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

Predicting perimetric defects from en face maps of retinal nerve fibre layer reflectance

PURPOSE

To develop criteria to predict visual hemifields with deep perimetric defects based on retinal nerve fibre layer (RNFL) reflectance, in a transparent process whose components can be assessed by independent laboratories analysing data from their own small groups.

METHODS

The analysis was carried out in four stages, using three independent groups of patients-30, 33 and 62 participants-with glaucoma and age-similar controls. The first stage used Group 1 to develop a criterion for RNFL reflectance images at 24, 36 or 48 μm below the inner limiting membrane (ILM). The second stage evaluated the criterion using Group 2. The third stage developed a second criterion to improve performance for Groups 1 and 2 combined. The fourth stage evaluated the second criterion with Group 3. Confidence intervals for sensitivity and specificity were then computed by combining results from all three groups.

RESULTS

The first criterion identified all hemifields with deep defects and no hemifields from controls, using a within-eye reference for healthy RNFL. For Group 2, specificity remained high but sensitivity was reduced. The second criterion improved sensitivity by using location-specific reference values. For Group 3, sensitivity remained high but reduced specificity was found. Confidence intervals showed substantial overlap for the two criteria.

CONCLUSIONS

We developed two criteria to identify patients with deep perimetric defects with high specificity and sensitivity. Several improvements are warranted: automated identification of the fovea-disc angle and optic disc locations, evaluation of normal variation in patterns of RNFL thickness, improved segmentation of ILM and major vasculature, reduction of within-eye variability in RNFL reflectance of healthy eyes, assessment of effects of image quality, assessment of effects of comorbidity and effectiveness of other devices.

Progression of Early Glaucomatous Damage: Performance of Summary Statistics From Optical Coherence Tomography and Perimetry

Purpose

Performance comparison of optical coherence tomography (OCT) and visual field (VF) summary metrics for detecting glaucomatous progression.

Methods

Thirty healthy control eyes (mean deviation [MD], -1.25 ± 2.03; pattern standard deviation [PSD] , 1.78 ± 0.77) and 91 patient eyes comprised of 54 glaucoma patients and 37 glaucoma suspects (MD, -1.58 ± 1.96; PSD, 2.82 ± 1.92) with a follow-up of at least 1 year formed a group to evaluate progression with event analyses (P-Event). A subset of eyes with an additional criterion of a minimum of four tests was used for trend analyses (P-Trend) (30 healthy controls and 73 patients). For P-Event analysis, test-retest variability thresholds (lower 5th percentile) were estimated with repeat tests within a 4-month period. A P-Event eye was considered a "progressor" if the difference between follow-up and baseline tests exceeded the variability thresholds. For the P-Trend analysis, rates of change were calculated based on least-squares regression. Negative rates with significant (P < 0.05) values were considered progressing. For a reference standard, 17 patient eyes were classified as definitely progressing based on clear evidence of structural and corresponding functional progression.

Results

Isolated OCT and VF summary metrics were either inadequately sensitive or not too specific. Combinations of OCT-OCT and OCT-VF metrics markedly improved specificity to nearly 100%. A novel combination of OCT metrics (circumpapillary retinal nerve fiber layer and ganglion cell layer) showed high precision, with 13 of the 15 statistical progressors confirmed as true positives.

Conclusions

Although relying solely on metrics is not recommended for clinical purposes, in situations requiring very high specificity and precision, combinations of OCT-OCT metrics can be used.

Translational Relevance

All available OCT and VF metrics can miss eyes with progressive glaucomatous damage and/or can falsely identify progression in stable eyes.

The ICD-10 Glaucoma Severity Score Underestimates the Extent of Glaucomatous Optic Nerve Damage

PURPOSE

To evaluate the International Classification of Disease, Tenth Revision (ICD-10) codes used for glaucoma severity classification, which are based on the location of visual field (VF) defects; given the known poor sensitivity of the 24-2 visual field test to early disease and macular damage, we hypothesized that the ICD-10 codes would not accurately reflect the extent of glaucomatous damage.

DESIGN

Retrospective validity and reliability analysis.

METHODS

We evaluated 80 eyes with glaucomatous optic neuropathy (GON). Masked reviewers assigned an ICD-10 severity grade based on 24-2 VF. Two additional masked examiners determined the presence of optical coherence tomography (OCT) structural damage in each hemifield and/or central 5 degrees to define an OCT-based equivalent ICD-10 classification.

RESULTS

A total of 80 eyes with GON were classified as mild, moderate and advanced in 15, 23, and 42 cases, respectively, based on the 24-2 VF, and in 6, 7, and 67 cases, respectively, based on OCT. The OCT classifications were more severe in 29 of 80 cases (36%). In 33 cases (41.3%), macular damage detected by OCT was missed by the 24-2. In 4 of 80 cases (5%), the VF overestimated the severity, likely due to variability of the 24-2 test.

CONCLUSIONS

The ICD-10 system relies solely on damage seen on the 24-2 and as provides a 24-2 functional score rather than a "glaucoma" severity score. OCT revealed wide variation of damage across grades, with a significant proportion of the eyes showing macular structural damage missed with the 24-2 VF. Adding OCT information to the ICD-10 system would help it to more accurately reflect the extent of glaucomatous damage.

The 24-2 Visual Field Guided Progression Analysis Can Miss the Progression of Glaucomatous Damage of the Macula Seen Using OCT

PURPOSE

To better understand the efficacy of the 24-2 guided progression analysis (GPA) in the detection of progression in eyes with early glaucoma (i.e., 24-2 mean deviation [MD] better than -6 dB) by comparing 24-2 GPA with a reference standard (RS) based on a combination of OCT and 24-2 and 10-2 visual field (VF) information.

DESIGN

Cross-sectional study.

PARTICIPANTS

Ninety-nine eyes from 99 individuals, including 70 suspected or early glaucomatous eyes (24-2 MD better than -6 dB) and 29 healthy controls (HCs).

METHODS

All the eyes had at least 4 OCT and VF test dates over a period that ranged from 12 to 59 months. The 24-2 VF tests included 2 baseline tests and at least 2 follow-up tests. The 2 baseline tests were performed within an average of 5.6 days (median, 7 days), and the last follow-up test was performed at least 1 year after the first baseline visit.

MAIN OUTCOME MEASURES

A commercial 24-2 GPA software, with default settings, characterized the eyes as having "likely progression" (LP) or "possible progression" (PP); both were considered "progressing" for this analysis. For RS, 3 authors graded progression using strict criteria and a combination of a custom OCT progression report and commercial 24-2 and 10-2 GPA reports for the same test dates as GPA.

RESULTS

The reference standard identified 10 (14%) of the 70 patient eyes and none of the HC eyes as having progression. The 24-2 guided progression analysis identified 13 of the 70 patient eyes as having progression (PP or LP). However, it correctly classified only 4 (40%) of the 10 RS progressors. All 6 of the RS progressors missed by the 24-2 GPA showed progression in the macula. In addition, the 24-2 GPA identified 2 of the 29 HC eyes as progressors and 9 patient eyes without progression based on the RS.

CONCLUSIONS

In eyes with early glaucoma (i.e., 24-2 MD, > -6 dB) in this study, the 24-2 GPA missed progression seen using OCT and exhibited a relatively high rate of false positives. Furthermore, the region progressing typically included the macula. The results suggest that including OCT and/or 10-2 VFs should improve the detection of progression.

Comparison between the Recommendations of Glaucoma Specialists and OCT Report Specialists for Further Ophthalmic Evaluation in a Community-Based Screening Study

PURPOSE

To compare glaucoma referral patterns between glaucoma and OCT report specialists and to determine what influence, if any, a designated OCT reading could have on a glaucoma specialist's judgments.

DESIGN

Retrospective, exploratory study.

SUBJECTS

We included 483 eyes (243 individuals) from high-risk New York City neighborhoods screened as part of a mobile van glaucoma screening study from July 2017 to October 2017.

METHODS

All participants underwent comprehensive testing, including visual acuity, commercial OCT imaging, gonioscopy, intraocular pressure, frequency-doubling testing, and funduscopic assessment. Three glaucoma specialists independently evaluated all the collected data to determine whether a further glaucoma workup referral was recommended. Two OCT report specialists evaluated only the OCT image for each eye using the commercial report as well as a specialized, customized report. In phase II, the glaucoma specialists then re-evaluated a subset of these eyes, this time with an OCT report specialist's judgments made available.

MAIN OUTCOME MEASURES

Comparison of glaucoma specialist referrals made by glaucoma specialists versus OCT report specialists.

RESULTS

Intergrader agreement between glaucoma specialists was 60% (κ = 0.43) and between report specialists was 95% (κ = 0.77). There was an agreement between a single OCT report specialist and the consensus (2 of 3) of glaucoma specialists in 74% of eyes (κ= 0.32). Of the eyes studied, 25% were referred for further glaucoma evaluation by the glaucoma specialists alone and 1% were referred for further glaucoma workup by only the report specialist. With the addition of the report specialist's judgments, referral pattern changes varied by glaucoma specialist but overall agreement increased to 85% (κ = 0.53).

CONCLUSIONS

There was a fair level of agreement regarding glaucoma referral recommendations between glaucoma specialists with access to comprehensive screening data and OCT report specialists with access to only OCT data. Overall agreement increased when the designated OCT evaluation was made available to the glaucoma specialists. These results may aid in the design of future large-scale glaucoma screening studies.

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

Purpose

To test a model of retinal nerve fiber bundle trajectories that predicts the arcuate-shaped patterns seen on optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) probability/deviation maps (p-maps) in glaucomatous eyes.

Methods

Thirty-one glaucomatous eyes from a database of 250 eyes had clear arcuate-shaped patterns on RNFL p-maps derived from an OCT cube scan. The borders of the arcuate patterns were extracted from the RNFL p-maps. Next, the trajectories from an arcuate model were compared against these borders via a normalized root-mean-square difference analysis. The model's parameter, β, was varied, and the best-fitting, initial clock-hour position of the trajectory to the border was found for each β. Finally, the regions, as determined by the arcuate border's best-fit, initial clock-hour positions, were compared against the abnormal regions on the circumpapillary retinal nerve fiber layer (cpRNFL) profile.

Results

The arcuate model's mean β_Sup and β_Inf parameters minimized large differences between the trajectories and the arcuate borders on the RNFL p-maps. Furthermore, on average, 68% of the cpRNFL regions defined by the arcuate border's best-fit, initial clock-hour positions were abnormal (i.e., below the ≤5% threshold).

Conclusions

The arcuate model performed well in predicting the borders of arcuate patterns seen on RNFL p-maps. It also predicted the associated abnormal regions of the cpRNFL thickness plots.

Translational Relevance

This model should prove useful in helping clinicians understand topographical comparisons among different OCT representations and should improve structure-structure, as well as structure-function agreement analyses.

Detecting glaucoma with only OCT: Implications for the clinic, research, screening, and AI development

A method for detecting glaucoma based only on optical coherence tomography (OCT) is of potential value for routine clinical decisions, for inclusion criteria for research studies and trials, for large-scale clinical screening, as well as for the development of artificial intelligence (AI) decision models. Recent work suggests that the OCT probability (p-) maps, also known as deviation maps, can play a key role in an OCT-based method. However, artifacts seen on the p-maps of healthy control eyes can resemble patterns of damage due to glaucoma. We document in section 2 that these glaucoma-like artifacts are relatively common and are probably due to normal anatomical variations in healthy eyes. We also introduce a simple anatomical artifact model based upon known anatomical variations to help distinguish these artifacts from actual glaucomatous damage. In section 3, we apply this model to an OCT-based method for detecting glaucoma that starts with an examination of the retinal nerve fiber layer (RNFL) p-map. While this method requires a judgment by the clinician, sections 4 and 5 describe automated methods that do not. In section 4, the simple model helps explain the relatively poor performance of commonly employed summary statistics, including circumpapillary RNFL thickness. In section 5, the model helps account for the success of an AI deep learning model, which in turn validates our focus on the RNFL p-map. Finally, in section 6 we consider the implications of OCT-based methods for the clinic, research, screening, and the development of AI models.

Did the OCT Show Progression Since the Last Visit?

Identifying progression is of fundamental importance to the management of glaucoma. It is also a challenge. The most sophisticated, and probably the most useful, commercially available clinical tool for identifying progression is the Guided Progression Analysis (GPA), which was initially developed to identify progression using 24-2 visual field tests. More recently, it has been extended to retinal nerve fiber layer (RNFL) and ganglion cell+inner plexiform layer thicknesses measured with optical coherence tomography (OCT). However, the OCT GPA requires a minimum of 3 tests to determine "possible loss (progression)" and a minimum of 4 tests to determine if the patient shows "likely loss (progression)." Thus, it is not designed to answer a fundamental question asked by both the clinician and the patient, namely: Did damage progress since the last visit? Some clinicians use changes in summary statistics, such as global/average circumpapillary RNFL thickness. However, these statistics have poor sensitivity and specificity due to segmentation and alignment errors. Instead of relying on the GPA analysis or summary statistics, one needs to evaluate RNFL and ganglion cell+inner plexiform layer probability maps and circumpapillary OCT B-scan images. In addition, we argue that the clinician can make a better decision about suspected progression between 2 test days by topographically comparing the changes in the different OCT maps and images, in addition to topographically comparing the changes in the visual field with the changes in OCT probability maps.

Focal Structure-Function Relationships in Primary Open-Angle Glaucoma Using OCT and OCT-A Measurements

Purpose

To evaluate the focal structure-function associations among visual field (VF) loss, optical coherence tomography angiography (OCT-A) vascular measurements, and optical coherence tomography (OCT) structural measurements in glaucoma.

Methods

In this cross-sectional study, subjects underwent standard automated perimetry, OCT-based nerve fiber thickness measurements, and OCT-A imaging. Mappings of focal VF test locations with OCT and OCT-A measurements were defined using anatomically adjusted nerve fiber trajectories and were studied using multivariate mixed-effects analysis. Segmented regression analysis was used to determine the presence of breakpoints in the structure-function associations.

Results

The study included 119 eyes from 86 Chinese subjects with primary open-angle glaucoma (POAG). VF mean deviation was significantly associated with global capillary perfusion density (β = 0.13 ± 0.08) and global retinal nerve fiber layer thickness (β = 0.09 ± 0.02). Focal capillary density (FCD) was significantly associated with VF losses at 34 VF test locations (66.7% of 24-2 VF), with 24 of the 34 locations being within 20° of retinal eccentricity. Focal nerve layer (FNL) thickness was significantly associated with 16 VF test locations (31.4% of 24-2 VF; eight locations within 20° eccentricity). For VF test locations in the central 10° VF, VF losses below the breakpoint were significantly associated with FCD (slope, 0.89 ± 0.12, P < 0.001), but not with FNL thickness (slope, 0.57 ± 0.39, P = 0.15).

Conclusions

Focal capillary densities were significantly associated with a wider range of visual field losses and in a larger proportion of the visual field compared to nerve fiber thickness.