Peripapillary nerve fiber layer thickness profile determined with high speed, ultrahigh resolution optical coherence tomography high-density scanning

Effect of magnification error and axial length on circumpapillary capillary density and retinal nerve fiber layer thickness

This study aimed to evaluate the effect of magnification error and axial length (AL) on circumpapillary capillary density (cpCD) and circumpapillary retinal nerve fiber layer thickness (cpRNFLT) in healthy eyes. Seventy-two healthy eyes of 72 subjects with AL 24.7 ± 1.5 mm (range: 20.9-28.0 mm) were enrolled in this retrospective cross-sectional study and underwent optical coherence tomography angiography scanning. Magnification corrected measurement areas were obtained using AL upon which corrected cpCD, cpRNFLT values were determined. Relationships between AL and the percentage difference between corrected and uncorrected values (ΔcpCD, ΔcpRNFLT) as well as the effect of AL on magnification corrected cpCD, cpRNFLT were evaluated. ΔcpCD significantly increased with AL in the global, inferior nasal and superior nasal sectors (all p < 0.001). ΔcpRNFLT significantly increased with AL in global and all sectors (all p < 0.001) and the correlations were significantly stronger than that of ΔcpCD-AL in all sectors (all p < 0.001). Corrected cpCD did not associate with AL while corrected cpRNFLT demonstrated a significant positive association with AL in the global (p = 0.005) and temporal sector (p < 0.001). Magnification error led to a significant underestimation of cpCD in eyes with longer AL although its underestimation and the effect of AL was smaller in comparison to that of cpRNFLT.

Deep Optic Nerve Head Structures Associated With Increasing Axial Length in Healthy Myopic Eyes of Moderate Axial Length

PURPOSE

To elucidate which swept-source optical coherence tomography (OCT)-derived optic nerve head (ONH) parameters are associated with longer axial length (AXL) in healthy myopic eyes.

DESIGN

Prospective cross-sectional observational study.

METHODS

Two hundred eleven healthy eyes of 140 participants (96 emmetropic-mild myopic [AXL: 22.2-24.5 mm], 83 moderately myopic [24.5-26.0 mm], and 32 highly myopic [26.0-27.4 mm] eyes) were enrolled. Bruch membrane opening (BMO), anterior scleral canal opening (ASCO) area and ovality, minimum rim width, parameters defining misalignment between the BMO and ASCO planes, OCT-defined region of perineural canal retinal epithelium atrophy and externally oblique choroidal border tissue, circumpapillary retinal nerve fiber layer thickness (cpRNFLT), circumpapillary choroidal thickness (cpChT), lamina cribrosa parameters, and peripapillary scleral (PPS) angle were calculated from BMO-centered radial scans reconstructed from 3D raster scans. Multivariate linear mixed models were used to elucidate ONH parameters that are independently associated with AXL.

RESULTS

Longer AXL was associated with a greater misalignment between ASCO and BMO planes, larger region of externally oblique choroidal border tissue, thinner cpChT, larger PPS angle, larger ASCO area, and thicker cpRNFLT (all P < .040 after Bonferroni's correction for number of included explanatory variables).

CONCLUSIONS

A greater misalignment between BMO and ASCO planes, thinner choroid, a more posteriorly bowed PPS, an enlargement of ASCO, and thicker cpRNFLT were each associated with longer AXL. An enhanced understanding of these AXL-associated configurations should provide essential information to improve our ability to detect glaucoma-induced ONH morphology in myopic eyes.

Wide-field optical coherence tomography deviation map for early glaucoma detection

BACKGROUND/AIMS

This study aimed to establish a wide-field optical coherence tomography (OCT) deviation map obtained from swept-source OCT (SS-OCT) scans. Moreover, it also aimed to compare the diagnostic ability of this wide-field deviation map with that of the peripapillary and macular deviation maps currently being used for the detection of early glaucoma (EG).

METHODS

Four hundred eyes, including 200 healthy eyes and 200 eyes with EG were enrolled in this retrospective observational study. Patients underwent a comprehensive ocular examination, including wide-field SS-OCT (DRI-OCT Triton; Topcon, Tokyo, Japan). The individual wide-field scan was converted into a uniform template using the fovea and optic disc centres as fixed landmarks. Subsequently, the wide-field deviation map was obtained via the comparison between individual wide-field data and a normative wide-field database that had been created by combining images of healthy eyes into a uniform template in a previous study. The ability of the new wide-field deviation map to distinguish between EG and healthy eyes was assessed by comparing it with conventional deviation maps based on the area under the receiver operating characteristic curve (AUC).

RESULTS

The wide-field deviation map obtained using the normative wide-field database showed the highest diagnostic ability for the diagnosis of EG (AUC=0.980 and 961 for colour-coded pixels presenting <5% and <1%, respectively) among various deviation maps. Its AUC was significantly superior to that of most conventional deviation maps (p<0.05). The wide-field deviation map demonstrated early structural glaucomatous damage well over a wider area.

CONCLUSION

The wide-field SS-OCT deviation map exhibited good performance for distinguishing between eyes with EG and healthy eyes. The visualisation of the wider damaged area on the wide-field deviation map could be useful for the diagnosis of EG in clinical settings.

Associations Between Diabetic Retinal Microvasculopathy and Neuronal Degeneration Assessed by Swept-Source OCT and OCT Angiography

Purpose: To provide clinical evidence of the associations between retinal neuronal degeneration and microvasculopathy in diabetic retinopathy (DR). Methods: This case-control study included 76 patients (76 eyes) with type 2 diabetes mellitus (DM), and refraction error between -3.0 and +3.0 D. The eyes were assigned into DM (without DR), non-proliferative DR (NPDR), and proliferative DR (PDR) groups. Age-, sex-, and refractive error-matched normal subjects were enrolled as controls. The mean retinal thickness (mRT), the relative mean thickness of the retinal nerve fiber layer (rmtRNFL, mtRNFL/mRT), ganglion cell layer (rmtGCL), ganglion cell complex (rmtGCC) layer, foveal avascular zone area (FAZa), FAZ perimeter (FAZp), FAZ circularity index (FAZ-CI), and vessel density (VD) in superficial capillary plexus (SCP) and deep capillary plexus (DCP) were assessed by swept-source optical coherence tomography (OCT) and OCT angiography (OCTA). Group comparison and Spearman's partial correlation coefficient analysis were applied to evaluate the correlation between these morphological parameters. Results: rmtRNFL, FAZa, and FAZp in SCP and DCP increased with the DR severity (p _rmtRNFL < 0.001; p _{FAZa, SCP} = 0.001; p _FAZa , _DCP = 0.005; p _FAZp , _SCP < 0.001; p _FAZp , _DCP < 0.001). The rmtGCL, FAZ-CI in SCP and DCP, and VD in DCP decreased with the DR severity (p _rmtGCL = 0.002, p _FAZ-CI , _SCP = 0.002; p _{FAZ-CI, DCP} < 0.001, p _VD , _DCP < 0.001). After controlling age, sex, duration of diabetes, and hypertension, the rmtRNFL, FAZa in SCP and DCP, and FAZp in SCP and DCP were correlated with the severity of DR (p < 0.05), while VD in SCP and DCP, FAZ-CI, and rmtGCL were negatively correlated with the severity of DR (p < 0.05). The rmtGCL was negatively correlated with the FAZa in SCP (r = -0.34, p = 0.002) and DCP (r = -0.23, p = 0.033), and FAZp in SCP (r = -0.37, p = 0.001) and DCP (r = -0.32, p = 0.003), but positively correlated with VD in SCP (r = 0.26, p = 0.016), VD in DCP (r = 0.28, p = 0.012), and FAZ-CI in DCP (r = 0.31, p = 0.006). Conclusions: rmtRNFL, FAZ-CI in SCP and DCP, and FAZp in SCP are strong predictors of the severity of DR. The ganglion cell body loss is highly correlated with increased FAZp and FAZa, decreased FAZ-CI, and reduced VD with the severity of DR.

Automatic detection of papilledema through fundus retinal images using deep learning

Papilledema is a syndrome of the retina in which retinal optic nerve is inflated by elevation of intracranial pressure. The papilledema abnormalities such as retinal nerve fiber layer (RNFL) opacification may lead to blindness. These abnormalities could be seen through capturing of retinal images by means of fundus camera. This paper presents a deep learning-based automated system that detects and grades the papilledema through U-Net and Dense-Net architectures. The proposed approach has two main stages. First, optic disc and its surrounding area in fundus retinal image are localized and cropped for input to Dense-Net which classifies the optic disc as papilledema or normal. Second, consists of preprocessing of Dense-Net classified papilledema fundus image by Gabor filter. The preprocessed papilledema image is input to U-Net to achieve the segmented vascular network from which the vessel discontinuity index (VDI) and vessel discontinuity index to disc proximity (VDIP) are calculated for grading of papilledema. The VDI and VDIP are standard parameter to check the severity and grading of papilledema. The proposed system is evaluated on 60 papilledema and 40 normal fundus images taken from STARE dataset. The experimental results for classification of papilledema through Dense-Net are much better in terms of sensitivity 98.63%, specificity 97.83%, and accuracy 99.17%. Similarly, the grading results for mild and severe papilledema classification through U-Net are also much better in terms of sensitivity 99.82%, specificity 98.65%, and accuracy 99.89%. The deep learning-based automated detection and grading of papilledema for clinical purposes is first effort in state of art.

A Wide-Field Optical Coherence Tomography Normative Database Considering the Fovea-Disc Relationship for Glaucoma Detection

Purpose

One purpose of this study was to collect wide-field swept-source optical coherence tomography (SS-OCT) data from healthy eyes and build a wide-filed normative database. Another purpose was to compare the glaucoma diagnostic ability of new parameters based on this normative database to the parameters that are currently in use, such as the peripapillary retinal nerve fiber layer (RNFL), macular ganglion cell-inner plexiform layer, and ganglion cell complex (GCC) thickness.

Methods

This study had 220 healthy eyes and 292 eyes with early-stage glaucoma (EG) and moderate-stage glaucoma (MG) enrolled. Using the wide-field SS-OCT images (12 × 9 mm) of healthy eyes, a wide-field normative database was constructed by transforming and combining the individual images into a uniform template using the fovea and optic disc centers as fixed landmarks. Adjustment for the disc size was conducted. With this normative database, new parameters based on the ratio of the fovea-disc distance (FDD) consisting of the fovea-disc relationship were evaluated. The glaucoma diagnostic ability was assessed based on the area under the receiver operating characteristic curve (AUC).

Results

Among the new peripapillary parameters, the RNFL of the circumference of the circle with diameter 0.8 FDD showed the highest AUC value for EG and MG, but the value was not significantly superior to that of the initial RNFL (AUC = 0.940 vs. 0.937, P = 0.631). Among the macular parameters, the GCC of the area of the circle of 1.5 FDD showed the highest AUC value for EG and MG, and the value was significantly superior to that of initial GCC (AUC = 0.929 vs. 0.919, P = 0.033). However, there was no significant difference between the initial and adjusted GCC thickness in patients included in the EG or MG groups separately.

Conclusions

A wide-field normative database was built to consider the relationship between the fovea and the optic disc. Considering this aspect, we found that the GCC analysis using a broader area presented a significantly greater glaucoma diagnostic performance for EG and MG in the macula than the initial parameter for the GCC.

Translational Relevance

Based on this wide-field normative database, the clinical use of a wide-field deviation map may help diagnose the patients with EG and MG in the future.

Effect of optic disc-fovea distance on the normative classifications of macular inner retinal layers as assessed with OCT in healthy subjects

Purpose

To determine the influence of the optic disc–fovea distance (DFD) on the normative classifications based on thickness measurements of macular inner retinal layers with spectral-domain optical coherence tomography (OCT) in healthy subjects.

Methods

A total of 182 eyes from 182 healthy subjects were included (mean (SD) spherical equivalent −0.8 (1.9) dioptres). We performed macula and optic disc imaging with the Topcon 3D OCT 2000. The thickness of the macular inner retinal layers (macular retinal nerve fibre layer (mRNFL), ganglion cell-inner plexiform layer (GCIPL) and both combined (ganglion cell complex; GCC)) and the corresponding classifications based on the built-in normative database were recorded. The occurrence of an abnormal normative classification (occurrence of any thickness variable below the fifth percentile) was related to the DFD and other factors (axial length/refraction, optic disc area, fovea–disc angle, age, gender, image quality, visual field mean deviation and peripapillary retinal nerve fibre layer thickness), using logistic regression.

Results

The mean (SD) DFD was 4.90 (0.29) mm. A greater DFD was associated with a higher percentage of abnormal normative classification in the OCT parameters describing the thickness of the mRNFL (OR (95%CI) per 0.1 mm increase in DFD: 1.30 (1.13 to 1.50), p<0.001), GCIPL (1.18 (1.02 to 1.38), p=0.023) and GCC measurement (1.29 (1.08 to 1.55), p=0.006).

Conclusions

Eyes with a greater DFD are prone to false-positive classifications in the thickness assessment of the macular inner retinal layers. The thicknesses should always be interpreted in the context of DFD.

Influence of optic disc-fovea distance on macular thickness measurements with OCT in healthy myopic eyes

Assessment of macular thickness is important in the evaluation of various eye diseases. This study aimed to determine the influence of the optic disc-fovea distance (DFD) on macular thickness in myopic eyes. We determined the DFD and the macular thickness in 138 eyes from 138 healthy myopic subjects using the Cirrus HD-OCT. Correlation analysis and multiple linear regression were performed to determine the influence of DFD, axial length, disc area, and β-PPA on macular thickness. To further remove the confounding effect of ocular magnification on the DFD and OCT scan area, a subgroup analysis was performed in eyes with a limited axial length range (24-25 mm). DFD was significantly correlated with both regional (central, inner, and outer ETDRS subfields) and overall average macular thickness at a Bonferroni corrected P value of 0.004 (r ranging from -0.27 to -0.47), except for the temporal outer (r = -0.15, P = 0.089) and inferior outer (r = -0.22, P = 0.011) macular thickness. In the multivariable analysis, DFD was significantly associated with the average inner and outer macular thickness, the central subfield thickness, and the overall macular thickness (all P < 0.001), independent of ocular magnification and other covariates. Our findings indicate that eyes with a greater DFD have a lower macular thickness.

EFFECT OF OPTIC DISK-FOVEA DISTANCE ON MEASUREMENTS OF INDIVIDUAL MACULAR INTRARETINAL LAYERS IN NORMAL SUBJECTS

PURPOSE

To investigate the effect of optic disk-fovea distance (DFD) on measurements of macular intraretinal layers using spectral domain optical coherence tomography in normal subjects.

METHODS

One hundred and eighty-two eyes from 182 normal subjects were imaged using spectral domain optical coherence tomography. The average thicknesses of eight macular intraretinal layers were measured using an automatic segmentation algorithm. Partial correlation test and multiple regression analysis were used to determine the effect of DFD on thicknesses of intraretinal layers.

RESULTS

Disk-fovea distance correlated negatively with the overall average thickness in all the intraretinal layers (r ≤ -0.17, all P ≤ 0.025) except the ganglion cell layer and photoreceptor. In multiple regression analysis, greater DFD was associated with thinner nerve fiber layer (6.78 μm decrease per each millimeter increase in DFD, P < 0.001), thinner ganglion cell-inner plexiform layer (2.16 μm decrease per each millimeter increase in DFD, P = 0.039), thinner ganglion cell complex (8.94 μm decrease per each millimeter increase in DFD, P < 0.001), thinner central macular thickness (18.16 μm decrease per each millimeter increase in DFD, P < 0.001), and thinner total macular thickness (15.94 μm decrease per each millimeter increase in DFD, P < 0.001).

CONCLUSION

Thinner measurements of macular intraretinal layers were significantly associated with greater DFD. A clinical assessment of macular intraretinal layers in the evaluation of various macular diseases should always be interpreted in the context of DFD.

Noninvasive methods of detecting increased intracranial pressure

The detection of elevated intracranial pressure (ICP) is of paramount importance in the diagnosis and management of a number of neurologic pathologies. The current gold standard is the use of intraventricular or intraparenchymal catheters; however, this is invasive, expensive, and requires anesthesia. On the other hand, diagnosing intracranial hypertension based on clinical symptoms such as headaches, vomiting, and visual changes lacks sensitivity. As such, there exists a need for a noninvasive yet accurate and reliable method for detecting elevated ICP. In this review, we aim to cover both structural modalities such as computed tomography (CT), magnetic resonance imaging (MRI), ocular ultrasound, fundoscopy, and optical coherence tomography (OCT) as well as functional modalities such as transcranial Doppler ultrasound (TCD), visual evoked potentials (VEPs), and near-infrared spectroscopy (NIRS).

Does the Stage of Keratoconus Affect Optical Coherence Tomography Measurements?

PURPOSE

To employ optical coherence tomography (OCT) to examine the relationship of changes in the retinal nerve fiber layer (RNFL) and macular thickness as well as ganglion cell (GC) parameters with the stage of keratoconus (KC), and to compare these changes with a control group.

METHODS

A total of 84 eyes of 68 patients with KC and 29 eyes of 29 normal age-matched subjects underwent RNFL, macular thickness measurements, and ganglion cell analysis using Cirrus high-definition (HD) OCT. Patients with KC were classified according to the Amsler-Krumeich Classification. The measurements were analyzed in all quadrants for each KC stage and compared with control subjects.

RESULTS

All RNFL, macular thickness, and ganglion cell parameters varied significantly among the groups (all p<0.001, analysis of variance). An increase in the stage of KC was correlated with decreased RNFL thickness, macular thickness, and ganglion cell parameters.

CONCLUSIONS

RNFL, macular thicknesses, and ganglion cell parameters in all KC stages were lower than those in the control group. The RNFL, macular thickness, and ganglion cell parameters of the Grade 1 KC group were most similar to those of the control group. The severity of irregular astigmatism at the same stages of KC had a significant effect on OCT measurements. It may therefore be beneficial to know the amount of change/deviation in OCT measurements in keratoconus patients and to report which parameters exceed the standards so that OCT can be used to correlate the stage of keratoconus with the extent of the ocular disorder.

Outer Retinal Structural Alternation and Segmentation Errors in Optical Coherence Tomography Imaging in Patients With a History of Retinopathy of Prematurity

PURPOSE

To evaluate retinal anatomy and segmentation errors from spectral-domain optical coherence tomography (SD-OCT) imaging in school-aged children.

DESIGN

A prospective cohort study in a referral medical center.

METHODS

One hundred thirty-three eyes of 133 patients were enrolled. Patients were grouped as those who were treated for retinopathy of prematurity (ROP) (ROP-Tx group); those with spontaneously regressed ROP (ROP-non-Tx group); other premature patients (premature group); and full-term age-matched children (full-term group). Anatomy and segmentation errors of retina were evaluated by SD-OCT.

RESULTS

The mean age at assessment was 9.5 years (range, 4-16 years). The external limiting membrane (ELM) and the cone outer segment tips (COST) line were least frequently identified in patients of the ROP-Tx group (65.2% and 47.8%, P = .002 and P < .001, respectively). The visual acuity of the patients did not correlate significantly with the absence of COST line (P = .140) but correlated with the absence of ELM (P < .001). The presence of artifacts, including misidentification of the inner retina, misidentification of the outer retina, out-of-register artifacts, off-center scans, and degraded scan images, was observed to range from 0.6% to 50.0% in 4 groups of patients. All types of errors occurred more frequently in the ROP-Tx group than in the full-term group (all P < .05).

CONCLUSIONS

Outer retinal abnormalities were commonly observed in the ROP-Tx group. The higher segmentation errors in the ROP-Tx group might be related to fine structural abnormalities in the outer retina. Future studies are needed to investigate the mechanisms for these structural changes.

Helvacioglu reproducibility index: a new algorithm to evaluate the effects of misalignments on the measurements of retinal nerve fiber layer by spectral-domain OCT

AIM

To evaluate the effect of misalignment on the measurements of retinal nerve fiber layer (RNFL) by spectral-domain optical coherence tomography (OCT).

METHODS

A total of 42 eyes from 21 healthy young subjects underwent RNFL measurements with RTVue spectral-domain OCT (Optovue Inc., Fremont, California, USA). Two baseline measurements with perfectly aligned central circle to the borders of the optic nerve and four misaligned measurements which were misaligned towards to four quadrants were taken. The differences in RNFL between the baseline and misaligned measurements were analyzed with a new algorithm called Helvacioglu reproducibility index (HRI) which is designed to measure the reproducibility of the scans by evaluating the RNFL changes in the four main quadrants.

RESULTS

The average RNFL scores of the first two baseline measurements have good correlation (c=0.930) and good reproducibility scores (0.15±0.07). Superior misaligned measurements had significantly lower superior quadrant score and higher inferior quadrant score, similar nasal and little higher temporal scores (P1, P2<0.001, P3=0.553, P4=0.001). Inferior misaligned measurements had significantly higher superior quadrant score and lower inferior quadrant score with similar temporal and little lower nasal scores (P1, P2<0.001, P3=0.315, P4=0.016). Nasal misaligned measurements had significantly higher temporal quadrant score and lower nasal quadrant score with little lower superior and inferior scores (P1, P2, P4<0.001, P3=0.005). Temporal misaligned measurements had significantly higher nasal quadrant score and lower temporal quadrant score with similar superior and little higher inferior scores (P1, P2<0.001, P3=0.943, P4=0.001).

CONCLUSION

Good alignment of the central circle to the borders of optic nerve is crucial to have correct and repeatable RNFL measurements. Misalignment to a quadrant resulted in falsely low readings at that quadrant and falsely high readings at the opposite quadrant.

Influence of disc area on retinal nerve fiber layer thickness measurement by spectral domain optical coherence tomography

BACKGROUND

To examine the effect of optic disc area on peripapillary RNFLT (retinal nerve fiber layer thickness) measurement at circle diameter of 3.4 mm around optic nerve head using spectral OCT/SLO (Optical coherence tomography/scanning laser ophthalmoscope).

MATERIALS AND METHODS

In this prospective, cross sectional study, one hundred and two eyes of 102 normal subjects underwent RNFLT and disc area measurement using spectral OCT/SLO. Based on disc area, subjects were divided into three groups i.e., <3 mm2 (32 eyes), 3-4 mm2 (36 eyes) and >4 mm2 (34 eyes). The effect of disc area on RNFLT parameters was analyzed using linear regression analysis.

RESULTS

The mean and quadrant RNFLT did not show significant correlation with disc area in subjects with disc area of <4 mm2, however in eyes with disc area >4 mm2, average RNFLT, superior and temporal quadrant RNFLT showed negative correlation with disc area, which was statistically significant (P = 0.004, P = 0.005 and P = 0.002, respectively).

CONCLUSION

In healthy eyes of disc area <4 mm2, disc size does not appear to affect peripapillary RNFLT measurement by spectral OCT/SLO. Average, superior and temporal quadrant RNFLT measurements were inversely proportional to disc area in eyes with disc area >4 mm2. Hence, RNFLT measurement by OCT in eyes with optic disc area of >4 mm2 should be interpreted carefully.

Effects of rigid contact lenses on optical coherence tomographic parameters in eyes with keratoconus

BACKGROUND

The aim was to evaluate the effect of irregular astigmatism on the retinal nerve fibre layer (RNFL), macular thickness and ganglion cell analysis obtained by spectral domain optical coherence tomography (OCT) in eyes with keratoconus.

METHODS

Fifty-two eyes of 31 patients (20 females) with keratoconus that required correction of irregular astigmatism with rigid gas-permeable (RGP) contact lenses were included to this study. The average, superior, nasal, inferior, temporal and 12 clock hour sector's RNFL, ganglion cell and macular thickness analyses before and 30 minutes after RGP contact lens (Rose K2 -Menicon Z material, David Thomas Contact Lenses Ltd, Northampton, United Kingdom) wear were performed to all patients with Cirrus HD spectral domain optical coherence tomography.

RESULTS

The average thickness of the retinal nerve fibre layer, the thickness at the nasal quadrants and 1-2-3-4 o'clock hour sectors and mean signal strength were increased significantly by RGP contact lens wearing independent of the stage of keratoconus. Central sub-field thickness increased after correction with RGP contact lens (p = 0.037). After wearing RGP contact lenses, changes on ganglion cell analysis were not significant (all p values ≥ 0.111).

CONCLUSIONS

OCT is a widely used device for retinal nerve fibre layer and macular thickness evaluation in patients with glaucoma and macular diseases. The study demonstrates that OCT parameters such as retinal nerve fibre layer, central sub-field thickness and mean signal strength are affected by irregular astigmatism. Correction of irregular astigmatism with RGP contact lenses should be recommended before analysing keratoconic eyes to obtain optimum results on OCT measurements.

Diagnostic specificities of retinal nerve fiber layer, optic nerve head, and macular ganglion cell-inner plexiform layer measurements in myopic eyes

PURPOSE

To evaluate and compare the diagnostic specificities of peripapillary retinal nerve fiber layer (RNFL) thickness, macular ganglion cell-inner plexiform layer (GC-IPL) thickness, and optic nerve head (ONH) measurements in nonglaucomatous myopic individuals.

METHODS

In a prospective, cross-sectional study, participants underwent a complete ophthalmic examination, a screening automated visual field test, and axial length measurement. The study eye then underwent optic nerve head and macular scanning using spectral-domain optical coherence tomography (OCT) instrumentation to determine RNFL thickness, GC-IPL thickness, and ONH measurements. False-positive rates for each of the OCT-derived parameters, using predefined criteria for an abnormal test, were calculated. Comparative analysis was performed using the McNemar test.

RESULTS

Data from 43 eligible subjects were analyzed. The mean age was 30±6.8 years (range, 22 to 50 y) with an average axial length of 25.26±1.21 mm (range, 23.06 to 29.07 mm) and mean spherical equivalent of -4.50±1.93 D (range, -1.00 to -9.00 D). The false-positive rate was higher when using RNFL parameters compared with both ONH (47% vs. 7%, respectively; P<0.001) and GC-IPL (47% vs. 26%, respectively; P=0.049) parameters. The false-positive rate was higher when using GC-IPL parameters, compared with ONH parameters (26% vs. 7%, respectively; P=0.039).

CONCLUSIONS

Caution should be exercised when relying on OCT-derived RNFL and GC-IPL thickness values to diagnose glaucoma in myopic individuals. OCT-derived ONH parameters perform better than RNFL and GC-IPL parameters and may increase diagnostic specificity in this population.

Quantitative 3D-OCT motion correction with tilt and illumination correction, robust similarity measure and regularization

Variability in illumination, signal quality, tilt and the amount of motion pose challenges for post-processing based 3D-OCT motion correction algorithms. We present an advanced 3D-OCT motion correction algorithm using image registration and orthogonal raster scan patterns aimed at addressing these challenges. An intensity similarity measure using the pseudo Huber norm and a regularization scheme based on a pseudo L0.5 norm are introduced. A two-stage registration approach was developed. In the first stage, only axial motion and axial tilt are coarsely corrected. This result is then used as the starting point for a second stage full optimization. In preprocessing, a bias field estimation based approach to correct illumination differences in the input volumes is employed. Quantitative evaluation was performed using a large set of data acquired from 73 healthy and glaucomatous eyes using SD-OCT systems. OCT volumes of both the optic nerve head and the macula region acquired with three independent orthogonal volume pairs for each location were used to assess reproducibility. The advanced motion correction algorithm using the techniques presented in this paper was compared to a basic algorithm corresponding to an earlier version and to performing no motion correction. Errors in segmentation-based measures such as layer positions, retinal and nerve fiber thickness, as well as the blood vessel pattern were evaluated. The quantitative results consistently show that reproducibility is improved considerably by using the advanced algorithm, which also significantly outperforms the basic algorithm. The mean of the mean absolute retinal thickness difference over all data was 9.9 um without motion correction, 7.1 um using the basic algorithm and 5.0 um using the advanced algorithm. Similarly, the blood vessel likelihood map error is reduced to 69% of the uncorrected error for the basic and to 47% of the uncorrected error for the advanced algorithm. These results demonstrate that our advanced motion correction algorithm has the potential to improve the reliability of quantitative measurements derived from 3D-OCT data substantially.

Potential Applications of Spectral-Domain Optical Coherence Tomography (SD-OCT) in the Study of Alzheimer's Disease

Alzheimer's Disease (AD) is the most common subtype of dementia. As the prevalence of dementia is projected to increase, the burden of the disease on society is expected to become increasingly significant. The link between eye pathology and neurodegenerative diseases has been established in multiple studies. In particular, optic nerve parameters associated with neuronal loss in AD include retinal ganglion cells (RGC). Retinal ganglion cells are similar to neurons in the cerebral cortex, and have been correlated to neurodegeneration in AD. Ocular imaging techniques such as optical coherence tomography (OCT) have provided a rapid and non-invasive method for quantifying optic nerve parameters in vivo. Spectral domain (SD)-OCT has shown good potential in the study of the optic nerve in AD as it enables more comprehensive assessment of RGCs. Earlier generation OCT techniques only assess the retinal nerve fibre layer, which consists of RGC axons. Spectral domain-OCT offers ultra-high scan speed and image resolution, enabling improved sampling of retinal layers. Retinal layers such as the ganglion cell-inner plexiform layer (GC-IPL), which contain the dendrites and nuclei of RGCs, can be assessed with SD-OCT. This article presents a review of literature associating eye pathology with AD, and explores the potential of SD-OCT in future AD studies. Spectral domain-OCT has the potential to draw more links between optic nerve pathology and neurodegeneration.

Influence of axial length on peripapillary retinal nerve fiber layer thickness in children: a study by RTVue spectral-domain optical coherence tomography

PURPOSE

To evaluate the influence of axial length on peripapillary retinal nerve fiber layer (RNFL) thickness in myopic, hyperopic and emmetropic children eyes by RTVue optical coherence tomography (OCT).

METHODS

One hundred twenty eyes of 120 children including 40 myopic, 40 emmetropic and 40 hyperopic eyes were enrolled in the study. Peripapillary RNFL thickness measurements were performed using spectral-domain RTVue OCT (Optovue, Fremont, CA). RNFL thickness parameters were obtained from all octametric sections: upper temporal (TU), superotemporal (ST), superonasal (SN), upper nasal (NU), lower nasal (NL), inferonasal (IN), inferotemporal (IT) and lower temporal (TL). Spherical equivalent refractive error was determined via cycloplegic auto-refraction (Topcon, Tokyo, Japan). The axial length was measured using IOLMaster (Carl Zeiss MEDITEC). Littmann formula was used for correction of axial length-related ocular magnification effect.

RESULTS

Peripapillary RNFL thicknesses were significantly different among the three groups in all sectors except for NU and IT sectors. RNFL thicknesses in all sectors except for TU and TL sectors had significant negative correlations with axial length. However, these differences (excluding TU and TL sectors) and correlations disappeared after correction of magnification effect.

CONCLUSION

In conclusion, axial length influences peripapillary RNFL thickness as measured by RTVue OCT. However, this appears to be due to the ocular magnification effects associated with axial length and can be corrected for with the application of the Littman formula.

Effect of axial length on retinal nerve fiber layer thickness in children

PURPOSE

To investigate the effect of axial length on peripapillary retinal nerve fiber layer (RNFL) thickness in myopic, hyperopic, and emmetropic eyes in children by Cirrus HD spectral-domain optical coherence tomography (OCT).

METHODS

Subjects were divided into 3 groups according to their refractive status: myopic (n = 36), emmetropic (n = 30), and hyperopic (n = 28) eyes. The RNFL thickness measurements were taken from the superior, inferior, nasal, and temporal quadrants in the peripapillary region by Cirrus HD OCT. Axial length was also determined for each patient.

RESULTS

The myopic eyes had thinner average RNFL and RNFLs of temporal, superior, nasal, and inferior quadrants than the hyperopic eyes (p1<0.001, p2 = 0.004, p3 = 0.011, p4 = 0.006, p5 = 0.033, respectively). In addition, average peripapillary RNFL thickness and RNFL thicknesses of all quadrants had significant negative correlations with axial length. On the other hand, after applying modified Littmann formula for correction of magnification effect, the differences among the 3 groups disappeared (all p>0.05).

CONCLUSIONS

We have shown that axial length and accordingly refractive status influenced peripapillary RNFL thickness measurements by Cirrus HD OCT in children. Therefore, to make a correct diagnosis of glaucoma or other optic neuropathies in children, either axial length-induced magnification effect should be corrected by ophthalmologists or the current Cirrus HD OCT database should be revised taking axial length into consideration.

Comparison of retinal nerve fiber layer thickness measurements in healthy subjects using fourier and time domain optical coherence tomography

Purpose. To compare the retinal nerve fiber layer (RNFL) measurements using two different ocular coherence tomography (OCT) devices: Cirrus Fourier domain OCT and Stratus time domain OCT. To analyze reproducibility of Fourier domain measurements in healthy subjects. Methods. One hundred and thirty-two eyes of 132 healthy subjects were scaned on the same day with both instruments, separated by 10 minutes from each other. Thickness of quadrant, average and the 12 different areas around the optic nerve were compared between Cirrus and Stratus. Repeatability, intraclass correlation coefficients (ICCs), and coefficients of variation (COVs) were calculated in RNFL measurements provided by Fourier domain device. Results. The average thickness in the optic cube was 95.50 μm using Cirrus and 97.85 μm using Stratus. Average thickness and temporal quadrant showed significant differences using Cirrus and Stratus methods. Reproducibility was better with Fourier domain OCT (mean COV of 4.54%) than with Stratus time-domain OCT (mean COV of 5.57%). Conclusions. Both scan options give reproducible RNFL thickness measurement, but there are differences between them. Measurements obtained using Fourier domain device show better reproducibility.

Visual acuity, optical components, and macular abnormalities in patients with a history of retinopathy of prematurity

PURPOSE

To examine the optical components and spectral-domain optical coherence tomography (OCT) findings in children with a history of retinopathy of prematurity (ROP) and to identify any associations between the OCT findings and the visual acuities of the patients.

DESIGN

Prospective, case-controlled study.

PARTICIPANTS AND CONTROLS

Children who were between 6 and 14 years of age were divided into the following 4 groups: Patients with a history of threshold ROP who had been treated using laser therapy or cryotherapy (group 1), patients with regressed ROP who had not received any treatment (group 2), patients who were born prematurely but who had no history of ROP (group 3), and normal full-term children (group 4). The posterior poles of the eyes of all of the patients seemed to be normal.

METHODS

Visual acuities, optical components, and macular thicknesses were measured in 4 groups of patients, and comparisons between the groups were made. Macular thicknesses were measured using OCT.

MAIN OUTCOME MEASURES

Visual acuity (VA), optical components, and OCT findings.

RESULTS

We enrolled 133 patients in the study. Patients in group 1 had significantly thicker foveas than the other patients, as demonstrated by OCT, and this finding was negatively correlated with gestational age. The incidence of abnormal foveal contours among patients in group 1 was significantly higher than among the rest of the patients. Retention of the inner retinal layers was noted in group 1 patients; however, the structure of the outer retina remained intact. Greater degrees of myopic shift and astigmatism, steeper corneal curvatures, shallower anterior chamber depths, and thicker lenses were noted in previously treated ROP patients. These findings corresponded with poor VA and high refractive errors in group 1 patients.

CONCLUSIONS

Patients with a history of threshold ROP are more likely to show abnormal foveal development and have a poorer visual prognosis than other patient groups despite a fundus with no macular dragging, disc dragging, or retinal detachment. A steeper corneal curvature, shallower anterior chamber, and greater lens thickness are the main changes in the optical components in these patients.

Evaluation of the nerve fiber layer and macula in the eyes of healthy children using spectral-domain optical coherence tomography

PURPOSE

To determine the normative values of the peripapillary retinal nerve fiber layer (RNFL), macular thickness, and macular volume in healthy children using spectral-domain optical coherence tomography (SD-OCT) and analyze the correlation of such values with age, refraction error, and biometric measurements.

DESIGN

Observational case series.

METHODS

This institutional study involved 107 eyes from 107 healthy pediatric patients (54 female, 53 male) with ages between 6 and 16 years. After the biometric measurements and refractive error values (in spherical equivalent) of the cases were obtained, the peripapillary RNFL, macular thickness, and macular volume values were calculated using the Spectralis OCT device.

RESULTS

Among the study group, with an average age of 10.46 ± 2.94 years, the average axial length (AL) was 23.33 ± 0.89 mm; the average spherical equivalent (SE) value was -0.27 ± 0.99 diopter. The average peripapillary RNFL thickness was 106.45 ± 9.41 μm; the average macular thickness was 326.44 ± 14.17 μm; and the average macular volume was 0.257 ± 0.011 mm(3). The aforementioned OCT measurements were not significantly correlated with age, SE, or AL values (P > .05 for all).

CONCLUSIONS

This study reports SD-OCT findings among healthy pediatric cases. SD-OCT can be reliably used for pediatric patients because of its short exposure time and high degree of image resolution.

Reproducibility of retinal nerve fiber layer measurements with manual and automated centration in healthy subjects using spectralis spectral-domain optical coherence tomography

Objective. The aim of this study was to test the reproducibility of the Heidelberg Spectralis SD-OCT and to determine if provided software retest function for follow-up exam is superior to manual centration. Design. Prospective, cross-sectional study. Participants. 20 healthy subjects. Methods. All subjects underwent SD-OCT testing to determine retinal nerve fiber layer (RNFL) measurements sequentially on two different days and with two different centration techniques. Within-subject standard deviation, coefficient of variation, and intraclass correlation coefficient were used to assess reproducibility. Results. RNFL measurements showed high reproducibility, low within-subject standard deviation (1.3), low coefficient of variation (0.63%), and low intra-class correlation coefficient (0.98 (95% CI 0.97–0.99)) in the automated centration and manual centration groups for average RNFL Thickness. Quadrants showed slightly higher variability in the manual group compared to the automated group (within-subject standard deviation 2.5–5.3 versus 1.1–2.4, resp.). Conclusions. SD-OCT provides high-resolution RNFL measurements with high reproducibility and low variability. The re-test function allows for easier recentration for longitudinal examinations with similar results in average RNFL, but less variability in quadrant RNFL. SD-OCT high reproducibility and low variability is a promising fact and should be further evaluated in longitudinal studies of RNFL.

Retinal nerve fiber layer measurement and diagnostic capability of spectral-domain versus time-domain optical coherence tomography

PURPOSE

To compare retinal nerve fiber layer (RNFL) thickness and diagnostic capability of spectral-domain (CirrusTM) versus time-domain (Stratus®) optical coherence tomography (OCT).

METHODS

A total of 123 eyes of 123 subjects including 68 normal, 32 glaucoma suspect, and 23 patients with glaucoma were prospectively recruited for the study. All subjects were scanned by Stratus® and CirrusTM OCT in the same session. Average and quadrant peripapillary RNFL measurements by both machines were correlated using Spearman correlation coefficient, and agreement between testing methods was analyzed by Bland-Altman plots. The area under receiver operating characteristic curves (AUC) for glaucoma diagnosis was calculated.

RESULTS

Average RNFL thickness were significantly thinner on the CirrusTM compared to the Stratus® OCT in normal subjects and glaucoma suspects (p<0.001), but thicker on the CirrusTM OCT in glaucoma patients, though the difference was not statistically significant (p = 0.53). There was good correlation between the measurements in all 3 groups. In normal controls, the average, superior, nasal, inferior, and temporal correlations were r = 0.668, 0.601, 0.508, 0.620, and 0.660, p<0.001, respectively. In glaucomatous eyes, the corresponding values were r = 0.560, p = 0.005; r = 0.423, p = 0.04; r = 0.117, p = 0.596; r = 0.742, p<0.001; r = 0.669, p<0.001, respectively. The 95% limits of agreement of average RNFL thickness were -30.2 to 13.8 µm. Area under receiver operating characteristic curves for diagnosing glaucoma were comparable (superior RNFL thickness by CirrusTM 0.925; average RNFL thickness by Stratus® 0.987). Highest correlated AUCs were for inferior and temporal quadrants.

CONCLUSIONS

Retinal nerve fiber layer measurements on the CirrusTM and Stratus® OCT correlate well but do not have clinically acceptable agreement between their measurements. The instruments may not be used interchangeably.

Astigmatism and optical coherence tomography measurements

BACKGROUND

To evaluate the effect of astigmatism change on measurement of retinal nerve fiber layer (RNFL) and macular thickness by Cirrus HD spectral-domain optical coherence tomography (Cirrus HD OCT; Carl Zeiss Meditec, Dublin, CA, USA).

METHODS

A total of 30 right eyes from 30 healthy young subjects underwent RNFL and macular thickness measurements using Cirrus HD OCT. Measurements were performed at the baseline state and induced with-the-rule (WTR) and against-the-rule (ATR) astigmatism states by wearing toric soft contact lenses (+1.50 -3.25 diopter × 90° and +1.50 -3.25 diopter × 180° respectively). Differences in RNFL and macular thickness between the baseline state and induced astigmatism states were analyzed.

RESULTS

Wearing toric soft contact lenses induced a mean 2.92 diopter WTR and 3.18 diopter ATR astigmatism respectively. After signal strength change adjustment, RNFL thicknesses of average, superior quadrant, 12 and 6 o'clock hour sectors decreased after induction of a WTR astigmatism (mean difference range, 1.58 to 6.88 μm); RNFL thicknesses of average, nasal, temporal quadrants, 2, 3, and 9 o'clock hour sectors decreased after induction of an ATR astigmatism (mean difference range, 0.75 to 5.11 μm) (all P values <0.05). Macular thickness was not significantly affected by astigmatism changes (all P values ≥ 0.250).

CONCLUSION

Although the amount of change was not substantial, RNFL thickness measured by Cirrus HD OCT was affected by astigmatism changes induced by contact lenses. It may be warranted to consider the effect of astigmatism on RNFL thickness measured by OCT in eyes with higher degrees of astigmatism.

Optical coherence tomography: history, current status, and laboratory work

Optical coherence tomography (OCT) imaging has become widespread in ophthalmology over the past 15 years, because of its ability to visualize ocular structures at high resolution. This article reviews the history of OCT imaging of the eye, its current status, and the laboratory work that is driving the future of the technology.

Correlation between nerve fibre layer thickness measured with spectral domain OCT and visual field in patients with different stages of glaucoma

BACKGROUND

To measure retinal nerve fibre layer (RNFL) thickness with spectral-domain OCT (SD-OCT) in patients with glaucoma, and to evaluate the correlation between visual field parameters and RNFL thickness.

METHODS

Two hundred twelve subjects-55 normal, 37 with preperimetric glaucoma (PPG) and 119 with different stages of primary open angle glaucoma (POAG) were enrolled in this study. Standard automated perimetry was performed in all eyes. RNFL thickness was measured for 6 segments of the 3.4 mm diameter circle and for 8 areas corresponding to the Early Treatment Diabetic Retinopathy Study (ETDRS) grid, both centred on the optic disc. RNFL thickness values were calculated for the inner ring surrounding the optic disc border and the outer ring of the ETDRS grid. The association between visual field parameters and RNFL thickness was evaluated with regression analysis and Pearson correlation coefficients.

RESULTS

In the normal group, mean RNFL thickness was 93 ± 9 μm for circle and 91 ± 14 μm for inner ring, for the POAG group the values were 58 ± 21 μm for circle and 40 ± 21 μm for inner ring, and for the PPG group the values were 77 ± 15 μm and 59 ± 15 μm, respectively. The differences in RNFL thickness between normal and glaucoma eyes were significant (p < 0.001) for all measurements. Mean RNFL thickness between normal and PPG eyes was significantly different for all regions except for the superior-temporal and temporal sector of the circle and for area 7 of the ETDRS grid. In POAG eyes only, RNFL thickness and both mean sensitivity (r = 0.558) and mean defect (r = -0.549) correlated significantly. The best parameters for differentiating normal from PPG eyes were inner ring surrounding the optic disc border (area under receiver operator characteristic curves (AUROC) = 0.940) and area 4 values (AUROC = 0.903) of the ETDRS grid.

CONCLUSIONS

SD-OCT showed significantly decreased mean RNFL thickness of the inner ring surrounding the optic disc border of the ETDRS grid by 35% in PPG eyes and by 46% in eyes with early glaucoma compared to the control group. These results support the usefulness of this technology.

Horizontal deviation of retinal nerve fiber layer peak thickness with stratus optical coherence tomography in glaucoma patients and glaucoma suspects

PURPOSE

To evaluate the prevalence of nasal or temporal shifts in retinal nerve fiber layer (RNFL) peak contours with Stratus optical coherence tomography (OCT) and possible associations with demographic or glaucoma-related variables in glaucoma patients and glaucoma suspects, and to emphasize the importance of this finding in clinical practice.

METHODS

This was a retrospective case series of glaucoma patients and glaucoma suspects (1 eye per patient) who underwent a Fast RNFL thickness study with the Stratus OCT. A study was considered to have a clinically significant horizontal deviation if there was greater than 20 degrees shift from the normative database in both superior and inferior peaks. A second cutoff value of 12 degrees was also used to examine smaller deviations. A linear regression model was used to assess correlations of demographic and glaucoma-related variables between eyes with and without significant deviations.

RESULTS

Of 400 subjects screened, 273 met the inclusion and exclusion criteria. Thirty-nine eyes (14.3%) had clinically significant horizontal deviation using the 20 degrees cutoff [95% confidence interval (CI), 10%-19%], whereas 122 (44.7%) met the definition with the 12 degrees cutoff (95% CI, 38%-51%). In addition, 121 eyes (44.3%) had a greater than 20 degrees horizontal shift of either the superior or inferior peak (95% CI, 38%-51%). There was no correlation with the demographic or glaucoma-related variables and the horizontal deviation of peak contours.

CONCLUSIONS

This study suggests that the significant horizontal deviation of peak RNFL contours with the Stratus OCT Fast RNFL is common and emphasizes the need for caution when interpreting the influence of such deviations on clock-hour segment thinning. It is not possible with this technology to distinguish between translational scan circle misalignment (horizontal or vertical) and anatomic variation as the explanation for the finding, and further study with newer technology is needed.

Three dimensional optical coherence tomography imaging: advantages and advances

Three dimensional (3D) ophthalmic imaging using optical coherence tomography (OCT) has revolutionized assessment of the eye, the retina in particular. Recent technological improvements have made the acquisition of 3D-OCT datasets feasible. However, while volumetric data can improve disease diagnosis and follow-up, novel image analysis techniques are now necessary in order to process the dense 3D-OCT dataset. Fundamental software improvements include methods for correcting subject eye motion, segmenting structures or volumes of interest, extracting relevant data post hoc and signal averaging to improve delineation of retinal layers. In addition, innovative methods for image display, such as C-mode sectioning, provide a unique viewing perspective and may improve interpretation of OCT images of pathologic structures. While all of these methods are being developed, most remain in an immature state. This review describes the current status of 3D-OCT scanning and interpretation, and discusses the need for standardization of clinical protocols as well as the potential benefits of 3D-OCT scanning that could come when software methods for fully exploiting these rich datasets are available clinically. The implications of new image analysis approaches include improved reproducibility of measurements garnered from 3D-OCT, which may then help improve disease discrimination and progression detection. In addition, 3D-OCT offers the potential for preoperative surgical planning and intraoperative surgical guidance.

Measurement of retinal nerve fiber layer thickness in optic atrophy eyes of patients with optic neuritis using optical coherence tomography

OBJECTIVE

To measure the retinal nerve fiber layer (RNFL) thickness using optical coherence tomography (OCT) in optic atrophy eyes of patients with optic neuritis and investigate the correlation between the RNFL thickness and the visual function.

METHODS

To compare the RNFL thickness using StratusOCT, three groups of the subjects were enrolled, including 72 patients with optic atrophy with definite demyelinating optic neuritis history (the neuritis group), 47 patients with advanced POAG atrophic neuropathy (the POAG group), and 47 healthy subjects (the control group). The correlation between the RNFL thickness and visual function parameters were investigated in the neuritis group, including the best-corrected visual acuity (BCVA), the visual field mean deviation (MD), pattern standard deviation (PSD), and P(100) latency of visual evoked potentials (VEP).

RESULTS

The average RNFL thickness, superior, nasal and inferior thicknesses were significantly thinner in both the neuritis group and the POAG group than those in the control group (p < 0.05), while they were higher in the neuritis group than the POAG group (p < 0.05). The significant correlations were found both between the average RNFL thickness and BCVA (r = 0.35, p < 0.05), MD (r = 0.43, p < 0.05), and PSD (r = 0.39, p < 0.05).

CONCLUSION

In comparison to the advanced POAG and normal eyes, the RNFL thickness was decreased moderately in the optic atrophy eyes resulting from demyelinating optic neuritis and was quantitatively correlated with the visual function parameters.

High-resolution ocular imaging: combining advanced optics and microtechnology

Recent developments in imaging technologies offer great potential for the assessment of retinal ganglion cell disorders, with particular relevance to glaucoma. In particular, advances in this field have allowed unprecedented in vivo access to the retinal layers, using many different properties of light to differentiate cellular structures. This article is a summary of currently available and investigational advanced, high-resolution imaging technologies and their potential applications to glaucoma. It represents the topics of discussion at the annual Optic Nerve Rescue and Restoration Think Tank, sponsored by The Glaucoma Foundation, entitled "High Resolution Imaging of the Eye: Advanced Optics, Microtechnology and Nanotechnology" and held in New York, New York, September 28-29, 2007.

Agreement between spectral-domain and time-domain OCT for measuring RNFL thickness

BACKGROUND/AIMS

To evaluate spectral-domain (SD) optical coherence tomography (OCT) reproducibility and assess the agreement between SD-OCT and Time-Domain (TD) OCT retinal nerve fibre layer (RNFL) measurements.

METHODS

Three Cirrus-SD-OCT scans and one Stratus-TD-OCT scan were obtained from Diagnostic Innovations in Glaucoma Study (DIGS) healthy participants and glaucoma patients on the same day. Repeatability was evaluated using Sw (within-subject standard deviation), CV (coefficient of variation) and ICC (intraclass correlation coefficient). Agreement was assessed using correlation and Bland-Altman plots.

RESULTS

16 healthy participants (32 eyes) and 39 patients (78 eyes) were included. SD-OCT reproducibility was excellent in both groups. The CV and ICC for Average RNFL thickness were 1.5% and 0.96, respectively, in healthy eyes and 1.6% and 0.98, respectively, in patient eyes. Correlations between RNFL parameters were strong, particularly for average RNFL thickness (R(2) = 0.92 in patient eyes). Bland-Altman plots showed good agreement between instruments, with better agreement for average RNFL thickness than for sectoral RNFL parameters (for example, at 90 microm average RNFL thickness, 95% limits of agreement were -13.1 to 0.9 for healthy eyes and -16.2 to -0.3 microm for patient eyes).

CONCLUSIONS

SD-OCT measurements were highly repeatable in healthy and patient eyes. Although the agreement between instruments was good, TD-OCT provided thicker RNFL measurements than SD-OCT. Measurements with these instruments should not be considered interchangeable.

Diagnostic tools for glaucoma detection and management

Early diagnosis of glaucoma is critical to prevent permanent structural damage and irreversible vision loss. Detection of glaucoma typically relies on examination of structural damage to the optic nerve combined with measurements of visual function. To aid the clinician in evaluation of visual function and structure, computer-based devices such as confocal scanning laser ophthalmoscopy, scanning laser polarimetry, and optical coherence tomography provide quantitative assessments of structural damage, and visual function testing includes standard automated perimetry as well as selective techniques, including short-wavelength automated perimetry and frequency-doubling technology perimetry are available. This article will review current literature on diagnostic modalities available for glaucoma with emphasis on the best evidence available in the literature to support their use in clinical practice.

Three-dimensional high resolution OCT imaging of macular pathology

Raster scanning spectral domain optical coherence tomography (SD-OCT) enables realistic three-dimensional (3D) imaging of macular disease. This approach allows the clinician to investigate the diagnostic situation in detail before and during pharmacological or surgical intervention. This study demonstrates the clinical potential of SD-OCT in chorioretinal disease. Selected datasets are presented to visualize typical morphologic findings, which are identified in more than 2700 patients. Scans are presented as online assessable 3D-models. Clinically relevant structures are visualized in macular disease and highlight the importance of precise imaging, which clearly is a clinical necessity to plan and indicate modern therapeutic strategies for our patients.

Comparison of Fourier-domain and time-domain optical coherence tomography in the detection of band atrophy of the optic nerve

PURPOSE

To compare the ability of Fourier-domain (FD) optical coherence tomography (3D OCT-1000; Topcon, Tokyo, Japan) and time-domain (TD) OCT (Stratus; Carl Zeiss Meditec Inc, Dublin, California, USA) to detect axonal loss in eyes with band atrophy (BA) of the optic nerve.

DESIGN

Cross-sectional study.

METHODS

Thirty-six eyes from 36 patients with BA and temporal visual field (VF) defect from chiasmal compression and 36 normal eyes were studied. Subjects were submitted to standard automated perimetry and macular and retinal nerve fiber layer (RNFL) measurements were taken using 3D OCT-1000 and Stratus OCT. Receiver operating characteristic (ROC) curves were calculated for each parameter. Spearman correlation coefficients were obtained to evaluate the relationship between RNFL and macular thickness parameters and severity of VF loss. Measurements from the two devices were compared.

RESULTS

Regardless of OCT device, all RNFL and macular thickness parameters were significantly lower in eyes with BA compared with normal eyes, but no statistically significant difference was found with regard to the area under the ROC curve. Structure-function relationships were also similar for the two devices. In both groups, RNFL and macular thickness measurements were generally and in some cases significantly smaller with 3D OCT-1000 than with Stratus OCT.

CONCLUSIONS

The introduction of FD technology did not lead to better discrimination ability for detecting BA of the optic nerve compared with TD technology when using the software currently provided by the manufacturer. 3D OCT-1000 FD OCT RNFL and macular measurements were generally smaller than TD Stratus OCT measurements. Investigators should be aware of this fact when comparing measurements obtained with these two devices.

Imaging of the retinal nerve fibre layer for glaucoma

BACKGROUND

Glaucoma is a group of diseases characterised by retinal ganglion cell dysfunction and death. Detection of glaucoma and its progression are based on identification of abnormalities or changes in the optic nerve head (ONH) or the retinal nerve fibre layer (RNFL), either functional or structural. This review will focus on the identification of structural abnormalities in the RNFL associated with glaucoma.

DISCUSSION

A variety of new techniques have been created and developed to move beyond photography, which generally requires subjective interpretation, to quantitative retinal imaging to measure RNFL loss. Scanning laser polarimetry uses polarised light to measure the RNFL birefringence to estimate tissue thickness. Optical coherence tomography (OCT) uses low-coherence light to create high-resolution tomographic images of the retina from backscattered light in order to measure the tissue thickness of the retinal layers and intraretinal structures. Segmentation algorithms are used to measure the thickness of the retinal nerve fibre layer directly from the OCT images. In addition to these clinically available technologies, new techniques are in the research stages. Polarisation-sensitive OCT has been developed that combines the strengths of scanning laser polarimetry with those of OCT. Ultra-fast techniques for OCT have been created for research devices. The continued utilisation of imaging devices into the clinic is refining glaucoma assessment. In the past 20 years glaucoma has gone from a disease diagnosed and followed using highly subjective techniques to one measured quantitatively and increasingly objectively.

Visual impairment and postural sway among older adults with glaucoma

PURPOSE

To investigate the effect of visual impairment on postural sway among older adults with open-angle glaucoma.

METHODS

This study included 54 community-dwelling participants with open-angle glaucoma, aged 65 and older. Binocular visual field loss was estimated from merged monocular Humphrey Field Analyzer visual field results and retinal nerve fiber layer (RNFL) thickness was obtained from the Stratus Optical Coherence Tomographer. Postural sway was measured under four conditions: eyes open and closed, on a firm, and a foam surface. Data were collected for additional vision measures (visual acuity and contrast sensitivity), physical performance measures (self-reported physical activity levels and 6-min walk test), and demographic measures (age, gender, body mass index, and medical history). Multivariate linear regressions, adjusting for confounding factors, were performed to determine the association between visual loss and postural sway.

RESULTS

Participants with greater binocular visual field loss or thinner RNFL thickness showed increased postural sway, both on firm and foam surfaces, independent of age, gender, body mass index, and physical performance levels. These visual loss measures were significant predictors of postural sway, explaining almost 20% of its variance on the foam surface. Furthermore, participants with greater inferior hemifield visual field loss showed increased postural sway on the foam surface. Increasing glaucomatous visual impairment was accompanied by a steady decrease of the visual contribution to postural control.

CONCLUSION

Among older adults with glaucoma, greater visual field loss or thinner RNFL thickness is associated with reduced postural stability. This postural instability may be a contributing factor in the increased risk of falls among older adults with glaucoma.

Ultrahigh-speed optical coherence tomography for three-dimensional and en face imaging of the retina and optic nerve head

PURPOSE

To demonstrate ultrahigh-speed optical coherence tomography (OCT) imaging of the retina and optic nerve head at 249,000 axial scans per second and a wavelength of 1060 nm. To investigate methods for visualization of the retina, choroid, and optic nerve using high-density sampling enabled by improved imaging speed.

METHODS

A swept-source OCT retinal imaging system operating at a speed of 249,000 axial scans per second was developed. Imaging of the retina, choroid, and optic nerve were performed. Display methods such as speckle reduction, slicing along arbitrary planes, en face visualization of reflectance from specific retinal layers, and image compounding were investigated.

RESULTS

High-definition and three-dimensional (3D) imaging of the normal retina and optic nerve head were performed. Increased light penetration at 1060 nm enabled improved visualization of the choroid, lamina cribrosa, and sclera. OCT fundus images and 3D visualizations were generated with higher pixel density and less motion artifacts than standard spectral/Fourier domain OCT. En face images enabled visualization of the porous structure of the lamina cribrosa, nerve fiber layer, choroid, photoreceptors, RPE, and capillaries of the inner retina.

CONCLUSIONS

Ultrahigh-speed OCT imaging of the retina and optic nerve head at 249,000 axial scans per second is possible. The improvement of approximately 5 to 10x in imaging speed over commercial spectral/Fourier domain OCT technology enables higher density raster scan protocols and improved performance of en face visualization methods. The combination of the longer wavelength and ultrahigh imaging speed enables excellent visualization of the choroid, sclera, and lamina cribrosa.

Optical coherence tomography scan circle location and mean retinal nerve fiber layer measurement variability

PURPOSE

To investigate the effect on optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) thickness measurements of varying the standard 3.4-mm-diameter circle location.

METHODS

The optic nerve head (ONH) region of 17 eyes of 17 healthy subjects was imaged with high-speed, ultrahigh-resolution OCT (hsUHR-OCT; 501 x 180 axial scans covering a 6 x 6-mm area; scan time, 3.84 seconds) for a comprehensive sampling. This method allows for systematic simulation of the variable circle placement effect. RNFL thickness was measured on this three-dimensional dataset by using a custom-designed software program. RNFL thickness was resampled along a 3.4-mm-diameter circle centered on the ONH, then along 3.4-mm circles shifted horizontally (x-shift), vertically (y-shift) and diagonally up to +/-500 microm (at 100-microm intervals). Linear mixed-effects models were used to determine RNFL thickness as a function of the scan circle shift. A model for the distance between the two thickest measurements along the RNFL thickness circular profile (peak distance) was also calculated.

RESULTS

RNFL thickness tended to decrease with both positive and negative x- and y-shifts. The range of shifts that caused a decrease greater than the variability inherent to the commercial device was greater in both nasal and temporal quadrants than in the superior and inferior ones. The model for peak distance demonstrated that as the scan moves nasally, the RNFL peak distance increases, and as the circle moves temporally, the distance decreases. Vertical shifts had a minimal effect on peak distance.

CONCLUSIONS

The location of the OCT scan circle affects RNFL thickness measurements. Accurate registration of OCT scans is essential for measurement reproducibility and longitudinal examination (ClinicalTrials.gov number, NCT00286637).