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

Nerve Fiber Flux Analysis Using Wide-Field Swept-Source Optical Coherence Tomography

PURPOSE

To devise a method to quantify nerve fibers over their arcuate courses over an extended peripapillary area using optical coherence tomography (OCT).

METHODS

Participants were imaged with 8 × 8-mm volumetric OCT scans centered at the optic disc. A new quantity, nerve fiber flux (NFF), represents the cross-sectional area transected perpendicular to the nerve fibers. The peripapillary area was divided into 64 tracks with equal flux. An iterative algorithm traced the trajectory of the tracks assuming that the relative distribution of the NFF was conserved with compensation for fiber connections to ganglion cells on the macular side. Average trajectory was averaged from normal eyes and use to calculate the NFF maps for glaucomatous eyes. The NFF maps were divided into eight sectors that correspond to visual field regions.

RESULTS

There were 24 healthy and 10 glaucomatous eyes enrolled. The algorithm converged on similar patterns of NFL tracks for all healthy eyes. In glaucomatous eyes, NFF correlated with visual field sensitivity in the arcuate sectors (Spearman ρ = 0.53-0.62). Focal nerve fiber loss in glaucomatous eyes appeared as uniform tracks of NFF defects that followed the expected arcuate fiber trajectory.

CONCLUSIONS

Using an algorithm based on the conservation of flux, we derived nerve fiber trajectories in the peripapillary area. The NFF map is useful for the visualization of focal defects and quantification of sector nerve fiber loss from wide-area volumetric OCT scans.

TRANSLATIONAL RELEVANCE

NFF provides a cumulative measure of volumetric loss along nerve fiber tracks and could improve the detection of focal glaucoma damage.

Comparison of Optical Coherence Tomography Angiography and Laser Speckle Flowgraphy for the Diagnosis of Normal-Tension Glaucoma

Purpose

To compare optical coherence tomography angiography (OCT-A) and laser speckle flowgraphy (LSFG) for the diagnosis of normal-tension glaucoma (NTG).

Methods

Twenty-eight eyes of 28 patients with NTG and 25 eyes of 25 normal subjects matched for age, refractive errors, systemic blood pressure, and central corneal thickness were evaluated. OCT-A was used to measure whole image vessel density, inside disc vessel density, and peripapillary vessel density; using LSFG, mean blur rate (MBR) inside the whole optic nerve head (ONH) area (MBR_A), and MBR of the vessel area (MBR_V) and tissue area (MBR_T) inside the ONH, were determined. Receiver operating characteristic (ROC) curves and areas under the ROC (AUROC) were used to assess the diagnostic ability of each variable.

Results

The AUROC for OCT-A whole image vessel density (0.950) was significantly greater than that for OCT-A peripapillary vessel density (0.830) and for all LSFG parameters (MBR_A = 0.793, MBR_V = 0.601, and MBR_T = 0.61) (P < 0.001). The AUROC for OCT-A inside disc vessel density (0.931) was significantly greater than that for all LSFG parameters (P < 0.005).

Conclusions

OCT-A vessel density had a higher glaucoma diagnostic ability compared to all LSFG parameters in patients with NTG.

Reproducibility of Optic Nerve Head Measurements Obtained by Optical Coherence Tomography

Purpose

To evaluate reproducibility of optic nerve head (ONH) morphometry measurements obtained by optical coherence tomography (the fast optical disk protocol of the Zeiss model 3000 OCT system) in normal and glaucomatous eyes.

Methods

Prospective instrument-evaluation study. ONH measurements for 20 eyes were obtained in eight scan sessions taken during two visits to an ophthalmology clinic (10 normal patients, 10 glaucoma patients, one eye per subject). At every one of the eight sessions for each eye, estimates of eight ONH morphometry variables (see Main outcome measures) were obtained. The first two sessions were performed by two operators, followed by a 30-minute break. The same operators then completed a third and fourth session. This sequence was duplicated on a second visit. Intrasession, intersession, intervisit, and interoperator reproducibility of the eight variables were calculated by the use of a components variance model. Intraclass correlation coefficients (ICC) were used to assess reliability.

Results

Vertical integrated rim area, horizontal integrated rim area, disk area, cup area, rim area, cup/disk area ratio, cup/disk horizontal ratio, cup/disk vertical ratio. With the exception of the horizontal integrated rim area and rim area in normal subjects, the factor subject was the most important source of variance for all variables. Reliability values as measured by ICC for normal eyes were above 81%, with the exception of measurements of the horizontal integrated rim area (23.1%), rim area (33.3%), and disk area (64.7%). For glaucomatous eyes all values were above 85%, with the exception of the disk area (68.1%).

Conclusions

ONH measurements obtained using the fast optical disk protocol of the Zeiss 3000 OCT system show good reproducibility, for both normal and glaucomatous eyes.

Segmental Analysis of Macular Layers in Patients With Rhegmatogenous Retinal Detachment Treated With Perfluoropropane or Silicon Oil

BACKGROUND AND OBJECTIVE

To determine possible changes in thickness profiles of retinal layers in patients with rhegmatogenous retinal detachment (RRD) treated with perfluoropropane (C3F8) or silicon oil (SiO).

PATIENTS AND METHODS

Seventy-two eyes of 36 patients were enrolled in this retrospective comparative study. Patients were divided into two groups according to intraocular tamponade: C3F8 or SiO. All study eyes were compared with fellow eyes via spectral-domain optical coherence tomography segment analysis at 6 months postoperatively. Macular layer thicknesses including retinal nerve fiber layer, ganglion cell layer, inner plexiform layer, inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), and retinal pigment epithelium were analyzed.

RESULTS

There was a statistically significant difference between eyes in terms of INL thickness (P = .044) in C3F8 group. Otherwise there was a statistically significant difference between eyes in terms of INL, OPL, and ONL thicknesses (P = .006, P = .048, and P = .004, respectively) in the SiO group.

CONCLUSION

The findings of the present study show that the tamponade used in RRD surgery can affect the retinal layers differently. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:41-47.].

Patterns of Retinal Ganglion Cell Damage in Neurodegenerative Disorders: Parvocellular vs Magnocellular Degeneration in Optical Coherence Tomography Studies

Many neurodegenerative disorders, such as Parkinson’s disease (PD) and Alzheimer’s disease (AD), are characterized by loss of retinal ganglion cells (RGCs) as part of the neurodegenerative process. Optical coherence tomography (OCT) studies demonstrated variable degree of optic atrophy in these diseases. However, the pattern of degenerative changes affecting the optic nerve (ON) can be different. In particular, neurodegeneration is more evident for magnocellular RGCs in AD and multiple system atrophy with a pattern resembling glaucoma. Conversely, in PD and Huntington’s disease, the parvocellular RGCs are more vulnerable. This latter pattern closely resembles that of mitochondrial optic neuropathies, possibly pointing to similar pathogenic mechanisms. In this review, the currently available evidences on OCT findings in these neurodegenerative disorders are summarized with particular emphasis on the different pattern of RGC loss. The ON degeneration could become a validated biomarker of the disease, which may turn useful to follow natural history and possibly assess therapeutic efficacy.

Peripapillary Retinal Nerve Fiber Measurement with Spectral-Domain Optical Coherence Tomography in Age-Related Macular Degeneration

Purpose: To evaluate the relationship between the peripapillary retinal nerve fiber layer (RNFL) measurements with Spectral-domain Optical Coherence Tomography (OCT) and Age-related macular degeneration (AMD). Methods: Patients >60 years of age without glaucoma or record of intraocular pressure >21 mmHg and no systemic or intraocular diseases or treatment or surgical intervention that affected the RNFL underwent OCT measurement of the RNFL. The severity of AMD was staged with the Clinical Age-Related Maculopathy Staging System. The relationship between RNFL measurements and AMD stages of one eye per patient was analyzed. Results: Eighty-six eyes (46 patients) with AMD and no glaucoma or other exclusion criteria received OCT RNFL measurements. Nine eyes (10.5%) were excluded because of distorted peripapillary anatomy from exudative AMD (7 eyes) or failure of the RNFL segmentation algorithm (2 eyes). Mean age ± S.D. of the 43 patients analyzed was 81.2 ± 7.3 years. The mean stage ± S.D. of AMD of the 77 eyes was 3.77 ± 1.05. Higher stages of AMD were statistically significantly associated with lower average RNFL and inferior sector RNFL (p = 0.049, 0 0015, respectively). The association of inferior sector RNFL and AMD stage remained statistically significant after adjusting for age. Conclusions: Spectral domain OCT is generally useful in measuring the peripapillary RNFL in eyes with different stages of AMD. Higher stage of AMD is associated with thinner peripapillary RNFL, which may masquerade as early glaucomatous damage.

[Bruch's membrane opening minimum rim width : Correlation and diagnostic accuracy in comparison to peripapillary retinal nerve fiber layer thickness]

BACKGROUND

Glaucoma is one of the main causes of blindness in the Western hemisphere. Because the disease often painlessly progresses it remains unnoticed until major optic nerve head damage occurs in many cases. That is why new, more sensitive diagnostic methods are needed. Bruch's membrane opening minimum rim width (BMO-MRW), measured with the new glaucoma module premium edition (GMPE) was recently introduced as a more accurate tool to detect glaucomatous changes. The purpose of this study was to assess the correlation of SPECTRALIS® spectral domain optical coherence tomography (SD-OCT) and the GMPE anatomic positioning module (APS module) for retinal nerve fiber layer thickness (RNFLT) measurements. The second aim was to assess the diagnostic accuracy of BMO-MRW.

METHODS

Prospective study of 41 eyes (41 patients) with glaucoma and 26 eyes from 26 healthy controls. Scans were obtained using SPECTRALIS® SD-OCT and RNFLT was measured with both modules and compared using Spearman's rank test. The BMO-MRW was assessed by GMPE. Sensitivity, specificity and area under receiver operating characteristics curves (AUROC) of each sector of the optic nerve were calculated and compared using the method of Delong et al.

RESULTS

We found a positive correlation (0.694-0.955, p < 0.0001) between RNFLT measurements by standard SD-OCT and all diameters of RNFLT of APS module within all sectors. The AUROC of RNFLT in standard SD-OCT was 0.693 for the inferior nasal sector (NI) and BMO-MRW was 0.85 in NI. The difference in AUROC was statistically significant (p = 0.0049). No other sector showed statistically significant differences.

CONCLUSION

The RNFLT measurements of both modules showed a positive correlation and appear to be comparable. The BMO-MRW in one sector (NI) showed a significantly higher accuracy of measurement than standard RNFLT. All other sectors showed a comparable accuracy of measurement.

Glaucoma

Glaucoma is a heterogeneous group of diseases characterised by cupping of the optic nerve head and visual-field damage. It is the most frequent cause of irreversible blindness worldwide. Progression usually stops if the intraocular pressure is lowered by 30-50% from baseline. Its worldwide age-standardised prevalence in the population aged 40 years or older is about 3·5%. Chronic forms of glaucoma are painless and symptomatic visual-field defects occur late. Early detection by ophthalmological examination is mandatory. Risk factors for primary open-angle glaucoma-the most common form of glaucoma-include older age, elevated intraocular pressure, sub-Saharan African ethnic origin, positive family history, and high myopia. Older age, hyperopia, and east Asian ethnic origin are the main risk factors for primary angle-closure glaucoma. Glaucoma is diagnosed using ophthalmoscopy, tonometry, and perimetry. Treatment to lower intraocular pressure is based on topical drugs, laser therapy, and surgical intervention if other therapeutic modalities fail to prevent progression.

Comparative analysis of mean retinal thickness measured using SD-OCT in normal young or old age and glaucomatous eyes

PURPOSE

To evaluate changes in macular thickness, ganglion cell layer/inner plexiform layer (GCL/IPL) thickness, and retinal nerve fiber layer (RNFL) thickness in normal eyes and glaucomatous eyes using spectral domain optical coherence tomography (SD-OCT).

METHODS

We enrolled 89 eyes (all left eyes), including 45 (of 45 patients) eyes with glaucoma and 44 (of 44 patients) normal eyes. The data from macular measurements using spectral domain optical coherence tomography were analyzed according to groups divided by age and glaucoma status. The macular thickness analysis, GCL/IPL thickness, and RNFL thickness values determined by SD-OCT scans were compared among the groups.

RESULTS

Mean macular thickness decreased significantly with age or glaucoma. Mean GCL/IPL thickness decreased significantly in glaucomatous eyes in all sectors but did not decrease with age. Mean RNFL thickness, which was divided into four quadrants (superior, nasal, inferior, and temporal), decreased significantly in glaucomatous eyes at all quadrants and decreased in the temporal quadrant with age in non-glaucomatous eyes. No significant differences were detected between eyes with normal tension glaucoma (NTG) and primary open angle glaucoma (POAG) in all sectors of mean GCL/IPL thickness, RNFL thickness, and macular thickness.

CONCLUSIONS

No significant difference in mean thickness was detected between eyes with NTG and POAG. Some of the sectors of RNFL thickness decreased with age or glaucoma. GCL/IPL thickness, however, decreased in glaucomatous eyes but not with age. Therefore, GCL/IPL thickness is less influenced by age when monitoring patients with glaucoma or suspect glaucoma.

Glaucoma Diagnostic Capability of Circumpapillary Retinal Nerve Fiber Layer Thickness in Circle Scans With Different Diameters

PURPOSE

To compare varying circumpapillary optical coherence tomographic (OCT) scan diameters for glaucoma diagnosis.

MATERIALS AND METHODS

Prospective, cross-sectional, observational study. Circumpapillary retinal nerve fiber layer thickness (RNFLT) was measured using spectral-domain OCT in 1 randomly selected eye. Scans with diameters of 3.5, 4.1, and 4.7 mm were obtained, each with 7 parameters: mean global (G) RNFLT and mean RNFLT for the temporal-inferior (TI), nasal-inferior (NI), temporal-superior (TS), nasal-superior (NS), nasal (N), and temporal (T) sectors. Areas under the receiver operating characteristic curve (AUCs) were calculated.

RESULTS

Mean age was 55±18 years in 68 healthy eyes and 59±15 years in 95 glaucomatous eyes (P=0.12). Visual field mean deviation was -7.55±6.61 dB in glaucomatous eyes. In all 3 circle scans, mean TI RNFLT had the greatest AUC (0.974 to 0.983), followed by mean G RNFLT (0.949 to 0.956). The AUC of mean TI RNFLT in the 4.1-mm scan (0.983) was greater than the AUCs of mean TI RNFLTs in the 4.7- (0.978; P=0.128) and 3.5-mm (0.974; P=0.049) scans. The AUC of mean TI RNFLT in the 4.1-mm scan (0.983) was greater than the AUCs of mean G RNFLTs in the 3.5- (0.954; P=0.011), 4.1- (0.956; P=0.016), and 4.7-mm (0.949; P=0.011) scans. In 2 eyes with large parapapillary atrophy, RNFL segmentation error was noted only in the 3.5-mm scan in the area of parapapillary atrophy.

CONCLUSIONS

Further investigations to find the spectral-domain OCT circle scan diameter with the best diagnostic capability and the least artifacts are warranted, especially focusing on larger-than-conventional circle scans.

Patterns of Retinal Nerve Fiber Layer Loss in Different Subtypes of Open Angle Glaucoma Using Spectral Domain Optical Coherence Tomography

PURPOSE OF THE STUDY

The purpose of the study was to determine whether there are different patterns of retinal nerve fiber layer (RNFL) thinning as measured by spectral domain optical coherence tomography (SD-OCT) for 4 subtypes of open angle glaucoma (OAG): primary OAG (POAG), normal tension glaucoma (NTG), pseudoexfoliation glaucoma (PXG), and pigmentary glaucoma (PDG) and to compare them with normal controls.

MATERIALS AND METHODS

SD-OCT RNFL thickness values were measured for 4 quadrants and for 4 sectors (ie, superior-nasal, superior-temporal, inferior-nasal, and inferior-temporal). Differences in RNFL thickness values between groups were analyzed using analysis of variance. Paired t tests were used for quadrant comparisons.

RESULTS

Two hundred eighty-five participants (102 POAG patients, 33 with NTG, 48 with PXG, 13 with PDG, and 89 normal patients) were included in this study. All 4 subtypes of OAG showed significant RNFL thinning in the superior, inferior, and nasal quadrants as well as the superior-temporal and inferior-temporal sectors (all P-values <0.0001) compared with normals. POAG and NTG patients had greater RNFL thinning inferiorly and inferior-temporally than superiorly (P-values: 0.002 to 0.018 and 0.006, respectively) compared with PXG patients. In contrast, PDG patients had greater RNFL thinning superiorly and superior-nasally than inferiorly compared with other OAG subtypes (ie, POAG, NTG, PXG groups, with P-values: 0.009, 0.003, 0.009, respectively). Of the 4 OAG subtypes, PXG patients exhibited the greatest degree of inter-eye RNFL asymmetry.

CONCLUSIONS

This study suggests that SD-OCT may be able to detect significant differences in patterns of RNFL thinning for different subtypes of OAG.

Bruch's Membrane Opening Minimum Rim Width Measurement with SD-OCT: A Method to Correct for the Opening Size of Bruch's Membrane

A precise evaluation of the retinal nerve fiber layer thickness (RNFLT) is key for diagnosing and monitoring glaucoma. The Bruch's membrane opening minimum rim width (BMO-MRW) has been proposed as a reproducible assessment of the optic nerve. The BMO-MRW measures the minimum distance from the BMO to the internal limiting membrane. We propose an approach to correct the BMO-MRW using the BMO size for increased accuracy in interindividual comparisons in future studies. Eighty-one healthy patients received SPECTRALIS spectral domain optical coherence tomography measurements for the peripapillary RNFLT and BMO-MRW. We calculated a BMO size-corrected BMO-MRW using the mean BMO size of our cohort. BMO size was defined using the manufacturer-provided BMO area and manually measured BMO perimeter. We observed that the BMO-MRW correlated highly with the perimeter (r = −0.553, p < 0.0001) and the area of the BMO (r = −0.546, p < 0.0001). Using these parameters, we provided a corrected BMO size-adjusted BMO-MRW which was better correlated with the RNFLT compared to the noncorrected one (z = −3.3495, p = 0.0004). We demonstrated the dependency of the BMO-MRW on ONH size. Furthermore, we showed the superiority of the corrected BMO-MRW using either the manually measured optic nerve head perimeter or the automatically provided ONH for future studies.

Diagnostic Capability of Peripapillary Three-dimensional Retinal Nerve Fiber Layer Volume for Glaucoma Using Optical Coherence Tomography Volume Scans

PURPOSE

To determine the diagnostic capability of peripapillary 3-dimensional (3D) retinal nerve fiber layer (RNFL) volume measurements from spectral-domain optical coherence tomography (OCT) volume scans for open-angle glaucoma (OAG).

DESIGN

Assessment of diagnostic accuracy.

METHODS

Setting: Academic clinical setting.

STUDY POPULATION

Total of 180 patients (113 OAG and 67 normal subjects).

OBSERVATION PROCEDURES

One eye per subject was included. Peripapillary 3D RNFL volumes were calculated for global, quadrant, and sector regions, using 4 different-size annuli. Peripapillary 2D RNFL thickness circle scans were also obtained.

MAIN OUTCOME MEASURES

Area under the receiver operating characteristic curve (AUROC) values, sensitivity, specificity, positive and negative predictive values, positive and negative likelihood ratios.

RESULTS

Among all 2D and 3D RNFL parameters, best diagnostic capability was associated with inferior quadrant 3D RNFL volume of the smallest annulus (AUROC value 0.977). Otherwise, global 3D RNFL volume AUROC values were comparable to global 2D RNFL thickness AUROC values for all 4 annulus sizes (P values: .0593 to .6866). When comparing the 4 annulus sizes for global RNFL volume, the smallest annulus had the best AUROC values (P values: .0317 to .0380). The smallest-size annulus may have the best diagnostic potential, partly owing to having no areas excluded for being larger than the 6 × 6 mm² scanned region.

CONCLUSION

Peripapillary 3D RNFL volume showed excellent diagnostic performance for detecting glaucoma. Peripapillary 3D RNFL volume parameters have the same or better diagnostic capability compared to peripapillary 2D RNFL thickness measurements, although differences were not statistically significant.

Choroidal thickness and structural glaucoma parameters in glaucomatous, preperimetric glaucomatous, and healthy eyes using swept-source OCT

PURPOSE

To evaluate choroidal thickness (CT) and its relationship with retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer thickness (GCIPLT) in glaucomatous, preperimetric glaucomatous, and healthy eyes using swept-source optical coherence tomography (SS-OCT).

METHODS

Fifty eyes with primary open-angle glaucoma, 20 eyes with preperimetric glaucoma, and 20 age-matched healthy eyes were enrolled. Three-dimensional wide-field (12 × 9 mm) images were obtained using a SS-OCT instrument. Peripapillary CT and RNFL thickness, as well as macular CT and GCIPLT, were recorded. The correlation of the CT with nerve fiber layer and GCIPLT measurements was assessed. The association between CT and potential confounding variables including age, sex, axial length, intraocular pressure, and central corneal thickness was also examined.

RESULTS

Mean peripapillary CTs were 111.7 ± 41.7, 127.7 ± 40.1, and 120.8 ± 35.4 μm in glaucomatous, preperimetric glaucomatous, and normal eyes, respectively. There was statistically significant but weak correlation for the mean RNFL and mean peripapillary CT in glaucomatous subjects (r = 0.341, p = 0.04). There was a significant correlation between RNFL thickness and peripapillary CT in 1, 2, 5, and 6 clock hours of glaucomatous eyes (r = 0.410, p = 0.005; r = 0.316, p = 0.03; r = 0.346, p = 0.02; r = 0.35, p = 0.04, respectively). Mean macular CT was 181.5 ± 70.5, 187.4 ± 65.5, and 185.4 ± 76.4 μm in glaucomatous, preperimetric glaucomatous, and healthy eyes, respectively (p = 0.7). There was no statistically significant correlation between the mean GCIPLT and mean macular CT in all subjects (p>0.05).

CONCLUSIONS

Choroidal thinning and its correlation with other parameters in patients with glaucoma should be further investigated with the proprietary software of SS-OCT.

OCT Glaucoma Staging System: a new method for retinal nerve fiber layer damage classification using spectral-domain OCT

PurposeTo describe a new method, the Optical Coherence Tomography (OCT) Glaucoma Staging System, for classifying retinal nerve fiber layer (RNFL) damage assessed with OCT.Patients and methodsThe OCT Glaucoma Staging System was created based on data obtained from Nidek RS 3000 spectral-domain (sd)-OCT. This system uses the superior and inferior quadrant RNFL thickness values, plotted on an x-y diagram for staging structural damage severity in glaucoma. A non-linear equation and two regression lines describe the boundary lines which separate the different sectors of the diagram. These mathematical formulas have been used to create a software, which provides a quick classification of the RNFL damage. Sensitivity and specificity of the system were assessed in a different cohort including 64 patients with early OAG, and 62 normal subjects.ResultsThree hundred and two OCT tests from 98 healthy controls and 284 patients affected by either ocular hypertension or chronic open-angle glaucoma were considered in order to design the new classification system. The OCT Glaucoma Staging System classifies RNFL defects into 6 stages of increasing severity ranging from borderline to stage 5, and 3 groups according to defect localization (superior, inferior, or diffuse). Sensitivity and specificity in discriminating between healthy and glaucomatous eyes were 95.2 and 91.9%, respectively, considering borderline results as abnormal.ConclusionsThe OCT Glaucoma Staging System appears to provide a standardized and objective classification of glaucomatous RNFL damage. It can be used in day-to-day clinical practice for an easy and fast interpretation of RNFL measurements obtained with OCT.

Peripapillary Retinal Nerve Fiber Layer Vascular Microcirculation in Glaucoma Using Optical Coherence Tomography-Based Microangiography

Purpose

To investigate the vascular microcirculation changes in the retinal nerve fiber layer (RNFL) in normal, glaucoma suspect, and open-angle glaucoma (OAG) groups using optical coherence tomography–based microangiography (OMAG).

Methods

One eye from each subject was scanned with a Cirrus HD-OCT 5000–based OMAG prototype system montage scanning protocol centered at the optic nerve head (ONH). Blood flow signals were extracted using OMAG algorithm. Retinal nerve fiber layer vascular microcirculation was measured by calculating the blood flux index and vessel area density within a 1.2-mm width annulus centered at the ONH with exclusion of big retinal vessels. One-way ANOVA were performed to analyze the RNFL microcirculation among groups. Linear-regression models were constructed to analyze the correlation between RNFL microcirculation and clinical parameters. Discrimination capabilities of the flow metrics were assessed with the area under the receiver operating characteristic curve (AROC).

Results

Twenty normal, 26 glaucoma suspect, and 42 OAG subjects were enrolled. Eyes from OAG subjects and glaucoma suspects showed significantly lower blood flux index compared with normal eyes (P ≤ 0.0015). Retinal nerve fiber layer blood flow metrics showed significant correlations with visual field indices and structural changes in glaucomatous eyes (P ≤ 0.0123). Similar discrimination capability of blood flux index compared with RNFL thickness was found in both disease groups.

Conclusions

Peripapillary RNFL vascular microcirculation measured as blood flux index by OMAG showed significant differences among OAG, glaucoma suspect, and normal controls and was significantly correlated with functional and structural defects. Retinal nerve fiber layer microcirculation measurement using OMAG may help physicians monitor glaucoma.

Optical Coherence Tomography for Retinal Surgery: Perioperative Analysis to Real-Time Four-Dimensional Image-Guided Surgery

Magnification of the surgical field using the operating microscope facilitated profound innovations in retinal surgery in the 1970s, such as pars plana vitrectomy. Although surgical instrumentation and illumination techniques are continually developing, the operating microscope for vitreoretinal procedures has remained essentially unchanged and currently limits the surgeon's depth perception and assessment of subtle microanatomy. Optical coherence tomography (OCT) has revolutionized clinical management of retinal pathology, and its introduction into the operating suite may have a similar impact on surgical visualization and treatment. In this article, we review the evolution of OCT for retinal surgery, from perioperative analysis to live volumetric (four-dimensional, 4D) image-guided surgery. We begin by briefly addressing the benefits and limitations of the operating microscope, the progression of OCT technology, and OCT applications in clinical/perioperative retinal imaging. Next, we review intraoperative OCT (iOCT) applications using handheld probes during surgical pauses, two-dimensional (2D) microscope-integrated OCT (MIOCT) of live surgery, and volumetric MIOCT of live surgery. The iOCT discussion focuses on technological advancements, applications during human retinal surgery, translational difficulties and limitations, and future directions.

Signal Normalization Reduces Image Appearance Disparity Among Multiple Optical Coherence Tomography Devices

Purpose

To assess the effect of the previously reported optical coherence tomography (OCT) signal normalization method on reducing the discrepancies in image appearance among spectral-domain OCT (SD-OCT) devices.

Methods

Healthy eyes and eyes with various retinal pathologies were scanned at the macular region using similar volumetric scan patterns with at least two out of three SD-OCT devices at the same visit (Cirrus HD-OCT, Zeiss, Dublin, CA; RTVue, Optovue, Fremont, CA; and Spectralis, Heidelberg Engineering, Heidelberg, Germany). All the images were processed with the signal normalization. A set of images formed a questionnaire with 24 pairs of cross-sectional images from each eye with any combination of the three SD-OCT devices either both pre- or postsignal normalization. Observers were asked to evaluate the similarity of the two displayed images based on the image appearance. The effects on reducing the differences in image appearance before and after processing were analyzed.

Results

Twenty-nine researchers familiar with OCT images participated in the survey. Image similarity was significantly improved after signal normalization for all three combinations (P ≤ 0.009) as Cirrus and RTVue combination became the most similar pair, followed by Cirrus and Spectralis, and RTVue and Spectralis.

Conclusions

The signal normalization successfully minimized the disparities in the image appearance among multiple SD-OCT devices, allowing clinical interpretation and comparison of OCT images regardless of the device differences.

Translational Relevance

The signal normalization would enable direct OCT images comparisons without concerning about device differences and broaden OCT usage by enabling long-term follow-ups and data sharing.

Optical coherence tomography based angiography [Invited]

Optical coherence tomography (OCT)-based angiography (OCTA) provides in vivo, three-dimensional vascular information by the use of flowing red blood cells as intrinsic contrast agents, enabling the visualization of functional vessel networks within microcirculatory tissue beds non-invasively, without a need of dye injection. Because of these attributes, OCTA has been rapidly translated to clinical ophthalmology within a short period of time in the development. Various OCTA algorithms have been developed to detect the functional micro-vasculatures in vivo by utilizing different components of OCT signals, including phase-signal-based OCTA, intensity-signal-based OCTA and complex-signal-based OCTA. All these algorithms have shown, in one way or another, their clinical values in revealing micro-vasculatures in biological tissues in vivo, identifying abnormal vascular networks or vessel impairment zones in retinal and skin pathologies, detecting vessel patterns and angiogenesis in eyes with age-related macular degeneration and in skin and brain with tumors, and monitoring responses to hypoxia in the brain tissue. The purpose of this paper is to provide a technical oriented overview of the OCTA developments and their potential pre-clinical and clinical applications, and to shed some lights on its future perspectives. Because of its clinical translation to ophthalmology, this review intentionally places a slightly more weight on ophthalmic OCT angiography.

Effect of Aging on Retinal Nerve Fiber Layer Thickness in Normal Asian Indian Eyes: A Longitudinal Study

PURPOSE

To determine longitudinal retinal nerve fiber layer (RNFL) thickness measurement change with aging, after a period of 3 years using spectral optical coherence tomography/scanning laser ophthalmoscope (OCT/SLO).

METHODS

A total of 50 eyes of 25 normal subjects underwent RNFL thickness measurement in 2008 and again in 2011 by a single operator, using spectral OCT/SLO. Measurements were compared at baseline and at follow-up. Linear mixed model analysis was used to measure the effect of age on RNFL thickness measurements over the 3 years.

RESULTS

Mean RNFL thickness was 107.92 ± 11.1 µm in 2008 and 106.56 ± 10.8 µm in 2011. For every year increase in age, mean RNFL thickness showed a statistically significant decrease by -0.54 µm (95% confidence interval, -0.76 to -0.31; p < 0.0001). There was a statistically significant loss of peripapillary RNFL thickness in most RNFL regions, except for the temporal quadrant (p = 0.37) and corresponding 7, 8, 9, and 10 o'clock hour sectors (p = 0.72, 0.75, 0.17, 0.14, respectively).

CONCLUSION

RNFL thickness as measured by spectral OCT/SLO decreased significantly with advancing age over a period of 3 years, and was not uniform across the four quadrants. This age-related variation should be taken into account in RNFL thickness measurements when evaluating patients for diagnosis and follow-up of glaucoma.

Reproducibility of retinal nerve fiber layer measurements across the glaucoma spectrum using optical coherence tomography

PURPOSE

The purpose was to determine intra-session and inter-session reproducibility of retinal nerve fiber layer (RNFL) thickness measurements with the spectral-domain Cirrus optical coherence tomography (OCT) ® (SD-OCT) in normal and glaucomatous eyes, including a subset of advanced glaucoma.

MATERIALS AND METHODS

RNFL measurements of 40 eyes of 40 normal subjects and 40 eyes of 40 glaucomatous patients including 14 with advanced glaucoma were obtained on the Cirrus OCT ® (Carl Zeiss Meditec, Dublin, CA, USA) five times on 1-day (intra-session) and on five separate days (inter-session). Intraclass correlation coefficient (ICC), coefficient of variation (COV), and test-retest variability (TRT) values were calculated for mean and quadrant RNFL in each group separately. Reproducibility values were correlated with age and stage of glaucoma.

RESULTS

For intra-session reproducibility, the ICC, COV, and TRT values for mean RNFL thickness in normal eyes were 0.993, 1.96%, and 4.02 µm, respectively, 0.996, 2.39%, and 3.84 µm in glaucomatous eyes, and 0.996, 2.41%, and 3.70 µm in advanced glaucoma. The corresponding inter-session values in normal eyes were 0.992, 2.16%, and 4.09 µm, 0.995, 2.62%, and 3.98 µm in glaucoma and 0.990, 2.70%, and 4.16 µm in advanced glaucoma. The mean RNFL thickness measurements were the most reproducible while the temporal quadrant had the lowest reproducibility values in all groups. There was no correlation between reproducibility and age or mean deviation on visual fields.

CONCLUSIONS

Peripapillary RNFL thickness measurements using Cirrus OCT ® demonstrated excellent reproducibility in normal and glaucomatous eyes, including eyes with advanced glaucoma. Mean RNFL thickness measurements appear to be the most reproducible and probably represent the best parameter to use for longitudinal follow-up.

Risk factors for visual field progression of normal-tension glaucoma in patients with myopia

OBJECTIVE

To identify risk factors for visual field progression of normal-tension glaucoma (NTG) in patients with myopia.

DESIGN

Longitudinal, observational study.

PARTICIPANTS

Fifty-one eyes of 51 NTG patients with myopia (less than -0.75D based on spherical equivalence) who had undergone visual field (VF) testing at least once per year for ≥6 years between November 2005 and December 2013.

METHODS

Progression was defined using event-based guided progression analysis. Risk factors were analyzed using the Cox proportional hazards model and further tested for independence in a multivariate model.

RESULTS

The mean observation period was 7.0 ± 1.3 years, and 16 of 51 subjects showed progression. In the univariate analysis, abnormal retinal nerve fibre layer (RNFL) colour codes (yellow or red sector) at the 11, 10, and 7 o'clock positions on optical coherence tomography showed significant associations with the VF progression (p = 0.03, 0.03, and 0.01, respectively). In the final multivariate models, the abnormal RNFL colour code of the 7 o'clock sector (inferotemporal sector) was the only significant risk factor for progression (hazard ratio = 4.07 and 4.37; 95% CI, 1.11-14.92 and 1.27-15.04; p = 0.03 and 0.02, respectively).

CONCLUSIONS

Inferotemporal RNFL thinning could be a risk factor for progression in NTG patients with myopia.

Retinal nerve fiber layer thickness in a healthy Turkish population measured by optical coherence tomography

BACKGROUND

Normative optical coherence tomography (OCT) data is required for different subsets of the population as ethnic differences in retinal nerve fiber layer (RNFL) thickness have been reported. An OCT database for the normal Turkish population is not commercially available.

OBJECTIVES

Quantify peripapillary RNFL thickness in a Turkish population.

DESIGN

Cross-sectional, descriptive study.

SETTING

Numune Training and Research Hospital, Adana, Turkey.

SUBJECTS AND METHODS

RNFL measurements performed by Spectral OCT with a circular scan with 3.4 mm circle were centered around the optic disc of the right eye of each subject. Correlation of the effects of age and gender on RNFL thickness was analyzed.

MAIN OUTCOME MEASURE(S)

Correlation and measurements of RNFL. Retinal nerve fiber layer thick- ness measurements were obtained for the entire circumference of the optic nerve head.

RESULTS

In 307 healthy subjects consisting of 135 (44%) males and 172 (56%) females, with a mean (SD) age of 35.1 (9.6) years (range, 20-50 years), RNFL was superior: 132.2 (16.63) micro m, inferior: 139.1 (14.53) micro m, nasal: 96.2 (14.23) micro m, temporal: 79.8 (10.7) micro m. The mean (SD) RNFL thickness for the group was 111.5 (9.3) micro m. There was no significant difference between the average RNFL thicknesses of age groups nor between males and females (P=.1, P=.42), and no significant correlation with respect to age (P=.430, r=-.04). There was a statistically significant difference between the inferior quadrants of the two genders (P=.04).

CONCLUSIONS

RNFL thickness did not vary significantly with gender. A weak negative but statistically nonsignificant correlation between average RNFL thickness and age was found.

LIMITATIONS

The participants were young adults or at early middle age so age effects on RNFL thickness may not be explained. The data does not reflect the entire Turkish population, which is not homogeneous.

Optic coherence tomography shows inflammation and degeneration in major depressive disorder patients correlated with disease severity

BACKGROUND

Previous research has consistently detected inflammation in the etiology of depression and neuroimaging studies have demonstrated gray matter abnormalities implying a neurodegenerative process in depression. The aim of this study was to compare ganglion cell layer (GCL), and inner plexiform layer (IPL) volumes and retinal nerve fiber layer (RNFL) thickness between first episode and recurrent major depressive disorder (MDD) patients and controls using optic coherence tomography (OCT) in order to detect findings supporting a degenerative process. Also choroid thicknesses of the same groups were compared to examine effects of inflammation on MDD.

METHODS

This study included 50 recurrent MDD patients, 50 first episode MDD patients and 50 controls. OCT measurements were performed by a spectral OCT device. GCL and IPL volumes and RNFL and choroid thicknesses were measured automatically by the device.

RESULTS

GCL and IPL volumes were significantly smaller in recurrent depression patients than first episode patients and in all MDD patients than controls. Also there were significant negative correlations between their volumes and disease severity parameters such as Ham-D and CGI scores, and disease duration. RNFL thicknesses were also lower in recurrent MDD patients than first episode patients and all MDD patients than controls but statistical significance was achieved only for global RNFL and temporal superior RNFL. Mean choroid thickness was higher in MDD patients than controls and in first episode MDD patients than recurrent MDD patients.

LIMITATIONS

Cross-sectional design of our study limits conclusions about progressive degeneration during the course of MDD. Lack of a control neuroimaging method like magnetic resonance imaging makes it hard to draw firm conclusions from our results.

CONCLUSIONS

OCT finding of decreased GCL and IPL volumes supports previous research suggesting degeneration in MDD. OCT may be an important tool to track neurodegeneration in patients with major depression. Considering RNFL to be the latest layer that will be affected during course of degeneration, GCL and IPL volumes appear to be better parameters to follow. In addition, choroid may be an important structure to detect acute attack period and to follow inflammatory process in MDD like in systemic inflammatory diseases.

Retinal nerve fibre layer thickness in a general population in Iran

BACKGROUND

To determine retinal nerve fibre layer (RNFL) thickness distribution and its related factors in a general population of 45 to 69 year olds in Iran.

DESIGN

Population-based cross-sectional study.

PARTICIPANTS

Of the 5190 participants of phase one of Shahroud Eye Cohort Study, 4737 participated in Phase two (participation rate = 91.3%).

METHODS

All study participants underwent visual acuity measurement, refraction tests, slit lamp examination and ophthalmoscopic fundus exam. Tests also included imaging with Cirrus HD-OCT 4000 and its RNFL thickness data were used in this study.

MAIN OUTCOME MEASURES

The overall RNFL thickness and the average RNFL thickness in different quadrants.

RESULTS

Mean RNFL thickness in the superior, inferior, nasal and temporal quadrants were 92.47 µm [95% confidence interval (CI): 92.14-92.80], 111.22 µm (95% CI: 110.7-111.73), 118.93 µm (95% CI: 118.31-119.55), 74.83 µm (95% CI: 74.07-75.59) and 65.48 µm (95% CI: 65.06-65.90). Multiple linear regression models indicated that RNFL thickness in all quadrants decreased with ageing, was lower in females (coefficient:-0.87 and P = 0.015), decreased by 1.42 µm (P < 0.001) for each millimetre increase in axial length and decreased by 0.41 µm (P = 0.041) for each diopter decrease in spherical equivalent refraction of myopia.

CONCLUSION

RNFL thickness in the 45 to 69-year-old Iranian population is lower compared to other studies. This difference should be noted in making disease diagnoses, particularly glaucoma. Also, there is a significant relationship between ageing and RNFL thinning in all quadrants. Longer axial length, myopia and male gender are associated with reduced RNFL thickness.

Relationship between visual field changes and optical coherence tomography measurements in advanced open-angle glaucoma

AIM

To assess relationships between functional changes in visual field and structural changes in advanced open-angle glaucoma (OAG) found using spectral-domain optical coherence tomography (SD-OCT).

METHODS

Thirty-one eyes of 25 patients with OAG were included in this study. Besides the routine ophthalmological exam the patients underwent standard automated perimetry (SAP) (Humphrey Field Analyzer) and SD-OCT (RTVue-100) performed within 6 months. The global perimetric indices in the study group were as follows: mean deviation (MD) 12.33±6.18 dB and pattern standard deviation (PSD) 9.17±3.41 dB. The relationship between OCT measurements and MD and PSD was evaluated by correlation analysis (Pearson's correlation coefficient) and regression analysis (linear and nonlinear regression models).

RESULTS

Thickness measurements of the lower halves of ganglion cell complex (GCC) and retinal nerve fiber layer by two scanning protocols (ONH and 3.45) showed these to be thinner than the upper halves, but the difference failed to reach statistical significance. The correlations between global indices MD/PSD and most of the analysed quantitative OCT measurements were moderate (r in the range between 0.3 and 0.6). The correlation between MD and GCC showed nonlinear cubic regression (R2=0.417, P=0.004). Good correlation was found between MD and GLV (R2=0.383; P=0.008). Linear regression (P<0.05) was found only between MD and Cup area (R2=0.175, P=0.024) and between MD and RNFL by 3.45 protocol (R2=0.131, P=0.045).

CONCLUSION

Nonlinear regressive models appear to be more appropriate in the assessment of the correlations between functional and structural changes in eyes with advanced glaucoma. The correlations we found were moderate.

Retinal Nerve Fiber and Optic Disc Morphology Using Spectral-Domain Optical Coherence Tomography in Scleroderma Patients

Purpose

To evaluate the optic nerve head parameters and peripapillary retinal nerve fiber layer using spectral-domain optical coherence tomography (SD-OCT) in a systemic sclerosis (SSc) cohort and age-matched controls to determine whether SSc patients have an increased risk of normal-tension glaucoma (NTG).

Methods

We examined 30 patients (3 male, 27 female) with SSc and 28 age- and sex-matched controls. Retinal nerve fiber and optic disc morphology were evaluated using Cirrus SD-OCT.

Results

Optic disc morphology measurements including disc area, rim area, average and vertical cup/disc (C/D) ratio, and cup volume were not significantly different between the study groups. The average and 4-quadrant retinal nerve fiber layer (RNFL) measurements of the C/D >0.3 subgroups were not significantly different in the patients and controls. These values were also similar for the C/D >0.5 subgroups except that the average inferior quadrant RNFL thickness of the right eyes in the patient subgroup was significantly thinner than in the control subgroup (p<0.05).

Conclusions

Our SSc cohort had relatively shorter disease duration but increased prevalence of early glaucomatous damage signs. Our findings indicate that SSc is a risk factor for developing normal-tension glaucoma. Further studies combined with visual field evaluation are necessary to identify the long-term glaucomatous effects of SSc.

The Development, Commercialization, and Impact of Optical Coherence Tomography

This review was written for the special issue of IOVS to describe the history of optical coherence tomography (OCT) and its evolution from a nonscientific, historic perspective. Optical coherence tomography has become a standard of care in ophthalmology, providing real-time information on structure and function - diagnosing disease, evaluating progression, and assessing response to therapy, as well as helping to understand disease pathogenesis and create new therapies. Optical coherence tomography also has applications in multiple clinical specialties, fundamental research, and manufacturing. We review the early history of OCT describing how research and development evolves and the important role of multidisciplinary collaboration and expertise. Optical coherence tomography had its origin in femtosecond optics, but used optical communications technologies and required advanced engineering for early OCT prototypes, clinical feasibility studies, entrepreneurship, and corporate development in order to achieve clinical acceptance and clinical impact. Critical advances were made by early career researchers, clinician scientists, engineering experts, and business leaders, which enabled OCT to have a worldwide impact on health care. We introduce the concept of an "ecosystem" consisting of research, government funding, collaboration and competition, clinical studies, innovation, entrepreneurship and industry, and impact - all of which must work synergistically. The process that we recount is long and challenging, but it is our hope that it might inspire early career professionals in science, engineering, and medicine, and that the clinical and research community will find this review of interest.

Morphometric Analysis of Peripapillary Thickness in Hypertensives and Normotensives using Optical Coherence Tomography (OCT)

INTRODUCTION

Hypotension following antihypertensive treatment is associated with retinal nerve fibre loss. There are studies that have reported the changes in RNFL in hypertensives.

AIM

To compare the Retinal Nerve Fibre Layer (RNFL) thickness using Optical Coherence Tomography (OCT) in hypertensive and normotensive individuals.

MATERIALS AND METHODS

The cross-sectional study was conducted from October 2012 to September 2014 to compare the RNFL thickness using SD OCT in hypertensive {no other ocular or systemic co-morbidity, vision better or equal to 6/9 (n=30)} and normotensive (n=30) individuals.

RESULTS

Statistically significant RNFL loss was detected in hypertensives (98.31 ± 7.01) when compared to the normotensives (102.51 ± 8.72) p=0.001.

CONCLUSION

Significant loss of RNFL in hypertensives point towards the altered autoregulation and warrants larger studies to assess the clinical relevance.

Facilitating Glaucoma Diagnosis With Intereye Retinal Nerve Fiber Layer Asymmetry Using Spectral-Domain Optical Coherence Tomography

PURPOSE

To test whether increased intereye retinal nerve fiber layer (RNFL) asymmetry may be indicative of glaucoma. To determine the best statistical methods and intereye RNFL cutoffs for differentiating between normal and glaucoma subjects to better alert clinicians to early glaucomatous damage.

METHODS

Sixty-six primary open-angle glaucoma (OAG) and 40 age-matched normal subjects had both eyes imaged at the Massachusetts Eye and Ear Infirmary with a commercially available spectral-domain optical coherence tomography (OCT) machine. Statistical methodologies were used to find cutoffs that achieved the best sensitivities and specificities for differentiating OAG from normal subjects.

RESULTS

Intereye RNFL asymmetry for global average, all quadrants, and all sectors was significantly greater in OAG than normal subjects. Intereye RNFL asymmetry for global average showed the greatest statistical difference (P<0.001) between OAG (23.64 ± 14.90 μm) and normal eyes (3.58 ± 3.96 μm), with 6.60 times greater asymmetry in OAG eyes. The inferior quadrant showed the second greatest difference, with 3.91 times greater asymmetry in OAG eyes. Using a statistically determined cutoff of 6.0 μm as abnormal, intereye RNFL asymmetry for global average achieved a sensitivity of 74.24% and specificity of 90% in differentiating between normal and OAG subjects, achieving a better combination of sensitivity and specificity than intereye RNFL asymmetry of any quadrant or sector.

CONCLUSIONS

Intereye RNFL asymmetry may be a useful clinical OCT measurement to provide quantitative assessment of early glaucomatous damage. Newly developed algorithms for intereye RNFL asymmetry may improve the ability to detect glaucoma.

Can the retinal ganglion cell layer (GCL) volume be a new marker to detect neurodegeneration in bipolar disorder?

PURPOSE

The aim of this study was to compare the ganglion cell layer (GCL) volume and retinal nerve fiber layer (RNFL) thickness in bipolar patients and controls using optic coherence tomography to demonstrate neurodegeneration in bipolar disorder.

METHODS

This study involved 43 euthymic bipolar I patients who were being followed by the Psychiatry Department of Adiyaman University Medical School and 43 healthy volunteers as controls. Optic coherence tomography (OCT) measurements were performed for both groups. The RNFL thickness and GCL volumes were measured and recorded automatically by a spectral OCT device.

FINDINGS

No differences in sociodemographics were detected between groups, except for unemployment status, which was significantly higher in the patient group. The RNFL thickness was lower in patients compared with controls at all measured regions, and this decrease was statistically significant for the global RNFL measurement. The GCL volume was also significantly lower in the patient group. There was a significant negative correlation between the disease parameters, such as the disease duration, YMRS score, CGI score, and number of hospitalizations, and GCL volume.

DISCUSSION

These findings suggest that neurodegeneration occurs during the course of bipolar disorder. This degeneration may be demonstrated by decreased GCL at early stages, and as the disease progresses, involvement of other retinal layers, such as the RNFL and IPL, may be observed.

Optical Coherence Tomography for the Radiologist

Optical coherence tomography is an imaging technique using low coherence light sources to produce high-resolution cross-sectional images. This article reviews pertinent anatomy and various pathologies causing optic atrophy (eg, compressive, infiltrating, demyelinating) versus optic nerve swelling (from increased intracranial pressure known as papilledema or other optic nerve intrinsic pathologies). On optical coherence tomography, optic atrophy is often associated with reduced average retinal nerve fiber layer thickness, whereas optic nerve swelling is usually associated with increased average retinal nerve fiber layer thickness.

Retinal Nerve Fiber Layer Thickness Measurement Comparison Using Spectral Domain and Swept Source Optical Coherence Tomography

Purpose

To investigate the retinal nerve fiber layer (RNFL) thickness concordance when measured by spectral domain (SD) and swept source (SS) optical coherence tomography (OCT), and to compare glaucoma-discriminating capability.

Methods

RNFL thicknesses were measured with the scan circle, centered on the optic nerve head, in 55 healthy, 41 glaucoma suspected, and 87 glaucomatous eyes. The RNFL thickness measured by the SD-OCT (sdRNFL thickness) and SS-OCT (ssRNFL thickness) were compared using the t-test. Bland-Altman analysis was performed to examine their agreement. We compared areas under the receiver operating characteristics curve and examined sdRNFL and ssRNFL thickness for discriminating glaucomatous eyes from healthy eyes, and from glaucoma suspect eyes.

Results

The average ssRNFL thickness was significantly greater than sdRNFL thickness in healthy (110.0 ± 7.9 vs. 100.1 ± 6.8 µm, p < 0.001), glaucoma suspect (96.8 ± 9.3 vs. 89.6 ± 7.9 µm, p < 0.001), and glaucomatous eyes (74.3 ± 14.2 vs. 69.1 ± 12.4 µm, p = 0.011). Bland-Altman analysis showed that there was a tendency for the difference between ssRNFL and sdRNFL to increase in eyes with thicker RNFL. The area under the curves of the average sdRNFL and ssRNFL thickness for discriminating glaucomatous eyes from healthy eyes (0.984 vs. 0.986, p = 0.491) and glaucoma suspect eyes (0.936 vs. 0.918, p = 0.132) were comparable.

Conclusions

There was a tendency for ssRNFL thickness to increase, compared with sdRNFL thickness, in eyes with thicker RNFL. The ssRNFL thickness had comparable diagnostic capability compared with sdRNFL thickness for discriminating glaucomatous eyes from healthy eyes and glaucoma suspect eyes.

Virtual Averaging Making Nonframe-Averaged Optical Coherence Tomography Images Comparable to Frame-Averaged Images

Purpose

Developing a novel image enhancement method so that nonframe-averaged optical coherence tomography (OCT) images become comparable to active eye-tracking frame-averaged OCT images.

Methods

Twenty-one eyes of 21 healthy volunteers were scanned with noneye-tracking nonframe-averaged OCT device and active eye-tracking frame-averaged OCT device. Virtual averaging was applied to nonframe-averaged images with voxel resampling and adding amplitude deviation with 15-time repetitions. Signal-to-noise (SNR), contrast-to-noise ratios (CNR), and the distance between the end of visible nasal retinal nerve fiber layer (RNFL) and the foveola were assessed to evaluate the image enhancement effect and retinal layer visibility. Retinal thicknesses before and after processing were also measured.

Results

All virtual-averaged nonframe-averaged images showed notable improvement and clear resemblance to active eye-tracking frame-averaged images. Signal-to-noise and CNR were significantly improved (SNR: 30.5 vs. 47.6 dB, CNR: 4.4 vs. 6.4 dB, original versus processed, P < 0.0001, paired t-test). The distance between the end of visible nasal RNFL and the foveola was significantly different before (681.4 vs. 446.5 μm, Cirrus versus Spectralis, P < 0.0001) but not after processing (442.9 vs. 446.5 μm, P = 0.76). Sectoral macular total retinal and circumpapillary RNFL thicknesses showed systematic differences between Cirrus and Spectralis that became not significant after processing.

Conclusion

The virtual averaging method successfully improved nontracking nonframe-averaged OCT image quality and made the images comparable to active eye-tracking frame-averaged OCT images.

Translational Relevance

Virtual averaging may enable detailed retinal structure studies on images acquired using a mixture of nonframe-averaged and frame-averaged OCT devices without concerning about systematic differences in both qualitative and quantitative aspects.

Relationship Between Peripapillary Choroid and Retinal Nerve Fiber Layer Thickness in a Population-Based Sample of Nonglaucomatous Eyes

PURPOSE

To describe the relationship between peripapillary choroidal thickness and retinal nerve fiber layer (RNFL) thickness in a population-based sample of nonglaucomatous eyes.

DESIGN

Population-based, cross-sectional study.

METHODS

A total of 478 nonglaucomatous subjects aged over 40 years were recruited from the Singapore Malay Eye Study (SiMES-2). All participants underwent a detailed ophthalmic examination, including Cirrus and Spectralis optical coherence tomography (OCT) for the measurements of RNFL thickness and peripapillary choroidal thickness, respectively. Associations between peripapillary choroidal thickness and RNFL thickness were assessed using linear regression models with generalized estimating equations.

RESULTS

Of the 424 included subjects (843 nonglaucomatous eyes), 60.9% were women, and the mean (SD) age was 66.74 (10.44) years. The mean peripapillary choroidal thickness was 135.59 ± 56.74 μm and the mean RNFL thickness was 92.92 ± 11.41 μm. In terms of distribution profile, peripapillary choroid was thickest (150.04 ± 59.72 μm) at the superior and thinnest (110.71 ± 51.61 μm) at the inferior quadrant, whereas RNFL was thickest (118.60 ± 19.83 μm) at the inferior and thinnest (67.36 ± 11.36 μm) at the temporal quadrant. We found that thinner peripapillary choroidal thickness (PPCT) was independently associated with thinner RNFL thickness globally (regression coefficient [β] = -1.334 μm for per-SD decrease in PPCT, P = .003), and in the inferior (β = -2.565, P = .001) and superior (β = -2.340, P = .001) quadrants even after adjusting for potential confounders.

CONCLUSIONS

Thinner peripapillary choroid was independently associated with thinner RNFL globally and in the inferior and superior regions. This structure-structure relationship may need further exploration in glaucomatous eyes prior to its application in clinical settings.

Retinal nerve fiber layer reflectometry must consider directional reflectance

Recent studies reveal that measurements of retinal nerve fiber layer (RNFL) reflectance provide more sensitive detection of glaucomatous damage than RNFL thickness, but most do not consider directional reflectance of the RNFL, an important source of variability. This study quantitatively compared RNFL directional reflectance, represented by an angular spread function (ASF), measured at different scattering angles, different wavelengths and different distances from the optic nerve head (ONH) and for bundles with different thicknesses (T). An ASF was characterized by its amplitude (A) and width (W). Internal reflectance of a bundle was expressed as A/T. The study found that A varied significantly with scattering angle and wavelength and that A/T was different among bundles but constant along the same bundle, indicating that the internal structure of axons may vary among bundles but does not change with distance. This study also found that W was larger near the ONH and at longer wavelengths, but did not depend on scattering angle or T. Because a 4.3° change in incident angle can change reflected intensity by a factor of 2.7, accounting for directional reflectance should improve the accuracy and reproducibility of RNFL reflectance measurements.

Changes in peripapillary retinal nerve fiber layer thickness in chronic glaucoma and non-glaucoma patients after phacoemulsification cataract surgery

Background: Phacoemulsification is a common cataract operation nowadays. During phacoemulsification, variation in intraocular pressure (IOP) may occur, which might change the retinal nerve fiber layer (RNFL) thickness. This study was aimed to evaluate the change in peripapillary RNFL thickness and mean deviation (MD) of visual field after phacoemulsification in chronic primary glaucoma and non-glaucoma patients. Methods: Cohort prospective study was done on 26 patients (13 chronic glaucoma eyes and 13 non-glaucoma eyes) who underwent phacoemulsification. The changes in peripapillary RNFL thickness and MD of visual field were measured as the primary outcome. Comparison between pre- and post-surgery was analyzed with paired t-test, while unpaired t-test was used for comparison between groups.Results: There were no significant changes in RNFL thickness on both groups. Average RNFL thickness in glaucoma group before and after phacoemulsification were 94.9±20.0 μm and 99.1±21.3 μm, respectively (p>0.05). Average RNFL thickness in non-glaucoma group were 100.2±11.1 μm and 101.7±6.8 μm, respectively (p>0.05). Glaucoma patients yielded decreasing mean deviation (MD) of visual field, but it was not statistically significant (p=0.071). In contrast, the MD of visual field after surgery was significantly increased in non-glaucoma group (p=0.005).Conclusion: Phacoemulsification tended to increase peripapillary RNFL thickness in glaucoma or non-glaucoma patients. The visual field tended to decrease in glaucoma patients, but was significantly increased in non-glaucoma patients.

Effect of Head Tilt and Ocular Compensatory Mechanisms on Retinal Nerve Fiber Layer Measurements by Cirrus Spectral Domain and Spectralis Optical Coherence Tomography in Normal Subjects

PURPOSE

To determine the effect of head tilt and ocular compensatory mechanisms on retinal nerve fiber layer (RNFL) thickness measurements using the Cirrus and Spectralis spectral-domain optical coherence tomography (OCT) in healthy eyes. Our secondary objective was to assess the visual influence on ocular compensatory mechanisms during head tilt.

MATERIALS AND METHODS

This is a prospective, observational study. A single randomly selected eye was scanned undilated in 3 positions (baseline, right, and left tilt) using both machines. In addition, patching was also done for the contralateral eye during head tilt and RNFL measurements repeated. The paired t test was used to analyze effect on RNFL thickness. One-way repeated-measures analysis of variance was used to compare differences in RNFL measurements.

RESULTS

In Cirrus OCT RNFL analysis, ipsilateral head tilt resulted in superior thinning and temporal thickening, whereas contralateral head tilt resulted in inferior thinning, nasal thickening, as well as temporal thickening (all P<0.05). Head tilt did not cause any significant change in RNFL thickness with Spectralis OCT (P>0.05). Patching the contralateral eye also did not alter Cirrus RNFL measurement errors due to head tilt.

CONCLUSIONS

Head tilt can affect the measurement of the RNFL thickness in Cirrus OCT, and ocular compensatory mechanisms were not sufficient to prevent this. In contrast, Spectralis OCT RNFL thickness measurements were not affected by head tilt. Patching the contralateral eye during head tilt in Cirrus OCT also did not affect RNFL variability. The visual influence on ocular compensatory mechanisms during head tilt appears insignificant.

Effect of Refractive Status and Axial Length on Peripapillary Retinal Nerve Fibre Layer Thickness: An Analysis Using 3D OCT

BACKGROUND

Accurate measurement of retinal nerve fiber layer (RNFL) is now possible with the high resolution optical coherence tomography (OCT). Effect of refractive status of the eye on RNFL thickness may be relevant in the diagnosis of glaucoma and other optic nerve diseases.

AIM

To assess the RNFL thickness and compare its correlation with refractive status and axial length of the eye.

MATERIAL AND METHODS

Three hundred eyes of 150 patients were included in this study, who underwent RNFL analysis using TOPCON 3D OCT 2000. Analysis of variance has been used to find the significance of study parameters between the study groups.

RESULTS

The study showed that refractive status/axial length affected the peripapillary RNFL thickness significantly.

CONCLUSION

The study suggests that the diagnostic accuracy of OCT may be improved by considering refractive status and axial length of the eye when RNFL is measured.

Retinal nerve fiber layer thickness in prematurity is correlated with stage of retinopathy of prematurity

PURPOSE

To compare retinal nerve fiber layer (RNFL) thickness profiles between preterm and full-term children and to investigate factors affecting the RNFL distribution in preterm children.

METHODS

We performed Spectral domain optical coherence tomography (SD-OCT) peripapillary RNFL circular scan centered on the optic disc in 50 premature and 58 full-term children. RNFL thickness profiles were compared between preterm and full-term children using a linear regression model. Among preterm patients in this study, 20 patients previously received laser treatment for severe retinopathy of prematurity (ROP).

RESULTS

Global average, nasal, and superior disc RNFL thickness profiles were significantly smaller in preterm children (92.70±16.57 μm, 56.02±17.04 μm, and 108.74±27.36 μm, respectively) compared with full-term children (101.63±9.21 μm, P=0.006, 69.14±14.15 μm, P<0.001, and superior, 129.11±18.14 μm, P<0.001, respectively). Multivariable analysis revealed that ROP stage was inversely correlated with nasal RNFL thickness (P=0.010).

CONCLUSIONS

Our SD-OCT data demonstrate decreased global average, nasal, and superior disc RNFL thicknesses in preterm children. ROP stage was inversely correlated with nasal RNFL thickness. Further studies are needed to better understand the association between these structural changes and visual functions in preterm children.

Study of Spectral-Domain Optical Coherence Tomography in Children: Normal Values and Influence of Age, Sex, and Refractive Status

Purpose

To establish normal values for retinal nerve fiber layer (RNFL), macular thickness, and macular volume in children using spectral-domain optical coherence tomography (OCT).

Methods

A descriptive cross-sectional study was performed in healthy children between 3 and 14 years of age. Each child underwent a comprehensive ophthalmic examination that included 3 OCT scans with Spectralis (Heidelberg Engineering, Heidelberg, Germany). All measurements were performed by the same operator, and one eye was randomly selected. The influence of age, sex, and refraction on OCT measurements was analyzed.

Results

The sample consisted of 162 Caucasian subjects, mean age 8.1 ± 3.03 years. The spherical equivalent was 0.03 ± 0.19 D (range ±4 D, astigmatism <1 D). The average values were 263.69 ± 4.54 µm for central macular thickness, 0.21 ± 0.01 mm3 for central macular volume, and 100.45 ± 1.98 µm for RNFL. A significant correlation between RNFL and spherical equivalent was found for the nasal (p = 0.001), inferior (p = 0.009), and inferior nasal (p = 0.005) sectors. No differences were found with regard to sex (p>0.05). However, central macular thickness and central macular volume were correlated with age (p = 0.027, p = 0.02).

Conclusions

This study provides reference values for macular thickness, macular volume, and RNFL in healthy children.

Size of the Optic Nerve Head and Its Relationship with the Thickness of the Macular Ganglion Cell Complex and Peripapillary Retinal Nerve Fiber Layer in Patients with Primary Open Angle Glaucoma

Purpose. To evaluate the relationships among the optic nerve head (ONH) area, macular ganglion cell complex (mGCC) thickness, circumpapillary retinal nerve fiber layer (cpRNFL) thickness, and visual field defects in patients with primary open angle glaucoma (POAG). Methods. This retrospective study included 90 eyes of 90 patients with POAG. The ONH area, rim area, mGCC thickness, and cpRNFL thickness were measured using optical coherence tomography. Mean deviation (MD) was measured using standard automated perimetry. The relationships among clinical factors including age, refraction, the ONH area, the rim area, the mGCC thickness, the cpRNFL thickness, and MD were evaluated using correlation coefficients and multiple regression analyses. Results. The significant correlation of the ONH area with refraction (r = 0.362, P < 0.001), the mGCC thickness (r = 0.225, P = 0.033), and the cpRNFL thickness (r = 0.253, P = 0.016) was found. Multiple regression analysis showed that the ONH area, rim area, and MD were selected as significant contributing factors to explain the mGCC thickness and cpRNFL thickness. No factor was selected to explain MD. Conclusions. The ONH area, in other words, the disc size itself may affect the mGCC thickness and cpRNFL thickness in POAG patients.

Anatomic and visual function outcomes in paediatric idiopathic intracranial hypertension

BACKGROUND

There is a paucity of literature describing risk factors for vision loss in paediatric idiopathic intracranial hypertension (IIH). We investigate the final visual function, spectral domain optical coherence tomography (SD-OCT) and enhanced depth imaging (EDI)-OCT findings in children with papilledema caused by IIH.

METHODS

Medical records of 31 patients with paediatric IIH (age ≤17 years) were retrospectively reviewed. Optic disc photographs on presentation and automated perimetry, SD-OCT and EDI-OCT imaging on final follow-up visit were statistically analysed to identify patient characteristics and anatomic findings associated with irreversible vision loss.

RESULTS

Permanent visual acuity or visual field loss developed in 19% of study eyes. Papilledema of modified Frisén grade ≥3 on presentation was highly predictive of permanent vision loss (p<0.001), while associations between pubertal status and visual function outcome failed to reach statistical significance. SD-OCT revealed optic atrophy in 13% and photoreceptor loss in 19% of eyes, with both findings highly associated with vision loss (p<0.0001). Optic disc drusen was noted in 48% of study eyes by EDI-OCT but was not found to be predictive of visual outcome.

CONCLUSIONS

Clinical observation of high papilledema grade on presentation is predictive of poor visual outcomes. Vision loss is associated not only with optic atrophy but also with photoreceptor damage. Interestingly, a high proportion of study eyes had optic disc drusen, which was not associated with vision loss, but can be a diagnostic challenge in distinguishing true papilledema from pseudopapilledema.