Histopathologic validation of Fourier-ellipsometry measurements of retinal nerve fiber layer thickness

Multifunctional adaptive optics optical coherence tomography allows cellular scale reflectometry, polarimetry, and angiography in the living human eye

Clinicians are unable to detect glaucoma until substantial loss or dysfunction of retinal ganglion cells occurs. To this end, novel measures are needed. We have developed an optical imaging solution based on adaptive optics optical coherence tomography (AO-OCT) to discern key clinical features of glaucoma and other neurodegenerative diseases at the cellular scale in the living eye. Here, we test the feasibility of measuring AO-OCT-based reflectance, retardance, optic axis orientation, and angiogram at specifically targeted locations in the living human retina and optic nerve head. Multifunctional imaging, combined with focus stacking and global image registration algorithms, allows us to visualize cellular details of retinal nerve fiber bundles, ganglion cell layer somas, glial septa, superior vascular complex capillaries, and connective tissues. These are key histologic features of neurodegenerative diseases, including glaucoma, that are now measurable in vivo with excellent repeatability and reproducibility. Incorporating this noninvasive cellular-scale imaging with objective measurements will significantly enhance existing clinical assessments, which is pivotal in facilitating the early detection of eye disease and understanding the mechanisms of neurodegeneration.

Association Between Retinal Nerve Fiber Layer Thickness and Incident Dementia in the European Prospective Investigation into Cancer in Norfolk Cohort

BACKGROUND

Retinal nerve fiber layer (RNFL) thickness may reflect cerebral status.

OBJECTIVE

This study assessed the relationship between RNFL thickness and incident all-cause dementia in the European Prospective Investigation into Cancer in Norfolk (EPIC-Norfolk) Eye Study.

METHODS

Glaucoma detection with variable corneal compensation (GDx-VCC) and Heidelberg Retinal Tomograph II (HRT II) derived global mean RNFL thickness from dementia-free participants at baseline within the EPIC-Norfolk Eye Study were analyzed. Incident dementia was identified through linkage to electronic medical records. Cox proportional hazard mixed-effects regression models adjusted for key confounders were used to examine the associations between RNFL thickness and incident dementia in four separate models.

RESULTS

6,239 participants were included with 322 cases of incident dementia and mean age of 67.5-years old, with 49.7% women (median follow-up 13.2-years, interquartile range (11.7 to 14.6 years). Greater RNFL thickness (GDx-VCC) was not significantly associated with a lower risk of incident dementia in the full adjusted model [HR per quartile increase 0.95; 95% CI 0.82-1.10]. Similarly, RNFL thickness assessed with HRT II was also not associated with incident dementia in any model (full adjusted model; HR per quartile increase: 1.06; [95% CI 0.93-1.19]. Gender did not modify any associations under study.

CONCLUSION

GDx-VCC and HRT II derived RNFL thickness are unlikely to be useful predictors of incident dementia. Higher resolution optical imaging technologies may clarify whether there are useful relationships between neuro-retinal morphology and brain measures.

Is retinal nerve fibre layer thickness correlated with visual function in individuals having optic neuritis?

CLINICAL RELEVANCE

The existence of a correlation between the results of paraclinical retinal imaging and clinical tests such as contrast sensitivity can reduce time and cost in diagnosing optic neuritis (ON).

BACKGROUND

To demonstrate whether changes of peripapillary retinal nerve fibre layer (RNFL) thickness are correlated with the results of visual acuity, contrast sensitivity and colour vision in eyes with acute ON.

METHODS

Thirty patients with acute ON, 23 females and seven males, who had no previous history of ON in neither eye, were examined. Inclusion criteria were: subjects had spherical refraction of less than ±5D, no prior ON or optic disc swelling, no history of amblyopia or colour blindness, and no history or ophthalmoscopic evidence of glaucoma, diabetic retinopathy, or maculopathies. Visual acuity, contrast sensitivity and colour vision were tested and optical coherence tomography was performed for all patients after complete ophthalmologic examinations including refraction, biomicroscopy, and funduscopy with a 90D lens by a neuro-ophthalmologist.

RESULTS

Thirty patients who were 18-45 years old entered the study. There was an inverse correlation between contrast sensitivity and nasal (r = -0.430, p = 0.018), inferior (r = -0.503, p = 0.005) and mean (r = -0.510, p = 0.004) RNFL thickness. The multiple linear regression model, after adjustment for age and sex, showed a significant association between visual acuity and nasal RNFL thickness (coefficient = 0.025, p = 0.032). There was also a significant inverse correlation between contrast sensitivity and nasal (coefficient = -0.003, p = 0.036), inferior (coefficient = -0.006, p = 0.010) and mean (coefficient = -0.007, p = 0.012) RNFL thickness. No significant correlation was found between colour vision and RNFL thickness.

CONCLUSION

Contrast sensitivity is more correlated with changes in RNFL thickness in comparison with visual acuity and colour vision. Contrast sensitivity measurement therefore can be used as one of the first assessments in patients with ON.

Early Identification of Retinal Neuropathy in Subclinical Diabetic Eyes by Reduced Birefringence of the Peripapillary Retinal Nerve Fiber Layer

Purpose

To study birefringence of the peripapillary retinal nerve fiber layer (RNFL) of diabetic eyes with no clinical signs of diabetic retinopathy (DR) or mild to moderate DR stages using spectral-domain polarization-sensitive (PS) optical coherence tomography (OCT).

Methods

In this observational pilot study, circular PS-OCT scans centered on the optic nerve head were recorded in prospectively recruited diabetic and age-matched healthy eyes. From averaged circumpapillary intensity and retardation tomograms plots of RNFL birefringence were obtained by a linear fit of retardation versus depth within the RNFL tissue for each A-scan position and mean birefringence values for RNFL calculated. Spectral-domain OCT imaging (Heidelberg Engineering) was performed to assess peripapillary RNFL thickness and macular ganglion cell complex (GCC).

Results

Out of 70 eyes of 43 diabetic patients (mean ± SD age: 50.86 ± 15.71) 36 showed no signs of DR, 17 mild and 17 moderate nonproliferative DR with no diabetic macular edema. Thirty-four eyes of 34 healthy subjects (53.21 ± 13.88 years) served as controls. Compared with healthy controls (0.143° ± 0.014°/µm) mean total birefringence of peripapillary RNFL was significantly reduced in subclinical diabetic eyes (0.131° ± 0.014°/µm; P = 0.0033), as well as in mild to moderate DR stages (0.125° ± 0.018°/µm, P < 0.0001) with borderline statistically significant differences between diabetic patients (P = 0.0049). Mean birefringence values were significantly lower in inferior compared with superior RNFL sectors (P < 0.0001) of diabetic eyes with no such difference detected in the healthy control group.

Conclusions

We identified evidence of early neuroretinal alteration in diabetic eyes through reduced peripapillary RNFL birefringence assessed by PS-OCT occurring before appearance of clinical microvascular lesions or GCC alterations.

The effect of waveform asymmetry on perception with epiretinal prostheses

Objective

Retinal prosthetic implants have helped improve vision in patients blinded by photoreceptor degeneration. Retinal implant users report improvements in light perception and performing visual tasks, but their ability to perceive shapes and letters is limited due to the low precision of retinal activation, which is exacerbated by axonal stimulation and high perceptual thresholds. A previous in vitro study in our lab used calcium imaging to measure the spatial activity of mouse retinal ganglion cells (RGCs) in response to electrical stimulation. Based on this study, symmetric anodic-first (SA) stimulation effectively avoided axonal activation and asymmetric anodic-first stimulation (AA) with duration ratios (ratio of the anodic to cathodic phase) greater than 10 reduced RGC activation thresholds significantly. Applying these novel stimulation strategies in clinic may increase perception precision and improve the overall patient outcomes.

Approach

We combined human subject testing and computational modeling to further examine the effect of SA and AA stimuli on perception shapes and thresholds for epiretinal stimulation of RGCs.

Main results

Threshold measurement in three Argus II participants indicated that AA stimulation could increase perception probabilities compared to a standard symmetric cathodic-first (SC) pulse, and this effect can be intensified by addition of an interphae gap (IPG). Our in silico RGC model predicts lower thresholds with AA and asymmetric cathodic-first (AC) stimuli compared to a SC pulse. This effect was more pronounced at shorter pulse widths. The most effective pulse for threshold reduction with short pulse durations (≤0.12 ms) was AA stimulation with small duration ratios (≤5) and long IPGs (≥2 ms). For the 0.5 ms pulse duration, SC stimulation with IPGs longer than 0.5 ms, or asymmetric stimuli with large duration ratios (≥20) were most effective in threshold reduction. Phosphene shape analysis did not reveal a significant change in percept elongation with SA stimulation. However, there was a significant increase in percept size (P < 0.01) with AA stimulation compared to the standard pulse in one participant.

Significane

Including asymmetric waveform capability will provide more flexible options for optimization and personalized fitting of retinal implants.

Subretinal Fibrosis Detection Using Polarization Sensitive Optical Coherence Tomography

Purpose

Subretinal fibrosis (SRFib) is an important cause of permanent loss-of-vision diseases with submacular neovascularization, but a reliable diagnostic method is currently missing. This study uses polarization-sensitive optical coherence tomography (PS-OCT) to detect SRFib within retinal lesions by measurement of its birefringent collagen fibers.

Methods

Twenty-five patients were enrolled with retinal pathology in one or both eyes containing (1) suspected SRFib, (2) lesions suspected not to be fibrotic, or (3) lesions with doubtful presence of SRFib. All eyes were evaluated for SRFIb using conventional diagnostics by three retinal specialists. PS-OCT images were visually evaluated for SRFib based on cumulative phase retardation, local birefringence, and optic axis uniformity.

Results

Twenty-nine eyes from 22 patients were scanned successfully. In 13 eyes, SRFib was diagnosed by all retinal specialists; of these, 12 were confirmed by PS-OCT and one was inconclusive. In nine eyes, the retinal specialists expected no SRFib, which was confirmed by PS-OCT in all cases. In seven eyes, the retinal specialists’ evaluations were inconsistent with regard to the presence of SRFib. PS-OCT confirmed the presence of SRFib in four of these eyes and the absence of SRFib in two eyes and was inconclusive in one eye.

Conclusions

In 21 out of 22 eyes, PS-OCT confirmed the evaluation of retinal specialists regarding the presence of SRFib. PS-OCT provided additional information to distinguish SRFib from other tissues within subretinal neovascular lesions in 6 out of 7 eyes.

Translational Relevance

PS-OCT can identify and quantify SRFib in doubtful cases for which a reliable diagnosis is currently lacking.

Optical coherence tomography and optical coherence tomography angiography in glaucoma: diagnosis, progression, and correlation with functional tests

The present review will summarize the most updated findings with regards to optical coherence tomography and optical coherence tomography angiography in glaucoma, highlighting their clinical use for detection and monitoring of the disease, and their correlation to functional tests (such as visual field) widely employed in the asset of modern glaucoma clinics.

Glaucoma Diagnosis: from the Artisanal to the Defined

In 400BC, Hippocrates wrote the first record of glaucoma. Since then, increasingly objective diagnostic techniques have enabled earlier detection of glaucoma and its progression, providing greater certainty in decision-making and early medical and surgical intervention.

Visible-light optical coherence tomography-based multimodal system for quantitative fundus autofluorescence imaging

IMPACT STATEMENT

Quantitative fundus autofluorescence imaging with simultaneous visible-light optical coherence tomography-based multimodal technology has potential significant impact on the diagnosis and monitoring the progression of retinal diseases.

Imaging Technologies for Assessing Neuroprotection in Glaucomatous Optic Neuropathy

The confocal scanning laser ophthalmoscope and the scanning laser polarimeter are two new imaging devices that may be beneficial in the diagnosis and monitoring of glaucoma patients. For each of these instruments, the authors describe benefits and limitations with regard to imaging mechanisms, sensitivity, and clinical applications. In comparison with currently used tests for glaucoma, these instruments provide quantitative assessment of the optic disc and RNFL at the clinic visit, with reduced need for pupil dilation and clear media. They also show promise for improving the ability to monitor progression of glaucomatous optic neuropathy and might allow better assessment of the efficacy of a neuroprotective agent.

Altered birefringence of peripapillary retinal nerve fiber layer in multiple sclerosis measured by polarization sensitive optical coherence tomography

Background

The retina has been used to study the pathophysiology of multiple sclerosis (MS). Peripapillary retinal nerve fiber layer (pRNFL) thinning has been suggested as an ocular biomarker of neurodegeneration in MS. The goal of this project was to determine the birefringence of the pRNFL by measuring the fiber birefringence using polarization sensitive optical coherence tomography (PS-OCT).

Methods

Sixty-six MS patients without history of optic neuritis (age: 39.9 ± 11.0 yrs. old, 53 females and 13 males) and 66 age- and gender-matched normal controls (age: 40.7 ± 11.4 yrs. old) were recruited. Custom built PS-OCT was used to measure phase retardation per unit depth (PR/UD, proportional to the birefringence) and pRNFL thickness in each quadrant of the pRNFL. In addition, clinical manifestation was used to correlate with the pRNFL birefringence.

Results

The pRNFL was thinner in the temporal and inferior quadrants in MS patients compared with normal controls (P < 0.05). The PR/UD of the pRNFL was significantly decreased in MS patients (P < 0.05) in all quadrants except for the nasal quadrant. In both groups, the PR/UD from all four quadrants was not related to the averaged pRNFL thickness (P > 0.05). In MS patients, the PR/UD was not related to the expanded disability status scale (EDSS) nor disease duration (r ranged from − 0.17 to 0.02, P > 0.05).

Conclusion

This is the first study using PS-OCT to study the pRNFL birefringence in MS patients. Decreased birefringence of the pRNFL may indicate microtubule abnormality, and could be a potential biomarker for detecting early neurodegeneration in MS.

Retinal Nerve Fiber Layer Measured by Heidelberg Retina Tomograph and Nerve Fiber Analyzer

Purpose

To compare retinal nerve fiber layer (RNFL) thickness measured by Heidelberg retina tomograph (HRT) and nerve fiber analyzer (GDx).

Methods

Twenty eyes of 20 consecutive healthy subjects were recruited for this study. Each subject had a normal visual field and a normal optic nerve head, which was assessed by slit-lamp biomicroscopy using a 90° lens. Using the HRT and GDx, RNFL measurement was calculated as for software vs 2.01 and vs 1.0.14, respectively. Retinal nerve fiber layer thickness was evaluated for the entire annulus surface every 5° degrees. RNFL was assessed by HRT and GDx. HRT RNFL measurement was calculated at 0 üm from the edge, while GDx RNFL measurement at 1.75 disc diameter as for software. The difference between the highest points and the deepest points was calculated and compared. Furthermore, because of the possibility of different scales in the two systems, the following ratio was calculated: superior/inferior, superior/temporal, superior/nasal, inferior/temporal, and inferior/nasal.

Results

When the entire RNFL thickness was considered, a significant (p<0.001) difference was found between the HRT and GDx measurements. A difference of 200 üm was found between the highest and the deepest HRT points while a difference of 40 üm was found between the highest and the deepest GDx points.

Conclusions

HRT and GDx RNFL measurements were statistically different in each sector. However, ratio parameters showed no difference between the obtained values except for superior/temporal ratio and inferior/temporal ratio.

Scanning Laser Polarimetry and Retinal Thickness Analysis before and after Laser in Situ Keratomileusis

Purpose

To evaluate changes in retinal nerve fiber layer (RNFL) thickness after laserin situ keratomileusis (LASIK) using a scanning laser Polarimeter with fixed corneal compensation (GDx) and the retinal thickness analyzer (RIA).

Methods

Thirty-eight eyes of 19 healthy subjects (10 female and 9 male; mean age 37.0±8.8 years) underwent GDx and RTA measurements before and after LASIK. All subjects revealed mild to high myopia (mean spherical refraction: −4.0±2.75 D). Measurements using GDx were followed by RTA measurements after pupil dilation. All measurements were performed the day before LASIK and 1 week postoperatively.

Results

GDX revealed a decrease in nerve fiber layer thickness measurements after LASIK, but did not reach statistical significance (p>0.05). Using RTA, mean RNFL thickness (MRNFL) and RNFL cross sectional area decreased significantly after LASIK (p=0.03 and p=0.02, respectively).

Conclusions

Scanning laser polarimetry revealed a slight decrease in RNFL thickness measurements after LASIK. MRNFL and RNFL cross section were significantly lower after LASIK using RTA. The changes might be artifacts in a small group of myopic subjects.

Nerve Fiber Layer Assessment with Scanning Laser Polarimetry in Glaucoma Patients and Glaucoma Suspects

PURPOSE

To investigate whether scanning laser polarimeter can differentiate glaucoma and suspected glaucoma patients from normals.

METHODS

Polarimetric measurements were obtained using the nerve fiber analyzer (NFA)-I from 80 eyes of patients with glaucoma with mostly moderate glaucomatous optic nerve damage (37 eyes with primary open angle glaucoma, 21 with normal tension glaucoma, 17 with pseudoexfoliative glaucoma, 3 with angle closure glaucoma, and 2 with juvenile glaucoma), 53 eyes of patients suspected of glaucoma based on disc appearance, and from age-matched healthy volunteers as control groups. Ratios (superior/nasal, inferior/nasal, superior/inferior) were used for assessing nerve fiber layer (NFL) thickness. Student's t-test and linear regression analysis were used for statistical analysis.

RESULTS

Both the glaucoma patients and glaucoma suspects had significantly lower NFL ratios (mean S/N 2.34 +/- 0.47, I/N 2.46 +/- 0.52, S/I 0.94 +/- 0.18) than the control groups (respectively 2.88 +/- 0.48, 2.88 +/- 0.48, 1.00 +/- 0.13) (p<0.05). There was an ample overlap between the patient groups and the normals. The superior and inferior NFL ratios in glaucoma patients gradually decreased as the mean defect in visual field increased (linear regression analysis, p<0.05).

CONCLUSIONS

The NFL of glaucomatous eyes and eyes suspected of glaucoma based on disc appearance was significantly less thick than normals. NFA-I detects pathological abnormalities in some patients with glaucomatous optic nerve damage and normal visual fields as measured by conventional achromatic computerized perimetry. NFA-I, however, is unable to distinguish these patients from normals, at least using these parameters, because of the considerable overlap.

Temporal Relation between Macular Ganglion Cell-Inner Plexiform Layer Loss and Peripapillary Retinal Nerve Fiber Layer Loss in Glaucoma

PURPOSE

To investigate the temporal relationship between inferior macular ganglion cell-inner plexiform layer (mGCIPL) loss and corresponding peripapillary retinal nerve fiber layer (pRNFL) defect on the optical coherence tomography (OCT) deviation map in glaucoma.

DESIGN

Retrospective, observational study.

PARTICIPANTS

A total of 151 patients with early-stage glaucoma (visual field [VF] mean deviation between -1.5 and -5.5 decibels [dB]).

METHODS

Spectral-domain OCT mGCIPL and pRNFL deviation maps were obtained for the baseline (from January 2012 to August 2012) and again for the follow-up (from January 2015 to August 2015). An integrated deviation map thereafter was merged by vascular landmark-guided superimposition of mGCIPL and pRNFL deviation maps onto RNFL imagery. On the basis of an earlier schematic model, the inferotemporal peripapillary area was divided into (1) the macular vulnerability zone (MVZ) and (2) the inferoinferior portion.

MAIN OUTCOME MEASURES

Temporal sequence of inferior mGCIPL loss and corresponding pRNFL (i.e., pRNFL in MVZ) defect on integrated deviation map.

RESULTS

At baseline, 99 (65.6%) of the 151 eyes showed inferior mGCIPL loss. In addition, 112 eyes (74.2%) and 5 eyes (3.3%) showed inferoinferior pRNFL defect and pRNFL defect in the MVZ, respectively. At the 3-year follow-up, 112 (74.2%) of the eyes showed inferior mGCIPL loss, whereas 123 eyes (81.5%) and 25 eyes (16.6%) showed inferoinferior pRNFL defect and pRNFL defect in the MVZ, respectively. Ninety-four eyes initially showed inferior mGCIPL loss without pRNFL defect in the MVZ; among them, 19 (20.2%) subsequently showed defect during the 3-year follow-up interval. Meanwhile, among the 52 eyes without preexisting inferior mGCIPL loss, only 1 (1.9%; P < 0.001) developed a pRNFL defect in the MVZ during the 3-year follow-up interval.

CONCLUSIONS

In eyes with early glaucoma, mGCIPL change is frequently detected before corresponding pRNFL change. This could be the result of a superior sensitivity of mGCIPL deviation map that allows detection of an abnormality in the mGCIPL thickness earlier. In this light, OCT pRNFL analysis alone likely would overlook macular damage. Macular OCT imaging should be included in the imaging algorithm for the serial observation of patients with glaucoma.

Polarization sensitive optical coherence tomography - a review [Invited]

Optical coherence tomography (OCT) is now a well-established modality for high-resolution cross-sectional and three-dimensional imaging of transparent and translucent samples and tissues. Conventional, intensity based OCT, however, does not provide a tissue-specific contrast, causing an ambiguity with image interpretation in several cases. Polarization sensitive (PS) OCT draws advantage from the fact that several materials and tissues can change the light's polarization state, adding an additional contrast channel and providing quantitative information. In this paper, we review basic and advanced methods of PS-OCT and demonstrate its use in selected biomedical applications.

Posterior rat eye during acute intraocular pressure elevation studied using polarization sensitive optical coherence tomography

Polarization sensitive optical coherence tomography (PS-OCT) operating at 840 nm with axial resolution of 3.8 µm in tissue was used for investigating the posterior rat eye during an acute intraocular pressure (IOP) increase experiment. IOP was elevated in the eyes of anesthetized Sprague Dawley rats by cannulation of the anterior chamber. Three dimensional PS-OCT data sets were acquired at IOP levels between 14 mmHg and 105 mmHg. Maps of scleral birefringence, retinal nerve fiber layer (RNFL) retardation and relative RNFL/retina reflectivity were generated in the peripapillary area and quantitatively analyzed. All investigated parameters showed a substantial correlation with IOP. In the low IOP range of 14-45 mmHg only scleral birefringence showed statistically significant correlation. The polarization changes observed in the PS-OCT imaging study presented in this work suggest that birefringence of the sclera may be a promising IOP-related parameter to investigate.

Stokes-vector and Mueller-matrix polarimetry [Invited]

This paper reviews the current status of instruments for measuring the full 4×1 Stokes vector S, which describes the state of polarization (SOP) of totally or partially polarized light, and the 4×4 Mueller matrix M, which determines how the SOP is transformed as light interacts with a material sample or an optical element or system. The principle of operation of each instrument is briefly explained by using the Stokes-Mueller calculus. The development of fast, automated, imaging, and spectroscopic instruments over the last 50 years has greatly expanded the range of applications of optical polarimetry and ellipsometry in almost every branch of science and technology. Current challenges and future directions of this important branch of optics are also discussed.

Correlation in retinal nerve fibre layer thickness in uveitis and healthy eyes using scanning laser polarimetry and optical coherence tomography

PURPOSE

To evaluate the correlation of retinal nerve fibre layer (RNFL) thickness measured using spectral domain optical coherence tomography (SD-OCT) and scanning laser polarimetry (SLP) in uveitic eyes compared with healthy eyes.

METHODS

A descriptive, observational, prospective, consecutive, cross-sectional, controlled, monocentre case series was conducted from May to October 2015. Clinical characteristics, best-corrected visual acuity, intraocular pressure, RNFL thickness measurement with SD-OCT and SLP using GDx variable corneal compensation (GDx VCC) were performed for each patient. An evaluation of anterior chamber inflammation with laser flare-cell meter was also carried out. Correlations between SD-OCT and GDx VCC RNFL measurement were evaluated by linear regression analysis.

RESULTS

Fifty-four patients were included and divided into two groups: 50 healthy eyes in 29 patients and 42 uveitic eyes in 25 patients. The mean RNFL thickness was 98.08(±8.42) and 113.21(±20.53) μm in the healthy group and the uveitic group, respectively, when measured with SD-OCT (p<0.001); and 56.43(±5.24) and 58.77(±6.67) μm, respectively, when measured with GDx VCC (p=0.078). There was a strong correlation between total average RNFL thickness measured using SD-OCT and GDX (r=0.48, p<0.001) in healthy eyes but there was no correlation in the uveitic eyes (r=0.2, p=0.19).

CONCLUSIONS

RNFL thickness was significantly greater when measured using SD-OCT in active uveitis as compared with GDx. There was no correlation between the RNFL thickness measurements obtained using the two techniques in uveitic eyes. The discrepancies between the results suggest that for these patients both techniques should be used in conjunction to obtain an accurate measurement of RNFL.

TRIAL REGISTRATION NUMBER

IRB 00008855 Société Française d'Ophtalmologie IRB#1.

Polarization properties of single layers in the posterior eyes of mice and rats investigated using high resolution polarization sensitive optical coherence tomography

We present a high resolution polarization sensitive optical coherence tomography (PS-OCT) system for ocular imaging in rodents. The system operates at 840 nm and uses a broadband superluminescent diode providing an axial resolution of 5.1 µm in air. PS-OCT data was acquired at 83 kHz A-scan rate by two identical custom-made spectrometers for orthogonal polarization states. Pigmented (Brown Norway, Long Evans) and non-pigmented (Sprague Dawley) rats as well as pigmented mice (C57BL/6) were imaged. Melanin pigment related depolarization was analyzed in the retinal pigment epithelium (RPE) and choroid of these animals using the degree of polarization uniformity (DOPU). For all rat strains, significant differences between RPE and choroidal depolarization were observed. In contrast, DOPU characteristics of RPE and choroid were similar for C57BL/6 mice. Moreover, the depolarization within the same tissue type varied significantly between different rodent strains. Retinal nerve fiber layer thickness, phase retardation, and birefringence were mapped and quantitatively measured in Long Evans rats in vivo for the first time. In a circumpapillary annulus, retinal nerve fiber layer birefringence amounted to 0.16°/µm ± 0.02°/µm and 0.17°/µm ± 0.01°/µm for the left and right eyes, respectively.

Relating Retinal Ganglion Cell Function and Retinal Nerve Fiber Layer (RNFL) Retardance to Progressive Loss of RNFL Thickness and Optic Nerve Axons in Experimental Glaucoma

PURPOSE

To relate changes in retinal function and retinal nerve fiber layer (RNFL) retardance to loss of RNFL thickness and optic nerve axon counts in a nonhuman primate (NHP) model of experimental glaucoma (EG).

METHODS

Bilateral longitudinal measurements of peripapillary RNFL thickness (spectral-domain optical coherence tomography, SDOCT; Spectralis), retardance (GDxVCC), and multifocal electroretinography (mfERG; VERIS) were performed in 39 NHP at baseline (BL; median, 5 recordings; range, 3-10) and weekly after induction of unilateral EG by laser photocoagulation of the trabecular meshwork. Multifocal ERG responses were high-pass filtered (>75 Hz) to measure high- and low-frequency component (HFC and LFC) amplitudes, including LFC features N1, P1, and N2. High-frequency component amplitudes are known to specifically reflect retinal ganglion cell (RGC) function. Complete (100%) axon counts of orbital optic nerves were obtained in 31/39 NHP.

RESULTS

Postlaser follow-up was 10.4 ± 7.9 months; mean and peak IOP were 18 ± 5 and 41 ± 11 mm Hg in EG eyes, 11 ± 2 and 18 ± 6 mm Hg in control (CTL) eyes. At the final available time point, RNFL thickness had decreased from BL by 14 ± 14%, retardance by 20 ± 11%, and the mfERG HFC by 30 ± 17% (P < 0.0001 each). Longitudinal changes in retardance and HFC were linearly related to RNFL thickness change (R2 = 0.51, P < 0.0001 and R2 = 0.22, P = 0.002, respectively); LFC N2 was weakly related but N1 or P2 (N1: R2 = 0.07, P = 0.11; P1: R2 = 0.04, P = 0.24; N2: R2 = 0.13, P = 0.02). At zero change from BL for RNFL thickness (Y-intercept), retardance was reduced by 11% (95% confidence interval [CI]: -15.3% to -6.8%) and HFC by 21.5% (95% CI: -28.7% to -14.3%). Relative loss of RNFL thickness, retardance, and HFC (EG:CTL) were each related to axon loss (R2 = 0.66, P < 0.0001; R2 = 0.42, P < 0.0001; R2 = 0.42, P < 0.0001, respectively), but only retardance and HFC were significantly reduced at zero relative axon loss (Y-intercept; retardance: -9.4%, 95% CI: -15.5% to -3.4%; HFC: -10.9%, 95% CI: -18.6% to -3.2%; RNFL thickness: +1.8%, 95% CI: -4.9% to +5.4%).

CONCLUSIONS

Retinal nerve fiber layer retardance and RGC function exhibit progressive loss from baseline before any loss of RNFL thickness or orbital optic nerve axons occurs in NHP EG. These in vivo measures might serve as potential biomarkers of early-stage glaucomatous damage preceding axon loss and RGC death.

Does Posterior Capsule Opacification Affect the Results of Diagnostic Technologies to Evaluate the Retina and the Optic Disc?

The visual outcome obtained after cataract removal may progressively decline because of posterior capsular opacification (PCO). This condition can be treated by creating an opening in the posterior lens capsule by Nd:YAG laser capsulotomy. PCO optical imperfections cause several light reflection, refraction, and diffraction phenomena, which may interfere with the functional and structural tests performed in different ocular locations for the diagnosis and follow-up of ocular disease, like macular and optic nerve diseases. Some parameters measured by visual field examinations, scanning laser polarimetry, and optical coherence tomography (OCT) have changed after PCO removal. Imaging quality also changes following capsulotomy. Consequently, the results of ancillary tests in pseudophakic eyes for studying ocular diseases like glaucoma or maculopathies should be correlated with other clinical examinations, for example, slit-lamp biomicroscopy or funduscopy. If PCO is clinically significant, a new baseline should be set for future comparisons following capsulotomy when using automated perimetry and scanning laser polarimetry. To perform OCT in the presence of PCO, reliable examinations (considering signal strength) apparently guarantee that measurements are not influenced by PCO.

Strategies to improve early diagnosis in glaucoma

Early diagnosis and treatment of glaucoma is important to reduce the risk of progressive and irreversible visual loss. The key to diagnosis is recognition of morphological changes to the optic nerve head and retinal nerve fiber layer, but in some patients, functional abnormalities are detected first. This review describes recent innovations with the potential to improve the early detection of glaucoma. Developments in imaging include novel optic nerve head metrics such as Bruch's membrane opening-minimum rim width, enhanced ability to quantify inner layers of the glaucomatous macula, and ability to image deep optic nerve head structures, including the lamina cribrosa. Developments in detection of early glaucomatous functional loss include novel perimetric tests using frequency-doubling technology and flicker-defined form stimuli. Methods to combine results of structural and functional assessments are also presented that may improve early detection of glaucoma.

In vivo imaging methods to assess glaucomatous optic neuropathy

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

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Modern technologies for retinal scanning and imaging: an introduction for the biomedical engineer

This review article is meant to help biomedical engineers and nonphysical scientists better understand the principles of, and the main trends in modern scanning and imaging modalities used in ophthalmology. It is intended to ease the communication between physicists, medical doctors and engineers, and hopefully encourage “classical” biomedical engineers to generate new ideas and to initiate projects in an area which has traditionally been dominated by optical physics. Most of the methods involved are applicable to other areas of biomedical optics and optoelectronics, such as microscopic imaging, spectroscopy, spectral imaging, opto-acoustic tomography, fluorescence imaging etc., all of which are with potential biomedical application. Although all described methods are novel and important, the emphasis of this review has been placed on three technologies introduced in the 1990’s and still undergoing vigorous development: Confocal Scanning Laser Ophthalmoscopy, Optical Coherence Tomography, and polarization-sensitive retinal scanning.

Comparison of the nerve fiber layer of type 2 diabetic patients without glaucoma with normal subjects of the same age and sex

BACKGROUND

The retinal nerve fiber layer (RNFL) thickness in patients with diabetes mellitus type 2 was compared to normal subjects of similar age and sex, having first excluded any risk factors for glaucoma. The correlation between the RNFL thickness and the severity of diabetic retinopathy was investigated at its primary stages and with other ocular and diabetic parameters.

METHODS

A prospective, case series study was carried out. Twenty-seven diabetic patients without diabetic retinopathy, 24 diabetic patients with mild retinopathy, and 25 normal, age-matched subjects underwent a complete ophthalmological examination and imaging with scanning laser polarimetry for the evaluation of the RNFL. Multivariate analysis was applied in order to investigate the correlation between RNFL and diabetic parameters, such as age, duration of diabetes, insulin therapy, levels of glycosylated hemoglobin; and ocular parameters, such as cup to disc ratio, levels of normal intraocular pressure, and central corneal thickness.

RESULTS

The mean inferior average of RNFL and the temporal-superior-nasal-inferior-temporal standard deviation were statistically significantly lower in both diabetic groups, and the nerve fiber index was higher (P=0.04) compared to the normal group. There was no statistically significant difference between the diabetic groups. The factor analysis showed no significant correlation between the RNFL and the previously mentioned diabetic and ocular parameters.

CONCLUSION

The existence of diabetes should be seriously considered in evaluating the results of scanning laser polarimetry. Multivariate analysis for RNFL was used for the first time.

Measurement of retinal nerve fiber layer thickness in eyes with optic disc swelling by using scanning laser polarimetry and optical coherence tomography

Background

The retinal nerve fiber layer thickness (RNFLT) in patients with optic disc swelling of different etiologies was compared using scanning laser polarimetry (SLP) and spectral-domain optical coherence tomography (OCT).

Methods

Forty-seven patients with optic disc swelling participated in the cross-sectional study. Both GDx SLP (enhanced corneal compensation) and Spectralis spectral-domain OCT measurements of RNFLT were made in 19 eyes with papilledema (PE), ten eyes with optic neuritis (ON), and 18 eyes with nonarteritic anterior ischemic optic neuropathy (NAION) at the neuro-ophthalmology clinic at Kyoto University Hospital. Differences in SLP (SLP-RNFLT) and OCT (OCT-RNFLT) measurements among different etiologies were investigated.

Results

No statistical differences in average OCT-RNFLT among PE, ON, and NAION patients were noted. Average SLP-RNFLT in NAION patients was smaller than in PE (P<0.01) or ON (P=0.02) patients. When RNFLT in each retinal quadrant was compared, no difference among etiologies was noted on OCT, but on SLP, the superior quadrant was thinner in NAION than in PE (P<0.001) or ON (P=0.001) patients. Compared with age-adjusted normative data of SLP-RNFLT, average SLP-RNFLT in PE (P<0.01) and ON (P<0.01) patients was greater. Superior SLP-RNFLT in NAION patients was smaller (P=0.026). The ratio of average SLP-RNFLT to average OCT-RNFLT was smaller in NAION than in PE (P=0.001) patients.

Conclusion

In the setting of RNFL thickening, despite increased light retardance in PE and ON eyes, SLP revealed that NAION eyes have less retardance, possibly associated with ischemic axonal loss.

Scanning laser polarimetry in glaucoma

Glaucoma is an acquired progressive optic neuropathy which is characterized by changes in the optic nerve head and retinal nerve fiber layer (RNFL). White-on-white perimetry is the gold standard for the diagnosis of glaucoma. However, it can detect defects in the visual field only after the loss of as many as 40% of the ganglion cells. Hence, the measurement of RNFL thickness has come up. Optical coherence tomography and scanning laser polarimetry (SLP) are the techniques that utilize the evaluation of RNFL for the evaluation of glaucoma. SLP provides RNFL thickness measurements based upon the birefringence of the retinal ganglion cell axons. We have reviewed the published literature on the use of SLP in glaucoma. This review elucidates the technological principles, recent developments and the role of SLP in the diagnosis and monitoring of glaucomatous optic neuropathy, in the light of scientific evidence so far.

Comparison of normal- and high-tension glaucoma: nerve fiber layer and optic nerve head damage

PURPOSE

The aim of this study was to investigate differences in the nerve fiber layer and glaucoma-induced structural optic nerve head (ONH) damage in patients with normal- (NTG) and high-tension (HTG) glaucoma.

METHODS

In this retrospective pair-matched comparative study, 22 NTG and 22 HTG eyes were matched according to the same glaucomatous damage based on rim volume, rim area and disk size, as measured by Heidelberg retinal tomography (HRT III). Visual fields (VF) were assessed by Humphrey perimetry, and nerve fiber layer thickness was determined both by scanning laser polarimetry (GDxVCC) and spectral-domain optical coherence tomography (SD-OCT). Comparisons of all measured parameters were made between NTG and HTG groups.

RESULTS

Based on HRT results, both NTG and HTG eyes displayed comparable structural damage to the ONH (NTG/HTG, mean: disk area, 2.30/2.31 mm(2), p = 0.942; rim area, 1.02/0.86 mm(2), p = 0.082; rim volume, 0.19/0.17 mm(3), p = 0.398). NTG eyes had significantly less VF damage than HTG eyes (NTG/HTG, mean deviation: -4.23/-12.12 dB, p = 0.002; pattern standard deviation: 5.39/8.23 dB, p = 0.022). The inferior nerve fiber layer of NTG patients was significantly thicker than that of HTG patients (NTG/HTG, mean: GDx inferior: 53.5/46.3 µm, p = 0.046). SD-OCT revealed a significantly thicker nerve fiber in NTG compared with HTG patients in all quadrants (NTG/HTG, total mean: 72.72/58.45 µm, p = 0.002).

CONCLUSION

At comparable glaucomatous stages, nerve fiber loss was more advanced in HTG patients compared with NTG patients.

Motion artifact and speckle noise reduction in polarization sensitive optical coherence tomography by retinal tracking

We present a novel polarization sensitive optical coherence tomography (PS-OCT) system with an integrated retinal tracker. The tracking operates at up to 60 Hz, correcting PS-OCT scanning positions during the acquisition to avoid artifacts caused by eye motion. To demonstrate the practical performance of the system, we imaged several healthy volunteers and patients with AMD both with B-scan repetitions for frame averaging and with 3D raster scans. Under large retinal motions with up to 1 mm amplitude at 0.5 ~a few Hz frequency range, motion artifact suppression in the PS-OCT images as well as standard deviation noise reduction in the frame averaged retardation images are presented.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Correlating perimetric indices with three nerve fiber layer thickness measures

PURPOSE

To determine which of three estimates of retinal nerve fiber layer thickness (RNFLT) correlate best with visual field sensitivity measured using standard automated perimetry (SAP).

METHODS

Data were collected from 400 eyes of 209 participants enrolled in the Portland Progression Project. These individuals ranged from high-risk suspects to having non-end-stage glaucoma. In each eye, three measures of average RNFLT (spectral domain optical coherence tomography [SDOCT], scanning laser polarimetry [SLP], confocal scanning laser tomography [CSLT]) and SAP (Humphrey HFAII) were performed on the same day. Mean deviation (MD), mean sensitivity (MS), and pattern standard deviation (PSD) were linearized using the equations MD(Lin) = 10(MD*0.1), MS(Lin) = 10(MS*0.1), and PSD(Lin) = 10(PSD*-0.1). Correlations between each of the estimates of RNFLT and each of the functional metrics were calculated (nine total). Pearson correlations and generalized estimating equations (GEE) were used to calculate the strength and significance of the correlations.

RESULTS

Linearized MS had the strongest correlation with SDOCT (r = 0.57), intermediate with SLP (r = 0.40), and weakest with CSLT (r = 0.13). When multiple RNFLT measures were included in a GEE model to predict MS(Lin), SDOCT was consistently predictive (p < 0.001) whereas CSLT was never predictive in these multivariate models. Similar findings were observed for MD(Lin) and PSD(Lin).

CONCLUSIONS

Average RNFLT estimated from SDOCT predicts SAP status significantly better than average RNFLT estimated from SLP or CSLT.

Retinal nerve fiber layer progression in glaucoma: a comparison between retinal nerve fiber layer thickness and retardance

OBJECTIVE

To investigate the performance of spectral-domain optical coherence tomography (OCT) and scanning laser polarimetry to detect progressive retinal nerve fiber layer (RNFL) changes and to determine whether reduction of the RNFL retardance occurred before thinning of the RNFL in glaucoma.

DESIGN

Prospective, longitudinal study.

PARTICIPANTS

One hundred eighty-four eyes of 116 glaucoma patients and 43 normal eyes of 23 healthy individuals.

METHODS

Patients were followed up every 4 months for at least 36 months with RNFL retardance (GDx Enhanced Corneal Compensation; Carl Zeiss Meditec) and RNFL thickness (Cirrus HD-OCT; Carl Zeiss Meditec) measured in the same visit. Progressive RNFL retardance and thickness changes were evaluated with event-based analysis (Guided Progression Analysis; Carl Zeiss Meditec) with reference to the RNFL retardance change map and the RNFL thickness change map, respectively. The area and frequency distribution of RNFL changes were examined by overlaying the RNFL retardance change maps and the RNFL thickness change maps in the latest follow-up. The agreement of RNFL retardance and RNFL thickness progression was evaluated with κ statistics.

MAIN OUTCOME MEASURES

Number of eyes with progressive RNFL changes over time.

RESULTS

A total of 2472 OCT thickness maps and 2472 RNFL retardance maps were collected and reviewed with a mean follow-up of 55.1 months. Twenty-seven eyes (14.6%; 26 glaucoma patients) showed progressive RNFL thinning, whereas 8 eyes (4.3%; 8 glaucoma patients) showed progressive reduction of RNFL retardance. Seven eyes (3.8%; 7 glaucoma patients) had progression that was detected by both instruments, all with progressive RNFL thinning detected before progressive reduction of RNFL retardance became evident, and the mean lag time was 13.4 months (range, 4.0-37.6 months). The agreement between RNFL thickness and RNFL retardance progression was fair (κ, 0.357). Progressive loss of RNFL thickness was observed most frequently at the inferotemporal 223° to 260°, whereas the inferotemporal 227° to 263° and superior 56° to 117° were observed most commonly for progressive loss of RNFL retardance. In the normal group, no eyes showed reduction in RNFL thickness or retardance.

CONCLUSIONS

At a comparable level of specificity, progressive RNFL thinning was detected more often than progressive reduction of RNFL retardance. For eyes with progressive loss of RNFL thickness and RNFL retardance, the former preceded the latter.

Onset and progression of peripapillary retinal nerve fiber layer (RNFL) retardance changes occur earlier than RNFL thickness changes in experimental glaucoma

PURPOSE

Longitudinal measurements of peripapillary RNFL thickness and retardance were compared in terms of time to reach onset of damage and time to reach a specific progression endpoint.

METHODS

A total of 41 rhesus macaques with unilateral experimental glaucoma (EG) each had three or more weekly baseline measurements in both eyes of peripapillary RNFL thickness (RNFLT) and retardance. Laser photocoagulation was then applied to the trabecular meshwork of one eye to induce chronic elevation of intraocular pressure and weekly imaging continued. Pairwise differences between baseline observations were sampled by bootstrapping to determine the 95% confidence limits of each measurement's repeatability. The first two sequential measurements below the lower confidence limit defined the endpoint for each parameter. Segmented linear and exponential decay functions were fit to each RNFL-versus-time series to determine the time to damage onset.

RESULTS

In all, 29 (71%) of the EG eyes reached endpoint by RNFL retardance and 25 (61%) reached endpoint by RNFLT. In total, 33 (80%) reached endpoint by at least one of the RNFL parameters and 21 (51%) reached endpoint by both RNFL parameters. Of the 33 EG eyes reaching any endpoint, a larger proportion reached endpoint first by retardance (n = 26, 79%) than did by RNFLT (n = 7, 21%; P = 0.002). Survival analysis indicated a shorter time to reach endpoint by retardance than by RNFLT (P < 0.001). Of the 21 EG eyes that reached endpoint by both measures, the median duration to endpoint was 120 days for retardance and 223 days for RNFLT (P = 0.003, Wilcoxon test). The time to onset was faster for retardance than that for RNFLT based on either segmented fits (by 31 days; P = 0.008, average R(2) = 0.89) or exponential fits (by 102 days; P = 0.01, average R(2) = 0.89).

CONCLUSIONS

The onset of progressive loss of RNFL retardance occurs earlier than the onset of RNFL thinning. Endpoints of progressive loss from baseline also occurred more frequently and earlier for RNFL retardance as compared with RNFLT.

Scanning laser polarimetry, but not optical coherence tomography predicts permanent visual field loss in acute nonarteritic anterior ischemic optic neuropathy

PURPOSE

Scanning laser polarimetry (SLP) reveals abnormal retardance of birefringence in locations of the edematous peripapillary retinal nerve fiber layer (RNFL), which appear thickened by optical coherence tomography (OCT), in nonarteritic anterior ischemic optic neuropathy (NAION). We hypothesize initial sector SLP RNFL abnormalities will correlate with long-term regional visual field loss due to ischemic injury.

METHODS

We prospectively performed automated perimetry, SLP, and high definition OCT (HD-OCT) of the RNFL in 25 eyes with acute NAION. We grouped visual field threshold and RNFL values into Garway-Heath inferior/superior disc sectors and corresponding superior/inferior field regions. We compared sector SLP RNFL thickness with corresponding visual field values at presentation and at >3 months.

RESULTS

At presentation, 12 eyes had superior sector SLP reduction, 11 of which had inferior field loss. Six eyes, all with superior field loss, had inferior sector SLP reduction. No eyes had reduced OCT-derived RNFL acutely. Eyes with abnormal field regions had corresponding SLP sectors thinner (P = 0.003) than for sectors with normal field regions. During the acute phase, the SLP-derived sector correlated with presentation (r = 0.59, P = 0.02) and with >3-month after presentation (r = 0.44, P = 0.02) corresponding superior and inferior field thresholds.

CONCLUSIONS

Abnormal RNFL birefringence occurs in sectors corresponding to regional visual field loss during acute NAION when OCT-derived RNFL shows thickening. Since the visual field deficits show no significant recovery, SLP can be an early marker for axonal injury, which may be used to assess recovery potential at RNFL locations with respect to new treatments for acute NAION.

Screening for glaucoma using GDx-VCC in a population with ≥1 risk factors

OBJECTIVE

To estimate the diagnostic accuracy of the GDx-VCC for glaucoma screening in a population with ≥1 risk factors for glaucoma.

DESIGN

Cross-sectional evaluation of a diagnostic test for screening.

PARTICIPANTS

Two hundred forty-seven community-based volunteer participants with risk factors for glaucoma.

METHODS

The peripapillary retinal nerve fibre layers (RNFL) of participants' eyes were scanned using the GDx-VCC. Based on an ophthalmologic examination and frequency doubling perimetry, eyes were classified into 4 categories: normal, possible glaucoma, probable glaucoma, and definitive glaucoma. The sensitivities, specificities, positive and negative predictive values, and positive and negative likelihood ratios of the RNFL parameters were calculated.

RESULTS

The right eyes were retained for analyses. After excluding 5 eyes because of missing data and 23 eyes because of poor scan quality, the data of 219 right eyes were analyzed. Four eyes had definitive glaucoma. The best performing parameter was the nerve fibre indicator using a cutoff of 35 with a sensitivity of 75% (95% CI 19.4-99.4) at a specificity of 95% (95% CI 91.3-97.3), a positive predictive value of 25 (95% CI 4.3-48.1), a negative predictive value of 99 (95% CI 97.5-100.0), a positive likelihood ratio of 16 (95% CI 6.69-32.5), and a negative likelihood ratio of 0.20 (95% CI 0.05-1.44).

CONCLUSIONS

The GDx-VCC has inadequate sensitivity for screening of definitive glaucoma.

Morphological and functional differences between normal-tension and high-tension glaucoma

PURPOSE

To compare visual field (VF) and nerve fibre loss in patients with normal-tension (NTG) and high-tension glaucoma (HTG) at an equal level of glaucomatous structural damage of the optic nerve head (ONH).

METHODS

In a retrospective, pair-matched, comparative study, 126 eyes with NTG and 126 eyes with HTG were matched according to the same glaucomatous ONH damage based on rim volume, rim area and disc size measured by the Heidelberg Retina Tomograph (HRT III). Visual field by Humphrey perimetry and nerve fibre layer thickness measured by scanning laser polarimetry (GdxVCC) were compared between both groups.

RESULTS

Based on the HRT, NTG and HTG displayed comparable structural damage of the ONH without a statistically significant difference between both groups (mean, NTG/HTG: disc area 2.32/2.32 mm², p =0.342; rim area 1.03/1.00 mm², p = 0.279; rim volume 0.2/0.19 mm³; p = 0.274). Eyes with NTG had significantly less VF damage than eyes with HTG (mean, NTG/HTG: mean deviation (MD) -3.69/-9.77 dB, p = 0.0001; pattern standard deviation (PSD) 4.80/7.17 dB, p = 0.0001). The nerve fibre layer of NTG patients was thicker than that of HTG patients (mean, NTG/HTG: GDx total: 46.9/44.0 μm, p = 0.073; GDx superior: 57.2/49.9 μm, p = 0.0001; GDx inferior: 54.9/49.7 μm, p = 0.001).

CONCLUSIONS

At an equal level of glaucomatous structural damage of the ONH indicated by cupping, rim area and rim volume, NTG patients seem to have a less affected visual field and a better preserved nerve fibre layer than HTG patients.

The glaucoma detection capability of spectral-domain OCT and GDx-VCC deviation maps in early glaucoma patients with localized visual field defects

PURPOSE

To evaluate and compare the glaucoma detection capabilities afforded by retinal nerve fiber layer (RNFL) thickness and deviation maps obtained using Cirrus spectral domain optical coherence tomography (Cirrus OCT), and GDx employing variable corneal compensation (GDx-VCC) in glaucoma patients with early, localized visual field (VF) loss.

METHODS

This prospective controlled, comparative study was performed on 42 eyes with localized VF defects, and 42 age/refractive error-matched healthy eyes. All participants were imaged by both imaging devices at the same visit. The area of the RNFL defect in each deviation map, corresponding to a VF defect, was analyzed by direct counting of color-coded superpixels in each device. Receiver operating characteristic (ROC) curves were constructed and compared between Cirrus OCT and GDx-VCC.

RESULTS

The areas under the ROCs (AUCs) of RNFL quadrant thicknesses in hemifields with visual field (VF) defects did not differ significantly (Cirrus OCT; 0.961, GDx-VCC; 0.919, P = 0.07). However, Cirrus OCT afforded a better diagnostic ability, by deviation map analysis, than did GDx-VCC (0.972 vs 0.887, P = 0.02).

CONCLUSIONS

The RNFL thicknesses assessed by either Cirrus OCT or GDx-VCC were comparable in terms of early glaucoma diagnostic capability. However, when areas containing RNFL defects were analyzed via deviation mapping, Cirrus OCT was better than GDx-VCC.

Predictive value of 1 month retinal nerve fiber layer thinning for deficits at 6 months after acute optic neuritis

BACKGROUND

Retinal nerve fiber layer (RNFL) loss occurs with multiple sclerosis and after optic neuritis. Vision or RNFL changes at presentation of optic neuritis are not predictive of outcome, but vision loss at 1 month correlates with vision deficits at 6 months. We hypothesized that RFNL thinning at 1 month would predict RNFL loss at 6 months.

METHODS

We prospectively studied the RNFL by optical coherence tomography (OCT) and scanning laser polarimetry (SLP), and determined the threshold field mean deviation, in 25 subjects with acute optic neuritis over a 6-month period. RNFL values, including the amount of thinning at 1-month, were correlated with 6-month outcome.

RESULTS

Baseline visual performance and RNFL values were similar for eyes grouped by 1 month RNFL thinning. Eyes with 1 month RNFL thinning had greater and significant RNFL thinning at 6 months, for all quadrants by OCT and for the nasal and inferior quadrants by SLP. RNFL thinning by OCT and SLP at 1 month correlated with 6-month OCT (r = 0.58; p = 0.006) and SLP (r = 0.59; p = 0.002) RNFL thinning, respectively.

CONCLUSION

Early RNFL loss at 1 month was predictive of the RNFL thinning at 6 months, which corroborated the importance of the 1-month time point for predicting the outcome of an optic neuritis attack.

Glaucoma diagnostics

This thesis addresses several aspects of glaucoma diagnostics from both a clinical and a screening perspective. New instruments for diagnosing glaucoma have been developed over the past years, but little information is available regarding their performance as screening methods and their usefulness in ordinary clinical practice. PURPOSE OF THE RESEARCH UNDERLYING THIS THESIS:  The objectives of this research were as follows: to compare the accuracy of results of analysis of the optic nerve head (ONH) achieved by computerized imaging using the Heidelberg Retina Tomograph (HRT) and by subjective assessment performed by physicians with different degrees of experience of glaucoma (paper III); to evaluate the effect of a continuous medical education (CME) lecture on subjective assessment of the ONH for diagnosis of glaucoma (paper II); to investigate subjective assessment of perimetric test results by physicians with varying knowledge of glaucoma with a trained artificial neural network (ANN) and to compare the certainty of the classifications (paper IV); and to compare the diagnostic performance of time-domain Stratus optical coherence tomography (OCT) with that of spectral-domain Cirrus OCT (paper I), frequency doubling technology (FDT) screening perimetry and scanning laser polarimetry with the GDx variable corneal compensator (VCC) in a random population-based sample and in patients with glaucoma of varying disease severity.

METHODS AND RESULTS

  In evaluation of the ONH, use of the HRT statistical tools, Moorfields regression analysis (MRA) and the Glaucoma Probability Score (GPS) was compared with subjective assessment performed by 45 physicians. Optic nerve head images and photographs from 138 healthy and 97 glaucoma subjects were included. The sensitivity of MRA was higher (87-94%) than that of the average physician (62-82%), considerably greater than that of ophthalmologists with subspecialties other than glaucoma (53-77%) and non-significantly better than that of glaucoma experts (72-88%). Sensitivity achieved by GPS (79-93%) was also greater than that of the average physician. MRA correctly classified all eyes with advanced glaucomatous visual field defects, a result that was not achieved by GPS or even by the glaucoma experts. In eyes with small discs, MRA sensitivity (88%) was comparable with that of glaucoma experts (85%) and much better than that of GPS (50%). Also, the group comprising all physicians provided specificity (75-92%) similar to that of both MRA (69 - 86%) and GPS (72-94%) (Andersson et al. 2011a). A 1-hr CME lecture on ONH assessment led to a significant improvement in sensitivity (from 70% to 80%) and a significant decrease in uncertain assessments (from 22% to 13%), whereas specificity remained unchanged (68%) (Andersson et al. 2011b). A rise in sensitivity was seen in all subgroups of physicians, including glaucoma experts. Thirty physicians assessing standard automated perimetry (SAP) test results as Humphrey Field Analyzer single-field analysis printouts with full StatPac information from 99 patients with glaucoma and 66 healthy subjects were compared with a trained ANN regarding diagnostic performance. ANN reached significantly higher sensitivity (93%) than the average physician (83%), whereas specificity was similar for these two groups (91% and 90%, respectively). Diagnostic accuracy was similar among the different groups of physicians and seemingly rather independent of experience. Sensitivity ranged from 82% in the subgroup of other subspecialists to 87% in the glaucoma expert group, and specificity ranged from 88% among general ophthalmologists to 91% for glaucoma experts. The ANN attained certainty of classification that was in parity with that provided by the glaucoma experts and did not make any completely incorrect classifications of the visual fields (i.e. erroneous classifications were in the borderline zone) (Andersson et al. 2012). From a population-based randomly selected sample (n=308) of older subjects (aged ≥ 50 years) living in southern Sweden, 170 subjects underwent a comprehensive examination that included Stratus OCT, Cirrus OCT, an FDT screening programme and the GDx VCC. The same test protocol was applied to 138 randomized clinical patients with different stages of glaucoma. In the population-based sample, both Stratus and Cirrus OCT showed high diagnostic accuracy with area under the receiver-operating curve (aROC) values close to 1.0 (Bengtsson et al. 2012). Both OCT instruments correctly classified all of the clinical glaucoma patients with advanced disease. FDT screening showed high sensitivity (91%) but erroneously gave normal test results for some eyes with advanced disease. GDx VCC had lower sensitivity (73-92%) and also led to a large proportion of examinations with an atypical retardation pattern that is known to affect the diagnostic efficiency of this instrument.

CONCLUSIONS

  The HRT MRA performed better than most physicians and was consistent with the glaucoma experts. These results suggest that MRA can be a valuable tool for diagnosing glaucoma in ordinary practice, particularly when only a few glaucoma experts are available. Even though MRA provided 100% sensitivity in eyes with advanced glaucoma, it probably does not offer sufficient specificity to make it suitable as a screening method. Continuing medical education on ONH analysis had a small, but positive effect on diagnostic accuracy for glaucoma. An ANN trained to classify visual fields seemed to perform at least as well as most of the participating physicians, whose performances were remarkably similar regardless of their level of experience. This indicates that available tools for interpreting SAP findings are helpful in assessments of visual field test results. However, SAP is associated with learning effects (Heijl et al. 1989) that may entail low specificity for untrained subjects, and hence, it is not an ideal screening method for glaucoma. By comparison, the screening test of FDT is rapid and easy, but it is probably less suitable for screening purpose, because some eyes with advanced glaucoma were missed in this investigation. GDx VCC images for a relatively large number of eyes could not be analysed and is thus not appropriate for screening. The OCT instruments offer both high sensitivity and high specificity, and all eyes with advanced disease were correctly classified as glaucomatous in this evaluation. However, these instruments are still expensive and require special operator skills. Additional development to obtain OCT instrument that is more compact, easier to use and less expensive might render such tomography suitable as a screening tool for glaucoma.

Optimizing the information yield of 3-D OCT in glaucoma

PURPOSE

To determine, first, which regions of 3-D optical coherence tomography (OCT) volumes can be segmented completely in the majority of subjects and, second, the relationship between analyzed area and thickness measurement test-retest variability.

METHODS

Three-dimensional OCT volumes (6 × 6 mm) centered around the fovea and optic nerve head (ONH) of 925 Rotterdam Study participants were analyzed; 44 participants were scanned twice. Volumes were segmented into 10 layers, and we determined the area where all layers could be identified in at least 95% (macula) or 90% (ONH) of subjects. Macular volumes were divided in 2 × 2, 4 × 4, 6 × 6, 8 × 8, or 68 blocks. We placed two circles around the ONH; the ONH had to fit into the smaller circle, and the larger circle had to fit into the segmentable part of the volume. The area between the circles was divided in 3 to 12 segments. We determined the test-retest variability (coefficient of repeatability) of the retinal nerve fiber layer (RNFL) and ganglion cell layer (RGCL) thickness measurements as a function of size of blocks/segments.

RESULTS

Eighty-two percent of the macular volume could be segmented in at least 95% of subjects; for the ONH, this was 65% in at least 90%. The radii of the circles were 1.03 and 1.84 mm. Depending on the analyzed area, median test-retest variability ranged from 8% to 15% for macular RNFL, 11% to 22% for macular RGCL, 5% to 11% for the two together, and 18% to 22% for ONH RNFL.

CONCLUSIONS

Test-retest variability hampers a detailed analysis of 3-D OCT data. Combined macular RNFL and RGCL thickness averaged over larger areas had the best test-retest variability.

[GDx-VCC NFI analysis in Lebanese glaucoma patients]

PURPOSE

To describe the Nerve Fiber Indicator (Nerve Fiber Index; NFI) parameter findings and progression in Lebanese glaucoma patients or suspects.

STUDY DESIGN

Retrospective, observational study.

PATIENTS AND METHODS

A review was conducted of the GDx VCC examinations performed between January 2003 and December 2008 in an ophthalmological diagnostic center, in 1063 Lebanese subjects referred for this testing by their ophthalmologists. This group of subjects included confirmed glaucoma patients and glaucoma suspects. GDx VCC examination was repeated one or more times, at a one-year interval, in only 136 patients. Since we only had access to their GDx VCC examinations, the number of subjects in each category was unknown prior to the exam. After GDx VCC examination, we divided the subjects into three categories according to their NFI score. Subjects were considered to be normal when the NFI score was below 30, glaucoma suspects when the score was between 30 and 40, and confirmed glaucoma patients when the score was above 40.

RESULTS

Among the 1063 patients studied, 525 were female and 538 male, with a mean age of 56.8 ± 14.2 years at the time of examination. The mean NFI score was 27.01 ± 14.23, higher in males than females in the various age groups, and higher in older than in younger subjects, the greatest difference being between the 11- to 20-year and the 81- to 90-year age groups (P=0.015). Eight hundred and eighty patients had an NFI score within normal limits, the score was consistent with glaucoma suspect in 280 patients and with confirmed glaucoma in 103 patients. Among the 136 patients who underwent multiple GDx VCC examinations, 69 were initially classified as normal. Upon repeat GDx VCC examinations over a five year period, 24 of these 69 patients (34.78%) presented with scores consistent with glaucoma suspect or confirmed glaucoma.

CONCLUSION

This study demonstrates that glaucoma was detected or suspected in at least one of three subjects referred for GDx VCC examination (383/1063). NFI scores were higher in males than females and in older compared to younger subjects.

Detection of glaucoma progression by population and individual derived variability criteria

PURPOSE

Ocular imaging devices provide quantitative structural information that might improve glaucoma progression detection. This study examined scanning laser polarimetry (SLP) population-derived versus individual-derived cut-off criteria for detecting progression.

METHODS

Forty-eight healthy, glaucoma suspect and glaucoma subjects, providing 76 eyes were used. All subjects had reliable visual field (VF) and SLP scans acquired at the same visits from ≥4 visits. VF progression was defined by guided progression analysis (GPA) and by the VF index. SLP measurements were analysed by fast mode (FM) GPA, compared with the population rate of progression, and extended mode (EM) GPA, compared with the individual variability. The agreement between progression detection methods was measured.

RESULTS

Poor agreement was observed between progression defined by VF and FM and EM. The difference in temporal-superior-nasal-inferior-temporal (TSNIT) average rate of change between VF defined progressors and non-progressors for both FM (p=0.010) and EM (p=0.015) was statistically significant.

CONCLUSIONS

There is poor agreement between VF and SLP progression regardless of the use of population derived or individual variability criteria. The best SLP progression detection method could not be ascertained, therefore, acquiring three SLP scans per visit is recommended.

Large-field high-speed polarization sensitive spectral domain OCT and its applications in ophthalmology

We present a novel spectral domain polarization sensitive OCT system (PS-OCT) that operates at an A-scan rate of 70 kHz and supports scan angles of up to 40° × 40°. The high-speed imaging allows the acquisition of up to 1024 × 250 A-scans per 3D scan, which, together with the large field of view, considerably increases the informative value of the images. To demonstrate the excellent performance of the new PS-OCT system, we imaged several healthy volunteers and patients with various diseases such as glaucoma, AMD, Stargardt's disease, and albinism. The results are compared with clinically established methods such as scanning laser polarimetry and autofluorescence.

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.