Computerized stereochronoscopy and alternation flicker to detect optic nerve head contour change

Longitudinal changes in optic disc cupping from the baseline in chiasmal lesion optic neuropathy and glaucoma

We aimed to investigate the changes in cupping in chiasmal lesion optic neuropathy (chON) compared to baseline optic disc and glaucoma. We used a novel study design to enroll patients who had fundus photographs incidentally taken during routine health check-ups prior to the onset of optic neuropathy. In 31 eyes (21 patients) with chON and 33 eyes (30 patients) with glaucoma, we investigated the change in cup-to-disc (C/D) area from the baseline to overt cupping using flicker analysis. Compared to the baseline, 23 eyes (74.2%) had increased cup size and 3 (9.7%) had vascular configuration changes in the chONgroup; in contrast, all glaucoma eyes exhibited changes in cup size and vascular configuration. The increase in C/D area ratio was significantly smaller in chON (0.04 ± 0.04) compared to glaucoma (0.10 ± 0.04, P < 0.001); the minimum residual neuroretinal rim width showed a more pronounced difference (29.7 ± 8.2% vs 7.1 ± 3.9%, P < 0.001). The changes distributed predominantly towards the nasal direction in chON, contrasting the changes to the arcuate fibers in glaucoma. In conclusion, our results provide the first longitudinal evidence of true pathological cupping in chONcompared to photographically disease-free baseline. The marked difference in the residual minimum rim width reaffirms the importance of rim obliteration in the differential diagnosis between the two diseases.

Noninvasive temporal detection of early retinal vascular changes during diabetes

Diabetes associated complications, including diabetic retinopathy and loss of vision, are major health concerns. Detecting early retinal vascular changes during diabetes is not well documented, and only few studies have addressed this domain. The purpose of this study was to noninvasively evaluate temporal changes in retinal vasculature at very early stages of diabetes using fundus images from preclinical models of diabetes. Non-diabetic and Akita/+ male mice with different duration of diabetes were subjected to fundus imaging using a Micron III imaging system. The images were obtained from 4 weeks- (onset of diabetes), 8 weeks-, 16 weeks-, and 24 weeks-old male Akita/+ and non-diabetic mice. In total 104 fundus images were subjected to analysis for various feature extractions. A combination of Canny Edge Detector and Angiogenesis Analyzer plug-ins in ImageJ were utilized to quantify various retinal vascular changes in fundus images. Statistical analyses were conducted to determine significant differences in the various extracted features from fundus images of diabetic and non-diabetic animals. Our novel image analysis method led to extraction of over 20 features. These results indicated that some of these features were significantly changed with a short duration of diabetes, and others remained the same but changed after longer duration of diabetes. These patterns likely distinguish acute (protective) and chronic (damaging) associated changes with diabetes. We show that with a combination of various plugging one can extract over 20 features from retinal vasculature fundus images. These features change during diabetes, thus allowing the quantification of quality of retinal vascular architecture as biomarkers for disease progression. In addition, our method was able to identify unique differences among diabetic mice with different duration of diabetes. The ability to noninvasively detect temporal retinal vascular changes during diabetes could lead to identification of specific markers important in the development and progression of diabetes mediated-microvascular changes, evaluation of therapeutic interventions, and eventual reversal of these changes in order to stop or delay disease progression.

Developing new automated alternation flicker using optic disc photography for the detection of glaucoma progression

PurposeTo evaluate a progression-detecting algorithm for a new automated matched alternation flicker (AMAF) in glaucoma patients.MethodsOpen-angle glaucoma patients with a baseline mean deviation of visual field (VF) test>-6 dB were included in this longitudinal and retrospective study. Functional progression was detected by two VF progression criteria and structural progression by both AMAF and conventional comparison methods using optic disc and retinal nerve fiber layer (RNFL) photography. Progression-detecting performances of AMAF and the conventional method were evaluated by an agreement between functional and structural progression criteria. RNFL thickness changes measured by optical coherence tomography (OCT) were compared between progressing and stable eyes determined by each method.ResultsAmong 103 eyes, 47 (45.6%), 21 (20.4%), and 32 (31.1%) eyes were evaluated as glaucoma progression using AMAF, the conventional method, and guided progression analysis (GPA) of the VF test, respectively. The AMAF showed better agreement than the conventional method, using GPA of the VF test (κ=0.337; P<0.001 and κ=0.124; P=0.191, respectively). The rates of RNFL thickness decay using OCT were significantly different between the progressing and stable eyes when progression was determined by AMAF (-3.49±2.86 μm per year vs -1.83±3.22 μm per year; P=0.007) but not by the conventional method (-3.24±2.42 μm per year vs -2.42±3.33 μm per year; P=0.290).ConclusionsThe AMAF was better than the conventional comparison method in discriminating structural changes during glaucoma progression, and showed a moderate agreement with functional progression criteria.

Agreement of New Automated Matched Alternation Flicker using Undilated Fundus Photography for the Detection of Glaucomatous Structural Change

PURPOSE

To determine the agreement among glaucoma experts and general ophthalmologists regarding detection of glaucomatous structural changes using a new automated matched alternation flicker (AMAF) method with fundus photographs (FPs) of undilated eyes.

METHODS

Sixty-six pairs of FPs of normal tension glaucoma patients were collected. FPs were taken at intervals of more than 12 months. Alternating flicker images were created using a new AMAF application. In a blinded manner, two glaucoma experts and two general ophthalmologists compared the presence of glaucomatous structural changes using either the AMAF method or the side-by-side comparison method. The interobserver and intraobserver agreements were compared using the Bland and Altman plot analysis.

RESULTS

The glaucoma experts detected more glaucoma progression using the AMAF method (average, 50.7%) compared with the side-by-side method (average, 32.5%). General ophthalmologists detected more glaucomatous progression with the AMAF method (average, 40.9%) than with the side-by-side method (average, 25.0%). The AMAF method showed fair to substantial interreader agreement (k = 0.511-0.724) and fair to perfect intrareader agreement (k = 0.631-0.943). Interreader and intrareader agreements using the AMAF method were better for the glaucoma experts compared with the general ophthalmologists.

CONCLUSIONS

The AMAF method showed more changes in FPs than the classical side-by-side comparison method. Regarding inter- and intrareader agreements, agreement for the glaucoma experts was best using the AMAF method, but for the general ophthalmologists agreement was best using the side-by-side comparison method.

Let's Use Cognitive Science to Create Collaborative Workstations

When informed by an understanding of cognitive science, radiologists' workstations could become collaborative to improve radiologists' performance and job satisfaction. The authors review relevant literature and present several promising areas of research, including image toggling, eye tracking, cognitive computing, intelligently restricted messaging, work habit tracking, and innovative input devices. The authors call for more research in "perceptual design," a promising field that can complement advances in computer-aided detection.

Comparison of retinal image evaluation techniques in novice clinicians

Retinal fundus evaluation is learned through experience and training. This study aimed to determine the image presentation characteristics and the accompanying evaluation techniques, which led to the most accurate and efficient retinal pathology detection method. Phase I included 25 novice clinicians asked to evaluate 14 different pathologies using spatial versus temporal image presentations. Phase II included 25 different novice clinicians asked to evaluate five different simulated pathologies at three different pixel sizes presented in both spatial and temporal image presentations. Accuracy and speed of recognition were evaluated between the spatial and temporal presentations of the same simulated pathology. In phase l, subjects were significantly faster at simulated pathology detection using a temporal presentation with a 95% accuracy rate versus a spatial presentation with a 79% accuracy rate. In phase II, subjects demonstrated significant differences in speed of detection using the temporal technique at all 3 pixel number sizes with the greatest difference in detection times shown at the smallest retinal defects. Accuracy and speed of recognition in simulated pathology assessment were improved in a temporal presentation and the greatest improvements were demonstrated at the smallest pixel numbers.

The fundus slit lamp

Fundus biomicroscopy with the slit lamp as it is practiced widely nowadays was not established until the 1980-es with the introduction of the Volk lenses +90 and +60D. Thereafter little progress has been made in retinal imaging with the slit lamp. It is the aim of this paper to fully exploit the potential of a video slit lamp for fundus documentation by using easily accessible additions.

Suitable still images are easily retrieved from videorecordings of slit lamp examinations. The effects of changements in the slit lamp itself (slit beam and apertures) and its examination equipment (converging lenses from +40 to +90D) on quality and spectrum of fundus images are demonstrated. Imaging software is applied for reconstruction of larger fundus areas in a mosaic pattern (Hugin®) and to perform the flicker test in order to visualize changes in the same fundus area at different points of time (Power Point®).

The three lenses +90/+60/+40D are a good choice for imaging the whole spectrum of retinal diseases. Displacement of the oblique slit light can be used to assess changes in the surface profile of the inner retina which occurs e.g. in macular holes or pigment epithelial detachment. The mosaic function in its easiest form (one strip macula adapted to one strip with the optic disc) provides an overview of the posterior pole comparable to a fundus camera’s image. A reconstruction of larger fundus areas is feasible for imaging in vitreoretinal surgery or occlusive vessel disease. The flicker test is a fine tool for monitoring progressive glaucoma by changes in the optic disc, and it is also a valuable diagnostic tool in macular disease.

Nearly all retinal diseases can be imaged with the slit lamp - irrespective whether they affect the posterior pole, mainly the optic nerve or the macula, the whole retina or only its periphery. Even a basic fundus controlled perimetry is possible. Therefore fundus videography with the slit lamp is a worthwhile approach especially for the many ophthalmologists without access to the most recent diagnostic equipment or a professional photographer at hand.

Retinal blood vessel positional shifts and glaucoma progression

PURPOSE

To determine the characteristics and significance of retinal blood vessel (RBV) positional shifts over time in a cohort of patients with progressive glaucoma.

DESIGN

Retrospective cohort study.

PARTICIPANTS

Baseline and serial stereophotographs from 1 eye of 125 patients with open-angle glaucoma with ≥8 reliable Swedish interactive threshold algorithm standard visual fields (VFs) were included. On the basis of global rates of threshold sensitivity change, patients with glaucoma were divided into groups of minimal (<-0.02 decibels [dB]/year), moderate (-0.02 to -0.65 dB/year), or fast (≥-0.65 dB/year) progression. To determine whether graders' assessments of RBV positional shifts were false-positives, a control group consisting of 33 patients with glaucoma with 2 sets of photographs taken on the same day was included.

METHODS

Masked graders reviewed serial photographs aligned with automated alternation flicker (EyeIC, Narbeth, PA) and assessed them for the presence of any discrete RBV positional shifts (2 graders) and for traditional measures of structural progression (2 graders), including neuroretinal rim loss, parapapillary atrophy progression, and disc hemorrhage (DH).

MAIN OUTCOME MEASURES

Presence or absence of RBV positional shifts, rates of VF progression, and presence or absence of traditional measures of structural progression.

RESULTS

A total of 158 image sets (125 longitudinal and 33 same-day controls) from patients with glaucoma were included. Retinal blood vessel shifts were noted in 33 of 125 (26.4%) longitudinally followed glaucomatous eyes and 2 of 33 (6%) same-day control patients (P = 0.01). Agreement between graders I and II was 90.4% (kappa=0.77; P< 0.001). Eyes with RBV positional change progressed more rapidly than those without (-0.55 vs. -0.29 dB/year; 95% confidence interval [CI], 0.03-0.48); P = 0.03). Retinal blood vessel shift was present in 12.1% of minimal progressors versus 31.5% of moderate and fast progressors (P = 0.04). Rate of VF progression was statistically associated with RBV shift (odds ratio [OR], 2.2; 95% CI, 1.1-4.5; P = 0.03). Other variables significantly associated with RBV shift included neuroretinal rim loss (OR, 21.9; 95% CI, 5.7-83.6; P< 0.001) and DH (OR, 4.6; 95% CI, 1.5-15.5; P< 0.01). A multivariable model revealed that rim loss and DH, but not rate of functional change, were significantly associated with RBV shift.

CONCLUSIONS

Retinal blood vessel positional shifts occurred in eyes with functionally progressive glaucoma, neuroretinal rim loss, and DH. This is a novel clinical finding that could help identify glaucoma progression or individuals at higher risk for future progression.

Association of blood and ocular perfusion pressure with structural glaucomatous progression by flicker chronoscopy

BACKGROUND

Vascular risk factors have been associated with glaucomatous visual field progression.

AIM

We determined the relationship between vascular risk factors and structural glaucomatous progression using serial flicker chronoscopy images.

METHODS

Two glaucoma fellowship-trained ophthalmologists, masked to temporal sequence, independently graded serial flicker chronoscopy images from one eye of a cohort of glaucoma patients for features of structural progression in this retrospective cohort study. After adjudication, simple and multiple logistic models were constructed to determine variables associated with increased odds of progression, including systolic blood pressure (BP), diastolic BP and mean ocular perfusion pressure.

RESULTS

Seventy-two eyes of 72 patients were analysed. Patients with any form of structural progression (n=40) were older (67.0 vs 58.8 years; p=0.005) and had lower diastolic BP (71.8 vs 76.5 mm Hg; p=0.02) than patients without progression (n=32). In the univariable model, diastolic BP was associated with progressive retinal nerve fibre layer (RNFL) loss (OR=0.2 per 10 mm Hg, 95% CI 0.1 to 0.6, p<0.006) and neuroretinal rim loss (OR=0.4 per 10 mm Hg, 95% CI 0.2 to 0.8, p<0.01). Diastolic BP was also significant in the multivariable model for RNFL loss (p=0.009) and neuroretinal rim loss (p=0.003).

CONCLUSIONS

This study is the first to use structural progression and flicker chronoscopy to identify vascular glaucoma risk factors. Older age and lower diastolic BP were associated with progression. By multivariable analysis diastolic BP was associated with RNFL and neuroretinal rim loss. These findings suggest that diastolic BP is associated with structural glaucomatous progression which may have implications for management.

Agreement of flicker chronoscopy for structural glaucomatous progression detection and factors associated with progression

PURPOSE

To evaluate agreement of flicker chronoscopy for structural glaucomatous progression detection and factors associated with progression.

DESIGN

Retrospective cohort study.

METHODS

Two glaucoma fellowship-trained ophthalmologists, masked to temporal sequence, independently graded serial flicker chronoscopy images from 1 eye of a cohort of glaucoma patients for features of structural progression. Agreement between graders was determined, as was accuracy for determining the temporal order of images. After adjudication, simple and multiple logistic models were constructed to determine baseline variables associated with increased odds of progression.

RESULTS

Fifty of 103 included eyes/patients (48.5%) had at least 1 sign of structural progression. Temporal sequence was incorrectly determined in 14 of 206 cases (6.4%). Interobserver agreements for identifying baseline photographs (κ = 0.9), global progression (κ = 0.7), parapapillary atrophy (PPA) progression (κ = 0.7), disc hemorrhages (κ = 0.7), neuroretinal rim loss (κ = 0.5), and retinal nerve fiber layer (RNFL) loss (κ = 0.2) were calculated. Age was significantly associated with global (1.8; 1.3-2.6, P < .001) (odds ratio; 95% confidence interval, significance) and PPA progression (1.7; 1.2-2.4, P = .002). Lower corneal hysteresis was associated with global progression (0.78; 0.56-0.99, P = .049) and RNFL loss (0.5; 0.3-0.9, P = .02). Goldmann-correlated intraocular pressure (1.0, 0.7-1.4, P = .9), visual field mean deviation (1.0, 0.9-1.0, P = .2), and central corneal thickness (0.9, 0.8-1.0, P = .1) were not significantly associated with progression. On multivariable analysis, only age was associated with global progression (1.8; 1.2-2.5, P = .002).

CONCLUSION

Flicker chronoscopy demonstrated acceptable interobserver agreement in structural progression detection. Corneal hysteresis and age were both associated with progression, but age was the only significant factor on multivariable analysis.

Cell-by-cell alignment of repeated specular microscopy images from the same eye

PURPOSE

Modern specular microscopes (SM) robustly depict the same central area of the corneal endothelium at different time points through a built-in fixation light. However, repeated image acquisitions slightly shift and rotate because of minute changes in head position in the chin and forehead rest. This prevents the manual retrieval of individual corneal endothelial cells (CECs) in repeated measurements because SM images usually lack obvious landmarks. We devised and validated an image registration algorithm that aligns SM images from the same eye to make corresponding CECs coincide.

METHODS

We retrospectively selected 27 image pairs for the presence of significant image overlap. Each image pair had been recorded on the same day and of the same eye. We applied our registration method in each image pair. Two observers independently validated, by means of alternation flicker, that the image pairs had been correctly aligned. We also repeatedly applied our registration method on unrelated image pairs by randomly drawing images and making certain that the images did not originate from the same eye. This was done to assess the specifity of our method.

RESULTS

All automated registrations of the same-day and same-eye image pairs were accurate. However, one single image incorrectly failed to trigger the non-match diagnosis twice in 81 registration attempts between unrelated images. As it turned out, this particular image depicted only 73 CECs. The average number of CECs was 253 (range 73-393).

CONCLUSION

Repeated non-contact SM images can be automatedly aligned so that the corresponding CECs coincide. Any successful alignment can be considered as proof of the retrieval of identical CECs as soon as at least 100 CEC centroids have been identified. We believe our method is the first to robustly confirm endothelial stability in individual eyes.

Evaluation of vascular disease progression in retinopathy of prematurity using static and dynamic retinal images

PURPOSE

To measure accuracy and speed for detection of vascular progression in retinopathy of prematurity (ROP) from serial images. Two strategies are compared: static side-by-side presentation and dynamic flickering of superimposed image pairs.

DESIGN

Prospective comparative study.

METHODS

Fifteen de-identified, wide-angle retinal image pairs were taken from infants who eventually developed plus disease. Image pairs representing vascular disease progression were taken ≥1 week apart, and control images without progression were taken on the same day. Dynamic flickering pairs were created by digital image registration. Ten experts independently reviewed each image pair on a secure website using both strategies, and were asked to identify progression or state that images were identical. Accuracy and speed were measured, using examination date and ophthalmoscopic findings as a reference standard.

RESULTS

Using static images, experts were accurate in a mean (%) ± standard deviation (SD) of 11.4 of 15 (76%) ± 1.7 image pairs. Using dynamic flickering images, experts were accurate in a mean (%) ± SD of 11.3 of 15 (75%) ± 1.7 image pairs. There was no significant difference in accuracy between these strategies (P = .420). Diagnostic speed was faster using dynamic flickering (24.7 ± 8.3 seconds) vs static side-by-side images (40.3 ± 18.3 seconds) (P = .002). Experts reported higher confidence when interpreting dynamic flickering images (P = .001).

CONCLUSIONS

Retinal imaging provides objective documentation of vascular appearance, with potentially improved ability to recognize ROP progression compared to standard ophthalmoscopy. Speed of identifying vascular progression was faster by review of dynamic flickering image pairs than by static side-by-side images, although there was no difference in accuracy.

The value of tests in the diagnosis and management of glaucoma

PURPOSE

To assess the noneconomic value of tests used in the diagnosis and management of glaucoma, and explore the contexts and factors that determine such value.

DESIGN

Perspective.

METHODS

Selected articles from primary and secondary sources were reviewed and interpreted in the context of the authors' clinical and research experience, influenced by our perspectives on the tasks of reducing the global problem of irreversible blindness caused by glaucoma. The value of any test used in glaucoma is addressed by 3 questions regarding: its contexts, its kind of value, and its implicit or explicit benefits.

RESULTS

Tonometry, slit-lamp gonioscopy, and optic disc evaluation remain the foundation of clinic-based case finding, whether in areas of more or less abundant resources. In resource-poor areas, there is urgency in identifying patients at risk for severe functional loss of vision; screening strategies have proven ineffective, and efforts are hindered by the inadequate allocation of support. In resource-abundant areas, the wider spectrum of glaucoma is addressed, with emphasis on early detection of structural changes of little functional consequence; these are increasingly the focus of new and expensive technologies whose clinical value has not been established in longitudinal and population-based studies. These contrasting realities in part reflect differences among the value ascribed, often implicitly, to the tests used in glaucoma.

CONCLUSIONS

The value of any test is determined by 3 aspects: its context of usage; its comparative worth and to whom its benefit accrues; and how we define historically what we are testing. These multiple factors should be considered in the elaboration of priorities for the development and application of tests in glaucoma.

Comparing the detection and agreement of parapapillary atrophy progression using digital optic disk photographs and alternation flicker

PURPOSE

Parapapillary atrophy (PPA) progression has been associated with progressive glaucoma, but has proven to be difficult to assess clinically. We compared inter- and intra-observer agreement using a novel automated alternation flicker technology and side-by-side digital photography inspection for the evaluation of PPA progression.

METHODS

Consecutive patients with serial digital optic nerve photographs at least 1 year apart were included. Two graders (NR, BV) masked to image chronology assessed a set of photographs for progressive PPA using predefined criteria based on reference photographs containing mild, moderate, extensive or no PPA progression. At a separate session, the graders evaluated photographs using alternation flicker (EyeIC, Narberth, PA, USA) applying the same criteria. The order of patients and technique was randomized. Graders then assessed the same set of flickers and photographs a second time with the order of presentation reversed. The main outcome measure was the assessment of progressive PPA as identified by alternation flicker and digital photography inspection. Inter- and intra-observer agreement using each technique was assessed using the kappa statistic. A bootstrap method for comparing correlated kappa coefficients was used to assess statistical significance.

RESULTS

Serial photographs from 131 eyes of 68 patients were evaluated. Both graders identified significantly more cases of PPA progression using flicker compared to photography (27-34% vs 8-13%; both p< or =0.003). Inter-observer agreement using flicker was better than using photographs (kappa=0.52 vs 0.18, p=0.02). Intra-observer agreement was similar for both graders (photos: kappa=0.58 vs 0.57, p=0.97; flicker: kappa=0.61 vs 0.70, p=0.37). When progression was assessed by the number of progressive quadrants identified by each grader using a weighted kappa statistic, flicker inter-observer agreement was still moderate (kappa=0.45) and significantly better (p=0.01) than photography, which showed poor agreement (kappa=0.15). Intra-observer agreement with a weighted kappa for quadrant progression was also similar for both graders (photos: grader 1 kappa=0.53 vs grader 2 kappa=0.52, p=0.92; flickers: grader 1 kappa=0.58 vs grader 2 kappa=0.69, p=0.22). Conclusion Flicker identified more cases of progressive PPA than photographic review. Agreement between observers was significantly higher when using the automated flicker technology.

Comparison of stereo disc photographs and alternation flicker using a novel matching technology for detecting glaucoma progression

BACKGROUND AND OBJECTIVE

To compare agreement of automated alternation flicker and serial stereophotograph inspection for detection of progressive glaucoma.

PATIENTS AND METHODS

Serial photographs of patients with glaucoma with at least 36 months of follow-up and perimetry every 4 months were assessed by four graders using predefined criteria with both flicker and stereophotography. The main outcome measure was progressive neuroretinal rim deterioration as identified by each technique.

RESULTS

Forty eyes (20 patients) were included and 12 eyes progressed with perimetry. Using stereophotography, the overall agreement (kappa ± standard error) was 0.19 ± 0.06 for rim change, 0.78 ± 0.06 for disc hemorrhage, and -0.04 ± 0.06 for vessel movement. Using flicker, the overall agreement was similar for rim change (0.28 ± 0.06; P = .29), worse for disc hemorrhage (0.43 ± 0.06; P < .001), and better for vessel movement (0.22 ± 0.06; P = .002). The agreement between perimetric and disc progression was similar using stereophotography (0.10 ± 0.05) and flicker (0.19 ± 0.05; P = .20).

CONCLUSION

Agreement between flicker and stereophotography was similar.

Tele-transmission of stereoscopic images of the optic nerve head in glaucoma via Internet

The objective was to describe an inexpensive system to visualize stereoscopic photographs of the optic nerve head on computer displays and to transmit such images via the Internet for collaborative research or remote clinical diagnosis in glaucoma. Stereoscopic images of glaucoma patients were digitized and stored in a file format (joint photographic stereoimage [jps]) containing all three-dimensional information for both eyes on an Internet Web site (www.trizax.com). The size of jps files was between 0.4 to 1.4 MB (corresponding to a diagonal stereo image size between 900 and 1400 pixels) suitable for Internet protocols. A conventional personal computer system equipped with wireless stereoscopic LCD shutter glasses and a CRT-monitor with high refresh rate (120 Hz) can be used to obtain flicker-free stereo visualization of true-color images with high resolution. Modern thin-film transistor-LCD displays in combination with inexpensive red-cyan goggles achieve stereoscopic visualization with the same resolution but reduced color quality and contrast. The primary aim of our study was met to transmit stereoscopic images via the Internet. Additionally, we found that with both stereoscopic visualization techniques, cup depth, neuroretinal rim shape, and slope of the inner wall of the optic nerve head, can be qualitatively better perceived and interpreted than with monoscopic images. This study demonstrates high-quality and low-cost Internet transmission of stereoscopic images of the optic nerve head from glaucoma patients. The technique allows exchange of stereoscopic images and can be applied to tele-diagnostic and glaucoma research.

Concordance of flicker comparison versus side-by-side comparison in glaucoma

BACKGROUND

Flicker comparison superimposes baseline photos of the optic nerve head to subsequent photos, alternating them at a high frequency rate to create the perception of motion showing glaucomatous structural changes over time. The primary purpose of this study was to determine the degree of concordance among examiners in judging glaucomatous progression between serial optic nerve head photos using digital image flicker comparison versus the traditional side-by-side photograph comparison method. The secondary purpose was to determine if flicker comparison was quicker than side-by-side comparison.

METHODS

A total of 29 eyes were selected from patient records at Nittany Eye Associates. Fourteen eyes showed various degrees of glaucomatous structural change among photos, while the remaining 15 eyes had no glaucomatous structural change. Three masked optometrists experienced in glaucoma management graded whether the photos represented glaucomatous change or no change when viewing photos randomly assigned to side-by-side or flicker comparison.

RESULTS

Among multiple graders, flicker comparison gave moderate agreement, whereas side-by-side analysis gave fair agreement. The difference in time between the 2 methods was not statistically significant.

CONCLUSIONS

Flicker comparison is a unique, easy to learn, and an accurate way to view serial optic nerve head photographs. More study is needed to determine if flicker comparison is a useful tool in the clinical management of structural glaucoma progression.

Integrated Analysis of Vascular and Nonvascular Changes From Color Retinal Fundus Image Sequences

Algorithms are presented for integrated analysis of both vascular and nonvascular changes observed in longitudinal time-series of color retinal fundus images, extending our prior work. A Bayesian model selection algorithm that combines color change information, and image understanding systems outputs in a novel manner is used to analyze vascular changes such as increase/decrease in width, and disappearance/appearance of vessels, as well as nonvascular changes such as appearance/disappearance of different kinds of lesions. The overall system is robust to false changes due to inter-image and intra-image nonuniform illumination, imaging artifacts such as dust particles in the optical path, alignment errors and outliers in the training-data. An expert observer validated the algorithms on 54 regions selected from 34 image pairs. The regions were selected such that they represented diverse types of vascular changes of interest, as well as no-change regions. The algorithm achieved a sensitivity of 82% and a 9% false positive rate for vascular changes. For the nonvascular changes, 97% sensitivity and a 10% false positive rate are achieved. The combined system is intended for diverse applications including computer-assisted retinal screening, image-reading centers, quantitative monitoring of disease onset and progression, assessment of treatment efficacy, and scoring clinical trials.

Diagnosing glaucoma progression: current practice and promising technologies

PURPOSE OF REVIEW

An update on recent work is provided that has broadened our understanding of the evaluation of visual function and structure, and their use in evaluating glaucoma progression.

RECENT FINDINGS

The challenge of determining visual-field progression and the implications of long-term fluctuation are reviewed and data to support the magnitude of the fluctuation are cited. The use of confirmatory testing can limit the over diagnosis of glaucoma progression. Focusing visual-field testing on the locations of present scotomas or using frequency doubling technology may provide new approaches to assessing visual function. New standardized techniques to interpret visual fields, including neural networks, unsupervised machine learning and pointwise linear regression, may provide more quantitative means for visual-field interpretation. These techniques, along with structural evaluation of the optic nerve and nerve fiber layer, are essential in glaucoma management. Optic-nerve-head photography is still a mainstay in evaluating glaucoma progression, although many technologies including scanning laser tomography, scanning laser polarimetry and optical coherence tomography offer more quantitative means to follow structural change. These modalities, in different ways, show promise in providing additional information regarding the stability of glaucoma.

SUMMARY

Identifying the functional visual component as well as structural changes is essential in evaluating glaucoma progression. New techniques of testing and evaluating visual fields, the optic-nerve head, and the retinal nerve fiber layer offer exciting opportunities to more accurately identify glaucoma progression, and are likely to become more central as imaging devices and software support develop further.

Digital imaging of the optic nerve head: monoscopic and stereoscopic analysis

AIMS

To compare monoscopic and stereoscopic assessment of the optic disc using novel software for the digital stereoscopic analysis of optic disc stereopairs.

METHODS

Software was developed for the stereoscopic display of digital optic disc images using an interlaced display method. Neuroretinal rim width was determined at 10 degree intervals around the optic disc using a custom (stereoscopic) cursor whose depth was adjusted to that of Elschnig's rim. Measurements were taken, first viewing the disc monoscopically and at a separate sitting, stereoscopically.

RESULTS

Measurements were made in 35 eyes from 35 patients (1260 estimates for each observer) using three observers. The mean cup to disc ratio (CDR) ranged from 0.57 to 0.66 (SD 0.13-0.14) for monoscopic viewing compared with 0.64 to 0.69 (SD 0.12-0.14) for stereoscopic viewing. Stereoscopic assessments gave higher CDRs in temporal, superior, nasal, and inferior aspects of the optic disc (p<0.001, Mann-Whitney U test). Agreement between observers in estimating CDR was high for monoscopic assessment (intraclass correlation coefficient 0.74 (CI 0.72 to 0.76) increasing to 0.80 (0.78 to 0.82) for stereoscopic assessment.

CONCLUSION

Digital stereoscopic optic disc assessment provides lower estimates of neuroretinal rim width and higher levels of interobserver agreement compared with monoscopic assessments.

Image change detection algorithms: a systematic survey

Detecting regions of change in multiple images of the same scene taken at different times is of widespread interest due to a large number of applications in diverse disciplines, including remote sensing, surveillance, medical diagnosis and treatment, civil infrastructure, and underwater sensing. This paper presents a systematic survey of the common processing steps and core decision rules in modern change detection algorithms, including significance and hypothesis testing, predictive models, the shading model, and background modeling. We also discuss important preprocessing methods, approaches to enforcing the consistency of the change mask, and principles for evaluating and comparing the performance of change detection algorithms. It is hoped that our classification of algorithms into a relatively small number of categories will provide useful guidance to the algorithm designer.

Mosaicking and enhancement of slit lamp biomicroscopic fundus images

AIMS

To process video slit lamp biomicroscopic fundus image sequences in order to generate wide field, high quality fundus image montages which might be suitable for photodocumentation.

METHODS

Slit lamp biomicroscopic fundus examination was performed on human volunteers with a contact or non-contact lens. A stock, charge coupled device camera permitted image capture and storage of the image sequence at 30 frames per second. Acquisition time was approximately 30 seconds. Individual slit lamp biomicroscope fundus image frames were aligned and blended with custom developed software.

RESULTS

The developed algorithms allowed for highly accurate alignment and blending of partially overlapping slit lamp biomicroscopic fundus images to generate a seamless, high quality, wide field montage.

CONCLUSIONS

Video image acquisition and processing algorithms allow for mosaicking and enhancement of slit lamp biomicroscopic fundus images. The improved quality and wide field of view may confer suitability for inexpensive, real time photodocumentation of disc and macular abnormalities.