The visual field in chronic open angle glaucoma: the rate of change in different regions of the field

The Relationship Between Corneal Hysteresis and Progression of Glaucoma After Trabeculectomy

PURPOSE

The purpose of this study was to investigate the association of corneal hysteresis (CH) measured with Ocular Response Analyzer on the progression of glaucoma after trabeculectomy.

MATERIALS AND METHODS

Twenty-four eyes of 19 patients with primary open-angle glaucoma underwent trabeculectomy. A series of visual fields (Humphery Field Analyzer 24-2 SITA-standard) were measured starting after 6 months after trabeculectomy (4.2±5.0 y, mean±SD). The mean total deviation (mTD) of the 52 test points were calculated. In addition, the mTD was divided into the following areas: central area (within central 10 degrees), superior area and inferior area: mTDcentre, mTDsuperior, and mTDinferior, respectively. The relationship between each area's progression rate of mTD and the 7 variables of baseline age, central corneal thickness, baseline mTD, mean intraocular pressure (IOP), SD of IOP divided by the mean IOP, the difference between baseline IOP obtained before the initiation of any treatment, mean IOP, and CH were analyzed using the linear mixed model, and the optimal model was selected using the model selection method with the second ordered Akaike Information Criterion.

RESULTS

In the optimal model for mTD progression rate, only CH was selected with the coefficient of 0.11. The optimal model for the mTDcentre progression rate included mean IOP with the coefficient of -0.043 and CH with the coefficient of 0.12, and that for mTDinferior included only CH with the coefficient of 0.089. There was no variable selected in the optimal model for the mTDsuperior progression rate.

CONCLUSION

CH is a useful measure in the management of glaucoma after trabeculectomy.

Rates of Visual Field Loss in Primary Open-Angle Glaucoma and Primary Angle-Closure Glaucoma: Asymmetric Patterns

Purpose

The purpose of this study was to evaluate the rate of visual field (VF) loss in primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).

Methods

Four hundred forty eyes of 282 patients with POAG (aged 53.4 ± 12.0: mean ± standard deviation, years) and 79 eyes of 49 patients with PACG (aged 62.7 ± 9.0 years) with at least six or more reliable VF tests were studied. Point-wise, region-wise, and global rates of VF change were assessed for POAG and PACG eyes. Only the VF records prior to laser iridotomy or cataract surgery were included in PACG eyes. The global and superior-inferior asymmetric rates of VF loss were compared between POAG and PACG eyes.

Results

The mean total deviation (mTD) values at baseline were -6.4 ± 5.7 dB in POAG patients and -6.4 ± 7.3 dB in PACG patients. There was not a significant difference in the progression rates of mTD between POAG eyes (-0.23 ± 0.38 dB/y) and PACG eyes (-0.29 ± 0.45 dB/y). In POAG eyes, the VF progression rate was significantly asymmetric across the horizontal line; the central, paracentral, and peripheral arcuate 2 regions in the superior hemifield had a significantly faster rate of VF loss than their inferior counterparts. In contrast, this asymmetry was not observed in the rate of VF loss in PACG eyes.

Conclusions

POAG eyes showed a faster rate of VF loss in the superior hemifield compared to in the inferior hemifield, particularly in central and paracentral regions. This difference was not observed in PACG eyes.

Distribution and Rates of Visual Field Loss across Different Disease Stages in Primary Open-Angle Glaucoma

PURPOSE

To identify patterns and rates of visual field (VF) loss in primary open-angle glaucoma (POAG) across different levels of severity.

DESIGN

Retrospective, observational case series.

PARTICIPANTS

Visual fields of 278 eyes of 139 patients with POAG (9 years of follow-up with ∼17 visits) from the Rotterdam Eye Hospital in The Netherlands were analyzed to identify patterns and rates of VF loss.

MAIN OUTCOME MEASURES

Rate of VF decline for the entire VF, each region, and test point. Hemifield asymmetric rate if VF decline for each region and test point.

METHODS

Total deviation (TD) values were extracted from the Humphrey VF Analyzer (Carl Zeiss Meditec, Dublin, CA). Eyes were stratified into 3 glaucoma stages by means of the mean deviation (MD): better than -6 decibels (dB), worse than -6 dB and better than -12 dB, and worse than -12 dB. Each hemifield was divided into 5 regions according to the Glaucoma Hemifield Test (GHT): central, paracentral, nasal, and peripheral arcuates 1 and 2. Point-wise and region-wise asymmetric patterns of VF loss and rate of VF loss were identified by comparing the values in the superior hemifield and the inferior hemifield at each severity level using a generalized estimating equation.

RESULTS

The mean age of the patients was 60.2±10.3 years (mean ± standard deviation [SD]). The rate of MD loss, for all eyes taken together, was -0.11 dB/year. In the cross-sectional analysis, in eyes in the early and moderate stages, central and peripheral arcuate 2 regions in the superior hemifield were worse than their inferior counterpart, whereas in the advanced stage all GHT regions in the superior hemifield were significantly worse than the corresponding regions in the inferior hemifield (P ≤ 0.05). In the longitudinal analysis, there was no significant difference in the rate of VF loss between the GHT regions in the superior and inferior hemifields.

CONCLUSIONS

Our findings suggest that in POAG, VF damage is worse in the superior hemifield than in the inferior hemifield.

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.

Patterns of glaucomatous visual field progression identified by three progression criteria

PURPOSE

To determine typical patterns of repeatable glaucomatous visual field progression.

DESIGN

Retrospective analysis of data obtained from two prospective studies.

METHODS

Included were 72 eyes of 72 patients tested up to six times over 2 years, and 40 eyes of 40 patients followed annually for up to 12 years. Each patient had two abnormal baseline visual fields, abnormal optic nerves, and serial fields. Progression was identified using three methods: by glaucoma change probability using total deviation (GCP-TD) and pattern deviation (GCP-PD) plots and by a clinical criteria. Progression was categorized as deepening or expansion of an existing scotoma, or a new scotoma.

RESULTS

The percentage of eyes repeatably progressed ranged from 17% to 27%. The most common pattern of progression was a deepening of an existing scotoma in the annual group, followed by expansion. With two follow-ups required, percentages for deepening only were 20% (clinical classifier). A combination of expansion and deepening was most common for the GCP criteria: 15% (GCP-TD classifier), and 10% (GCP-PD classifier) for the annual group. For the semiannual group, deepening was most common with the clinical criteria (11% of eyes), and deepening with expansion was most common by GCP criteria (14%, GCP-TD and GCP-PD). No eyes showed repeatable new scotomas.

CONCLUSIONS

Glaucomatous visual fields progress in the area of the visual field where baseline testing showed an existing scotoma. Follow-up testing might be improved by concentrating on already defective locations and using sparser test patterns or screening algorithms in normal areas of the visual field.

Increased Rate of Visual Field Loss Associated with Larger Initial Visual Field Threshold Values on Follow-Up of Open-Angle Glaucoma

PURPOSE

To determine the changes in the visual field over time and the factors that contribute to these changes on follow-up of open-angle glaucoma patients.

PATIENTS AND METHODS

From a retrospective review of patients' charts and visual fields, 30 eyes from 30 patients with open-angle glaucoma with a minimum of 3 years of follow-up were chosen. Visual fields were obtained with the Octopus perimeter about every 4 months. Regression analysis was used to obtain the slope for all the threshold values for each eye for the total field and nine different regions over time. Optic disc area was measured from single fundus photographs obtained at the beginning of the period of observation.

RESULTS

The open-angle glaucomas were observed for a mean of 6.7 +/- 2.3 years. The number of visual fields per eye was 20.7 +/- 8.0. The mean threshold value of the total field for the first three visual fields was 18.0 +/- 5.2 dB. The visual fields of the 30 eyes with a mean intraocular pressure of 18 +/- 2 mm Hg during follow-up showed a significant decrease in their visual field slope of -0.384 dB/y for the total visual field. On multivariate analysis, the slope or rate of visual field loss was significantly correlated with the average of the first three initial visual field thresholds for the total visual field, temporal, and central regions so that the greater the threshold value the more rapid the rate of the visual field loss. For the total visual field and for the nasal, superior nasal, and temporal regions with lower initial threshold values, the rate of visual field loss was curvilinear with the rate of visual field loss increasing at greater initial mean threshold values. The other regions of the visual field showed a linear increasing rate of visual field loss with larger initial threshold values. Other factors significantly associated with progression of visual field loss were refractive error, race, the slope of the pulse rate, and the mean percent false positives and false negatives for initial to final observations. The mean and the slope of intraocular pressure from initial to final observation were not significant variables.

CONCLUSION

In open-angle glaucomas observed for 6.7 +/- 2.3 years, there was a more rapid rate of visual field loss associated with larger initial threshold values and a less rapid rate of visual field loss associated with smaller initial threshold values indicating that the progression of visual field loss is greater in an earlier stage of disease.

Randomised controlled trial comparing the effect of brimonidine and timolol on visual field loss after acute primary angle closure

AIM

To compare the effect of brimonidine and timolol in reducing visual field loss in patients with acute primary angle closure (APAC).

METHODS

In addition to standard acute medical treatment, patients presenting with APAC were randomised to either brimonidine 0.2% or timolol 0.5% upon diagnosis, then twice daily for 4 weeks. After laser peripheral iridotomy (LPI), subjects underwent three baseline perimetry tests during the first week, and then at weeks 4, 8, 12, and 16. Pointwise linear regression analysis was applied to the field series of each of these subjects starting with the third test (total of five tests per subject). Progression was defined as a significant regression slope (p<0.05) showing 1 dB per year or more of sensitivity loss at the same test location in the series. Patients were also compared for prevalence of abnormal fields at 16 weeks, which was defined as an abnormal glaucoma hemifield test result and/or corrected pattern standard deviation outside the 95% confidence limits.

RESULTS

59 subjects (31 in the brimonidine group; 28 in the timolol group) completed the study. There were 47 females (79.7%), the majority of subjects (94.9%) were Chinese and the mean age was 59.2 (SD 7.2) years. There were no significant differences between the two groups with respect to demographic features, presenting intraocular pressure (IOP), duration of symptoms, time from presentation to LPI, or mean IOP at each study visit. Over the 16 week study period, despite adequate statistical power, no difference was found between groups in terms of the number of patients with progressing locations, the mean number of progressing locations per subject, or the mean slope of the progressing locations. Nine (29%) subjects in the brimonidine group and 10 (35.7%) in the timolol group were found to have significant visual field defects at 16 weeks (p = 0.58). 15 out of these 19 subjects (78.9%) already had these visual field defects in the first week.

CONCLUSIONS

In the first 16 weeks after APAC, there was no difference in the prevalence of visual field defects or rate of visual field progression between brimonidine and timolol treated groups.

Patterns of glaucomatous visual field defects in an older population: the Blue Mountains Eye Study

This report aims to describe the frequency of different patterns of visual field loss in open-angle glaucoma (OAG). The Blue Mountains Eye Study examined 3654 persons (aged 49+) during 1992-1994. Humphrey supra-threshold visual fields were performed in 88.9%. Those classified as glaucoma suspects had 30-2 full-threshold fields (9.2%). Of OAG cases (n = 108) with field tests in both eyes (n = 97), unilateral defects were present in 49 (50.5%) and bilateral in 48 (49.5%). Advanced field loss was found in 16 (15.4%) subjects and in 22 (10.9%) eyes, with bilateral loss present in 6 (6.2%) cases. Of all eyes of OAG cases (n = 201), 49 (24.4%) had no defects, 52 (25.9%) upper, 61 (30.3%) lower, and 17 (8.5%) had combined upper and lower loss. Of the upper and lower cases (n = 113), the types of defects included nasal step (36), arcuate (26), nasal plus arcuate (26), and hemispherical defects (25). Of subjects with fields in at least one eye (n = 104), there was a similar proportion in the worse eye of upper defects (28.8%), lower (31.7%), and combined upper and lower (24.0%). Undiagnosed OAG was more frequent in unilateral (65.3%) than bilateral (34.7%) cases (P = 0.003). This study reports the pattern of typical glaucomatous field loss in an older Australian population.

Interobserver agreement on visual field progression in glaucoma: a comparison of methods

AIM

To examine the level of agreement between clinicians in assessing progressive deterioration in visual field series using two different methods of analysis.

METHODS

Each visual field series satisfied the following criteria: more than 19 reliable fields, patient age over 40 years, macular threshold at least 30 dB. The first three fields in each series were excluded to minimise learning effects: the following 16 were studied. Five expert clinicians assessed the progression status of each series using both standard Humphrey printouts and pointwise linear regression (PROGRESSOR). The level of agreement between the clinicians was evaluated using a weighted kappa statistic.

RESULTS

A total of 432 tests comprising 27 visual field series of 16 tests each were assessed by the clinicians. The level of agreement on progression status between the clinicians was always higher when they used PROGRESSOR (median kappa = 0.59) than when they used Humphrey printouts (median kappa = 0.32). This was statistically significant (p = 0.006, Wilcoxon matched pairs signed rank sum test).

CONCLUSIONS

Agreement between expert clinicians about visual field progression status is poor when standard Humphrey printouts are used, even when the field series studied are long and consist solely of reliable fields. Under these ideal conditions, clinicians agree more closely about patients' visual field progression status when using PROGRESSOR than when inspecting series of Humphrey printouts.

Progression of visual field loss in untreated glaucoma patients and glaucoma suspects in St. Lucia, West Indies

PURPOSE

A 1986-1987 survey found 8.8% prevalence of open-angle glaucoma in the black population of St. Lucia, West Indies. This follow-up study assessed visual field loss progression in untreated glaucoma patients and glaucoma suspects 10 years later.

DESIGN

Cohort study.

METHODS

Subjects were 205 glaucoma patients and suspects; 1987 data included age, sex, visual acuity, and visual fields measured by automated threshold perimetry (Humphrey C 30-2 test), and 1997 data included intraocular pressure, visual acuity, and visual fields measured by the same test. Exclusion criteria included field unreliability, field improvement due to vision improvement, nonglaucomatous vision deterioration, glaucoma treatment since 1988, and scoring of a visual field as end stage in 1987. Visual fields were scored by algorithms for the Advanced Glaucoma Intervention Study (AGIS) and Collaborative Initial Glaucoma Treatment Study (CIGTS).

RESULTS

By AGIS criteria, 55% of 146 right eyes and 52% of 141 left eyes showed progression of visual field loss. In linear regressions, progression severity was unassociated with sex, intraocular pressure, or baseline visual field score, but was positively associated with age (P <.001, right; P =.002, left). The cumulative probability of reaching end stage in 10 years in at least one eye was approximately 16% by AGIS criteria. By CIGTS criteria, 73% of 146 right eyes and 72% of 141 left eyes progressed.

CONCLUSIONS

These data provide a unique opportunity to study progression of untreated glaucoma. The percentage of eyes showing visual field loss progression and the percentage reaching end stage were considerably higher than in studies of visual field progression in treated eyes.

Frequency of testing for detecting visual field progression

AIMS

To investigate the effect of frequency of testing on the determination of visual field progression using pointwise linear regression (PLR).

METHODS

A "virtual eye" was developed to simulate series of sensitivities over time at a given point in the eye. The user can input the actual behaviour of the point (for example, stable or deteriorating steadily), and then a configurable amount of noise is added to produce a realistic series over time. The advantage of this over using patient data is that the actual status of the eye is known. Series were generated using different frequencies of testing, and the diagnosis that would have been made from each series was compared with the true status of the eye. A point was diagnosed as progressing if the regression line for the series showed a deterioration of at least 1 dB per year, significant at the 1% level. From these results, graphs were produced showing the number of points correctly or incorrectly diagnosed as progressing.

RESULTS

With the virtual eye deteriorating at a rate of 2 dB/year, it was found that the point was determined to be progressing quicker when more tests were carried out each year. With a stable virtual eye, it was found that increasing the frequency of testing increased the number of series that were falsely labelled as progressing during the first 3 years of testing.

CONCLUSIONS

As the frequency of testing increases, the sensitivity of PLR increases. However, the specificity decreases; possibly meaning more unnecessary changes in treatment. Three tests per year provide a good compromise between sensitivity and specificity.

Identification of progressive glaucomatous visual field loss

In normal individuals, visual field measures are not perfectly repeatable and individual test locations exhibit both short- and long-term sensitivity variations. This physiologic variability is greatly increased in glaucoma and confounds detection of real progressive loss in visual function. Distinguishing progressive glaucomatous visual field loss from test variability therefore represents a complex task. Procedures used for detection of glaucomatous visual field progression may be broadly grouped into four categories: 1) clinical judgment, which consists of simple subjective observation of sequential visual field test results; 2) defect classification systems, whereby specific criteria are used to stratify field loss by discrete score and define progression as score change over time, such as the Advanced Glaucoma Intervention Study scoring system; 3) trend analyses, which follow test parameters sequentially over time to determine the magnitude and significance of patterns within the data, for example linear regression; and 4) event analyses, which identify single events of significant change relative to a reference examination. All of these methods demonstrate distinct benefits and drawbacks, making each useful in specific circumstances, although no single method appears universally ideal. At the present time the best method of detection of progression may be to rely upon confirmation of change at successive examinations and also by correlation of visual field changes with other clinical observations. Alternative analysis methods may become available in the near future to help identify cases of progressive loss.

Early detection of visual field progression in glaucoma: a comparison of PROGRESSOR and STATPAC 2

AIM

To compare the performance of PROGRESSOR (pointwise linear regression) and STATPAC 2 (comparison with baseline values) in detecting early deterioration in the visual fields of glaucoma patients.

METHODS

Visual field series from 19 untreated normal tension glaucoma eyes which were deteriorating on clinical grounds were analysed by PROGRESSOR and STATPAC 2. Progression criteria for PROGRESSOR were (1) inner points: slope < -1 dB/year, p < 0.05 and (2) edge points: slope < -2 dB/year, p < 0.05. Criteria for STATPAC 2 were p < 0.05 change probability for any point on three consecutive fields. Detection time was defined as the time interval between the initial field and the first field in which at least one progressing point was identified. Detection times produced by the two techniques were compared.

RESULTS

PROGRESSOR and STATPAC 2 agreed on progression in all 19 eyes. Mean detection time for PROGRESSOR was 1.077 (SD 0.985) years and for STATPAC 2 was 2.161 (1.357) years. PROGRESSOR detected progression sooner than STATPAC 2 in 18 eyes (p < 0.01), Wilcoxon matched pairs signed rank test). PROGRESSOR detected progression earlier by a mean of 1.085 (0.936) years.

CONCLUSIONS

PROGRESSOR consistently detected progression earlier than STATPAC 2. The PROGRESSOR software is a useful tool for the early detection of visual field deterioration in glaucoma.

How often do patients need visual field tests?

BACKGROUND

This study was undertaken to determine whether the interval between visual field tests affects the ability to detect progressive glaucomatous field loss.

METHODS

One hundred and nineteen retinal locations which were deteriorating significantly by > or = 1 dB/ year (untreated normal tension glaucoma patients: 6 eyes) were studied. Analysis was repeated using 'thinned' visual field tests: one test per year instead of the complete three per year over a period of 4 years.

RESULTS

The 'thinned' tests identified only 45.4% of the deteriorating points over the 4-year period. Furthermore, there was a mean delay of 1.10 years in detection (P < 0.01).

CONCLUSIONS

Less frequent visual field testing detects fewer progressing locations and detects them later.

Comparison of methods to detect visual field progression in glaucoma

OBJECTIVE

The purpose of the study is to develop alternative statistical approaches for evaluating the trend of visual field series over time and to compare the results to human observers.

DESIGN

Retrospective analysis of visual field results.

PARTICIPANTS

Eighty-three eyes of 83 patients (phakic or pseudophakic) with open-angle glaucoma and 5 or more eligible fields were included in the study.

INTERVENTION

Three experienced observers independently reviewed the field series to determine stability or progression.

MAIN OUTCOME MEASURES

The following additional methods to determine progression of visual field loss were used: (1) pointwise univariate regression analysis and a glaucoma change analysis; (2) univariate regression analysis on visual field indices mean deviation, corrected loss variance, and glaucoma pattern index; (3) pointwise multivariate regression analysis with fixed effects on panel data; and (4) clusterwise multivariate regression analysis with fixed effects on panel data. The results of different statistical methods were compared by determining the pairwise agreement (Cohen's weighted kappa) between each technique and three experienced observers.

RESULTS

Patients were observed for a mean (+/-standard deviation) of 5.6 (+/-1.4) years. The visual fields of 27 (33%) and 56 (67%) eyes were considered to have progressed or remained stable, respectively, based on agreement of at least 2 of 3 observers. Univariate regression analysis on visual field indices was not useful for detection of visual field progression. Pointwise and clusterwise regression analyses with fixed effects on panel data performed as well as pointwise univariate regression analysis compared with human observers (kappa = 0.52, 0.53, and 0.55, respectively). Both methods showed better agreement with human observers than with glaucoma change analysis (kappa = 0.41).

CONCLUSIONS

A new statistical model, multivariate regression analyses with fixed effects on panel data, is an appropriate method to evaluate the course of visual field series over time and shows reasonable agreement with experienced observers and pointwise univariate regression analysis.

Pointwise univariate linear regression of perimetric sensitivity against follow-up time in glaucoma

PURPOSE

The authors compared pointwise univariate linear regression (ULR) of sensitivity against follow-up as an indicator of visual field progression with that of the corresponding ULR of mean deviation (MD) and with the Glaucoma Change Probability (GCP) analysis. The authors determined the influence of the number and sequence of prior examinations on the slope of the pointwise function.

METHODS

Univariate linear regression was undertaken at each stimulus location on the arbitrarily assigned left eyes of 38 patients with glaucoma examined with the Humphrey Field Analyzer Programs 30-2 or 24-2 (stimulus size III, Humphrey Instruments Inc, San Leandro, CA). The mean age was 59.0 years (standard deviation [SD] = 12.9), the mean number of fields per patients was 12.0 (SD = 2.8), and the mean duration of follow-up was 6.0 years (SD = 1.6).

RESULTS

Four patients showed statistically significant MD slopes. Of the 34 patients exhibiting a nonsignificant MD slope, 15 exhibited clusters of at least two contiguous progressing locations. Less than half of these locations were designated as progressing by GCP. The GCP detected less than one third of the locations considered progressing by ULR for the last six fields in the series: this was attributed to the nonlinear nature of the decline in sensitivity.

CONCLUSIONS

The degree of agreement between the outcomes of ULR and GCP was dependent on the quality of the collected data, the magnitude of the baseline sensitivity, the extent and type of the subsequent visual field progression, and the position of the fields within the examination series. Good agreement was illustrated at those locations where the deterioration fell outside the limits of expected variability in stable glaucoma.

Analysis of visual field progression in glaucoma

BACKGROUND

Despite the widespread use of computerised perimetry the diagnosis of visual field deterioration in following glaucoma patients over time remains particularly difficult. A new method of analysis using a novel graphical display of longitudinal field data is presented.

METHODS

A linear regression model of the luminance sensitivity at each stimulus location against time of follow up transforms the quantitative data from a series of fields into a colour coded form which illustrates the spatial configuration of change to aid the interpretation of field loss. The method of analysis and the developed computer software (PROGRESSOR) is described. Comparison with STATPAC-2 glaucoma change probability analysis is given including levels of agreement between the techniques using series of fields of 10 eyes from patients with normal tension glaucoma.

RESULTS

Examples of this new method compare well with STATPAC-2 analysis. The level of agreement between the techniques to separate progressing from stable retinal locations is good (kappa = 0.62; SE = 0.04).

CONCLUSIONS

This new technique, which combines the change in perimetric sensitivity over time with colour coding of significant change into one image may provide an efficient method to detect true progression in glaucomatous field loss.

Modelling series of visual fields to detect progression in normal-tension glaucoma

BACKGROUND

Use of statistical modelling techniques to identify models that both describe glaucomatous sensitivity decay and allow predictions of future field status.

METHOD

Twelve initially normal fellow eyes of untreated patients with confirmed normal tension glaucoma were studied. All had in excess of 15 Humphrey fields (mean follow-up 5.7 years). From this cohort individual field locations were selected for analysis if they demonstrated unequivocal deterioration at the final two fields. Forty-seven locations from five eyes satisfied this criterion and were analysed using curve-fitting software which automatically applies 221 different models to sensitivity (y) against time of follow up (x). Curve-fitting was then repeated on the first five fields, followed by projection to the date of the final field to generate a predicted threshold which was compared to the actual threshold. Competing models were therefore assessed on their performance at adequately fitting the data (R2) and their potential to predict future field status.

RESULTS

Models that provide the best fit to the data were all complex polynomial expressions (median R2 0.93). Other simple expressions fitted fewer locations and exhibited lower R2 values. However, accuracy in predicting future deterioration was superior with these less complex models. In this group a linear expression demonstrated an adequate fit to the majority of the data and generated the most accurate predictions of future field status.

CONCLUSIONS

A linear model of the pointwise sensitivity values against time of follow-up can provide a framework for detecting and forecasting glaucomatous field progression. Linear modelling allows the clinically important rate of sensitivity loss to be estimated.

Flicker perimetry using a luminance threshold strategy at frequencies from 5-25 Hz in glaucoma, ocular hypertension and normal controls

A prototype automated flicker perimeter was used to investigate flicker luminance thresholds in glaucoma patients (n = 11), ocular hypertensives (high risk n = 10, low and intermediate risk n = 21) and normal controls (n = 10). Differential light sensitivity was measured for one eye of each subject using a flickering stimulus at frequencies of 5, 10, 15, 20 and 25 Hz at ten test locations of 1 degree in the arcuate and nasal regions of the central 50 degrees of the visual field using a 4-2 dB staircase. The glaucoma patients had significantly reduced sensitivities for all frequencies (p < 0.001) with minimum sensitivity at 15 Hz. The 'high risk' ocular hypertensives had significantly reduced sensitivities at 10 and 15 Hz (p < 0.02). At present the ocular hypertensive patients in this study show no abnormalities demonstrable by conventional automated static perimetry. These findings may represent the earliest of perimetric deficits in patients with glaucomatous optic neuropathy.