Effect of stimulus size on static visual fields in patients with retinitis pigmentosa

Investigating the Spatiotemporal Summation of Perimetric Stimuli in Dry Age-Related Macular Degeneration

Purpose

To measure achromatic spatial, temporal, and spatiotemporal summation in dry age-related macular degeneration (AMD) compared to healthy controls under conditions of photopic gaze-contingent perimetry.

Methods

Twenty participants with dry AMD (mean age, 74.6 years) and 20 healthy controls (mean age, 67.8 years) performed custom, gaze-contingent perimetry tests. An area-modulation test generated localized estimates of Ricco's area (RA) at 2.5° and 5° eccentricities along the 0°, 90°, 180°, and 270° meridians. Contrast thresholds were measured at the same test locations for stimuli of six durations (3.7-190.4 ms) with a Goldmann III stimulus (GIII, 0.43°) and RA-scaled stimuli. The upper limit (critical duration) of complete temporal summation (using the GIII stimulus) and spatiotemporal summation (using the RA stimuli) was estimated using iterative two-phase regression analysis.

Results

Median (interquartile range [IQR]) RA estimates were significantly larger in AMD participants (2.5°: 0.21 [0.09-0.41] deg2; 5°: 0.32 [0.15-0.65 deg2]) compared to healthy controls (2.5°: 0.08 [0.05-0.13] deg2; 5°: 0.15 [0.08-0.22] deg2) at all test locations (all P < 0.05). No significant difference in median critical duration was found in AMD participants with the GIII stimulus (19.6 [9.9-30.4] ms) and RA-scaled stimuli (22.9 [13.9-40.3] ms) compared to healthy controls (GIII: 17.0 [11.3-24.0] ms; RA-scaled: 22.4 [14.3-33.1] ms) at all test locations (all P > 0.05).

Conclusions

Spatial summation is altered in dry AMD, without commensurate changes in temporal summation.

Translational Relevance

The sensitivity of perimetry to AMD may be improved by utilizing stimuli that probe alterations in spatial summation in the disease.

Investigating the linkage between mesopic spatial summation and variations in retinal ganglion cell density across the central visual field

PURPOSE

The relationship between perimetric stimulus area and Ricco's area (RA) determines measured thresholds and the sensitivity of perimetry to retinal disease. The nature of this relationship, in addition to effect of retinal ganglion cell (RGC) number on this, is currently unknown for the adaptation conditions of mesopic microperimetry. In this study, achromatic mesopic spatial summation was measured across the central visual field to estimate RA with the number of RGCs underlying RA also being established.

METHODS

Achromatic luminance thresholds were measured for six incremental spot stimuli (0.009-2.07 deg2 ) and 190.4 ms duration, at four locations, each at 2.5°, 5° and 10° eccentricity in five healthy observers (mean age 61.4 years) under mesopic conditions (background 1.58 cd/m2 ). RA was estimated using two-phase regression analysis with the number of RGCs underlying RA being calculated using normative histological RGC counts.

RESULTS

Ricco's area exhibited a small but statistically insignificant increase between 2.5° and 10° eccentricity. Compared with photopic conditions, RA was larger, with the difference between RA and the Goldmann III stimulus (0.43°) being minimised. RGC number underlying RA was also higher than reported for photopic conditions (median 70 cells, IQR 36-93), with no significant difference being observed across test locations.

CONCLUSIONS

Ricco's area and the number of RGCs underlying RA do not vary significantly across the central visual field in mesopic conditions. However, RA is larger and more similar to the standard perimetric Goldmann III stimulus under mesopic compared with photopic adaptation conditions. Further work is required to determine if compensatory enlargements in RA occur in age-related macular degeneration, to establish the optimal stimulus parameters for AMD-specific microperimetry.

Relationship between visual acuity and visual field and its reproducibility in patients with retinitis pigmentosa

BACKGROUND/OBJECTIVES

To investigate the association between visual acuity (VA) and visual field (VF) and its reproducibility in patients with retinitis pigmentosa (RP).

SUBJECTS/METHODS

The study cohort comprised 227 eyes of 227 patients with RP. The reproducibility of two Humphrey VF tests (10-2 Swedish Interactive Threshold Algorithm [SITA] tests) performed within a period of 3 months was calculated using the root mean squared error (RMSE) of each VF test point's sensitivity. The association between the logarithm of the minimum angle of resolution (logMAR) VA and VF sensitivity was investigated. Additionally, the relationship between RMSE and age, fixation loss, false positives, false negatives, and logMAR VA was determined.

RESULTS

The association between visual sensitivity and VA was most tight at the fovea, and it became weak toward the peripheral region in an eccentric manner. VF reproducibility appreciably increased as VA decreased. In particular, reproducibility was significantly decreased when logMAR VA was >0.5 compared with logMAR VA ≤ 0.

CONCLUSION

Reproducibility of VF tests decreases with a decrease in VA. Careful consideration is necessary when a patient's logMAR VA is >0.5.

Association between the number of visual fields and the accuracy of future prediction in eyes with retinitis pigmentosa

Purpose

To evaluate the minimum number of visual fields (VFs) required to precisely predict future VFs in eyes with retinitis pigmentosa (RP).

Methods

A series of 12 VFs (Humphrey Field Analyzer 10–2 test (8.9 years in average) were analysed from 102 eyes of 52 patients with RP. The absolute error to predict the 12th VF using the prior 11 VFs was calculated in a pointwise manner, using the linear regression, and the 95% CI range was determined. Then, using 3–10 initial VFs, next VFs (4th to 11th VFs, respectively) were also predicted. The minimum number of VFs required for the mean absolute prediction error to reach the 95% CI was identified. Similar analyses were iterated for the second and third next VF predictions. Similar analyses were conducted using mean deviation (MD).

Results

In the pointwise analysis, the minimum number of VFs required to reach the 95% CI for the 12th VF was five (first and second next VF predictions) and six (third next VF prediction). For the MD analysis, three (first and second next VF predictions) and four (third next VF prediction) VFs were required to reach 95% CI for the 12th VF.

Conclusions

The minimum number of VFs required to obtain accurate predictions of the future VF was five or six in the pointwise analysis and three or four in the analysis with MD.

Detecting Progression of Retinitis Pigmentosa Using the Binomial Pointwise Linear Regression Method

Purpose

A method of evaluating central visual field (VF) progression in eyes with retinitis pigmentosa (RP) has still to be established. We previously reported the potential merit of applying a binomial test to pointwise linear regression (binomial PLR) in glaucoma progression. In the current study, we investigated the usefulness of binomial PLR in eyes with RP.

Methods

A series of 10 VFs (VF 1–10, Humphrey field analyzer, 10-2 test) from 196 eyes of 103 patients with RP were collected retrospectively. The PLR was performed by regressing the total deviation of all test points with the complete series of 10 VFs. The accuracy (positive predictive value, negative predictive value, and false-positive rate) and the time required to detect VF progression with shorter VF series (from VF 1–5 to VF 1–9) were compared across the binomial PLR, a permutation analysis of PLR (PoPLR), and a mean deviation (MD) trend analysis.

Results

In evaluating VF progression, the binomial PLR was comparable with the PoPLR and MD trend analyses in its positive predictive value (0.55 to 0.95), negative predictive value (0.67 to 0.92), and false-positive rate (0.01 to 0.05). The binomial PLR required significantly less time to detect VF progression (5.0 ± 2.0 years) than the PoPLR and MD trend analyses (P < 0.01, P < 0.001, respectively).

Conclusions

The application of a binomial PLR achieved reliable and earlier detection of central VF progression in eyes with RP.

Translational Relevance

A binomial PLR was useful in assessing VF progression in RP.

Macular Rod Function in Retinitis Pigmentosa Measured With Scotopic Microperimetry

Purpose

To investigate the validity and reliability of macular rod photoreceptor function measurement with a microperimeter.

Methods

Macular sensitivity in dark-adapted retinitis pigmentosa (RP) patients (22 eyes; 9–67 years of age) and controls (five eyes; 22–55 years of age) was assessed with a modified Humphrey field analyzer (mHFA), as well as a scotopic microperimeter (Nidek MP-1S). Sensitivity loss (SL) was estimated at rod-mediated locations. All RP eyes were re-evaluated at a second visit 6 months later. The dynamic range of the MP-1S was expanded with a range of neutral-density filters (NDFs).

Results

In controls, a 4 NDF was used at all macular locations tested. In patients with RP, 0 to 3 NDFs were used, depending on the local disease severity. At rod-mediated locations (n = 281), SL estimates obtained with the MP-1S were highly correlated (r = 0.80) with those of the mHFA. The inter-perimeter difference of SL averaged less than 3 decibels (dB) with all NDFs, except those with most severe locations evaluated with a 0 NDF, where the difference averaged more than 6 dB. The results were similar on the second visit.

Conclusions

The MP-1S estimates of SL are highly correlated with those of the mHFA over a wide range of disease severity replicated at two visits; however, there was an unexplained bias in the magnitude of SL estimated by the MP-1S especially at loci with severe disease.

Translational Relevance

MP-1S scotopic microperimetry can be used to evaluate changes to macular rod function, but evaluation of treatment potential by quantitative comparison of SL to retinal structure will be more challenging.

Development and validation of a visual field cluster in retinitis pigmentosa

The aim was to establish and evaluate a new clustering method for visual field (VF) test points to predict future VF in retinitis pigmentosa. A Humphrey Field Analyzer 10-2 test was clustered using total deviation values from 858 VFs. We stratified 68 test points into 24 sectors. Then, mean absolute error (MAE) of the sector-wise regression with them (S1) was evaluated using 196 eyes with 10 VF sequences and compared to pointwise linear regression (PLR), mean sensitivity of total area (MS) and also another sector-wise regression basing on VF mapping for glaucoma (29 sectors; S2). MAE with S1 were smaller than with PLR when between the first-third and first-seventh VFs were used. MAE with the method were significantly smaller than those of S2 when between the first-sixth and first-ninth VFs were used. The MAE of MS was smaller than those with S1 only when first to 3rd and first to 4th VFs were used; however, the prediction accuracy became far larger than any other methods when larger number of VFs were used. More accurate prediction was achieved using this new sector-wise regression than with PLR. In addition, the obtained cluster was more useful than that for glaucoma to predict progression.

A Prediction Method of Visual Field Sensitivity Using Fundus Autofluorescence Images in Patients With Retinitis Pigmentosa

Purpose

The purpose of this study was to investigate the association between fundus autofluorescence (FAF) and visual field (VF) sensitivities in eyes with retinitis pigmentosa (RP). We also investigated the model we developed to predict VF sensitivity using the FAF ring and its prediction accuracy.

Methods

The training dataset consisted of 51 eyes of 28 patients, and the testing dataset consisted of 42 eyes of 25 patients with RP. VF and FAF measurements were conducted using the Humphrey Field Analyzer (HFA) 10-2 test and Optos. The HFA 10-2 test was divided into three sectors according to the association with the FAF (IN, ON, and OUT). Moreover, concentric curves were drawn at 1-degree intervals outside the FAF ring and OUT was divided into six sectors (from OUT1 to OUT6 toward the periphery). Finally, the total deviation (TD) value was predicted using age and visual acuity (VA) in the whole field, and each of the eight sectors was compared.

Results

The TD value decreased significantly from IN, ON, and then toward OUT6. The absolute prediction error with the FAF ring (average, 7.6 dB) was significantly smaller than that without the FAF ring (average, 8.7 dB). The absolute prediction error with the FAF ring was significantly smaller in the central areas (IN, 4.4 dB and ON, 5.3 dB) than those in the peripheral areas (OUT1-6, 6.8-9.1 dB).

Conclusions

VF sensitivity decreases in association with the FAF ring. We developed a model to predict 10-2 VF sensitivity values using the FAF ring, which enabled us to predict 10-2 TD values.

Clinical trial design for neuroprotection in RHO autosomal dominant retinitis pigmentosa; outcome measure considerations

Purpose: To identify structural and functional outcome measures among patients with Rho-positive autosomal dominant Retinitis Pigmentosa (adRP) to aid neuroprotection trial design.Methods: This was a retrospective cohort study of 52 patients with Rho-positive adRP. We measured Goldmann Visual Fields (GVF) constriction in four sectors (nasal, temporal, inferior, superior), and sectoral Ellipsoid Zone (EZ) width degeneration using Spectral Domain Optical Coherence Tomography (OCT) scans. Disease progression trajectories were projected using mixed effects modeling.Results: Superior GVF was most constricted at presentation and had the shallowest trajectory (less steep negative slope); Inferior GVF was less constricted (corrected p < .001) and had a steeper negative slope (corrected p = .019) than superior GVF. Temporal EZ was most stable on OCT with a relatively shallow negative trajectory (corrected p = .011).Conclusions: Patients' superior visual fields presented with more constriction and subsequently had a shallow negative slope suggesting the corresponding inferior retina may be "burned out" at presentation. Targeted therapies for adRP will likely show a greater efficacy signal if delivered to the superior and nasal retina, which may demonstrate more change on OCT and GVF over the course of a neuroprotection trial.Translational Relevance: Mixed effects analysis of sectoral visual field constriction and EZ degeneration in Rho-positive adRP can prove useful in monitoring therapeutic efficacy and identifying targets for local therapies.

Effect of Oral Valproic Acid vs Placebo for Vision Loss in Patients With Autosomal Dominant Retinitis Pigmentosa: A Randomized Phase 2 Multicenter Placebo-Controlled Clinical Trial

Importance

There are no approved drug treatments for autosomal dominant retinitis pigmentosa, a relentlessly progressive cause of adult and childhood blindness.

Objectives

To evaluate the potential efficacy and assess the safety of orally administered valproic acid (VPA) in the treatment of autosomal dominant retinitis pigmentosa.

Design, Setting, and Participants

Multicenter, phase 2, prospective, interventional, placebo-controlled, double-masked randomized clinical trial. The study took place in 6 US academic retinal degeneration centers. Individuals with genetically characterized autosomal dominant retinitis pigmentosa were randomly assigned to receive treatment or placebo for 12 months. Analyses were intention-to-treat.

Interventions

Oral VPA 500 mg to 1000 mg daily for 12 months or placebo.

Main Outcomes and Measures

The primary outcome measure was determined prior to study initiation as the change in visual field area (assessed by the III4e isopter, semiautomated kinetic perimetry) between baseline and month 12.

Results

The mean (SD) age of the 90 participants was 50.4 (11.6) years. Forty-four (48.9%) were women, 87 (96.7%) were white, and 79 (87.8%) were non-Hispanic. Seventy-nine participants (87.8%) completed the study (42 [95.5%] received placebo and 37 [80.4%] received VPA). Forty-two (46.7%) had a rhodopsin mutation. Most adverse events were mild, although 7 serious adverse events unrelated to VPA were reported. The difference between the VPA and placebo arms for mean change in the primary outcome was -150.43 degree2 (95% CI, -290.5 to -10.03; P = .035).

Conclusions and Relevance

This negative value indicates that the VPA arm had worse outcomes than the placebo group. This study brings to light the key methodological considerations that should be applied to the rigorous evaluation of treatments for these conditions. This study does not provide support for the use of VPA in the treatment of autosomal dominant retinitis pigmentosa.

Trial Registration

ClinicalTrials.gov Identifier: NCT01233609.

Early visual field changes in patients with type 1 diabetes mellitus

PURPOSE

To assess the visual field sensitivity changes and investigate the association between visual field sensitivity and retinal nerve fiber layer thickness in patients with type 1 diabetes mellitus.

MATERIALS AND METHODS

In this cross-sectional and observational study, 46 patients (22 males, 24 females) with type 1 diabetes mellitus and no diabetic retinopathy formed the diabetes mellitus group and 50 age-matched healthy subjects (32 males, 18 females) formed the control group. Retinal nerve fiber layer thickness, full-threshold standard automated perimetry, and short-wavelength automated perimetry were performed. Main outcomes were retinal nerve fiber layer thickness, mean deviation, pattern standard deviation, and short fluctuation.

RESULTS

Average retinal nerve fiber layer thickness was significantly thinner in the diabetes mellitus group (p < 0.001). The mean values of mean deviation and pattern standard deviation of the full-threshold standard automated perimetry did not differ between the groups (p = 0.179, p = 0.139, respectively). Mean short fluctuation was significantly greater in the diabetes mellitus group (p < 0.001). Both mean deviation and pattern standard deviation of the short-wavelength automated perimetry were significantly greater in the diabetes mellitus group (p < 0.001, p < 0.001, respectively). Pattern standard deviation of short-wavelength automated perimetry equal or higher than 1.57 dB had 91% sensitivity and 90% specificity (area under the curve = 0.969, p < 0.001) and short fluctuations of full-threshold standard automated perimetry equal or higher than 0.80 dB had 80% sensitivity and 76% specificity over detecting early retinal nerve fiber layer loss in patients with type 1 diabetes mellitus (area under the curve = 0.855, p < 0.001).

CONCLUSION

This study showed that thinner retinal nerve fiber layer in patients with type 1 diabetes mellitus may be associated with abnormal retinal sensitivity to short-wavelength stimulations in short-wavelength automated perimetry; however, retinal sensitivity to white stimulus was similar to that in healthy subjects in full-threshold standard automated perimetry.

Expediency of the Automated Perimetry Using the Goldmann V Stimulus Size in Visually Impaired Patients with Glaucoma

Introduction

White-on-white standard automated perimetry (AP) uses a white round stimulus with 0.43° diameter and 4.0 mm² area (Goldmann size III). Patients with low vision have difficulty seeing such a small stimulus and are often tested with perimetry using the size V stimulus with 1.72° diameter and 64 mm² area. We undertook an observational case-control study to compare the performance of patients on AP using two differently sized stimuli.

Methods

Patients with glaucoma and visual acuity worse than 20/100 underwent AP using the standard size III stimulus Swedish Interactive Threshold Algorithm (SITA) standard test and size V stimulus full threshold test. All patients were familiar with the procedure, having done the test at least twice previously. Another group of glaucoma patients with visual acuity better than 20/40 served as controls. The main outcome measures included test time, mean retinal sensitivity (MRS), foveal sensitivity (FS), fixation loss (FL), false positive (FP), false negative (FN), and the patient's subjective preference.

Results

Fifty patients were included in the study. Most preferred the size V stimulus target size test. For glaucoma patients, test time was shorter with size III; MRS and FS were higher with size V; FL, FP, and FN did not differ between the tests.

Conclusion

AP with stimulus size V may be a good alternative to standard size III in selected visually debilitated patients who report difficulty undergoing a standard SITA 24-2 test.

Electronic supplementary material

The online version of this article (10.1007/s40123-019-0175-9) contains supplementary material, which is available to authorized users.

Characterization of Visual Function, Interocular Variability and Progression Using Static Perimetry-Derived Metrics in RPGR-Associated Retinopathy

Purpose

To characterize bilateral visual function, interocular variability and progression by using static perimetry-derived volumetric and pointwise metrics in subjects with retinitis pigmentosa associated with mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene.

Methods

This was a prospective longitudinal observational study of 47 genetically confirmed subjects. Visual function was assessed with ETDRS and Pelli-Robson charts; and Octopus 900 static perimetry using a customized, radially oriented 185-point grid. Three-dimensional hill-of-vision topographic models were produced and interrogated with the Visual Field Modeling and Analysis software to obtain three volumetric metrics: VTotal, V30, and V5. These were analyzed together with Octopus mean sensitivity values. Interocular differences were assessed with the Bland-Altman method. Metric-specific exponential decline rates were calculated.

Results

Baseline symmetry was demonstrated by relative interocular difference values of 1% for VTotal and 8% with V30. Degree of symmetry varied between subjects and was quantified with the subject percentage interocular difference (SPID). SPID was 16% for VTotal and 17% for V30. Interocular symmetry in progression was greatest when quantified by VTotal and V30, with 73% and 64% of subjects possessing interocular rate differences smaller in magnitude than respective annual progression rates. Functional decline was evident with increasing age. An overall annual exponential decline of 6% was evident with both VTotal and V30.

Conclusions

In general, good interocular symmetry exists; however, there was both variation between subjects and with the use of various metrics. Our findings will guide patient selection and design of RPGR treatment trials, and provide clinicians with specific prognostic information to offer patients affected by this condition.

A Novel Method for the Objective Identification of Hyperautofluorescent Ring in Retinitis Pigmentosa Using Binarization Processing

PURPOSE

To assess precision and accuracy of a new objective algorithm using binarization in a software for identifying the hyperautofluorescent ring (AF ring) in retinitis pigmentosa (RP) compared with subjective visual inspection.

METHODS

Ultra-widefield AF images were obtained from 23 eyes of 13 patients with retinitis pigmentosa (RP). We defined the borders of the AF rings using semiautomatic binarization algorithm in Fiji software. We compared the degree of precision (intra- and interrater agreements) of this algorithm and that of subjective visual inspection (freehand method) using Jaccard indices (JIs). To compare the classification performance (whether 68 points of Humphrey Field Analyzer is classified as inside, on, or outside AF rings), we calculated percent agreement and weighted kappa statistic between the two methods. The relationship between the distance from the AF ring and retinal sensitivities was also investigated.

RESULTS

The binarization method showed significantly higher JIs than the freehand method (for interrater: 0.94-0.95 vs. 0.73-0.78, respectively, P = 0.002; for intrarater: 0.95 vs. 0.68-0.71, respectively, P = 0.005). Percent agreement for classification between the two methods were 0.94 and weighted kappa statistic was 0.94 (P < 0.001). The retinal sensitivities decreased significantly and eccentrically from 2° inside to 3° outside the AF ring.

CONCLUSIONS

Defining the AF ring in RP using the binarization algorithm showed significantly higher precision and the same degree of accuracy compared with visual inspection.

TRANSLATION RELEVANCE

This novel method may enable quantitative analysis of the AF ring, an indicator of retinal function in RP.

Face size biases emotion judgment through eye movement

Faces are the most commonly used stimuli to study emotions. Researchers often manipulate the emotion contents and facial features to study emotion judgment, but rarely manipulate low-level stimulus features such as face sizes. Here, I investigated whether a mere difference in face size would cause differences in emotion judgment. Subjects discriminated emotions in fear-happy morphed faces. When subjects viewed larger faces, they had an increased judgment of fear and showed a higher specificity in emotion judgment, compared to when they viewed smaller faces. Concurrent high-resolution eye tracking further provided mechanistic insights: subjects had more fixations onto the eyes when they viewed larger faces whereas they had a wider dispersion of fixations when they viewed smaller faces. The difference in eye movement was present across fixations in serial order but independent of morph level, ambiguity level, or behavioral judgment. Together, this study not only suggested a link between emotion judgment and eye movement, but also showed importance of equalizing stimulus sizes when comparing emotion judgments.

A comparison of Goldmann III, V and spatially equated test stimuli in visual field testing: the importance of complete and partial spatial summation

PURPOSE

Goldmann size V (GV) test stimuli are less variable with a greater dynamic range and have been proposed for measuring contrast sensitivity instead of size III (GIII). Since GIII and GV operate within partial summation, we hypothesise that actual GV (aGV) thresholds could predict GIII (pGIII) thresholds, facilitating comparisons between actual GIII (aGIII) thresholds with pGIII thresholds derived from smaller GV variances. We test the suitability of GV for detecting visual field (VF) loss in patients with early glaucoma, and examine eccentricity-dependent effects of number and depth of defects. We also hypothesise that stimuli operating within complete spatial summation ('spatially equated stimuli') would detect more and deeper defects.

METHODS

Sixty normal subjects and 20 glaucoma patients underwent VF testing on the Humphrey Field Analyzer using GI-V sized stimuli on the 30-2 test grid in full threshold mode. Point-wise partial summation slope values were generated from GI-V thresholds, and we subsequently derived pGIII thresholds using aGV. Difference plots between actual GIII (aGIII) and pGIII thresholds were used to compare the amount of discordance. In glaucoma patients, the number of 'events' (points below the 95% lower limit of normal), defect depth and global indices were compared between stimuli.

RESULTS

90.5% of pGIII and aGIII points were within ±3 dB of each other in normal subjects. In the glaucoma cohort, there was less concordance (63.2% within ±3 dB), decreasing with increasing eccentricity. GIII found more defects compared to GV-derived thresholds, but only at outermost test locations. Greater defect depth was found using aGIII compared to aGV and pGIII, which increased with eccentricity. Global indices revealed more severe loss when using GIII compared to GV. Spatially equated stimuli detected the greatest number of 'events' and largest defect depth.

CONCLUSIONS

Whilst GV may be used to reliably predict GIII values in normal subjects, there was less concordance in glaucoma patients. Similarities in 'event' detection and defect depth in the central VF were consistent with the fact that GIII and GV operate within partial summation in this region. Eccentricity-dependent effects in 'events' and defect depth were congruent with changes in spatial summation across the VF and the increase in critical area with disease. The spatially equated test stimuli showed the greatest number of defective locations and larger sensitivity loss.

Structure-Function Modeling of Optical Coherence Tomography and Standard Automated Perimetry in the Retina of Patients with Autosomal Dominant Retinitis Pigmentosa

Purpose

To assess relationships between structural and functional biomarkers, including new topographic measures of visual field sensitivity, in patients with autosomal dominant retinitis pigmentosa.

Methods

Spectral domain optical coherence tomography line scans and hill of vision (HOV) sensitivity surfaces from full-field standard automated perimetry were semi-automatically aligned for 60 eyes of 35 patients. Structural biomarkers were extracted from outer retina b-scans along horizontal and vertical midlines. Functional biomarkers were extracted from local sensitivity profiles along the b-scans and from the full visual field. These included topographic measures of functional transition such as the contour of most rapid sensitivity decline around the HOV, herein called HOV slope for convenience. Biomarker relationships were assessed pairwise by coefficients of determination (R²) from mixed-effects analysis with automatic model selection.

Results

Structure-function relationships were accurately modeled (conditional R²>0.8 in most cases). The best-fit relationship models and correlation patterns for horizontally oriented biomarkers were different than vertically oriented ones. The structural biomarker with the largest number of significant functional correlates was the ellipsoid zone (EZ) width, followed by the total photoreceptor layer thickness. The strongest correlation observed was between EZ width and HOV slope distance (marginal R² = 0.85, p<10⁻¹⁰). The mean sensitivity defect at the EZ edge was 7.6 dB. Among all functional biomarkers, the HOV slope mean value, HOV slope mean distance, and maximum sensitivity along the b-scan had the largest number of significant structural correlates.

Conclusions

Topographic slope metrics show promise as functional biomarkers relevant to the transition zone. EZ width is strongly associated with the location of most rapid HOV decline.

VFMA: Topographic Analysis of Sensitivity Data From Full-Field Static Perimetry

PURPOSE

To analyze static visual field sensitivity with topographic models of the hill of vision (HOV), and to characterize several visual function indices derived from the HOV volume.

METHODS

A software application, Visual Field Modeling and Analysis (VFMA), was developed for static perimetry data visualization and analysis. Three-dimensional HOV models were generated for 16 healthy subjects and 82 retinitis pigmentosa patients. Volumetric visual function indices, which are measures of quantity and comparable regardless of perimeter test pattern, were investigated. Cross-validation, reliability, and cross-sectional analyses were performed to assess this methodology and compare the volumetric indices to conventional mean sensitivity and mean deviation. Floor effects were evaluated by computer simulation.

RESULTS

Cross-validation yielded an overall R² of 0.68 and index of agreement of 0.89, which were consistent among subject groups, indicating good accuracy. Volumetric and conventional indices were comparable in terms of test-retest variability and discriminability among subject groups. Simulated floor effects did not negatively impact the repeatability of any index, but large floor changes altered the discriminability for regional volumetric indices.

CONCLUSIONS

VFMA is an effective tool for clinical and research analyses of static perimetry data. Topographic models of the HOV aid the visualization of field defects, and topographically derived indices quantify the magnitude and extent of visual field sensitivity.

TRANSLATIONAL RELEVANCE

VFMA assists with the interpretation of visual field data from any perimetric device and any test location pattern. Topographic models and volumetric indices are suitable for diagnosis, monitoring of field loss, patient counseling, and endpoints in therapeutic trials.

Detecting changes in retinal function: Analysis with Non-Stationary Weibull Error Regression and Spatial enhancement (ANSWERS)

Visual fields measured with standard automated perimetry are a benchmark test for determining retinal function in ocular pathologies such as glaucoma. Their monitoring over time is crucial in detecting change in disease course and, therefore, in prompting clinical intervention and defining endpoints in clinical trials of new therapies. However, conventional change detection methods do not take into account non-stationary measurement variability or spatial correlation present in these measures. An inferential statistical model, denoted ‘Analysis with Non-Stationary Weibull Error Regression and Spatial enhancement’ (ANSWERS), was proposed. In contrast to commonly used ordinary linear regression models, which assume normally distributed errors, ANSWERS incorporates non-stationary variability modelled as a mixture of Weibull distributions. Spatial correlation of measurements was also included into the model using a Bayesian framework. It was evaluated using a large dataset of visual field measurements acquired from electronic health records, and was compared with other widely used methods for detecting deterioration in retinal function. ANSWERS was able to detect deterioration significantly earlier than conventional methods, at matched false positive rates. Statistical sensitivity in detecting deterioration was also significantly better, especially in short time series. Furthermore, the spatial correlation utilised in ANSWERS was shown to improve the ability to detect deterioration, compared to equivalent models without spatial correlation, especially in short follow-up series. ANSWERS is a new efficient method for detecting changes in retinal function. It allows for better detection of change, more efficient endpoints and can potentially shorten the time in clinical trials for new therapies.

Senescent changes in photopic spatial summation

Previous studies have demonstrated an inverse relation between the size of the complete spatial summation area and ganglion cell density. We hypothesized that if this relation is dynamic, the spatial summation area at 6° nasal would expand to compensate for age-related losses of retinal ganglion cells but not in the fovea where age-related loss in ganglion cell density is not significant. This hypothesis was tested by measuring contrast thresholds with a series of Gabor patches varying in size. The spatial summation area was defined by the intersection of the segments of a two-branched, piece-wise linear function fitted to the data with slopes of -0.5 and 0 on a plot of log threshold vs. log area. Results demonstrate a 31% increase in the parafoveal spatial summation area in older observers with no significant age-related change in the fovea. The average foveal data show a significant increase in thresholds with age. Contrary to the foveal data, age comparisons of the parafoveal peak contrast thresholds display no significant difference above [corrected] the summation area. Nevertheless, as expected from the increase in summation area, expressing the parafoveal thresholds as contrast energy reveals a significant difference for stimuli that are smaller than the maximal summation area.

Disclosing disease mechanisms with a spatio-temporal summation paradigm

BACKGROUND

We develop the logic for a stimulus that can evaluate cone-dependent spatial summation and detail the modelling and interpretation of thresholds obtained with this stimulus.

METHODS

Fifteen observers participated, including two young normals tested extensively in control experiments, and a clinical trial based on four observers with age-related macular degeneration (AMD), four age-similar controls and five young observers. Monocular spatial summation functions were measured with contrast-modulated Gabor targets that approximated the optimal visual contrast detector. Thresholds were returned from a yes/no adaptive psychophysical algorithm. By fine titration along the size domain it was demonstrated that the spatial summation of normal observers can be adequately described by a two-component model. A reduced set of variables are proposed for clinical applications and the model was applied to data derived using these variables in persons with AMD and age-similar controls.

RESULTS

We do not find a significant age-related loss of contrast sensitivity in our normal group. On the other hand, persons with early AMD exhibited a 0.41 log unit loss of sensitivity (P=0.04) from age-similar controls, without any change in their maximum summation area (A(max)).

CONCLUSIONS

The nature of the spatial summation is consistent with the interpretation that early AMD produces a decrease in cone input to post-receptoral mechanisms in the absence of neural remodelling.

Visual field defects and neural losses from experimental glaucoma

Glaucoma is a relatively common disease in which the death of retinal ganglion cells causes a progressive loss of sight, often leading to blindness. Typically, the degree of a patient's visual dysfunction is assessed by clinical perimetry, involving subjective measurements of light-sense thresholds across the visual field, but the relationship between visual and neural losses is inexact. Therefore, to better understand of the effects of glaucoma on the visual system, a series of investigations involving psychophysics, electrophysiology, anatomy, and histochemistry were conducted on experimental glaucoma in monkeys. The principal results of the studies showed that, (1) the depth of visual defects with standard clinical perimetry are predicted by a loss of probability summation among retinal detection mechanisms, (2) glaucomatous optic atrophy causes a non-selective reduction of metabolism of neurons in the afferent visual pathway, and (3) objective electrophysiological methods can be as sensitive as standard clinical perimetry in assessing the neural losses from glaucoma. These experimental findings from glaucoma in monkeys provide fundamental data that should be applicable to improving methods for assessing glaucomatous optic neuropathy in patients.