Effect of a variability-adjusted algorithm on the efficiency of perimetric testing

Evaluating Visual Field Progression in Advanced Glaucoma Using Trend Analysis of Targeted Mean Total Deviation

PURPOSE

Trend analysis of visual field (VF) global indices may underestimate the rate of progression in severe glaucoma because of the influence of test points without detectable sensitivity. To test this hypothesis, we compared the rates of change of VF global indices with and without exclusion of undetectable points at various disease stages.

MATERIALS AND METHODS

Six hundred and forty-eight eyes of 366 glaucoma patients with 8 or more reliable 30-2 standard automated perimetry over more than 2 years were enrolled. We calculated targeted mean total deviation (TMTD) by averaging total deviation except points which were consistently undetectable in 3 baseline tests. Eyes were classified as early (≥-6 dB), moderate (-6 dB to -12 dB), advanced (-12 dB to -20 dB), and severe (<-20 dB) based on baseline mean deviation (MD). The rates of change of MD and TMTD in each stage were statistically compared.

RESULTS

Mean age±SD at baseline was 56.9±11.9 years. The MD slope (-0.34 dB/y) in severe glaucoma was significantly slower than TMTD slope (-0.42 dB/y, P=0.028) and was slower than MD slopes in the other stages. Difference between MD slopes and TMTD slopes was most prominent in eyes with MD values less than -25 dB (P=0.002).

CONCLUSIONS

Undetectable locations in eyes with severe glaucoma may underestimate the rates of VF progression. Trend analysis of TMTD rather than global indices offers a practical and simple approach for alleviating underestimation of VF progression in severe glaucoma.

Detecting Progression in Advanced Glaucoma: Are Optical Coherence Tomography Global Metrics Viable Measures?

SIGNIFICANCE

Optical coherence tomography (OCT) summary measures have been suggested as a way to detect progression in eyes with advanced glaucoma. Here, we show that these measures have serious flaws largely due to segmentation errors. However, inspection of the images and thickness maps can be clinically useful.

PURPOSE

This study aimed to test the hypothesis that recently suggested global OCT measures for detecting progression in eyes with advanced progression are seriously affected by segmentation mistakes and other errors that limit their clinical utility.

METHODS

Forty-five eyes of 38 patients with a 24-2 mean deviation worse than -12 dB had at least two spectral domain OCT sessions (0.8 to 4.4 years apart) with 3.5-mm circle scans of the disc and cube scans centered on the fovea. Average (global) circumpapillary retinal nerve fiber layer thickness, GcRNFL, and ganglion cell plus inner plexiform layer thickness, GGCLP, were obtained from the circle and cube scan, respectively. To evaluate progression, ΔGcRNFL was calculated for each eye as the GcRNFL value at time 2 minus the value at time 1, and ΔGGCLP was calculated in a similar manner. The b-scans of the six eyes with the highest and lowest ΔGcRNFL and ΔGGCLP values were examined for progression as well as segmentation, alignment, and centering errors.

RESULTS

Progression was a major factor in only 7 of the 12 eyes with the most negative values of either ΔGcRNFL or ΔGGCLP, whereas segmentation played a role in 8 eyes and was the major factor in all 12 eyes with the largest positive values. In addition, alignment (one eye) and other (three eyes) errors played a secondary role in four of the six eyes with the most negative ΔGcRNFL values.

CONCLUSIONS

For detecting the progression of advanced glaucoma, common summary metrics have serious flaws largely due to segmentation errors, which limit their utility in clinical and research settings.

Evidence for Structural and Functional Damage of the Inner Retina in Diabetes With No Diabetic Retinopathy

Purpose

To provide structural and functional evidence of inner retinal loss in diabetes prior to vascular changes and interpret the structure-function relationship in the context of an established neural model.

Methods

Data from one eye of 505 participants (134 with diabetes and no clinically evident vascular alterations of the retina) were included in this analysis. The data were collected as part of a large population-based study. Functional tests included best-corrected visual acuity, Pelli-Robson contrast sensitivity, mesopic microperimetry, and frequency doubling technology perimetry (FDT). Macular optical coherence tomography volume scans were collected for all participants. To interpret the structure-function relationship in the context of a neural model, ganglion cell layer (GCL) thickness was converted to local ganglion cell (GC) counts.

Results

The GCL and inner plexiform layer were significantly thinner in participants with diabetes (P < 0.05), with no significant differences in the macular retinal nerve fiber layer or the outer retina. All functional tests except microperimetry showed a significant loss in diabetic patients (P < 0.05). Both FDT and microperimetry showed a significant relationship with the GC count (P < 0.05), consistent with predictions from a neural model for partial summation conditions. However, the FDT captured additional significant damage (P = 0.03) unexplained by the structural loss.

Conclusions

Functional and structural measurements support early neuronal loss in diabetes. The structure-function relationship follows the predictions from an established neural model. Functional tests could be improved to operate in total summation conditions in the macula, becoming more sensitive to early loss.

Improving Spatial Resolution and Test Times of Visual Field Testing Using ARREST

Purpose

Correctly classifying progression in moderate to advanced glaucoma is difficult. Pointwise visual field test–retest variability is high for sensitivities below approximately 20 dB; hence, reliably detecting progression requires many test repeats. We developed a testing approach that does not attempt to threshold accurately in areas with high variability, but instead expends presentations increasing spatial fidelity.

Methods

Our visual field procedure Australian Reduced Range Extended Spatial Test (ARREST; a variant of the Bayesian procedure Zippy Estimation by Sequential Testing [ZEST]) applies the following approach: once a location has an estimated sensitivity of <17 dB (a “defect”), it is checked that it is not an absolute defect (<0 dB, “blind”). Saved presentations are used to test extra locations that are located near the defect. Visual field deterioration events are either: (1) decreasing in the range of 40 to 17 dB, (2) decreasing from >17 dB to “defect”, or (3) “defect” to blind. To test this approach we used an empirical database of progressing moderate-advanced 24-2 visual fields (121 eyes) that we “reverse engineered” to create visual field series that progressed from normal to the end observed field. ARREST and ZEST were run on these fields with test accuracy, presentation time, and ability to detect progression compared.

Results

With specificity for detecting progression matched at 95%, ZEST and ARREST showed similar sensitivity for detecting progression. However, ARREST used approximately 25% to 40% fewer test presentations to achieve this result in advanced visual field damage. ARREST spatially defined the visual field deficit with greater precision than ZEST due to the addition of non–24-2 locations.

Conclusions

Spending time trying to accurately measure visual field locations that have high variability is not productive. Our simulations indicate that giving up attempting to quantify size III white-on-white sensitivities below 17 dB and using the presentations saved to test extra locations should better describe progression in moderate-to-advanced glaucoma in shorter time.

Translational Relevance

ARREST is a new visual field test algorithm that provides better spatial definition of visual field defects in faster test time than current procedures. This outcome is achieved by substituting inaccurate quantification of sensitivities <17 dB with new spatial locations.

Can Macula and Optic Nerve Head Parameters Detect Glaucoma Progression in Eyes with Advanced Circumpapillary Retinal Nerve Fiber Layer Damage?

PURPOSE

To evaluate the ability of OCT optic nerve head (ONH) and macular parameters to detect disease progression in eyes with advanced structural glaucomatous damage of the circumpapillary retinal nerve fiber layer (cRNFL).

DESIGN

Longitudinal study.

PARTICIPANTS

Forty-four eyes from 37 patients with advanced average cRNFL damage (≤60 μm) followed up for an average of 4.0 years.

METHODS

All patients were examined with spectral-domain OCT and visual field (VF) assessment during at least 4 visits.

MAIN OUTCOME MEASUREMENTS

Visual field mean deviation (MD) and VF index. OCT cRNFL (average, superior, and inferior quadrants), ganglion cell-inner plexiform layer (GCIPL) (average, superior, and inferior), rim area, cup volume, average cup-to-disc (C:D) ratio, and vertical C:D ratio.

RESULTS

At baseline, patients had a median VF MD of -10.18 dB and mean cRNFL of 54.55±3.42 μm. The rate of change for MD and VF index were significant. No significant rate of change was noted for cRNFL, whereas significant (P < 0.001) rates were detected for GCIPL (-0.57±0.05 μm/year) and ONH parameters such as rim area (-0.010±0.001 mm²/year).

CONCLUSIONS

Macula GCIPL and ONH parameters may be useful in tracking progression in patients with advanced glaucoma.

The Future of Imaging in Detecting Glaucoma Progression

Ocular imaging has been heavily incorporated into glaucoma management and provides important information that aids in the detection of disease progression. Longitudinal studies have shown that the circumpapillary retinal nerve fiber layer is an important parameter for glaucoma progression detection, whereas other studies have demonstrated that macular parameters, such as the ganglion cell inner plexiform layer and optic nerve head parameters, also are useful for progression detection. The introduction of novel technologies with faster scan speeds, wider scanning fields, higher resolution, and improved tissue penetration has enabled the precise quantification of additional key ocular structures, such as the individual retinal layers, optic nerve head, choroid, and lamina cribrosa. Furthermore, extracting functional information from scans such as blood flow rate and oxygen consumption provides new perspectives on the disease and its progression. These novel methods promise improved detection of glaucoma progression and better insight into the mechanisms of progression that will lead to better targeted treatment options to prevent visual damage and blindness.

Multidimensional Functional and Structural Evaluation Reveals Neuroretinal Impairment in Early Diabetic Retinopathy

Purpose

To test whether quantitative functional tests and optical coherence tomography (OCT)-defined structure can serve as effective tools to diagnose and monitor early diabetic neuroretinal disease.

Methods

Fifty-seven subjects with diabetes (23 without diabetic retinopathy [no DR], 19 with mild nonproliferative diabetic retinopathy [mild NPDR], 15 with moderate to severe [moderate NPDR]), and 18 controls underwent full ophthalmic examination, fundus photography, spectral-domain optical coherence tomography (SD-OCT), e-ETDRS (Early Treatment Diabetic Retinopathy Study) acuity, and the quick contrast sensitivity function (qCSF) method. Perimetry testing included short-wavelength automated perimetry (SWAP), standard automated perimetry (SAP), frequency doubling perimetry (FDP), and rarebit perimetry (RBP).

Results

ETDRS acuity and RBP were not sensitive for functional differences among subjects with diabetes. AULCSF, a metric of qCSF, was reduced in diabetics with moderate compared to mild NPDR (P = 0.03), and in subjects with no DR compared to controls (P = 0.04). SWAP and SAP mean deviation (MD) and foveal threshold (FT) were reduced in moderate compared to mild NPDR (SWAP, MD P = 0.002, FT P = 0.0006; SAP, MD P = 0.02, FT P = 0.007). FDP 10-2 showed reduced MD in moderate compared to mild NPDR (P = 0.02), and FDP 24-2 revealed reduced pattern standard deviation (PSD) in mild NPDR compared to no DR (P = 0.02). Structural analysis revealed thinning of the ganglion cell layer and inner plexiform layer (GCL+IPL) of moderate NPDR subjects compared to controls. The thinner GCL+IPL correlated with impaired retinal function.

Conclusions

This multimodal testing analysis reveals insights into disruption of the neuroretina in diabetes and may accelerate the testing of novel therapies.

Management of advanced glaucoma: Characterization and monitoring

Recent advances in glaucoma diagnosis focus on diagnosing the disease in early stages. Despite the importance of such efforts, a meaningful proportion of patients present in advanced stages. The cost for treatment and monitoring of advanced glaucoma often exceeds that with earlier disease, not to mention the significant effect of visual impairment on quality of life. Moreover, structural and functional tests used to monitor changes encounter technical limitations in advanced cases that can delay detection of true progression. New technologies and methods to analyze longitudinal data may prove helpful for monitoring patients with advanced glaucoma and reduce the burdens of the disease.