Diffuse and localized glaucomatous field loss in light-sense, flicker and resolution perimetry

The psychophysics of glaucoma: improving the structure/function relationship

Perimetry of some kind remains an important tool in the detection, diagnosis and monitoring of glaucomatous damage to the visual pathway. However, recent studies have served to reinforce the suspicion that conventional perimetry does not possess the sensitivity to detect the earliest signs of functional loss resulting from glaucoma. The relationship between differential light threshold and ganglion cell loss is extremely weak and, in the early stages of glaucoma, non-existent. Alternative, more novel perimetric techniques seem to offer promise of better detectability for early loss by claiming to tap in to one or other of the separate parallel pathways of the visual system. While some of these tests show potential for better detection and monitoring of glaucoma, the reasons why this might be so are not always clearly formulated or represented. This leads to misunderstanding of what the test actually measures and of the glaucomatous disease process itself. This paper seeks to revisit and review the theory underlying psychophysical testing of visual function related to glaucoma and stresses the importance of developing tests that are based on a firm theoretical understanding of visual function and processing in order to both detect glaucoma at an earlier stage and better understand the mechanisms of loss from the disease process.

Using unsupervised learning with variational bayesian mixture of factor analysis to identify patterns of glaucomatous visual field defects

PURPOSE

To determine whether an unsupervised machine learning classifier can identify patterns of visual field loss in standard visual fields consistent with typical patterns learned by decades of human experience.

METHODS

Standard perimetry thresholds for 52 locations plus age from one eye of each of 156 patients with glaucomatous optic neuropathy (GON) and 189 eyes of healthy subjects were clustered with an unsupervised machine classifier, variational Bayesian mixture of factor analysis (vbMFA).

RESULTS

The vbMFA formed five distinct clusters. Cluster 5 held 186 of 189 fields from normal eyes plus 46 from eyes with GON. These fields were then judged within normal limits by several traditional methods. Each of the other four clusters could be described by the pattern of loss found within it. Cluster 1 (71 GON + 3 normal optic discs) included early, localized defects. A purely diffuse component was rare. Cluster 2 (26 GON) exhibited primarily deep superior hemifield defects, and cluster 3 (10 GON) held deep inferior hemifield defects only or in combination with lesser superior field defects. Cluster 4 (6 GON) showed deep defects in both hemifields. In other words, visual fields within a given cluster had similar patterns of loss that differed from the predominant pattern found in other clusters. The classifier separated the data based solely on the patterns of loss within the fields, without being guided by the diagnosis, placing 98.4% of the healthy eyes within the same cluster and spreading 70.5% of the eyes with GON across the other four clusters, in good agreement with a glaucoma expert and pattern standard deviation.

CONCLUSIONS

Without training-based diagnosis (unsupervised learning), the vbMFA identified four important patterns of field loss in eyes with GON in a manner consistent with years of clinical experience.

What's new in perimetry

Despite important refinements that have improved quantitation and shortened test time, modern perimetry remains relatively insensitive and plagued by high test-retest variability. Some novel methods, though not yet fully vetted, offer the promise of improving sensitivity and reducing variability.

Glaucoma: squaring the psychophysics and neurobiology

Advances in our understanding of the pathophysiology of retinal ganglion cell death in glaucoma are providing important insights into the functional changes occurring in retinal ganglion cells in the early stages of the disease. These exciting new findings may help us develop psychophysical tests to monitor early retinal ganglion cell damage, possibly before neurons are committed to the process of cell death.

Psychophysical Measurement of Glaucomatous Damage

Within the past twenty years, a number of new psychophysical test procedures have been adapted for use in perimetry and visual field testing. These procedures are designed to measure the functional properties of different types of retinal ganglion cell subpopulations. Although many of these new procedures exhibit better performance characteristics than standard automated perimetry, no single test procedure appears to be decidedly superior to all others. Comparison of multiple functions in patients with early glaucomatous damage suggests that visual function losses are not selective for specific retinal ganglion cell subpopulations in all patients. For evaluation of the efficacy of neuroprotective agents in glaucoma, one of the challenges facing the development of new psychophysical tests is to be able to distinguish visual function losses that are due to ganglion cell drop-out ("dead" cells) from those that are due to malfunctioning retinal nerve fibers ("sick" cells).

Testing for glaucoma with the spatial frequency doubling illusion

We examined the performance of tests for glaucoma based on the spatial frequency doubling (FD) illusion. Contrast thresholds for seeing the FD illusion in four large visual field regions were measured from 340 subjects who were tested up to seven times over 2 years. Median sensitivities of 91% at specificities of 95% were obtained. Test-retest variability for the worst hemifield thresholds averaged 2.22 db +/- 0.09 S.E. for all tested groups, and significant progression was observed for glaucoma suspects over the seven visits, indicating that tests based on the FD illusion can detect diffuse early glaucomatous loss.

Optic nerve head appearance in juvenile-onset chronic high-pressure glaucoma and normal-pressure glaucoma

OBJECTIVE

To evaluate the appearance of the optic nerve head in chronic high-pressure glaucoma and normal-pressure glaucoma.

DESIGN

Clinic-based cross-sectional study.

PARTICIPANTS

The study included 52 eyes with normal-pressure glaucoma and 28 eyes with juvenile-onset primary open-angle glaucoma that served as models for chronic high-pressure glaucoma.

METHODS

Color stereo optic disc photographs and wide-angle retinal nerve fiber layer photographs were morphometrically examined.

MAIN OUTCOME MEASURES

Localized retinal nerve fiber layer defects; parapapillary chorioretinal atrophy; disc hemorrhages; optic cup shape; retinal arteriole narrowing.

RESULTS

Both study groups did not vary significantly in count of localized retinal nerve fiber layer defects, size of parapapillary atrophy, optic cup depth, steepness of disc cupping, rim/disc area ratio, diameter of retinal arterioles, and frequency and degree of focal retinal arteriole narrowing. In normal-pressure glaucoma versus juvenile open-angle glaucoma, localized retinal nerve fiber layer defects were significantly broader, disc hemorrhages were found significantly more often and were larger, and neuroretinal rim notches were present more frequently and were deeper.

CONCLUSIONS

Chronic high-pressure glaucoma and normal-pressure glaucoma show morphologic similarities in the appearance of the optic nerve head. The lower frequencies of detected disc hemorrhages and rim notches in high-pressure glaucoma may be due to a smaller size of hemorrhages and localized retinal nerve fiber layer defects in high-pressure glaucoma. Both glaucoma types have morphologic features in common, suggesting that they may possibly belong to a spectrum of the same pathologic process.

Diagnosis and pathogenesis of glaucomatous optic neuropathy: morphological aspects

Glaucomatous optic neuropathy is classified by morphologic changes in the intrapapillary and parapapillary region of the optic nerve head and the retinal nerve fibre layer. These changes can be evaluated using descriptive optic nerve head variables which are the size and shape of the optic disc; size, shape and pallor of the neuroretinal rim; size of the optic cup in relation to the area of the disc; configuration and depth of the optic cup; cup-to-disc diameter ratio and cup-to-disc area ratio; position of the exit of the central retinal vessel trunk on the lamina cribrosa surface; presence and location of splinter-shaped haemorrhages; occurrence, size, configuration and location of parapapillary chorioretinal atrophy; diffuse and/or focal decrease of the diameter of the retinal arterioles; and visibility of the retinal nerve fibre layer. Assessment of these variables is useful for the early detection of glaucomatous optic nerve damage, to follow-up patients with glaucoma, to differentiate various types of the chronic open-angle glaucomas, and to get hints for the pathogenesis of glaucomatous optic nerve fibre loss.

Optic disk appearances in primary open-angle glaucoma

Primary open-angle glaucoma almost certainly develops in a multifactorial manner, with interplay between numerous risk factors affecting the disease. These risk factors, in addition to intraocular pressure, include a number of cardiovascular factors. Some of these factors may determine the appearance of the damaged glaucomatous optic nerve head. Patients with four specific optic disk appearances have been investigated, and differences have been identified in their demographic characteristics, prevalence of certain risk factors, the pattern of visual field damage, and circulatory abnormalities in their retrobulbar vessels. The findings provide evidence of the existence of subgroups of primary open-angle glaucoma with correlations between risk factor and type of optic disk. A reliable method by which the different disk appearances could be distinguished in an objective manner would be clinically valuable, and the scanning laser ophthalmoscope has shown potential promise to achieve this. The results of studies relating to various glaucomatous optic disk appearances are presented and discussed.

The full-field flicker test in early diagnosis of chronic open-angle glaucoma

PURPOSE

To evaluate whether the full-field flicker test, a psychophysical test employing full-field flickering stimuli to measure temporal contrast sensitivity, can detect glaucomatous optic nerve damage in patients with increased intraocular pressure and glaucomatous optic disk abnormalities but normal visual fields.

METHODS

Temporal contrast sensitivity was determined with a sinusoidally flickering light (frequency, 37.1 Hz) of constant mean photopic luminance (10 cd/m2) presented in a full-field bowl of 58-cm diameter. The prospective study included three groups of individuals: the "preperimetric" glaucoma group of 80 patients with increased intraocular pressure, glaucomatous optic disk abnormalities, and normal visual fields; the "perimetric" glaucoma group of 56 glaucomatous patients with increased intraocular pressure and glaucomatous changes of the optic disk and visual field; and the control group of 96 normal subjects.

RESULTS

Temporal contrast sensitivity was significantly (P < .001) lower in the two glaucoma groups than in the control group. In the preperimetric glaucoma group, 34% of the patients (27/ 80) were recognized by the full-field flicker test at a specificity of 99%. For all study subjects, temporal contrast sensitivity decreased significantly (P < .001) with decreasing neuroretinal rim area, enlarging peripapillary atrophy, and diminishing retinal nerve fiber layer visibility.

CONCLUSIONS

The full-field flicker test can detect glaucomatous optic nerve damage in patients with increased intraocular pressure, glaucomatous optic disk abnormalities, and normal visual fields. Considering its feasibility, simplicity, quick performance, and low costs, the full-field flicker test may be helpful in clinics and in screening examinations as a supplement to glaucoma diagnosis.

Repeatable diffuse visual field loss in open-angle glaucoma

PURPOSE

The authors determined the frequency of repeatable diffuse loss as the only form of visual field damage in patients with early to moderate open-angle glaucoma in a prospective follow-up study.

METHODS

The study contained 113 patients (median age, 64 years; range, 17-89 years) who were tested at 6-month intervals with program 30-2 of the Humphrey Field Analyzer (Humphrey Instruments Inc., San Leandro, CA). Although the inclusion criterion for visual acuity was > or = 20/40, on entry, 94 (83.2%) patients had an acuity of > or = 20/25. Cumulative defect curves were generated for all visual fields (median per patient, 7; range, 4-9). After randomizing the order and removing all patient information, two observers independently rated each visual field as being "normal" or showing "diffuse," "localized," or "diffuse and localized" loss. We defined repeatable diffuse loss as occurring when at least two thirds of the number of fields in the follow-up were classified as "diffuse."

RESULTS

Fourteen patients (12.4%) had repeatable diffuse loss according to the cumulative defect curves. After reviewing their clinical charts, we excluded six of these patients because of early lens changes despite good visual acuity and three because of a suggestion of localized loss (on pattern deviation probability plots) in addition to the predominantly diffuse loss. The remaining five (4.4%) patients had repeatable diffuse loss that was due solely to open-angle glaucoma.

CONCLUSION

Although diffuse visual field loss is exaggerated by factors other than glaucoma in the majority of patients, it can occur repeatedly in a small number of patients as the only sign of visual field damage.

Various glaucomatous optic nerve appearances: clinical correlations

PURPOSE

To study the prevalence of risk factors for glaucoma as well as the pattern of visual field defects and their progression in patients with open angle glaucoma with different and distinct optic nerve appearances.

METHODS

One thousand seven hundred eleven optic disc stereo photographs of patients with glaucoma and ocular hypertension and of those suspected of having glaucoma were reviewed to identify pure examples of discs with four different optic disc appearances: focal ischemic discs, myopic glaucomatous discs, senile sclerotic discs, and generalized enlargement of the optic cup discs. The clinical charts of the selected patients were reviewed, with emphasis on the presence of predetermined ocular and systemic risk factors. Their automated visual fields also were analyzed.

RESULTS

Thiry-four patients with focal ischemic discs, 38 with myopic glaucomatous discs, 22 with senile sclerotic discs, and 23 with generalized enlargement of the optic cup discs were selected. Patients with myopic glaucoma and generalized enlargement of the optic cup discs were significantly younger than patients with focal ischemic and senile sclerotic discs. There were more women in the focal ischemic group. Patients with senile sclerotic discs had a significantly higher prevalence of ischemic heart disease; they also had a higher prevalence of systemic hypertension, which did not reach statistical significance. Migraine was 2.5 times more frequent in the focal ischemic group than in the other groups. Intraocular pressure was significantly higher in the generalized enlargement group. The pattern of visual field defect in the four groups also was distinctly different.

CONCLUSIONS

Patients with different disc appearances, selected only from their disc photographs, showed differences in their demographic characteristics, prevalence of certain systemic risk factors, intraocular pressure levels, and the pattern of their visual field damage. These findings suggest that these various disc appearances probably represent different populations of patients with glaucoma with, possibly, different pathogenic mechanisms.

Newer visual function tests in the evaluation of glaucoma

Conventional visual field testing, with a uniform white-on-white stimulus, is used routinely to diagnose and follow patients with chronic open-angle glaucoma. Many investigators, however, believe that conventional perimetry may not detect the earliest visual dysfunction in patients with chronic open-angle glaucoma. Consequently, much research has been performed over the past decade to develop a visual function test which might diagnose chronic open-angle glaucoma earlier than conventional perimetry. This review discusses the mechanisms, clinical studies and the current usefulness of the most common new visual function techniques. These tests attempt to detect early glaucomatous visual loss, generally by placing the visual system under stress and by minimizing the influence of extensive functional redundancy in the retinal ganglion cell network due to widely overlapping receptive fields. Success of new visual function tests depends on the specificity and the sensitivity of the instrument, excellent patient acceptance, short test duration, standardization of techniques, and limited expense. In addition to searching for newer visual function tests to evaluate glaucoma, we should continue efforts to improve the diagnostic capability and shorten the test duration of conventional perimetry.

Interpretation of high-pass resolution perimetry with a probability plot

BACKGROUND

The interpretation of high-pass resolution perimetry (HRP) fields can be difficult. An age-related probability plot was derived from a known data base to determine whether this improved specificity and sensitivity in early glaucoma detection.

METHODS

Forty glaucoma patients with minor field loss and 40 normals of equivalent age and sex underwent HRP. All had previous Humphrey field data available for comparison. The detection of previously confirmed field defects by HRP was examined using different parameters.

RESULTS

Using the age-corrected 95% confidence levels gave the best results, with sensitivity of 82.5% (33/40) and specificity of 85% (34/40). Using the contour plot yielded lower sensitivity (67.5%), while subjectively "eyeballing" the ring printout gave higher sensitivity (90%), but led to poor specificity (72.5%).

CONCLUSION

The use of a probability plot enhances the performance of HRP. A certain proportion of cases may be missed using one criterion alone, but combining the information with other indices can increase the yield.

Optic disk appearance in ocular hypertensive eyes

We examined the optic disk appearance in ocular hypertensive eyes that had a normal result of conventional computed perimetry. Color stereo-optic disk photographs of 104 ocular hypertensive subjects and of 216 normal individuals were morphometrically evaluated. In the ocular hypertensive eyes as compared to the normal eyes, significant differences (P < .0001) were detected for a smaller area and an abnormal shape of the neuroretinal rim, larger zones alpha and beta of the parapapillary chorioretinal atrophy, a decreased visibility of the retinal nerve fiber layer, and a higher frequency of localized nerve fiber layer defects. The variables most useful to indicate optic nerve damage were an abnormal shape of the neuroretinal rim and a decreased visibility of the nerve fiber layer. The most specific variable was the presence of localized retinal nerve fiber layer defects. Evaluation of these variables may be helpful for the early diagnosis of glaucoma.

Longitudinal comparison of temporal-modulation perimetry with white-on-white and blue-on-yellow perimetry in ocular hypertension and early glaucoma

We obtained data over 3 years on temporal-modulation perimetry (TMP), standard automated [white-on-white (W/W)] perimetry, and short-wavelength-sensitive [blue-on-yellow (B/Y)] perimetry in ocular hypertensive (OH) patients and patients with early glaucomatous visual-field loss (EG). Evidence of visual-field defects was obtained with the use of both B/Y perimetry and TMP in the majority of OH and EG eyes that demonstrated progression on W/W perimetry as well as in all stable EG eyes. Using the nerve-fiber-bundle pattern to compare testing procedures, we determined that these defects were generally as extensive or more extensive than the concurrent W/W abnormalities. In terms of location over the 3 years of testing, TMP and B/Y defects were reasonably consistent in the EG eyes, somewhat less consistent in the OH eyes demonstrating progression, and both inconsistent and infrequent in the stable OH eyes. The greatest degree of overlap occurred between the location of defects obtained by use of the higher TMP frequencies (8 and 16 Hz) and that of defects obtained by use of B/Y perimetry. Since these two methods are thought to isolate different visual mechanisms subserved by different visual pathways, these results suggest that early glaucomatous visual-field damage as revealed by TMP and B/Y perimetry may not be specific to a single visual pathway.

High-pass resolution perimetry. A clinical review

Review of all available reports comparing high-pass resolution perimetry (HRP) and conventional perimetry in normals and in subjects with different visual disorders reveals closely comparable aspects of sensitivity, specificity, and reliability. HRP shows important advantages concerning variability, test duration, and subject preferences. Drawbacks seem largely limited to somewhat loose renditions of visual field defects of small area and large depth. Otherwise HRP's novel format of graphic result presentation may be better suited to visual evaluation than conventional gray-scale maps with their lumping of thresholds and extensive interpolations. Several examples are provided of visual field defects due to various lesions throughout the visual system.

Diffuse nerve fiber layer loss in normal tension glaucoma

14 eyes of 14 normal tension glaucoma (NTG) patients with the maximum intraocular pressure (IOP) > or = 19 mmHg and 16 eyes of 16 NTG patients with the maximum IOP < 19 mmHg were examined. All patients had a scotoma confined to the upper or lower hemifield. Eyes with the maximum IOP > or = 19 mmHg showed significantly diffuse retinal nerve fiber layer (RNFL) loss in the RNFL area corresponded to the spared visual hemifield as compared to those with the maximum IOP < 19 mmHg. The results suggests that, even in NTG, IOP may be an important factor causing optic nerve damage.

Central function and visual field damage in glaucoma

82 eyes of 82 patients with different types of glaucoma were examined with various psychophysical tests assessing central and paracentral function, including foveal temporal contrast sensitivity function, FM 100-Hue test, and foveal and parafoveal blue-on-yellow-sensitivity. For all eyes visual field tests were performed with the Humphrey-Field-Analyzer, program 30-2. Global visual field indices were calculated as follows: Mean Sensitivity MS, Mean Deviation MD, and Corrected Pattern Standard Deviation CPSD. Linear regression analysis and multiple regression analysis correcting for a possible influence of age between the central and paracentral criteria and the global indices was performed. For the entire study population highly significant correlations are present between foveal and parafoveal blue-on-yellow-sensitivity and MS, MD and CPSD. Whereas in the Normal Tension Glaucoma subgroup (19/82 eyes) no significant correlations are found, the subgroup of 35/82 eyes with markedly elevated intraocular pressure (> or = 30 mmHg) shows highly statistically significant correlations between the low- and high-frequency end of the foveal temporal contrast sensitivity function and foveal and parafoveal blue-on-yellow-sensitivity and the global field indices. The results of the present study support the idea that there are two different mechanisms of glaucomatous damage, one which is pressure-dependent and one which may be pressure-independent. The pressure-dependent mechanism is responsible for deficits of central or paracentral function which are correlated to overall visual field damage.

Correlation of retinal nerve-fiber-layer loss, changes at the optic nerve head and various psychophysical criteria in glaucoma

In 61 eyes of 61 patients with glaucoma, semiquantitative assessment of retinal nerve-fiber-layer (RNFL) loss and neuroretinal rim measurement of the optic nerve head by means of the Optic Nerve Head Analyzer were correlated to the outcomes of automated light-sense, flicker and resolution perimetry and the Farnsworth-Munsell (FM) 100-Hue test. A significant influence of age on total RNFL and total diffuse RNFL scores was found, but there was no measurable effect of age on neuroretinal rim area. Total RNFL and total diffuse RNFL scores showed a good correlation to the various visual field indices: total RNFL score vs mean flicker frequency as determined by flicker perimetry, r = -0.606, P less than 0.0001; total RNFL score vs mean sensitivity as determined by light-sense perimetry, r = -0.385, P = 0.002; and total RNFL score vs mean ring score as determined by resolution perimetry, r = 0.341, P = 0.007. There was no significant correlation between RNFL scores and the FM 100-Hue score. Correlation between the neuroretinal rim area and the various psychophysical indices was poor and mostly not statistically significant. The high correlation of flicker scores with RNFL loss provides interest for future applications of this perimetric technique.