Random dot motion perimetry in patients with glaucoma and in normal subjects

Rapid Campimetry-A Novel Screening Method for Glaucoma Diagnosis

One of the most important functions of the retina-the enabling of perception of fast movements-is largely suppressed in standard automated perimetry (SAP) and kinetic perimetry (Goldmann) due to slow motion and low contrast between test points and environment. Rapid campimetry integrates fast motion (=10°/4.7 s at 40 cm patient-monitor distance) and high contrast into the visual field (VF) examination in order to facilitate the detection of absolute scotomas. A bright test point moves on a dark background through the central 10° VF. Depending on the distance to the fixation point, the test point automatically changes diameter (≈0.16° to ≈0.39°). This method was compared to SAP (10-2 program) for six subjects with glaucoma. Rapid campimetry proved to be comparable and possibly better than 10-2 SAP in identifying macular arcuate scotomas. In four subjects, rapid campimetry detected a narrow arcuate absolute scotoma corresponding to the nerve fiber course, which was not identified as such with SAP. Rapid campimetry promises a fast screening method for the detection of absolute scotomas in the central 10° visual field, with a potential for cloud technologies and telemedical applications. Our proof-of-concept study motivates systematic testing of this novel method in a larger cohort.

Motion perception and its disorders

As we live in a dynamic world, motion is a fundamental aspect of our visual experience. The advent of computerized stimuli has allowed controlled study of a wide array of motion phenomena, including global integration and segmentation, speed and direction discrimination, motion aftereffects, the optic flow that accompanies self-motion, perception of object form derived from motion cues, and point-light biological motion. Animal studies first revealed the existence of a motion-selective region, the middle temporal (MT) area, also known as V5, located in the lateral occipitotemporal cortex, followed by areas such as V5A (also known as MST, the middle superior temporal area), V6/V6A, the ventral intraparietal area, and others. In humans there are rare cases of bilateral lesions of the V5/V5A complex causing cerebral akinetopsia, a severe impairment of motion perception. Unilateral V5/V5A lesions are more common but cause milder asymptomatic deficits, often limited to the contralateral hemifield, while parietal lesions can impair perception of point-light biological motion or high-level motion tasks that are attentionally demanding. Impairments of motion perception have also been described in optic neuropathy, particularly glaucoma, as well as Alzheimer's disease, Parkinson's disease with dementia, and dementia with Lewy body disease. Prematurity with or without periventricular leukomalacia and developmental syndromes such as Williams' syndrome, autism, and dyslexia have also been associated with impaired motion perception, suggesting a developmental vulnerability of the dorsal pathway.

The Effect of Simulated Visual Field Loss on Optokinetic Nystagmus

Purpose

Assessment of functional vision across the visual field is hampered by a reliance on patients' subjective judgement of the presence of a stimulus, and the accompanying demands (time and attention) this places on them. As a first step toward determining whether an objective measure of an involuntary eye movement (optokinetic nystagmus [OKN]) could provide an objective measure of field loss, we determined how various measures of OKN depend on the extent of simulated visual field loss (SVFL).

Methods

We used infrared eye-tracking to measure the eye movements of 16 healthy participants viewing horizontally translating 2-dimensional noise patterns over trials of varying contrasts and different levels of SVFL. We quantified the strength of OKN by estimating the velocity of tracking eye movements compared to the stimulus (OKN gain). These measurements were made using an open-loop SVFL paradigm, where a varying amount of gaze-contingent peripheral stimuli was occluded.

Results

Full-field stimulation led to an average OKN gain of 0.92 ± 0.15. This value fell steadily with increasing SVFL to a value of 0.38 ± 0.20 when the periphery was not stimulated at all (i.e., the stimulus was a 5-deg. diameter foveal patch). We note considerable individual variation in OKN gain in all conditions.

Conclusions

Measuring the extent of visual field loss using an objective measure of OKN gain is feasible.

Translational Relevance

Simulated visual field loss reduces optokinetic nystagmus, but further refinement of this technique would be required to overcome individual differences and to pick up clinically relevant field defects.

A novel Bayesian adaptive method for mapping the visual field

Measuring visual functions such as light and contrast sensitivity, visual acuity, reading speed, and crowding across retinal locations provides visual-field maps (VFMs) that are extremely valuable for detecting and managing eye diseases. Although mapping light sensitivity is a standard glaucoma test, the measurement is often noisy (Keltner et al., 2000). Mapping other visual functions is even more challenging. To improve the precision of light-sensitivity mapping and enable other VFM assessments, we developed a novel hybrid Bayesian adaptive testing framework, the qVFM method. The method combines a global module for preliminary assessment of the VFM's shape and a local module for assessing individual visual-field locations. This study validates the qVFM method in measuring light sensitivity across the visual field. In both simulation and psychophysics studies, we sampled 100 visual-field locations (60° × 60°) and compared the performance of qVFM with the qYN procedure (Lesmes et al., 2015) that measured light sensitivity at each location independently. In the simulations, a simulated observer was tested monocularly for 1,000 runs with 1,200 trials/run, to compare the accuracy and precision of the two methods. In the experiments, data were collected from 12 eyes (six left, six right) of six human subjects. Subjects were cued to report the presence or absence of a target stimulus, with the luminance and location of the target adaptively selected in each trial. Both simulations and a psychological experiment showed that the qVFM method can provide accurate, precise, and efficient mapping of light sensitivity. This method can be extended to map other visual functions, with potential clinical signals for monitoring vision loss, evaluating therapeutic interventions, and developing effective rehabilitation for low vision.

Dot Motion Perception in Young Adult Emmetropes and Myopes

SIGNIFICANCE

Central motion perception, as assessed by minimum displacement detection, was reduced in highly myopic eyes. Peripheral motion detection may be influenced by myopia, particularly in the inferior-nasal retina.

PURPOSE

Motion discrimination is a complex visual task processed mainly via the magnocellular pathway. We investigated whether it is affected in myopia.

METHODS

Ninety young adults aged 18 to 28 years participated: 30 emmetropes (spherical equivalent refractions +1.00 to -0.50 diopters [D]), 30 low myopes -1.00 to -4.75 D) and 30 higher myopes (<-5 D). Random dot patterns were used to measure motion perception thresholds for minimum displacement (Dmin), maximum displacement (Dmax), and motion coherence tasks. Each task was performed centrally and at four oblique peripheral visual field locations (at 3.65 and 12 degrees for Dmin and Dmax tasks, respectively). Macular retinal thickness was measured with optical coherence tomography.

RESULTS

The central Dmin task was correlated significantly with refraction (r = -0.303, P = .004) and axial length (r = +0.224, P = .04), and the superior-temporal field Dmin task was correlated significantly with axial length (r = 0.230, P = .04). Higher myopes had poorer performance than emmetropes by 25% (higher values). For the Dmin peripheral task and for Dmax and coherence tasks at both central and peripheral locations, there were no significant correlations with refraction or axial length. At three of four positions, the peripheral Dmin task was correlated significantly with thickness in the corresponding retinal region: superior-temporal Dmin (Pearson r = -0.357, P < .001), inferior-nasal Dmin (r = -0.237, P = .03) and inferior-temporal Dmin (r = -0.233, P = .03).

CONCLUSIONS

Central motion perception, as assessed by minimum displacement detection, was reduced by 25% in highly myopic eyes. Peripheral motion detection may be influenced by myopia, particularly in the inferior-nasal retina. Retinal stretching due to axial elongation may be linked to reduced performance in higher myopes.

Impaired saccadic eye movement in primary open-angle glaucoma

PURPOSE

Our study aimed at investigating the extent to which saccadic eye movements are disrupted in patients with primary open-angle glaucoma (POAG). This approach followed upon the discovery of differences in the eye-movement behavior of POAG patients during the exploration of complex visual scenes.

METHODS

The eye movements of 8 POAG patients and 4 healthy age-matched controls were recorded. Four of the patients had documented visual field scotoma, and 4 had no identifiable scotoma on visual field testing. The eye movements were monitored as the observers watched static and kinetic targets. The gain, latency, and velocity-peak latency of the saccades recorded were then analyzed.

RESULTS

In POAG patients, with abnormal visual fields, watching a static target, the saccades were delayed and their accuracy was reduced, compared with those of normal observers. In POAG patients, with normal and abnormal visual fields, watching a kinetic target, a task involving precise motion analysis, the latency and accuracy of the saccades were impaired, compared with those of normal observers.

CONCLUSIONS

Our findings suggest that POAG alters saccade programming and execution particularly in the case of moving targets.

A history of perimetry and visual field testing

Perimetry and visual field testing have been used as clinical ophthalmic diagnostic tools for many years, and this manuscript will provide a brief historical overview of these procedures and the individuals who developed them. Today, we have many different forms of perimetry that are designed to evaluate different locations within the visual pathways and various mechanisms and subsets of mechanisms within the visual system. However, the most widely used method of performing perimetry and visual field testing has not substantially changed for more than 150 years, consisting of detecting a small target superimposed on a uniform background at different locations within the field of view. Although the basic test procedure has remained similar throughout the ages, there have been many advances in test administration, standardization, statistical evaluation, clinical analysis, interpretation, and prediction of outcome based on visual field findings.

The loss of visual function in glaucoma

This article reviews innovative techniques for assessing the visual field and for examining glaucoma patients for evidence of visual field progression. The authors discuss the algorithms for assessing change in visual fields used in each of several multicenter studies sponsored by the National Eye Institute. The authors also give a brief review of 2 currently available alternatives to standard automated perimetry. Both are visual function specific tests that attempt to evaluate a subpopulation of retinal ganglion cells. Shortwavelength automated perimetry isolates the small bistratified (blue-yellow) ganglion cells, and Frequency Doubling Technology Perimetry tests functions that should be primarily handled by the magnocellular ganglion cells. These new perimetric procedures are promising as improvements over standard automated perimetry; however, there is still no agreed upon method for determination of glaucomatous visual field progression.

Effects of retinal image degradation on pre-attentive visual search (PAVS) efficiency for flicker, movement and orientation stimuli

BACKGROUND

Previous research has shown that several clinical conditions cause increased pre-attentive visual search (PAVS) times, implying reduced parallel search capabilities in glaucoma and DLB dementia. The purpose of the research reported here was to examine for the first time the resistance of PAVS to dioptric blur using targets differing from the background in terms of flicker, vertical displacement, and orientation. Resistance would enhance the applicability of PAVS as a screening method for glaucoma and other clinical conditions affecting performance of a substantial area of the retina.

METHOD

Computer generated flicker, orientation and vertical displacement targets were used to assess PAVS efficiency. The subject's task was to locate a small single target subtending 0.92 degrees as quickly as possible (embedded in a field of 119 distractors) on either the left- or right-hand side of a computer monitor. Average PAVS response times were calculated for 40 presentations of each target type presented randomly in any one of 120 positions within +/-15 degrees of fixation. Subjects performed the test using their distance spectacles (unless emmetropic), then three tests using positive lenses simulating myopia of up to -3 D, and finally using optimum correction again.

RESULTS

ANOVA revealed that blur of up to 3 D had no statistically significant effect on response times to the flicker target. Blur of over 2.0 D however resulted in increased response times for the displacement target, but only for eyes which were not cyclopleged. The orientation target became significantly more difficult to locate, response times becoming progressively slower with increasing levels of blur (p < 0.05%).

CONCLUSIONS

The present flicker and displacement targets are relatively resistant to the effects of reduced acuity, while the orientation target is only suitable for testing subjects with good visual acuity.

Psychophysical investigation of ganglion cell loss in early glaucoma

PURPOSE

To evaluate ganglion cell loss in early glaucoma using a variety of psychophysical tests and to identify optimal perimetric technique(s) for detection of early glaucomatous visual function loss.

METHODS

Five perimetric tests, short wavelength automated perimetry (SWAP), temporal modulation perimetry (TMP), frequency doubling technology perimetry (FDT), detection acuity perimetry (DAP), and resolution acuity perimetry (RAP) were compared in their ability to discriminate between normal individuals and patients with early glaucoma or glaucoma suspects. Comparisons were also made by their ability to produce repeatable defects. The tests examined different visual functions that are likely to be mediated by different retinal ganglion cell subpopulations, thereby permitting examination of hypotheses of ganglion cell death in early glaucoma.

RESULTS

All visual field tests demonstrated high performance in separating glaucoma patients from normal individuals. SWAP, TMP, FDT, and DAP provided the greatest discrimination between normal individuals and high- and low-risk glaucoma suspects. However, SWAP, TMP, and FDT obtained better consistency across the various analysis approaches (global indices and pointwise) than DAP and RAP. Of all the test types, FDT exhibited the highest proportion of repeatable abnormal test locations, with poor confirmation rates achieved by DAP and RAP.

CONCLUSION

The performance of SWAP, FDT, and TMP suggests that these test types may all be suitable for detection of early loss of visual function in glaucoma. Ganglion cell subpopulations with lower levels of redundancy and/or those with larger cell sizes offer the most parsimonious explanation for earliest ganglion cell losses occurring in glaucoma.

Motion perception in glaucoma patients: a review

Most of the histopathological and psychophysical studies in glaucoma reveal a preferential damage to the magnocellular (M) pathway although a few of them support a damage to the parvocellular (P) pathway as well. In glaucoma, the visual fields are usually evaluated by conventional perimetry. However, it has been demonstrated that 20-40% of ganglion cells are lost before field defects are detected using conventional perimetry. Therefore, new psychophysical tests have recently been designed in order to specifically isolate and evaluate the visual mechanisms that are impaired at the early stages of glaucoma. In this context, several authors have addressed the issue of motion perception under the hypothesis of a predominant damage of the M pathway in glaucoma, and that motion perception is mediated mainly by M pathway. The results of these studies depict a large variation in the percentage of patients showing anomalous motion perception. Overall, motion thresholds are elevated in both glaucoma and ocular hypertensive patients as compared to control subjects, irrespective of the stimulus size and eccentricity. The test which discriminates best between patients and normal subjects is motion perimetry. The visual field defects in glaucoma patients identified by conventional perimetry and motion perimetry are similar, but the sizes of the defects are usually larger with motion perimetry. However, motion tests in central vision have no correlation with visual field defect on conventional perimetry. In glaucoma, loss of performance on motion perception tests does not necessarily support the existence of a specific deficit in the M pathway, because some behavioral studies suggest that the P pathway can also mediate motion perception. It is also difficult to conclude that motion perception is specifically affected in glaucoma because most of these studies do not yield a comparison with other visual functions. Despite these difficulties, localized motion perception tests at eccentricities of more than 15 degrees can be considered as a promising diagnostic tool.

Automated perimetry: a report by the American Academy of Ophthalmology

OBJECTIVE

The purpose of this document is to summarize and evaluate the effectiveness of new automated perimetry tests and algorithms in diagnosing glaucoma and detecting disease progression.

METHODS

A literature search on automated perimetry retrieved over 300 citations from 1994 to 2001, of which 71 were selected as relevant to this assessment. The quality of the evidence obtained from these studies was assessed by the methodologist.

RESULTS

The four automated perimetry techniques described in this assessment are short wavelength automated perimetry (SWAP), frequency doubling technology perimetry (FDT), high-pass resolution perimetry (HPRP), and motion automated perimetry (MAP). The algorithms described are Swedish interactive threshold algorithm (SITA) and SITA fast. With the exception of SWAP, these techniques and algorithms reduce testing time and inconsistent patient performance when compared with conventional full threshold testing.

CONCLUSIONS

Short wavelength automated perimetry detected visual field loss earlier than standard threshold automated perimetry, with a sensitivity and specificity of about 88% and 92% respectively. However, it is a lengthy, demanding test, is sensitive to media opacities, and has a greater magnitude of long-term fluctuation compared with standard threshold automated perimetry, which make it difficult to assess disease progression accurately. When compared to standard threshold automated perimetry, FDT perimetry showed sensitivity and specificity greater than 97% for detecting moderate and advanced glaucoma, and sensitivity of 85% and specificity of 90% for early glaucoma. As FDT perimetry has a short testing time and is resistant to blur and pupil size, it may be a useful screening tool. In a longitudinal study, high-pass resolution perimetry was more effective than standard threshold automated perimetry in monitoring progressive glaucomatous loss, detecting progression at a median of 12 months earlier in 54% of patients studied. Motion automated perimetry demonstrated usefulness in detecting early glaucomatous visual loss in a longitudinal study. Studies on SITA demonstrated greater sensitivity and reproducibility and less intertest variability when compared to standard full threshold testing and a 50% reduction in testing times. A study comparing standard full threshold, SITA, and SITA fast found a sensitivity of 95% for the first two techniques and 93% for SITA fast. Long-term follow-up studies are needed to assess the ability of these techniques to detect progression of glaucoma over time.

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.

The Topographic Relationship Between Multifocal Electroretinographic and Behavioral Perimetric Measures of Function in Glaucoma

PURPOSE

To study the spatial relationship between local functional abnormalities found using multifocal electroretinography (MERG) and those measured using standard automated perimetry (SAP) in a group of glaucoma patients with well-defined, localized visual field loss.

METHODS

MERG's were measured for 15 patients with longstanding, stable, localized SAP visual field loss and for 27 normal controls using VERIS Science (EDI, San Mateo, CA). Most glaucoma patients had substantial asymmetry of visual field defects across the horizontal midline so that within-eye comparisons of MERG changes could be made in addition to comparisons between glaucoma and healthy, aged-matched controls.

RESULTS

For the glaucoma patient group as a whole, conventional measurements of MERG responses, such as peak-to-trough amplitude, peak implicit time, and scalar-product density, did not reveal abnormalities that spatially corresponded to local sensitivity losses determined by SAP visual field thresholds. Some of the patients had MERG abnormalities (e.g., reduced amplitudes) in areas of advanced SAP visual field loss that indicated local retinal dysfunction. On average, glaucoma patients were missing a MERG component that resembled the optic nerve head component as described by Sutter and Bearse.

CONCLUSIONS

Different MERG components may be affected at different stages of glaucoma, perhaps reflecting a diversity of pathophysiologic mechanisms. This may complicate spatial and temporal relationships between abnormalities found using the MERG and behavioral perimetry, particularly when conventional measurements of MERG responses are used to characterize a diverse patient group/disease.

Aliasing for rapidly counterphasing stimuli: a failure to demonstrate an M-cell sampling limit to resolution

We investigated whether resolution is sampling limited for stimuli optimized for detection by magnocellular mechanisms. We measured peripheral (15 degrees and 30 degrees) spatial detection and resolution thresholds using 50% and 90% contrast flicker-defined gratings (25 Hz) and 90% contrast counterphasing sinusoidal gratings (25 Hz). Direction-discrimination performance for 90% contrast counterphasing sinusoidal gratings (25 Hz) was measured foveally. Our results indicate that resolution of rapidly counterphasing stimuli is sampling limited in peripheral vision but is consistent with limiting of performance by parvocellular mechanisms. Also, undersampling may not be necessary to account for motion reversals observed with gratings that both drift and flicker.

Short-wavelength automated perimetry: it's role in the clinic and for understanding ganglion cell function

Short-wavelength automated perimetry (SWAP) is a more sensitive test than standard achromatic perimetry for early loss of vision due to glaucoma and other ocular and neurological diseases. SWAP is also more successful for detecting changes in vision as glaucoma progresses. Results from various visual function-specific tests, including SWAP, suggest that there are individual differences in ocular hypertensive and glaucoma eyes in the subtype of ganglion cell first affected. However, the disease targets the same retinal area for all function-specific tests that show a deficit in a given individual. Psychophysical tests of vision are critical to understand glaucoma's effect on retinal ganglion cells, to verify the success or failure of treatment including new neuroprotective agents, and to determine the relationship of genetic markers for glaucoma to the presence and progress of the disease.

Characteristics of frequency-of-seeing curves for a motion stimulus in glaucoma eyes, glaucoma suspect eyes, and normal eyes

This study compared frequency-of-seeing curves for a line displacement test in glaucoma patients and normals. Probit analysis of the frequency-of-seeing curves provided the motion thresholds and the slopes of the frequency-of-seeing curves, represented by the interquartile range. The thresholds and interquartile ranges were significantly elevated in the glaucoma eyes and suspect eyes, compared to controls. A logistic regression model incorporating both the interquartile range and threshold significantly improved the sensitivity of the motion test in the suspects. Abnormal shallowing of the slope of the motion frequency-of-seeing curve may represent one of the earliest changes in glaucoma.

Abnormal motion displacement thresholds are associated with fine scale luminance sensitivity loss in glaucoma

This study tests the hypothesis that abnormal motion displacement thresholds coexist with scotomas on a finer spatial scale than is measurable by conventional Humphrey perimetry. Eighteen patients with primary open angle glaucoma in one eye, and 18 age matched normal controls underwent motion displacement threshold testing and high spatial resolution perimetry. The motion displacement thresholds were significantly elevated in the glaucoma eyes, in 73% this exceeded normal limits. Ten glaucoma eyes had normal Humphrey 24-2 field nearest the motion test site: of these seven had abnormally elevated motion displacement thresholds and six had fine scale threshold depressions detected with high spatial resolution perimetry. This result suggests that glaucomatous elevations of motion displacement threshold may be present in areas of normal Humphrey 24-2 field, and this may coexist with measurable scotomas beyond the resolution of conventional Humphrey perimetry in some, but not all patients.

Motion perimetry in anisometropic amblyopia: elevated size thresholds extend into the midperiphery

PURPOSE

Our purpose was to determine whether motion detection abnormalities in patients with anisometropic amblyopia exist and to determine the extent of these abnormalities in the central and midperipheral visual field.

METHODS

We used of motion perimetry to evaluated 10 anisometropic subjects with no manifest strabismus. Each of 44 locations in the visual field corresponding to the test sites of the Humphrey 24-2 program was tested with circular patches of motion (random dot cinematograms) displayed on a computer screen. Stimulus patch size was reduced in a 2/1 staircase manner to determine the smallest patch of motion detectable at each test location (threshold). Data from 15 age-matched normal subjects were used as controls.

RESULTS

Vision in the amblyopic eye ranged from 20/25 to count fingers. The overall mean size threshold for amblyopic eyes was elevated (61% +/- 73%) compared with fellow eyes and age-matched normal eyes (p < 0.03) (i.e., the moving patch of dots in the field had to be larger for it to be detected when viewing with the amblyopic eye). The increase in size threshold was consistent across the visual field and was not greater for central locations.

CONCLUSION

The amblyopia caused by anisometropia is associated with an abnormality in motion detection that extends into the midperiphery of the visual field.

Perimetric motion thresholds are elevated in glaucoma suspects and glaucoma patients

The purpose of this study was to determine if a clinically feasible perimetric motion test utilizing random-dot kinematograms could identify glaucomatous visual field defects. Using a staircase procedure, an automated perimetric motion test and a larger foveally presented target were given to normal (n = 30), glaucoma suspects (n = 31) and primary open-angle glaucoma patients (n = 19). Motion thresholds at specific locations throughout the whole visual field were significantly elevated in glaucoma patients (P < or = 0.001). Perimetric motion testing identified 84.2% of the primary open-angle glaucoma patients and 25.8% of the glaucoma suspects as abnormal. A larger foveal stimulus was unable to distinguish between the different subject groups (P < or = 0.185). Perimetric motion thresholds were significantly correlated with Humphrey standard visual field thresholds in the glaucoma and glaucoma-suspect patients (P < or = 0.0002).