glaucoma subjects (1 eye per subject) were recruited from an academic institution. All patients had VF examinations (Swedish Interactive Threshold Algorithm 24-2 test of the Humphrey Visual Field Analyzer 750i) and spectral-domain optical coherence tomography RNFL scans. Comparison of RNFL thickness values with VF threshold values showed a plateau of VF threshold values at high RNFL thickness values and then a sharp decrease at lower RNFL thickness values. A broken stick statistical analysis was used to estimate the tipping point at which RNFL thickness values are associated with VF defects. The slope for the association between structure and function was computed for data above and below the tipping point.

RESULTS

The mean RNFL thickness value that was associated with initial VF loss was 89 μm. The superior RNFL thickness value that was associated with initial corresponding inferior VF loss was 100 μm. The inferior RNFL thickness value that was associated with initial corresponding superior VF loss was 73 μm. The differences between all the slopes above and below the aforementioned tipping points were statistically significant (P < .001).

CONCLUSIONS

In open-angle glaucoma, substantial RNFL thinning or structural loss appears to be necessary before functional visual field defects become detectable.

Prevalence of myelinated retinal nerve fibres in adult Indians: the Central India Eye and Medical Study

PURPOSE

To determine the prevalence of myelinated retinal nerve fibers in the adult Indian population.

METHODS

The Central India Eye and Medical Study performed in rural Central India included 4711 participants aged 30+ years. The participants underwent a detailed ophthalmic and medical examination.

RESULTS

Readable fundus photographs were available for 8645 eyes of 4485 (95.2%) subjects. Myelinated retinal nerve fibers were detected in 52 eyes (46 subjects) with a prevalence rate of 0.58±0.08 per 100 eyes [95% confidence interval (CI): 0.42, 0.74] and 1.03±0.15 per 100 subjects (95%CI: 0.73, 1.32). Prevalence of myelinated retinal nerve fibers was significantly associated hyperopic refractive error (p=0.008; OR: 1.31; 95%CI: 1.07, 1.59). It was not significantly associated with age (p=0.11), best corrected visual acuity (logMAR; p=0.33), intraocular pressure (p=0.09), amount of nuclear cataract (p=0.93), optic disc area (p=0.60), presence of glaucomatous optic nerve atrophy (p=0.62), and early age-related macular degeneration (p=0.53).

CONCLUSIONS

Myelinated retinal nerve fibers are present in about 10 out of 1000 adult Indians in rural Central India, with a higher prevalence in hyperopic eyes. Prevalence of myelinated retinal nerve fibers was not associated with age, visual acuity, glaucoma and macular degeneration.

Probabilistic intra-retinal layer segmentation in 3-D OCT images using global shape regularization

With the introduction of spectral-domain optical coherence tomography (OCT), resulting in a significant increase in acquisition speed, the fast and accurate segmentation of 3-D OCT scans has become evermore important. This paper presents a novel probabilistic approach, that models the appearance of retinal layers as well as the global shape variations of layer boundaries. Given an OCT scan, the full posterior distribution over segmentations is approximately inferred using a variational method enabling efficient probabilistic inference in terms of computationally tractable model components: Segmenting a full 3-D volume takes around a minute. Accurate segmentations demonstrate the benefit of using global shape regularization: We segmented 35 fovea-centered 3-D volumes with an average unsigned error of 2.46 ± 0.22 μm as well as 80 normal and 66 glaucomatous 2-D circular scans with errors of 2.92 ± 0.5 μm and 4.09 ± 0.98 μm respectively. Furthermore, we utilized the inferred posterior distribution to rate the quality of the segmentation, point out potentially erroneous regions and discriminate normal from pathological scans. No pre- or postprocessing was required and we used the same set of parameters for all data sets, underlining the robustness and out-of-the-box nature of our approach.

Multiple-object geometric deformable model for segmentation of macular OCT

Optical coherence tomography (OCT) is the de facto standard imaging modality for ophthalmological assessment of retinal eye disease, and is of increasing importance in the study of neurological disorders. Quantification of the thicknesses of various retinal layers within the macular cube provides unique diagnostic insights for many diseases, but the capability for automatic segmentation and quantification remains quite limited. While manual segmentation has been used for many scientific studies, it is extremely time consuming and is subject to intra- and inter-rater variation. This paper presents a new computational domain, referred to as flat space, and a segmentation method for specific retinal layers in the macular cube using a recently developed deformable model approach for multiple objects. The framework maintains object relationships and topology while preventing overlaps and gaps. The algorithm segments eight retinal layers over the whole macular cube, where each boundary is defined with subvoxel precision. Evaluation of the method on single-eye OCT scans from 37 subjects, each with manual ground truth, shows improvement over a state-of-the-art method.

Ganglion cell layer-inner plexiform layer thickness and vision loss in young children with optic pathway gliomas

PURPOSE

To determine if measures of macular ganglion cell layer-inner plexiform layer (GCL-IPL) thickness can discriminate between children with and without vision loss (visual acuity or field) from their optic pathway glioma (OPG) using spectral-domain optical coherence tomography (SD-OCT).

METHODS

Children with OPGs (sporadic or secondary to neurofibromatosis type 1) enrolled in a prospective study of SD-OCT were included if they were cooperative for vision testing and macular SD-OCT images were acquired. Manual segmentation of the macular GCL-IPL and macular retinal nerve fiber layer (RNFL) was performed using elliptical annuli with diameters of 1.5, 3.0, and 4.5 mm. Logistic regression assessed the ability of GCL-IPL and RNFL thickness measures (micrometers) to differentiate between the normal and abnormal vision groups.

RESULTS

Forty-seven study eyes (normal vision = 31, abnormal vision = 16) from 26 children with OPGs were included. Median age was 5.3 years (range, 2.5-12.8). Thickness of all GCL-IPL and RNFL quadrants differed between the normal and abnormal vision groups (P < 0.01). All GCL-IPL measures demonstrated excellent discrimination between groups (area under the curve [AUC] > 0.90 for all diameters). Using the lower fifth percentile threshold, the number of abnormal GCL-IPL inner macula (3.0 mm) quadrants achieved the highest AUC (0.989) and was greater than the macula RNFL AUCs (P < 0.05).

CONCLUSIONS

Decreased GCL-IPL thickness (<fifth percentile) can discriminate between children with and without vision loss from their OPG. Ganglion cell layer-inner plexiform layer thickness could be used as a surrogate marker of vision in children with OPGs.

Retinal nerve fibre layer thickness measured by Spectralis spectral-domain optical coherence tomography: The Beijing Eye Study

PURPOSE

The aim of this study was to measure retinal nerve fibre layer thickness (RNFLT) and its associated factors in a population-based setting.

METHODS

The population-based Beijing Eye Study 2011 included 3468 individuals. The study participants underwent spectral-domain optical coherence tomography (Spectralis(®) ; Spectralis OCT)-assisted measurement of the RNFLT. For this study, exclusion criteria were glaucoma, pseudoexfoliation, best-corrected visual acuity of >0.5 logMAR, macular diseases, previous ocular surgery and known neurological diseases. The only inclusion criterion was an age of 50+ years.

RESULTS

The inclusion criteria were fulfilled by 2548 participants. Mean RNFLT was 102 ± 11 μm. RNFLT was significantly (p < 0.001) thicker in the temporal inferior sector (153 ± 21 μm) than in the temporal superior sector (138 ± 21 μm), nasal inferior sector (118 ± 24 μm), nasal superior sector (106 ± 21 μm), temporal sector (76 ± 13 μm) and nasal sector (73 ± 15 μm). The mean intereye difference in RNFLT was 4.4 ± 6.0 μm. In multivariate analysis, thicker RNFLT was associated with younger age (p < 0.001), female gender (p < 0.001), urban region (p = 0.003), larger optic disc size (p < 0.001), larger neuroretinal rim area (p < 0.001), hyperopic refractive error (p < 0.001), larger beta zone of parapapillary atrophy (p = 0.008) and thicker subfoveal choroidal thickness (p = 0.02). RNFLT decreased by about 0.2 μm (0.2%) per year of life and by 1 μm (1%) per dioptre of myopia.

CONCLUSION

Mean RNFLT (measured by Spectralis(®) OCT; 102 ± 11 μm) was associated with younger age, female gender, urban region of habitation, larger optic disc, larger rim, hyperopic refractive error, larger parapapillary beta zone and thicker subfoveal choroidal thickness. Independent of age and refractive error, the RNFL was thickest temporal inferiorly and thinnest temporally and nasally.

Anterior-segment imaging for assessment of glaucoma

This article summarizes the physics, technology and clinical application of ultrasound biomicroscopy (UBM) and optical coherence tomography (OCT) for assessment of the anterior segment in glaucoma. UBM systems use frequencies ranging from approximately 35 to 80 MHz, as compared with typical 10-MHz systems used for general-purpose ophthalmic imaging. OCT systems use low-coherence, near-infrared light to provide detailed images of anterior segment structures at resolutions exceeding that of UBM. Both technologies allow visualization of the iridocorneal angle and, thus, can contribute to the diagnosis and management of glaucoma. OCT systems are advantageous, being noncontact proceedures and providing finer resolution than UBM, but UBM systems are superior for the visualization of retroiridal structures, including the ciliary body, posterior chamber and zonules, which can provide crucial diagnostic information for the assessment of glaucoma.

Correlation between retinal vessel density profile and circumpapillary RNFL thickness measured with Fourier-domain optical coherence tomography

AIM

To assess circumpapillary retinal vessel density (RVD) profiles and correlate them with retinal nerve fibre layer (RNFL) thickness measured by Fourier domain optical coherence tomography (FD-OCT).

METHODS

RNFL thickness of 106 healthy volunteers was measured using Cirrus FD-OCT. A proprietary software was developed in MATLAB to assess the thickness and position of circumpapillary retinal vessels using the scanning laser ophthalmoscopy fundus image, centred on the optic disc. The individual retinal vessel positions and thickness values were integrated in a 256-sector RVD profile, and intrasubject and intersubject correlations were calculated.

RESULTS

The mean value ± SD for intrasubject correlation between RVD and RNFL was 0.5349 ± 0.1639, with 101 of 106 subjects presenting significant correlation (p<0.05). 181 (out of 256) sectors presented a significant correlation between RVD and RNFL, with a mean value ± SD of 0.2600 ± 0.1140 (p<0.05).

CONCLUSIONS

Using our model of the circumpapillary retinal vessel distribution, 70% of the RNFL thickness is influenced by RVD. On average, 7% of the interindividual variance of the RNFL thickness may be explained by RVD. A normative database that takes into account the circumpapillary blood vessels might slightly improve the diagnostic power of RNFL measurement.

Parafoveal retinal vascular response to pattern visual stimulation assessed with OCT angiography

We used optical coherence tomography (OCT) angiography with a high-speed swept-source OCT system to investigate retinal blood flow changes induced by visual stimulation with a reversing checkerboard pattern. The split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was used to quantify blood flow as measured with parafoveal flow index (PFI), which is proportional to the density of blood vessels and the velocity of blood flow in the parafoveal region of the macula. PFI measurements were taken in 15 second intervals during a 4 minute period consisting of 1 minute of baseline, 2 minutes with an 8 Hz reversing checkerboard pattern stimulation, and 1 minute without stimulation. PFI measurements increased 6.1±4.7% (p = .001) during the first minute of stimulation, with the most significant increase in PFI occurring 30 seconds into stimulation (p<0.001). These results suggest that pattern stimulation induces a change to retinal blood flow that can be reliably measured with OCT angiography.

The Heidelberg retina tomograph ancillary study to the European glaucoma prevention study: study design and baseline factors

PURPOSE

To describe the study design and baseline factors of the Heidelberg Retina Tomograph ancillary study within the EGPS. Furthermore, to examine the relationship between HRT optic disc topographic measurements and baseline demographic and ocular factors.

METHODS

Four hundred and eighty-nine ocular hypertensive participants were included. Each participant completed HRT imaging at least annually. The associations between HRT measurements and IOP, central corneal thickness (CCT), baseline photographic estimates of vertical CDR ratio (CDR), asymmetry between the two eyes in CDR ratio and baseline visual field indices were assessed using regression analysis.

RESULTS

Associations between HRT measurements and vertical CDR by photographs were found for almost all stereometric optic disc parameters in both univariate and multivariate analysis. The strongest association was found between vertical CDR measurements and disc, cup and rim area; cup and rim volume, CDR area, linear CDR, mean and maximum cup depth and cup shape measure (all p < 0.0001). In multivariate analysis, pattern standard deviation (PSD) and HRT disc area had significant associations with several HRT optic disc measurements. Furthermore, CCT was significantly associated with reference height and the glaucoma probability score (GPS, outside normal limits).

CONCLUSIONS

The EGPS is the first multicentre, placebo-controlled randomized clinical trial to use HRT for monitoring optic disc changes in participants with ocular hypertension. We found strong associations between stereophotographic vertical CDR estimates, HRT disc area, PSD and several HRT parameters. We found, furthermore, that the parameters reference height and GPS were significantly related to central corneal thickness.

Quantification of retinal nerve fiber layer thickness using spectral domain optical coherence tomography in normal Indian population

The purpose of this study was to measure peripapillary retinal nerve fiber layer thickness (RNFLT) using spectral domain optical coherence tomography (SD-OCT) in normal Indian eyes, for which, 210 normal volunteers were recruited. One eye of each subject underwent RNFL scanning at 3.4 mm circle diameter around optic nerve using SD OCT. The data were analyzed to determine RNFLT in the sample population and its variation with age and gender. The average peripapillary RNFLT was 114.03 ± 9.59 μm. There was no effect of gender on RNFLT parameters. Age had significant negative correlation with average (P = 0.005), superior (P = 0.04), temporal (P = 0.049), and nasal quadrants (P = 0.01) RNFLT. Inferior quadrant RNFLT also had a negative correlation with age, but it was not statistically significant (P = 0.15).