Jack Phu

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

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.

Pattern recognition analysis reveals unique contrast sensitivity isocontours using static perimetry thresholds across the visual field

Purpose To determine the locus of test locations that exhibit statistically similar age-related decline in sensitivity to light increments and age-corrected contrast sensitivity isocontours (CSIs) across the central visual field (VF). We compared these CSIs with test point clusters used by the Glaucoma Hemifield Test (GHT). Methods Sixty healthy observers underwent testing on the Humphrey Field Analyzer 30-2 test grid using Goldmann (G) stimulus sizes I-V. Age-correction factors for GI-V were determined using linear regression analysis. Pattern recognition analysis was used to cluster test locations across the VF exhibiting equal age-related sensitivity decline (age-related CSIs), and points of equal age-corrected sensitivity (age-corrected CSIs) for GI-V. Results There was a small but significant test size–dependent sensitivity decline with age, with smaller stimuli declining more rapidly. Age-related decline in sensitivity was more rapid in the periphery. A greater number of unique age-related CSIs was revealed when using smaller stimuli, particularly in the mid-periphery. Cluster analysis of age-corrected sensitivity thresholds revealed unique CSIs for GI-V, with smaller stimuli having a greater number of unique clusters. Zones examined by the GHT consisted of test locations that did not necessarily belong to the same CSI, particularly in the periphery. Conclusions Cluster analysis reveals statistically significant groups of test locations within the 30-2 test grid exhibiting the same age-related decline. CSIs facilitate pooling of sensitivities to reduce the variability of individual test locations. These CSIs could guide future structure-function and alternate hemifield asymmetry analyses by comparing matched areas of similar sensitivity signatures.

The value of visual field testing in the era of advanced imaging: clinical and psychophysical perspectives

White‐on‐white standard automated perimetry (SAP) is widely used in clinical and research settings for assessment of contrast sensitivity using incremental light stimuli across the visual field. It is one of the main functional measures of the effect of disease upon the visual system. SAP has evolved over the last 40 years to become an indispensable tool for comprehensive assessment of visual function. In modern clinical practice, a range of objective measurements of ocular structure, such as optical coherence tomography, have also become invaluable additions to the arsenal of the ophthalmic examination. Although structure‐function correlation is a highly desirable determinant of an unambiguous clinical picture for a patient, in practice, clinicians are often faced with discordance of structural and functional results, which presents them with a challenge. The construction principles behind the development of SAP are used to discuss the interpretation of visual fields, as well as the problem of structure‐function discordance. Through illustrative clinical examples, we provide useful insights to assist clinicians in combining a range of clinical results obtained from SAP and from advanced imaging techniques into a coherent picture that can help direct clinical management.

The Effect of Attentional Cueing and Spatial Uncertainty in Visual Field Testing.

Purpose To determine the effect of reducing spatial uncertainty by attentional cueing on contrast sensitivity at a range of spatial locations and with different stimulus sizes. Methods Six observers underwent perimetric testing with the Humphrey Visual Field Analyzer (HFA) full threshold paradigm, and the output thresholds were compared to conditions where stimulus location was verbally cued to the observer. We varied the number of points cued, the eccentric and spatial location, and stimulus size (Goldmann size I, III and V). Subsequently, four observers underwent laboratory-based psychophysical testing on a custom computer program using Method of Constant Stimuli to determine the frequency-of-seeing (FOS) curves with similar variables. Results We found that attentional cueing increased contrast sensitivity when measured using the HFA. We report a difference of approximately 2 dB with size I at peripheral and mid-peripheral testing locations. For size III, cueing had a greater effect for points presented in the periphery than in the mid-periphery. There was an exponential decay of the effect of cueing with increasing number of elements cued. Cueing a size V stimulus led to no change. FOS curves generated from laboratory-based psychophysical testing confirmed an increase in contrast detection sensitivity under the same conditions. We found that the FOS curve steepened when spatial uncertainty was reduced. Conclusion We show that attentional cueing increases contrast sensitivity when using a size I or size III test stimulus on the HFA when up to 8 points are cued but not when a size V stimulus is cued. We show that this cueing also alters the slope of the FOS curve. This suggests that at least 8 points should be used to minimise potential attentional factors that may affect measurement of contrast sensitivity in the visual field.

How Many Subjects are Needed for a Visual Field Normative Database? A Comparison of Ground Truth and Bootstrapped Statistics

Purpose The number of subjects needed to establish the normative limits for visual field (VF) testing is not known. Using bootstrap resampling, we determined whether the ground truth mean, distribution limits, and standard deviation (SD) could be approximated using different set size (x) levels, in order to provide guidance for the number of healthy subjects required to obtain robust VF normative data. Methods We analyzed the 500 Humphrey Field Analyzer (HFA) SITA-Standard results of 116 healthy subjects and 100 HFA full threshold results of 100 psychophysically experienced healthy subjects. These VFs were resampled (bootstrapped) to determine mean sensitivity, distribution limits (5th and 95th percentiles), and SD for different ‘x’ and numbers of resamples. We also used the VF results of 122 glaucoma patients to determine the performance of ground truth and bootstrapped results in identifying and quantifying VF defects. Results An x of 150 (for SITA-Standard) and 60 (for full threshold) produced bootstrapped descriptive statistics that were no longer different to the original distribution limits and SD. Removing outliers produced similar results. Differences between original and bootstrapped limits in detecting glaucomatous defects were minimized at x = 250. Conclusions Ground truth statistics of VF sensitivities could be approximated using set sizes that are significantly smaller than the original cohort. Outlier removal facilitates the use of Gaussian statistics and does not significantly affect the distribution limits. Translational Relevance We provide guidance for choosing the cohort size for different levels of error when performing normative comparisons with glaucoma patients.

Reducing Spatial Uncertainty Through Attentional Cueing Improves Contrast Sensitivity in Regions of the Visual Field With Glaucomatous Defects

Purpose Current clinical perimetric test paradigms present stimuli randomly to various locations across the visual field (VF), inherently introducing spatial uncertainty, which reduces contrast sensitivity. In the present study, we determined the extent to which spatial uncertainty affects contrast sensitivity in glaucoma patients by minimizing spatial uncertainty through attentional cueing. Methods Six patients with open-angle glaucoma and six healthy subjects underwent laboratory-based psychophysical testing to measure contrast sensitivity at preselected locations at two eccentricities (9.5° and 17.5°) with two stimulus sizes (Goldmann sizes III and V) under different cueing conditions: 1, 2, 4, or 8 points verbally cued. Method of Constant Stimuli and a single-interval forced-choice procedure were used to generate frequency of seeing (FOS) curves at locations with and without VF defects. Results At locations with VF defects, cueing minimizes spatial uncertainty and improves sensitivity under all conditions. The effect of cueing was maximal when one point was cued, and rapidly diminished when more points were cued (no change to baseline with 8 points cued). The slope of the FOS curve steepened with reduced spatial uncertainty. Locations with normal sensitivity in glaucomatous eyes had similar performance to that of healthy subjects. There was a systematic increase in uncertainty with the depth of VF loss. Conclusions Sensitivity measurements across the VF are negatively affected by spatial uncertainty, which increases with greater VF loss. Minimizing uncertainty can improve sensitivity at locations of deficit. Translational Relevance Current perimetric techniques introduce spatial uncertainty and may therefore underestimate sensitivity in regions of VF loss.

Atypical Features of Fuchs Uveitis Syndrome.

Purpose To review the atypical features of Fuchs uveitis syndrome. Methods A retrospective review of records of a private optometric practice of patients with diagnosed Fuchs uveitis syndrome was performed. Results Three atypical cases of Fuchs uveitis syndrome are presented. Patient 1 is a patient who required the use of topical corticosteroids to alleviate acute symptoms of uveitis. Patient 2 is a patient who presented at a very young age with aggressive Fuchs uveitis and who subsequently developed secondary open-angle glaucoma. Patient 3 presented with primary open-angle glaucoma, was treated with topical ocular hypotensive medications, but then subsequently presented with manifest Fuchs uveitis syndrome in the affected eye. Patient 3 was treated with topical prostaglandin analogs among other medical therapies. Conclusions Fuchs uveitis syndrome has a diverse clinical spectrum. It is a syndrome that is diagnosed using a constellation of clinical signs. However, some cases may present atypically and clinicians should be prepared to use less conventional therapies such as topical corticosteroids and prostaglandin analogs in the treatment of acute uveitic attacks and secondary open-angle glaucoma, respectively.

Consistency of Structure-Function Correlation Between Spatially Scaled Visual Field Stimuli and In Vivo OCT Ganglion Cell Counts

Purpose To investigate the effect of stimulus size and disease status on the structure-function relationship within the central retina, we correlated the differential light sensitivity (DLS) with Goldmann stimulus size I to V (GI-V) and optical coherence tomography (OCT) derived in vivo ganglion cell count per stimulus area (GCc) within the macular area in normal subjects and patients with early glaucoma. Methods Humphrey Field Analyzer 10-2 visual field data with GI through V and Spectralis OCT macular ganglion cell layer (GCL) thickness measurements were collected from normal and early glaucoma cohorts including 25 subjects each. GCc was calculated from GCL thickness data and correlated with DLSs for different stimulus sizes. Results Correlation coefficients attained with smaller stimulus size were higher compared to larger stimulus sizes in both normal (GI-GII: R2 = 0.41-0.43, GIII-GV: R2 = 0.16-0.41) and diseased cohorts (GI-GII: R2 = 0.33-0.41, GIII-GV: R2 = 0.19-0.36). Quadratic regression curves for combined GI to V data demonstrated high correlation (R2= 0.82-0.90) and differed less than 1 dB of visual sensitivity within the GCc range between cohorts. The established structure-function relationship was compatible with a histologically derived model correlation spanning the range predicted by stimulus sizes GI to GIII. Conclusions Stimulus sizes within critical spatial summation area (GI-II) improved structure-function correlations in the central visual field. The structure-function relationship was identical in both normal and diseased cohort when GI to GV data were combined. Congruency of GI and GII structure-function correlation with those previously derived with GIII from more peripheral locations further suggests that the structure-function relationship is governed by the number of ganglion cell per stimulus area.

Differences in Static and Kinetic Perimetry Results are Eliminated in Retinal Disease when Psychophysical Procedures are Equated

Purpose We tested the hypothesis that clinical statokinetic dissociation (SKD, defined as the difference in sensitivity to static and kinetic stimuli) at the scotoma border in retinal disease is due to individual criterion bias and that SKD can be eliminated by equating the psychophysical procedures for testing static and kinetic stimulus detection. Methods Six subjects with glaucoma and six with retinitis pigmentosa (RP) were tested. Clinical procedures (standard automated perimetry [SAP] and manual kinetic perimetry [MKP]) were used to determine clinical SKD and the region of interest for laboratory-based testing. Two-way Method of Limits (MoL) was used to establish the isocontrast region at the scotoma border in glaucoma and RP subjects. Method of Constant Stimuli (MoCS) and a two-interval forced choice (2IFC) procedure then were used to present static or kinetic (inward or outward) stimuli at different eccentricities within the isocontrast region. The results were fitted with psychometric functions to determine threshold eccentricities. Results Clinical SKD was found in glaucoma and RP subjects, with variable magnitude among subjects, but significantly exceeding expected typical measurement variability. The resultant psychometric functions when using MoCS and 2IFC showed equal sensitivity to static and kinetic targets, thus eliminating SKD. Conclusions Clinical SKD found using clinical techniques is due to methodologic differences and criterion bias, and is eliminated by using an equated and more objective psychophysical task, similar to normal subjects. Translational relevance Eliminating SKD using a psychophysical approach minimizing criterion bias suggests that it is not useful to distinguish between normal and diseased fields.

A Method Using Goldmann Stimulus Sizes I to V–Measured Sensitivities to Predict Lead Time Gained to Visual Field Defect Detection in Early Glaucoma

Purpose To predict the lead time (difference in time taken for a visual field [VF] defect to be detected) obtained when using stimulus sizes within or near the size of the critical area of spatial summation (Ac), and to test these predictions using sensitivity measurements from a cohort of glaucoma patients. Methods Thirty-seven patients with early open-angle glaucoma and 60 healthy observers underwent VF testing on the Humphrey Field Analyzer in full threshold mode using Goldmann stimulus sizes I to V (GI–V) across the 30-2 test grid. We used the sensitivities measured using GI to V in healthy patients to predict the lead time gained by using stimulus sizes within the size of Ac at all locations within the 30-2 grid. Then, we used sensitivities measured in the glaucoma patients to test this predictive model. Results Median lead time to VF defect detection when using stimulus sizes within Ac compared with stimulus sizes larger than Ac was 4.1 years across the 30-2 test grid (interquartile range, 3.1 and 5.1 years). Sensitivities of the glaucoma patients showed good agreement with the predictive model of lead time gained (77.5%–84.3% were within ±3 dB). Conclusions Our model predicted substantial lead time differences when using stimulus sizes within or near Ac. Such stimulus sizes could potentially detect VF defects, on average, 4 years earlier than current paradigms. Translational Relevance Stimulus sizes within or near Ac may be more suitable for early detection of glaucomatous VF defects. Larger stimulus sizes may be more suitable for later monitoring of established disease.