Development of a test grid using Eye Movement Perimetry for screening glaucomatous visual field defects.

BACKGROUND: Eye Movement Perimetry (EMP) uses Saccadic Eye Movement (SEM) responses for visual field evaluation. Previous studies have demonstrated significant delay in initiation of SEMs among glaucoma patients in comparison with healthy subjects. The aim of the current study was to develop an EMP-based screening grid to identify glaucomatous visual field defects. METHODS: An interactive test consisting of 36 locations and two stimulus contrasts (162 cd/m2 and 190 cd/m2 on a background of 140 cd/m2) was evaluated in 54 healthy subjects and 50 primary glaucoma patients. Each subject was presented a central fixation target combined with the random projection of Goldmann size III peripheral targets. Instructions were given to look at each peripheral target on detection and then re-fixate at the central fixation target while the saccades were assessed using an eye tracker. From each seen peripheral target, the Saccadic Reaction Time (SRT) was calculated for contrast level 162 cd/ m2. These values were used to plot Receiver Operating Characteristic (ROC) curves for each test locations and the Area Under the Curve (AUC) values were used to identify the locations with highest susceptibility to glaucomatous damage. Each stimulus location with an AUC less than 0.75 along with its mirrored test location around the horizontal axis were eliminated from the grid. RESULTS: The mean age was 48.1 ± 16.6 years and 50.0 ± 14.5 years for healthy subjects and glaucoma patients respectively. A significant increase of SRT values by 76.5% (p < 0.001) was found in glaucoma patients in comparison with the healthy subjects. From the ROC analysis, ten out of 36 locations meeting the cut-off criteria of AUC were eliminated resulting in a new grid containing 26 test locations. SRT values were significantly different (p < 0.05) between the healthy subjects and glaucoma irrespective of the grids used. CONCLUSIONS: The present study resulted in a screening grid consisting of 26 locations predominantly testing nasal, superior and inferior areas of the visual field. An internal validation of the modified grid showed 90.4% of screening accuracy which makes it a potential approach for population based glaucoma screening.

The Effect of Cataract on Eye Movement Perimetry.

Purpose. To determine how different grades of cataract affect sensitivity threshold and saccadic reaction time (SRT) in eye movement perimetry (EMP). Methods. In EMP, the visual field is tested by assessing the saccades that a subject makes towards peripheral stimuli using an eye tracker. Forty-eight cataract patients underwent pre- and postoperative EMP examination in both eyes. The subjects had to fix a central stimulus presented on the eye tracker monitor and to look at any detected peripheral stimulus upon its appearance. A multilevel mixed model was used to determine the factors that affected the sensitivity threshold and the SRT as a function of cataract grade. Results. We found no effect of cataract severity (LOCS III grades I through IV) on SRT and the sensitivity thresholds. In cataract of LOCS III grade V, however, we found an increase by 27% and 21% (p < 0.001), respectively, compared to the SRT and the sensitivity threshold in LOCS III grade I. Eyes that underwent cataract surgery showed no change in mean SRTs and sensitivity thresholds after surgery in LOCS III grade IV and lower. Conclusion. The present study shows that EMP can be readily used in patients with cataract with LOCS III grade IV and below.

Depth-resolved model-based reconstruction of attenuation coefficients in optical coherence tomography.

We present a method, based on a single scattering model, to calculate the attenuation coefficient of each pixel in optical coherence tomography (OCT) depth profiles. Numerical simulations were used to determine the model's response to different depths and attenuation coefficients. Experiments were performed on uniform and layered phantoms with varying attenuation coefficients. They were measured by a 1300 nm OCT system and their attenuation coefficients were evaluated by our proposed method and by fitting the OCT slope as the gold standard. Both methods showed largely consistent results for the uniform phantoms. On the layered phantom, only our proposed method accurately estimated the attenuation coefficients. For all phantoms, the proposed method largely reduced the variability of the estimated attenuation coefficients. The method was illustrated on an in-vivo retinal OCT scan, effectively removing common imaging artifacts such as shadowing. By providing localized, per-pixel attenuation coefficients, this method enables tissue characterization based on attenuation coefficient estimates from OCT data.

Surveillance for ocular hypertension: an evidence synthesis and economic evaluation.

OBJECTIVES: To determine effective and efficient monitoring criteria for ocular hypertension [raised intraocular pressure (IOP)] through (i) identification and validation of glaucoma risk prediction models; and (ii) development of models to determine optimal surveillance pathways. DESIGN: A discrete event simulation economic modelling evaluation. Data from systematic reviews of risk prediction models and agreement between tonometers, secondary analyses of existing datasets (to validate identified risk models and determine optimal monitoring criteria) and public preferences were used to structure and populate the economic model. SETTING: Primary and secondary care. PARTICIPANTS: Adults with ocular hypertension (IOP > 21 mmHg) and the public (surveillance preferences). INTERVENTIONS: We compared five pathways: two based on National Institute for Health and Clinical Excellence (NICE) guidelines with monitoring interval and treatment depending on initial risk stratification, 'NICE intensive' (4-monthly to annual monitoring) and 'NICE conservative' (6-monthly to biennial monitoring); two pathways, differing in location (hospital and community), with monitoring biennially and treatment initiated for a ≥ 6% 5-year glaucoma risk; and a 'treat all' pathway involving treatment with a prostaglandin analogue if IOP > 21 mmHg and IOP measured annually in the community. MAIN OUTCOME MEASURES: Glaucoma cases detected; tonometer agreement; public preferences; costs; willingness to pay and quality-adjusted life-years (QALYs). RESULTS: The best available glaucoma risk prediction model estimated the 5-year risk based on age and ocular predictors (IOP, central corneal thickness, optic nerve damage and index of visual field status). Taking the average of two IOP readings, by tonometry, true change was detected at two years. Sizeable measurement variability was noted between tonometers. There was a general public preference for monitoring; good communication and understanding of the process predicted service value. 'Treat all' was the least costly and 'NICE intensive' the most costly pathway. Biennial monitoring reduced the number of cases of glaucoma conversion compared with a 'treat all' pathway and provided more QALYs, but the incremental cost-effectiveness ratio (ICER) was considerably more than £30,000. The 'NICE intensive' pathway also avoided glaucoma conversion, but NICE-based pathways were either dominated (more costly and less effective) by biennial hospital monitoring or had a ICERs > £30,000. Results were not sensitive to the risk threshold for initiating surveillance but were sensitive to the risk threshold for initiating treatment, NHS costs and treatment adherence. LIMITATIONS: Optimal monitoring intervals were based on IOP data. There were insufficient data to determine the optimal frequency of measurement of the visual field or optic nerve head for identification of glaucoma. The economic modelling took a 20-year time horizon which may be insufficient to capture long-term benefits. Sensitivity analyses may not fully capture the uncertainty surrounding parameter estimates. CONCLUSIONS: For confirmed ocular hypertension, findings suggest that there is no clear benefit from intensive monitoring. Consideration of the patient experience is important. A cohort study is recommended to provide data to refine the glaucoma risk prediction model, determine the optimum type and frequency of serial glaucoma tests and estimate costs and patient preferences for monitoring and treatment. FUNDING: The National Institute for Health Research Health Technology Assessment Programme.

Event-based progression detection strategies using scanning laser polarimetry images of the human retina.

Monitoring glaucoma patients and ensuring optimal treatment requires accurate and precise detection of progression. Many glaucomatous progression detection strategies may be formulated for Scanning Laser Polarimetry (SLP) data of the local nerve fiber thickness. In this paper, several strategies, all based on repeated GDx VCC SLP measurements, are tested to identify the optimal one for clinical use. The parameters of the methods were adapted to yield a set specificity of 97.5% on real image series. For a fixed sensitivity of 90%, the minimally detectable loss was subsequently determined for both localized and diffuse loss. Due to the large size of the required data set, a previously described simulation method was used for assessing the minimally detectable loss. The optimal strategy was identified and was based on two baseline visits and two follow-up visits, requiring two-out-of-four positive tests. Its associated minimally detectable loss was 5-12 µm, depending on the reproducibility of the measurements.

Automated segmentation by pixel classification of retinal layers in ophthalmic OCT images.

Current OCT devices provide three-dimensional (3D) in-vivo images of the human retina. The resulting very large data sets are difficult to manually assess. Automated segmentation is required to automatically process the data and produce images that are clinically useful and easy to interpret. In this paper, we present a method to segment the retinal layers in these images. Instead of using complex heuristics to define each layer, simple features are defined and machine learning classifiers are trained based on manually labeled examples. When applied to new data, these classifiers produce labels for every pixel. After regularization of the 3D labeled volume to produce a surface, this results in consistent, three-dimensionally segmented layers that match known retinal morphology. Six labels were defined, corresponding to the following layers: Vitreous, retinal nerve fiber layer (RNFL), ganglion cell layer & inner plexiform layer, inner nuclear layer & outer plexiform layer, photoreceptors & retinal pigment epithelium and choroid. For both normal and glaucomatous eyes that were imaged with a Spectralis (Heidelberg Engineering) OCT system, the five resulting interfaces were compared between automatic and manual segmentation. RMS errors for the top and bottom of the retina were between 4 and 6 µm, while the errors for intra-retinal interfaces were between 6 and 15 µm. The resulting total retinal thickness maps corresponded with known retinal morphology. RNFL thickness maps were compared to GDx (Carl Zeiss Meditec) thickness maps. Both maps were mostly consistent but local defects were better visualized in OCT-derived thickness maps.

Patients' experiences and preferences with co-managed care in a cataract pathway.

BACKGROUND/AIMS: Co-managed care in cataract pathways allows ophthalmologists more time to treat other patients. However, little is known on how patients experience pathways that greatly reduce the amount of time spent with ophthalmologists. PURPOSE: To determine experiences and preferences of cataract patients with co-managed postoperative care. METHODS: In a nested-case control study, 194 patients who received their first-day review and final review by an ophthalmologist and 289 patients who received a telephone first-day review by a nurse and a final review by an optometrist were included. The Consumer Quality Index Cataract Questionnaire was used to measure patients' experiences with the quality of care after uncomplicated first-eye cataract surgery. RESULTS: Patients in the co-managed care pathway reported similarly good experiences with the quality of care as patients who received their reviews by an ophthalmologist. Patients who were reviewed by a nurse reported to prefer the same first-day review method significantly more often than those who were reviewed by an ophthalmologist. Most patients preferred the final review by an ophthalmologist. CONCLUSION: Overall, patients with cataract highly rated co-managed care pathways without any postoperative contact with ophthalmologists. Nevertheless, patients still preferred ophthalmologists for their final review to optometrists. Any added patients' benefits should be clearly determined before substituting activities from ophthalmologists to other care professionals.

Split bundle detection in polarimetric images of the human retinal nerve fiber layer.

OBJECTIVES: One method for assessing pathological retinal nerve fiber layer (NFL) appearance is by comparing the NFL to normative values, derived from healthy subjects. These normative values will be more specific when normal physiological differences are taken into account. One common variation is a split bundle. This paper describes a method to automatically detect these split bundles. METHODS: The thickness profile along the NFL bundle is described by a non-split and a split bundle model. Based on these two fits, statistics are derived and used as features for two non-parametric classifiers (Parzen density based and k nearest neighbor). Features were selected by forward feature selection. Three hundred and nine superior and 324 inferior bundles were used to train and test this method. RESULTS: The prevalence of split superior bundles was 68% and the split inferior bundles' prevalence was 13%. The resulting estimated error of the Parzen density- based classifier was 12.5% for the superior bundle and 10.2% for the inferior bundle. The k nearest neighbor classifier errors were 11.7% and 9.2%. CONCLUSIONS: The classification error of automated detection of split inferior bundles is not much smaller than its prevalence, thereby limiting the usefulness of separate cut-off values for split and non-split inferior bundles. For superior bundles, however, the classification error was low compared to the prevalence. Application of specific cut-off values, selected by the proposed classification system, may therefore increase the specificity and sensitivity of pathological NFL detection.

Diagnostic accuracy of scanning laser polarimetry with enhanced versus variable corneal compensation.

PURPOSE: To compare the diagnostic accuracy of scanning laser polarimetry (SLP) parameters between images taken with enhanced corneal compensation (ECC) and those with variable corneal compensation (VCC) and to explore the effect of atypical birefringence patterns on this accuracy. DESIGN: Cross-sectional observational study. PARTICIPANTS: Forty-one healthy subjects and 92 patients with primary open-angle glaucoma. METHODS: Variable corneal compensation and ECC images were obtained of 1 eye per subject, selected randomly if both eyes were eligible. For both ECC and VCC, the areas under the receiver operating characteristic curves (AUROCs) and the sensitivity at a specificity of > or =95% were calculated per parameter in all eyes. The analyses were reperformed separately in eyes with and without atypical birefringence patterns (ABP) images. MAIN OUTCOME MEASURES: The AUROCs and sensitivities at a specificity of > or =95% for various SLP parameters in all eyes and in eyes without ABP images. RESULTS: The diagnostic accuracy for most standard parameters (temporal-superior-nasal-inferior-temporal [TSNIT] average, superior average, inferior average, and TSNIT standard deviation) in all eyes was statistically significantly higher with ECC than with VCC, except for the nerve fiber indicator (NFI). When only eyes without ABP were used for the analysis, the diagnostic accuracy of SLP parameters with VCC improved, and the differences in diagnostic accuracy between ECC and VCC for these parameters lost their statistical significance. CONCLUSIONS: Standard SLP parameters (except for the NFI) generally had a higher diagnostic accuracy when eyes were imaged with ECC than with VCC because there were fewer ABP images with ECC than with VCC. Enhanced corneal compensation therefore may be more reliable than VCC for the detection of glaucoma. A future automated classifier, similar to the current NFI, may perform better if it is trained on data obtained with ECC. Clinically, retinal nerve fiber layer images with marked ABP, acquired with either ECC or VCC, should be viewed with caution.

Baerveldt glaucoma implant in paediatric patients.

AIM: To evaluate the Baerveldt glaucoma implant (BGI) in paediatric glaucoma treatment. METHODS: In a retrospective non-comparative case series 55 eyes of 40 consecutive paediatric patients (< or =16 years) with primary or secondary glaucoma underwent Baerveldt (350 mm2) implantation. Surgical outcome was evaluated by Kaplan-Meier table analysis. RESULTS: The overall success rate was 80% at last follow up, with a mean follow up of 32 (range 2-78) months. Cumulative success was 94% at 12 months and 24 months, 85% at 36 months, 78% at 48 months, and 44% at 60 months. 11 eyes (20%) failed postoperatively because of an IOP >21 mm Hg (eight eyes), persistent hypotony (two eyes), and choroidal haemorrhage following cataract surgery (one eye). The most frequent complication needing surgery was tube related (20%). A new observation was mild to moderate dyscoria in 22% of the eyes, all buphthalmic, caused by entrapment of a tuft of peripheral iris in the tube track. CONCLUSIONS: The BGI is effective and safe in the management of primary and secondary glaucoma. When angle surgery has proved to be unsuccessful or inappropriate in paediatric patients, a BGI is a good treatment option. One must be prepared to deal with the tube related problems.

Automated detection of wedge-shaped defects in polarimetric images of the retinal nerve fibre layer.

PURPOSE: Automated glaucoma detection in images obtained by scanning laser polarimetry is currently insensitive to local abnormalities, impairing its performance. The purpose of this investigation was to test and validate a recently proposed algorithm for detecting wedge-shaped defects. METHODS: In all, 31 eyes of healthy subjects and 37 eyes of glaucoma patients were imaged with a GDx. Each image was classified by two experts in one of four classes, depending on how clear any wedge could be identified. The detection algorithm itself aimed at detecting and combining the edges of the wedge. The performance of both the experts and the algorithm were evaluated. RESULTS: The interobserver correlation, expressed as ICC(3,1), was 0.77. For the clearest cases, the algorithm yielded a sensitivity of 80% at a specificity of 93%, with an area under the ROC of 0.95. Including less obvious cases by the experts resulted in a sensitivity of 55% at a specificity of 95%, with an area under the ROC of 0.89. CONCLUSIONS: It is possible to automatically detect many wedge-shaped defects at a fairly low rate of false-positives. Any detected wedge defect is presented in a user-friendly way, which may assist the clinician in making a diagnosis.

Estimating the clinical usefulness of optic disc biometry for detecting glaucomatous change over time.

PURPOSE: First, to determine the absolute measurement precision of scanning laser ophthalmoscopy (SLO) parameters, by expressing them as 95% limits of agreement (LA(95%)). Second, to propose a method for mathematically estimating the clinical ability of a parameter to monitor disease progression, expressed as the Discriminating Capacity Index (DCI). METHODS: We measured the optic disc of 14 healthy volunteers and 14 glaucoma patients. LA(95%)-values were calculated from the average standard deviation of three measurements on the same day for repeatability, and three measurements on separate days within a 6-week period for reproducibility. We then calculated the DCI by dividing the measurement range by its LA(95%) in healthy subjects and glaucoma patients separately. Thus, the DCI takes into account both the dynamic range of disease progression and the extent of measurement variance, providing an index of the possible clinical usefulness of a parameter. As the DCI is dimensionless it allows comparison across various parameters and across technologies. RESULTS: In the glaucoma group, the SLO parameters with the highest DCIs were 'volume below' (DCI, 9.38) and 'mean contour depth' (DCI, 8.02). In the healthy group, 'Neuroretinal rim area' had the highest index (DCI, 2.15). CONCLUSION: SLO optic disc biometry is uniformly reproducible and may prove a clinically useful method for glaucoma follow-up, due to the high DCI found for several parameters. The capacity to detect conversion from health to glaucoma is less pronounced, possibly due to a larger biological variability found in healthy volunteers.

A model based method for retinal blood vessel detection.

Retinal blood vessels are important structures in ophthalmological images. Many detection methods are available, but the results are not always satisfactory. In this paper, we present a novel model based method for blood vessel detection in retinal images. It is based on a Laplace and thresholding segmentation step, followed by a classification step to improve performance. The last step assures incorporation of the inner part of large vessels with specular reflection. The method gives a sensitivity of 92% with a specificity of 91%. The method can be optimized for the specific properties of the blood vessels in the image and it allows for detection of vessels that appear to be split due to specular reflection.

Detecting glaucomatous wedge shaped defects in polarimetric images.

Wedge shaped defects of the retinal nerve fiber layer (RNFL) may occur in glaucoma. Currently, automatic detection of wedge shaped defects in Scanning Laser Polarimetry (SLP) images of the RNFL is not available. An automatic classification is currently based only on global parameters, thereby ignoring important local information. Our method works by a modified dynamic programming technique that searches for locally strong edges with a preference for straight edges. These edges are initially classified based on their strength and next combined into wedge shaped defects. Our method yields a sensitivity of 73% and a specificity of 90% on a limited set of 65 images.

Surgical revision of filtration blebs: a follow-up study.

PURPOSE: To assess the clinical outcome of one technique for surgical revision of filtration blebs in terms of bleb function and intraocular pressure control. METHODS: Retrospective analysis of 36 consecutive cases of leaking, overfiltrating, or oversized blebs treated with bleb excision and conjunctiva and Tenon advancement in a glaucoma referral center between January 1991 and December 1999. Surgical success was defined as a final intraocular pressure between 6 and 22 mm Hg with or without topical antiglaucoma medication, resolution of the bleb leak, hypotony maculopathy and symptoms, and no need for repeat glaucoma surgery. RESULTS: With a minimum of 12 months and an average of 29.5 months of follow-up, the overall success rate was 86.1%, with 51.6% of patients not requiring medication. In the success group, mean (SD) intraocular pressure was 23.7 (5.9) mm Hg before the original trabeculectomy, 4.3 (3.7) mm Hg prior to revision surgery, and 13.5 (SD 3.8) mm Hg at the last follow-up visit after the revision surgery. Mean number of antiglaucoma medications was 2.1 (range, 1-4) before the original trabeculectomy, none before the revision surgery, and 0.8 (range, 0-3) at the last follow-up visit. CONCLUSIONS: The surgical revision technique offers a definitive solution for most of these bleb complications and a satisfactory intraocular pressure control in the majority of patients.

Scanning laser polarimetry in a selected group of patients with glaucoma and normal controls.

PURPOSE: To evaluate the ability of scanning laser polarimetry to discriminate between subjects with glaucoma with specific patterns of visual field defect and normal controls. METHODS: This cross-sectional, prospective study in a glaucoma practice, focused on subjects with glaucoma with predefined types of visual field defect, including advanced (group A, n = 14), localized (group L, n = 46), or mixed (diffuse and localized) defects (group M, n = 22) and normal controls (n = 32). Scanning laser polarimetry was performed in one study eye per subject. Two methods of analysis were used: a subjective analysis, in which examination printouts with the image of the optic disk manually blocked were classified by two observers masked to the diagnosis, and a logistic regression analysis of the retardation parameters included in the printouts. RESULTS: The observers correctly identified 97% of the controls and 68% of subjects with glaucoma (overall correct classification of 77%), with 93%, 70%, and 47% of patients from groups A, L, and M, respectively, being correctly identified. The best discrimination obtained with the logistic regression correctly identified 69% of controls and 94% of glaucoma subjects (overall correct classification of 87%). The performance was only slightly better for cases from group A compared with L and M. CONCLUSIONS: Subjective assessment of the scanning laser polarimetry standard printout of single eyes might not be sensitive enough to detect cases of glaucoma with localized or milder mixed types of visual field defect. The discriminating ability of scanning laser polarimetry improves slightly when logistic regression analysis is employed.

The value of polarimetry in the evaluation of the optic nerve in glaucoma.

Scanning laser polarimetry (SLP) is a technology used to measure the thickness of the human retinal nerve fiber layer (NFL) in vivo. SLP has been demonstrated to well differentiate between glaucomatous, ocular hypertensive, and normal eyes, despite overlapping data. Recently increased interest is seen in the polarizing properties of the cornea and crystalline lens that may lead to spurious measurements. Although the instruments that use SLP compensate for these anterior segment polarizing properties, recent interest has focused on the extent and effects of incomplete compensation. If well compensated in all, SLP may better separate diseased from normal eyes. Its promising role in the follow-up of glaucoma is still under investigation.

Upper eyelid motility in blepharoptosis and in the aging eyelid.

PURPOSE: To study the metrics of lid saccades in blepharoptosis and to distinguish any differences in the dynamics of eyelid movements that are related to the cause of blepharoptosis and to aging. METHODS: The lid and vertical eye saccades of 7 patients with congenital blepharoptosis and those of 18 patients with aponeurogenic blepharoptosis, either involutional or rigid-contact-lens-induced, were recorded with electromagnetic search coils. For each saccade, two parameters were assessed: amplitude and peak velocity. Two age-matched control groups were assessed in the same manner. Repeated measures analysis of variance was used to investigate any observed differences between the included groups. RESULTS: Congenital and rigid-contact-lens-induced blepharoptosis were readily distinguishable from one another, as well as from the age-matched control group, in both lid saccadic amplitude and peak velocity. For example, 40 degrees downward lid saccades in the congenital blepharoptosis group averaged 22.9 degrees +/- 4.0 degrees (SD), whereas 30.0 degrees +/- 4.7 degrees lid saccades were made by the age-matched control group. The subjects in the two groups with aponeurogenic blepharoptosis also made lid saccades that were distinctive for their group (P: < 0.02), in both amplitude and peak velocity. For 40 degrees downward saccades in involutional and rigid-contact-lens-induced blepharoptosis, lid saccadic amplitude averaged 32.7 degrees +/- 4.3 degrees and 40.3 degrees +/- 3.5 degrees, respectively. Lid saccadic peak velocity declined significantly with age. Lid saccadic peak velocity for 40 degrees upward saccades in the younger control group averaged 401.7 +/- 11.4 deg/sec, whereas the older control group achieved an average peak velocity of 360.7 +/- 60.4 deg/sec. The lid saccadic dynamics in the involutional blepharoptosis group proved to be similar (P: > 0.05) in saccadic amplitude and peak velocity to those of age-matched controls. CONCLUSIONS: In different forms of blepharoptosis, distinctive metrics of lid saccades occur. The current data suggest that involutional blepharoptosis is not a consequence of normal age-related changes in eyelid function.

Prevalence of split nerve fiber layer bundles in healthy eyes imaged with scanning laser polarimetry.

PURPOSE: The GDx (Laser Diagnostic Technologies, San Diego, CA) is a scanning laser polarimeter designed to assess the peripapillary nerve fiber layer in vivo. On the GDx, a nerve fiber bundle can appear as a single or as a split bundle. The aim of our study was to determine the prevalence of split nerve fiber layer bundles and to demonstrate their clinical relevance. DESIGN: Cross-sectional study. PARTICIPANTS: Two hundred fifty-four healthy volunteers participated. METHODS: We imaged 454 eyes of 254 healthy white persons with the GDx. All eyes had intraocular pressure of 21 mmHg or less, normal appearance of the optic nerve head, and normal visual fields (Humphrey Field Analyzer 24-2 full threshold program). According to our working definition, a bundle appeared 'split' when the color-coded pixels corresponding to areas of higher retardation were clearly divided into two more-or-less symmetrical parts not resembling a wedge defect. The classification was performed by two independent observers who used an identical set of reference examples to standardize the classification. MAIN OUTCOME MEASURES: The presence of a split nerve fiber layer bundle. RESULTS: Interobserver agreement was very good (kappa = 0.83), and a consensus was reached in all cases. In 419 eyes (92.3%) there was no split bundle. A split superior bundle was seen in 29 eyes (6.4%). A split inferior bundle was observed in five eyes (1.1%), and in one eye (0.2%) a split bundle was seen superiorly and inferiorly. When considering subjects, a split superior bundle (either in the right eye, or in the left eye, or in both eyes) occurred in 12.0% of normal subjects. The 'superior maximum' parameter was significantly lower in eyes with a split superior bundle than in eyes with a single superior bundle (67.2 microm vs. 89.9 microm; P<0.001). The same was observed for the 'symmetry' parameter (0.88 microm vs. 0.98 microm; P<0.001). CONCLUSIONS: Split nerve fiber layer bundles are a common finding in healthy eyes when imaged with the GDx. A split superior bundle is the most frequent variation, in which cases an abnormal superior maximum or symmetry parameter, otherwise potential indicators of glaucoma, should not readily be interpreted as abnormal.

Axonal loss in a patient with anterior ischemic optic neuropathy as measured with scanning laser polarimetry.

PURPOSE: To report Nerve Fiber Analyzer (NFA/GDx; Laser Diagnostic Technologies, San Diego, California) measurements in a patient during the early phase of an anterior ischemic optic neuropathy. METHODS: Case report. A 58-year old man with acute anterior ischemic optic neuropathy had repeated NFA/GDx scans of the nerve fiber layer adjacent to the optic nerve head of the involved eye, as well as repeated HFA 30.2 (Humphrey Field Analyzer; Humphrey Systems, San Leandro, California) visual field examinations. RESULTS: At presentation (day 0), he had a normal superior nerve fiber bundle on the NFA/GDx, with a deep inferior hemifield scotoma. By day 21 and day 36, the superior nerve fiber bundle thinned on the NFA/GDx, whereas the scotoma remained practically unchanged. CONCLUSION: These findings suggest that after the onset of an anterior ischemic optic neuropathy, acute loss of axonal function results in scotoma, presumably from ischemia. This is followed by a gradual disappearance of nerve fiber tissue, as measured with the NFA/GDx, within several weeks.