Retinal Nerve Fiber Bundle Research Articles

Post-fever Retinitis With a Positive Weil-Felix Test: A Study From a Tertiary Center in South India.

Background Post-fever retinitis (PFR) is reported two to six weeks after fever and affects one or both eyes. Rickettsial fever is one of the most common causes of PFR. This study aimed to report the clinical features and treatment outcomes of PFR cases with a positive Weil-Felix test. Methodology In this study, we collected demographic data, fever details, eye symptoms, ocular examination findings, optical coherence tomography (OCT) and fundus fluorescein angiography findings, laboratory findings, and length of follow-up of consecutive PFR cases with a positive Weil-Felix test. All cases were treated with oral doxycycline and prednisolone. Final best-corrected visual acuity (BCVA) and ocular examination findings were recorded. Visual field examination and follow-up OCT results were noted if available. Results A total of nine patients (eight males) with a mean age of 39.1 years with fever before ocular symptoms and positive Weil-Felix test were included.Six patients had bilateral disease. The mean initial and final BCVA in the affected eyes was 1.16 and 0.35 logMAR units, respectively (p < 0001). All 15 eyes had typical white retinitis patches and retinal hemorrhages which resolved after treatment. OCT showed hyperreflectivity and inner retinal disorganization over retinitis patches. White subretinal lines were noted in three patients and retinal nerve fiber bundle defect with corresponding visual field defect was seen in one eye. Conclusions In this study, PFR due to rickettsia infections has been reported from our region for the first time. Hence, eye specialists in the region should be aware of this entity.

Concordance of Objectively Detected Retinal Nerve Fiber Bundle Defects in En Face OCT Images with Conventional Structural and Functional Changes in Glaucoma

To assess how objectively detected defects in retinal nerve fiber bundle (RNFB) reflectance on en face OCT images relate to circumpapillary retinal nerve fiber layer thickness (cpRNFLT) and visual field defects. Cross-sectional study. Sixteen participants with early glaucoma and 29 age-matched healthy controls, of whom 22 had usable en face images for the establishment of normative levels of RNFB reflectance. All the participants underwent cpRNFLT scans, visual field examination, and wide-field OCT. En face reflectivity was assessed objectively using the Summary of Multiple Anatomically Adjusted Slabs method. En face defects were deemed concordant with cpRNFLT when they had at least 1 cpRNFLT point with P < 0.01, within ± 15° of the predicted insertion on the optic disc. Visual fields were examined using custom suprathreshold perimetry and SITA Standard 24-2. For each visual field location, the corresponding reflectance was deemed abnormal if any en face superpixel within ± 1° was abnormal. The overall, positive, and negative agreements were measured in each participant. Proportion of concordant defects between en face reflectance analysis and cpRNFLT (%) as well as overall, positive, and negative agreements between en face reflectance analysis and visual field results. Most en face abnormalities had concordant cpRNFLT defects in the mapped sector (median proportion concordant, 0.85; interquartile range, 0.74-0.95). In eyes with glaucoma, a median of 8.1% (range, 2.4%-23.7%) and 14.9% (range, 3.5%-29.1%) locations showed corresponding en face and visual field defects using 24-2 and custom perimetry, respectively. Both the perimetric strategies had moderate-to-good raw agreement with en face analysis (0.66-0.68), with stronger agreement on normal findings than on defects (0.77-0.78 and 0.4-0.44). Objectively extracted reflectance defects showed strong concordance with conventional cpRNFLT damage and good agreement with perimetry, which could be enhanced by further minimization of image artifacts.

Test of a Retinal Nerve Fiber Bundle Trajectory Model Using Eyes With Glaucomatous Optic Neuropathy.

PurposeTo test a model of retinal nerve fiber bundle trajectories that predicts the arcuate-shaped patterns seen on optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) probability/deviation maps (p-maps) in glaucomatous eyes.MethodsThirty-one glaucomatous eyes from a database of 250 eyes had clear arcuate-shaped patterns on RNFL p-maps derived from an OCT cube scan. The borders of the arcuate patterns were extracted from the RNFL p-maps. Next, the trajectories from an arcuate model were compared against these borders via a normalized root-mean-square difference analysis. The model's parameter, β, was varied, and the best-fitting, initial clock-hour position of the trajectory to the border was found for each β. Finally, the regions, as determined by the arcuate border's best-fit, initial clock-hour positions, were compared against the abnormal regions on the circumpapillary retinal nerve fiber layer (cpRNFL) profile.ResultsThe arcuate model's mean βSup and βInf parameters minimized large differences between the trajectories and the arcuate borders on the RNFL p-maps. Furthermore, on average, 68% of the cpRNFL regions defined by the arcuate border's best-fit, initial clock-hour positions were abnormal (i.e., below the ≤5% threshold).ConclusionsThe arcuate model performed well in predicting the borders of arcuate patterns seen on RNFL p-maps. It also predicted the associated abnormal regions of the cpRNFL thickness plots.Translational RelevanceThis model should prove useful in helping clinicians understand topographical comparisons among different OCT representations and should improve structure-structure, as well as structure-function agreement analyses.

Automatic retinal nerve fiber bundle tracing based on large field of view polarization sensitive OCT data.

A technique to accurately estimate trajectories of retinal nerve fiber bundles (RNFB) in a large field of view (FOV) image covering 45° is described. The method utilizes stitched projections of polarization-sensitive optical coherence tomography (PS-OCT) data, as well as a mathematical model of average RNFB trajectories as prior. The fully automatic process was applied to data recorded in healthy subjects and glaucoma patients and automatically detected individual RNFB trajectories are compared to manual traces.

Enhanced Objective Detection of Retinal Nerve Fiber Bundle Defects in Glaucoma With a Novel Method for En Face OCT Slab Image Construction and Analysis.

PurposeTo introduce and evaluate the performance in detecting glaucomatous abnormalities of a novel method for extracting en face slab images (SMAS), which considers varying individual anatomy and configuration of retinal nerve fiber bundles.MethodsDense central retinal spectral domain optical coherence tomography scans were acquired in 16 participants with glaucoma and 19 age-similar controls. Slab images were generated by averaging reflectivity over different depths below the inner limiting membrane according to several methods. SMAS considered multiple 16 µm thick slabs from 8 to 116 µm below the inner limiting membrane, whereas 5 alternative methods considered single summary slabs of various thicknesses and depths. Superpixels in eyes with glaucoma were considered abnormal if below the first percentile of distributions fitted to control data for each method. The ability to detect glaucoma defects was measured by the proportion of abnormal superpixels. Proportion of superpixels below the fitted first percentile in controls was used as a surrogate false-positive rate. The effects of slab methods on performance measures were evaluated with linear mixed models.ResultsThe ability to detect glaucoma defects varied between slab methods, χ2(5) = 120.9, P < 0.0001, with SMAS showing proportion of abnormal superpixels 0.05 to 0.09 greater than alternatives (all P < 0.0001). No slab method found abnormal superpixels in controls.ConclusionsSMAS outperformed alternatives in detecting abnormalities in eyes with glaucoma. SMAS evaluates all depths with potential retinal nerve fiber bundle presence by combining multiple slabs, resulting in greater detection of reflectance abnormalities with no increase in surrogate false positives.Translational RelevanceSMAS may be used to objectively detect glaucoma defects in en face optical coherence tomography images.

Association between Topographic Features of the Retinal Nerve Fiber Bundle and Good Visual Acuity in Patients with Glaucoma

ABSTRACT Purpose: Maintaining visual acuity in glaucoma patients is an important part of preventing the deterioration of quality of vision. We identified specific areas of the papillomacular bundle (PMB) that were strongly associated with visual acuity, based on en-face images derived from optical coherence topography (OCT) wide scans. Methods: The study recruited 23 eyes of 21 glaucoma patients (age: 61.3 ± 13.0 years, M: F = 9:12, Humphrey field analyzer-measured mean deviation: -19.9 ± 6.5 dB) with good best-corrected visual acuity (20/20 or more) and a remaining PMB with a maximum width no more than half that of the vertical disc diameter. En-face images were derived from 12 × 9 mm wide-scan images made with DRI-OCT (Triton, Topcon). Averaged en-face images were created by identifying the disc center and fovea line (DFL) and aligning it between images. We then measured the frequency of remaining PMB at 10 µm intervals along a vertical line intersecting the DFL at its midpoint. Finally, we used a logistic analysis in a much larger group of patients to identify cases of glaucoma with low BCVA (<20/20). Results: In the averaged en-face image, the residual PMB area appeared as a high-intensity region above the DFL. Analysis showed that residual PMB was most common in an area 830–870 µm above the DFL. The correlation coefficient of residual PMB in this area to BCVA was -0.57 (p < .01), and among OCT parameters in this residual PMB area, the AUC to identify decreased BCVA was highest for ganglion cell complex thickness (0.85, p < .01), with a cutoff of 87.5 µm. Conclusions: This study identified specific areas of the PMB that were associated with BCVA in wide-scan, en-face OCT images from glaucoma patients. This suggests that it may be possible to identify visual impairment during glaucoma treatment by measuring this area.

A Novel Stimulus to Improve Perimetric Sampling within the Macula in Patients with Glaucoma.

SIGNIFICANCEIdentifying glaucomatous damage to the macula has become important for diagnosing and managing patients with glaucoma. In this study, we presented an approach that provides better perimetric sampling for the macular region, by testing four locations, with a good structure-function agreement.PURPOSEWe previously presented a basis for customizing perimetric locations within the macula. In this study, we aimed to improve perimetric sampling within the macula by presenting a stimulus at four locations, with maintaining a good structure-function agreement.METHODSWe tested one eye each of 30 patients (aged 50 to 88 years). Patients were selected based on observed structural damage to the macula, whereas perimetric defect (using 24-2) did not reflect the locations and extent of this damage. We used en face images to visualize retinal nerve fiber bundle defects. To measure perimetric sensitivities, we used a blob stimulus (standard deviation of 0.25°) at the 10-2 locations. A perimetric defect for a location was defined as any value equal to or deeper than −4, −5, and −6 dB below the mean sensitivity for 37 age-similar controls (aged 47 to 78 years). We also presented an elongated sinusoidal stimulus for 20 patients at four locations within the macula, in which we defined a perimetric defect as any value below the 2.5th percentile from controls.RESULTSThe −4, −5, and −6 dB criteria identified perimetric defects in 14, 13, and 11 patients, respectively. When testing with the elongated stimulus, 18 patients were identified with perimetric defect. The perimetric defects were consistent with the structural damage.CONCLUSIONSThe elongated stimulus showed a good structure-function agreement with only four testing locations as compared with 68 locations used with the blob stimulus. This demonstrates a clinical potential for this new stimulus in the next generation of perimetry.

Anatomical Location of the Raphe and Extended Raphe in the Human Retina: Implications for Assessment of the Optic Nerve with OCT.

PurposeTo determine the location of (1) the superior–inferior watershed between the fovea and optic disc (extended raphe) at the peripapillary optical coherence tomography (OCT) measurement circle and (2) the raphe, temporal to the fovea.MethodsWe used existing data consisting of 2285 traced retinal nerve fiber bundle trajectories from 83 fundus images. For localization of the extended raphe at the 3.46-mm-diameter OCT measurement circle, trajectories were classified as belonging to the superior or inferior hemiretina, using predefined criteria. For the raphe, we localized the endings of trajectories coming from the superior and inferior arcuate bundles.ResultsAt the measurement circle, the extended raphe is located 14° (range, 12°–16°) inferiorly to a horizontal line through the optic disc center. The raphe follows a horizontal line at the latitude of the fovea if the disc is assumed to be located 15° nasal to and 2° above the fovea.ConclusionsAt the measurement circle, OCT brands use either the 9 o'clock location or a straight line connecting the center of the optic disc and the fovea as a reference for separating the hemiretinas. This results, on average, in a 14° and 6° misalignment with respect to the anatomical watershed, respectively. For the macular area, the commonly used line through the center of the optic disc and the fovea fails to describe the raphe adequately.Translational RelevanceAn unbiased asymmetry assessment of the optic nerve requires a detailed knowledge of the shape and location of the (extended) raphe.

Improving the Detection of Glaucoma and Its Progression: A Topographical Approach.

Glaucoma is typically defined as a progressive optic neuropathy characterized by a specific (arcuate) pattern of visual field (VF) and anatomic changes. Therefore, we should be comparing arcuate patterns of damage seen on VFs with those seen on optical coherence tomography (OCT) maps. Instead, clinicians often use summary metrics such as VF pattern standard deviation, OCT retinal nerve fiber (RNF) global thickness, etc. There are 2 major impediments to topographically comparing patterns of damage on VF and OCT maps. First, until recently, it was not easy to make these comparisons with commercial reports. While recent reports do make it easier to compare VF and OCT maps, they have shortcomings. In particular, the 24-2 VF covers a larger retinal region than the commercial OCT scans, and, further, it is not easy to understand the topographical relationship among the different maps/plots within the current OCT reports. Here we show how a model of RNF bundles can overcome these problems. The second major impediment is the lack of a quantitative, and automated, method for comparing patterns of damage seen on VF and OCT maps. However, it is now possible to objectively and automatically quantify this agreement. Together, the RNF bundle model and the automated structure-function method should improve the power of topographical methods for detecting glaucoma and its progression. This should prove useful in clinical studies and trials, as well as for training and validating artificial intelligence/deep learning approaches for these purposes.

Expansion of retinal nerve fiber bundle narrowing in glaucoma: An adaptive optics scanning laser ophthalmoscopy study

PurposeTo investigate longitudinal changes in the retinal nerve fiber bundle in eyes with primary open angle glaucoma using adaptive optics scanning laser ophthalmoscopy. MethodsA prospective observational case series. Fourteen eyes from 12 patients with primary open angle glaucoma that exhibited retinal nerve fiber layer defects on fundus photography were imaged with adaptive optics scanning laser ophthalmoscopy over time. ResultsThe expansion of retinal nerve fiber bundle narrowing was observed on adaptive optics scanning laser ophthalmoscopy in 8 eyes (57.1%) over a period of 1.44 ± 0.42 years. Retinal nerve fiber bundle narrowing expanded horizontally in 2 eyes and vertically in 6 eyes. In 3 eyes, changes in the retinal nerve fiber layer were only detectable on adaptive optics scanning laser ophthalmoscopy images. Conclusions and ImportanceThe expansion of retinal nerve fiber bundle narrowing was observed using adaptive optics scanning laser ophthalmoscopy. Accordingly, this tool may be a useful tool for detecting glaucoma-related changes in retinal nerve fibers in a short time.

Within-subject variability in human retinal nerve fiber bundle width

With the growing availability of high-resolution imaging there has been increased interest in developing new metrics for integrity of the retinal nerve fiber layer. In particular, it has been suggested that measurement of width of retinal nerve fiber bundles (RNFBs) may be useful in glaucoma, due to low between-subject variability in mean RNFB width. However, there have also been reports of substantial within-subject variability in the width of individual RNFBs. To assess within-subject variability as a potential source of selection bias in measurements of RNFB width, we used an adaptive optics scanning laser ophthalmoscope (AOSLO) to measure widths of individual RNFBs in one eye each of 11 young adults in good ocular health. In a pilot study we analyzed a large AOSLO image of RNFL in one participant then, based on those findings, in the main study we used AOSLO to image a smaller region in 10 additional healthy young adults. The pilot study of one eye found RNFB widths ranging from 10 μm to 44 μm. This suggested that biological variability was too high for measuring small changes arising from disease processes. This was confirmed in measurements of 10 eyes in the main study, RNFB widths ranged from 9 μm to 55 μm and every eye had large within-subject variability (exceeding 19 μm in all eyes) in RNFB width for nearby bundles. The within-subject variability in RNFB width, as well as variation in the width of single RNFBs over relatively short distances (<300 um) depending on the precise location of measurement, suggests that bundle width measurements would be highly susceptible to selection bias and therefore of limited clinical use.

Retinal nerve fiber bundle trajectories in Chinese myopic eyes: Comparison with a Caucasian based mathematical model

Previously we developed a mathematical model for describing the retinal nerve fiber bundle (RNFB) trajectories in the human retina. The model was based on Caucasian eyes that were not selected regarding refraction. The aim of this study was to determine the characteristics of the RNFB trajectories in Chinese myopic eyes. We collected high quality red free fundus images from 80 eyes of 80 Chinese myopic subjects (median [interquartile range/range] refraction −3.9 [-6.0 to −2.5/-10 to −1] D). We traced all visible RNFBs (n = 1460) and evaluated their trajectories using the previously published mathematical model. In the superior-temporal region, the RNFB trajectories of the Chinese myopic eyes were similar to that of the Caucasian eyes (86% of trajectories within the 95% central range of the Caucasian model). In the inferior-temporal region, the trajectories of the Chinese low to moderate myopic eyes were also similar to that of the Caucasian eyes (85%); trajectories of the high myopic eyes (spherical equivalent beyond −6.00 D) were clearly less curved (75%). Associations between individual deviations from the model and axial length, retinal vessel course, and optic disc anatomy were studied with multiple linear regression analysis. In the superior-temporal region, the trajectories were associated with retinal vessel course (P = 0.008) and optic disc size (P = 0.016). In the inferior-temporal region, there was a significant association with axial length (P < 0.001), retinal vessel course (P = 0.006), and disc torsion (P = 0.009).

Novel Technique for Quantifying Retinal Nerve Fiber Bundle Abnormality in the Temporal Raphe.

SIGNIFICANCEGlaucomatous nasal visual field abnormalities correspond to damage in the temporal raphe—where individual nerve bundles can be visualized. The ability to quantify structural abnormality in the raphe, with a clinically applicable protocol, sets the stage for investigating the raphe as a potential site for assessing early glaucoma.PURPOSETo develop a clinically applicable imaging and analysis technique for identifying retinal nerve fiber bundle abnormalities in the temporal raphe.METHODSSpectralis optical coherence tomography scans customized for the temporal raphe were gathered from 30 younger controls, 30 older controls, and 29 patients with glaucoma. An analysis technique was developed based on the reflectance of the nerve fiber bundles. The technique was first developed in the younger controls, and then applied to the older controls to generate normative data for quantifying nerve fiber bundle reflectance abnormalities in the patients with glaucoma. Matrix perimetric data were gathered in the patients with glaucoma to evaluate the reflectance technique’s findings. Reflectance abnormality in the patients was defined when the fraction of enface area showing reflectance abnormality was greater than the 95th percentile estimated from controls. Spearman’s rho was used to quantify the relation between the total deviation at the perimetric testing locations and the fraction of corresponding enface area showing reflectance abnormality.RESULTSTwenty-five of the 29 patients had reflectance abnormalities. Eight of these had mild to no perimetric mean deviation abnormality. Similar results were found when perimetric total deviations were compared to reflectance abnormalities in the corresponding enface locations. Spearman’s rho comparing the total deviations to reflectance abnormalities found rs(174) = −0.72, P < .001.CONCLUSIONSThe technique typically identified reflectance abnormality when perimetric abnormality was present. It also identified reflectance abnormalities even when perimetric abnormality was mild or absent. The findings support the potential of raphe imaging in detecting early glaucomatous damage.

Influence of the Retinal Blood Vessel Topography on the Variability of the Retinal Nerve Fiber Bundle Trajectories in the Human Retina.

To determine the relationship between the retinal blood vessel topography and the retinal nerve fiber bundle (RNFB) trajectories in the human retina. A previously collected dataset comprising 28 fundus photographs with traced RNFB trajectories was used. For all traced trajectories, the departure from our previously published RNFB trajectory model was calculated. Subsequently, we calculated, per subject, a "mean departure" for the superior-temporal and inferior-temporal region. We measured angles between a line connecting the optic nerve head (ONH) center and the fovea and lines connecting the ONH center and the crossings of the superior and inferior temporal arteries (arterial angles) and veins (venous angles) with circles around the ONH; circle radii were 25%, 50%, and 100% of the ONH center-to-fovea distance. We also defined two angles based on the location of the first arteriovenous crossing. Multiple linear regression analysis was performed with mean departure as dependent variable and refraction, ONH inclination, and vessel angles as independent variables. In the superior-temporal region, refraction (P = 0.017), ONH inclination (P = 0.021), and the arterial angle corresponding to the middle circle (P < 0.001) were significant determinants of mean departure. Explained variance was 0.54. In the inferior-temporal region, the arterial angle corresponding to the largest circle (P = 0.002) was significant. Explained variance was 0.32. The retinal blood vessel topography explains a significant part of the RNFB trajectory variability but only if (1) the vessel topography is assessed at an appropriate distance from the ONH and (2) the superior and inferior hemifield are addressed independently.

Confocal Adaptive Optics Imaging of Peripapillary Nerve Fiber Bundles: Implications for Glaucomatous Damage Seen on Circumpapillary OCT Scans.

To improve our understanding of glaucomatous damage as seen on circumpapillary disc scans obtained with frequency-domain optical coherence tomography (fdOCT), fdOCT scans were compared to images of the peripapillary retinal nerve fiber (RNF) bundles obtained with an adaptive optics-scanning light ophthalmoscope (AO-SLO). The AO-SLO images and fdOCT scans were obtained on 6 eyes of 6 patients with deep arcuate defects (5 points ≤-15 db) on 10-2 visual fields. The AO-SLO images were montaged and aligned with the fdOCT images to compare the RNF bundles seen with AO-SLO to the RNF layer thickness measured with fdOCT. All 6 eyes had an abnormally thin (1% confidence limit) RNF layer (RNFL) on fdOCT and abnormal (hyporeflective) regions of RNF bundles on AO-SLO in corresponding regions. However, regions of abnormal, but equal, RNFL thickness on fdOCT scans varied in appearance on AO-SLO images. These regions could be largely devoid of RNF bundles (5 eyes), have abnormal-appearing bundles of lower contrast (6 eyes), or have isolated areas with a few relatively normal-appearing bundles (2 eyes). There also were local variations in reflectivity of the fdOCT RNFL that corresponded to the variations in AO-SLO RNF bundle appearance. Relatively similar 10-2 defects with similar fdOCT RNFL thickness profiles can have very different degrees of RNF bundle damage as seen on fdOCT and AO-SLO. While the results point to limitations of fdOCT RNFL thickness as typically analyzed, they also illustrate the potential for improving fdOCT by attending to variations in local intensity.

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

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

Retinal vessel course and retinal nerve fiber bundle trajectories in the human eye

AbstractPurpose To determine the relationship between the retinal vessel course and the retinal nerve fiber bundle (RNFB) trajectories in the human retina.Methods High‐quality fundus photographs were used, comprising 28 eyes of 28 subjects (Exp Eye Res 2012). Mean (range) refraction was ‐0.4 (‐8.75 to +6.25) D. In total 625 RNFB trajectories were traced. For all individual trajectories, the departure from the previously published RNFB trajectory model (Vision Res 2009) was calculated. Subsequently, we calculated, per subject, a 'mean departure' for the superior‐temporal and inferior‐temporal regions. To quantify the retinal vessel course, we measured the angles between a line connecting the centers of the fovea and the ONH and a line connecting the center of the ONH and the crossing of the superior or inferior temporal artery or vene with a circle around the ONH; circle radius was half the fovea‐ONH distance. This yielded four angles: AAS, AVS, AAI, and AVI. Multiple linear regression analysis was performed for the superior‐temporal and inferior‐temporal regions separately, with mean departure as dependent variable and refraction, ONH inclination, and the vessel angles as independent variables.Results In the superior‐temporal region, refraction (P=0.017), ONH inclination (P=0.021), and AAS (P&lt;0.001) were significantly associated with mean departure. The explained variance was 0.54. In the inferior‐temporal region, AAI (P=0.037) and AVI (P=0.021) were significantly associated with mean departure. The explained variance was 0.30.Conclusion The wiring of the human retina displays a considerable variability. The angles at which the vessels leave the ONH explain an important part of this variability.

A mathematical model for describing the retinal nerve fiber bundle trajectories in the human eye: Average course, variability, and influence of refraction, optic disc size and optic disc position

Previously we developed a mathematical model for describing the retinal nerve fiber bundle trajectories in the superior-temporal and inferior-temporal regions of the human retina, based on traced trajectories extracted from fundus photographs. Aims of the current study were to (i) validate the existing model, (ii) expand the model to the entire retina and (iii) determine the influence of refraction, optic disc size and optic disc position on the trajectories. A new set of fundus photographs was collected comprising 28 eyes of 28 subjects. From these 28 photographs, 625 trajectories were extracted. Trajectories in the temporal region of the retina were compared to the existing model. In this region, 347 of 399 trajectories (87%) were within the 95% central range of the existing model. The model was extended to the nasal region. With this extension, the model can now be applied to the entire retina that corresponds to the visual field as tested with standard automated perimetry (up to approximately 30° eccentricity). There was an asymmetry between the superior and inferior hemifields and a considerable location-specific inter-subject variability. In the nasal region, we found two “singularities”, located roughly at the one and five o'clock positions for the right optic disc. Here, trajectories from relatively widespread areas of the retina converge. Associations between individual deviations from the model and refraction, optic disc size and optic disc position were studied with multiple linear regression. Refraction (P = 0.021) and possibly optic disc inclination (P = 0.09) influenced the trajectories in the superior-temporal region.

Distribution of Damage to the Entire Retinal Ganglion Cell Pathway

OBJECTIVES To test the hypothesis that the amount and distribution of glaucomatous damage along the entire retinal ganglion cell-axonal complex (RGC-AC) can be quantified and to map the RGC-AC connectivity in early glaucoma using automated image analysis of standard spectral-domain optical coherence tomography. METHODS Spectral-domain optical coherence tomography volumes were obtained from 116 eyes in 58 consecutive patients with glaucoma or suspected glaucoma. Layer and optic nerve head (ONH) analysis was performed; the mean regional retinal ganglion cell layer thickness (68 regions), nerve fiber layer (NFL) thickness (120 regions), and ONH rim area (12 wedge-shaped regions) were determined. Maps of RGC-AC connectivity were created using maximum correlation between regions' ganglion cell layer thickness, NFL thickness, and ONH rim area; for retinal nerve fiber bundle regions, the maximum "thickness correlation paths" were determined. RESULTS The mean (SD) NFL thickness and ganglion cell layer thickness across all macular regions were 22.5 (7.5) μm and 33.9 (8.4) μm, respectively. The mean (SD) rim area across all ONH wedge regions was 0.038 (0.004) mm2. Connectivity maps were obtained successfully and showed typical nerve fiber bundle connectivity of the RGC-AC cell body segment to the initial NFL axonal segment, of the initial to the final RGC-AC NFL axonal segments, of the final RGC-AC NFL axonal to the ONH axonal segment, and of the RGC-AC cell body segment to the ONH axonal segment. CONCLUSIONS In early glaucoma, the amount and distribution of glaucomatous damage along the entire RGC-AC can be quantified and mapped using automated image analysis of standard spectral-domain optical coherence tomography. Our findings should contribute to better detection and improved management of glaucoma.

Spatial Pattern of Glaucomatous Visual Field Loss Obtained with Regionally Condensed Stimulus Arrangements

To assess the spatial distribution of glaucomatous visual field defects (VFDs) obtained with regionally condensed stimulus arrangements. Sixty-three eyes of 63 glaucoma subjects were examined with threshold-estimating automated static perimetry (full threshold 4-2-1 dB strategy with at least three reversals) on an automatic campimeter or a full-field perimeter. Stimuli were added by the examiner to regionally enhance spatial resolution in regions that were suspicious for a glaucomatous VFD. These regions were characterized by contiguous local VFDs, attributable to the retinal nerve fiber bundle course according to the impression of the examiner. The added stimulus locations were subsets of a predefined, dense perimetric grid. All VFD locations with P < 0.05 (total deviation plots) were assessed by superimposing the visual field records of all participants. Glaucomatous VFD loss occurred more frequently in the upper than in the lower hemifield, with a typical retinal nerve fiber-related pattern and a preference of the nasal step region. More than 50% of the eyes with predominantly mild to moderate glaucomatous field loss showed defective locations in the immediate superior paracentral region within an eccentricity of 3°. Conventional thresholding white-on-white perimetry with regionally enhanced spatial resolution reveals that glaucomatous visual field loss affects the immediate paracentral area, especially the upper hemifield, in many eyes with only mild to moderate glaucomatous visual field loss. Detailed knowledge about the spatial pattern and the local frequency distribution of glaucomatous VFDs is an essential prerequisite for creating regionally condensed stimulus arrangements for adequate detection and follow-up of functional glaucomatous damage.