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Biomedical subjects

P G Spry

Publications and source records attributed to P G Spry.

13 recordsLinked to original sources
PubMed2001

Frequency doubling perimetry using a liquid crystal display.

PURPOSE: To compare frequency doubling contrast thresholds using a new liquid crystal window display with those obtained with the commercial video-based Frequency Doubling Technology perimeter. METHODS: One eye of 49 glaucoma patients and one eye of 49 normal controls were tested with the liquid crystal window and Frequency Doubling Technology systems. Both displays employed identical stimulus conditions and test strategies, although the dynamic range of the liquid crystal window-based display was approximately 30% smaller than that of the Frequency Doubling Technology system. Measurements were repeated using the video-based Frequency Doubling Technology perimeter in a subset of 21 eyes. Relationships between and within displays were assessed using a chance-corrected agreement measure (quadratic weighted kappa) and paired measurement differences. Variability was quantified using standard deviation from the mean paired measurement difference. RESULTS: Over the restricted operating range of the liquid crystal display system, between-display and within-video display variability was 2.3 dB and 3.2 dB, respectively, between-display agreement was 0.66, and within-display agreement (test-retest for Frequency Doubling Technology) was 0.65. CONCLUSIONS: Levels of agreement and variability between the two frequency doubling displays were of similar magnitude to repeated (test-retest) Frequency Doubling Technology measures, suggesting that contrast threshold measurements made using the two displays may be used interchangeably. However, the operating range of the current liquid crystal window-based display is smaller.

Aged↗
PubMed2001

Senescent changes of the normal visual field: an age-old problem.

PURPOSE: To examine the effect of normal aging on visual field sensitivity and identify the best-fitting function for normal populations. METHODS: Full Threshold standard automated perimetry data (program 24-2, Humphrey Field Analyzer) was collated retrospectively from clinically normal subjects who had previously been recruited for studies of normal visual function. One eye of each subject was randomly selected for analysis. Linear, bilinear, and simple nonlinear candidate functions of mean sensitivity vs. age (independent variable) were applied to these cross-sectional population data. Differences in the aging effect by eccentricity and hemifield were also considered. RESULTS: Data from 562 normal eyes were available for analysis. A significant negative relationship existed between age and mean visual field sensitivity within the cross-sectional population data. Coefficients of determination for the linear, bilinear, and nonlinear functions were 0.21, 0.20, and 0.26, respectively, indicating that the nonlinear function provided best characterization of the effect of age on mean sensitivity. A small but significant increase in the aging effect was present both peripherally (p < 0.001) and superiorly (p < 0.001). DISCUSSION: The nonlinear function that provided the best fit to cross-sectional population data indicates that age exerts an increasing effect on perimetric sensitivity with age, which has implications for clinical devices that use linear age coefficients to correct for normal aging effects. A linear age correction will overestimate aging changes for younger subjects and, therefore, may miss early pathologic changes in visual sensitivity. Conversely, linear age correction will also underestimate aging changes for older subjects and, thus, may overcall pathological sensitivity loss in this group. The effect of age within subjects requires further investigation to provide reliable estimates of the effect of age on sensitivity.

Adolescent↗
PubMed2001

Variability components of standard automated perimetry and frequency-doubling technology perimetry.

PURPOSE: To evaluate and compare intra- and intertest variability components for both standard automated perimetry (SAP) and frequency-doubling technology (FDT) perimetry in a small group of normal individuals and patients with glaucoma. METHODS: The method of constant stimuli (MOCS) was used to examine matched test locations with both SAP and FDT perimetry stimuli in a group of eight normal individuals and seven patients with glaucoma. Subjects were tested weekly at three predetermined visual field loci for 5 consecutive weeks. Frequency-of-seeing (FOS) curves were generated and used to quantify threshold sensitivity (50% seen on FOS, in decibels), intratest variability (FOS interquartile range, in decibels), and intertest variability (interquartile range of weekly repeated threshold determinations, in decibels). RESULTS: In patients with glaucoma, SAP intra- and intertest variabilities were found to increase with sensitivity reductions, as previously reported. FDT perimetry revealed that both intra- and intertest variability components did not appreciably change with reductions in sensitivity. With the measurement scales used in this investigation, both intra- and intertest variability components were significantly greater for SAP than for FDT perimetry (P < 0.001 and P = 0.003, respectively). Intratest variability exceeded intertest variability for both SAP (P = 0.001) and FDT perimetry (P < 0.001). CONCLUSIONS: For both SAP and FDT perimetry, variability occurring within a single test session contributed more to total variability than between-session variability. When the measurement scales available on commercial instrumentation were used, FDT perimetry exhibited significantly less variability than SAP, especially within regions of visual field sensitivity loss. FDT perimetry therefore shows promise as an effective test for detecting progressive glaucomatous visual field loss, although prospective longitudinal validation is still required to determine sensitivity to change.

Adult↗
PubMed2000

Quantitative comparison of static perimetric strategies in early glaucoma: test-retest variability.

PURPOSE: The aim of this study is to describe and compare test-retest variability of threshold-related suprathreshold and threshold examination strategies. METHODS: Threshold-related suprathreshold and FASTPAC threshold central visual field examinations were performed twice (test and retest) within a 4-week period on 322 subjects with early to moderate primary open-angle glaucoma and glaucoma suspects. For both strategies, defects were quantified by a count, or score, of the number of defective locations within the field as a whole and by hemifield, thereby providing a simple measure of defect extent. This quantification was obtained for the suprathreshold strategy at three suprathreshold increments (5, 8, and 12 dB) and for the full threshold strategy at two levels of pattern deviation probability, although absolute full threshold defect depth was not considered. Mean test-retest score differences and spread of score differences were used to describe variability. An index of relative variability was used to compare the two visual field examination strategies. RESULTS: Marked degrees of defect extent variability were found to exist in both suprathreshold and FASTPAC examination strategies. In general, the suprathreshold strategy exhibited lower test-retest variability of defect extent than the FASTPAC strategy. Suprathreshold test variability was dependent on the suprathreshold increment. FASTPAC examination variability was independent of defect depth when analyzed on the basis of pattern deviation probability values and was also found to be independent of the area of visual field loss. CONCLUSIONS: Suprathreshold examination techniques may provide a reliable perimetric alternative to thresholding strategies for monitoring individuals with early and moderate glaucoma, although they may not be suitable for individuals with advanced glaucomatous visual field loss.

Glaucoma, Open-Angle↗
PubMed2000

The Bristol shared care glaucoma study: outcome at follow up at 2 years.

AIM: To examine the outcome of care for patients with glaucoma followed up by the hospital eye service compared with those followed up by community optometrists. METHODS: A randomised study with patients allocated to follow up by the hospital eye service or community optometrists was carried out in the former county of Avon in south west England. 403 patients with established or suspected primary open angle glaucoma attending Bristol Eye Hospital and meeting defined inclusion and exclusion criteria were studied. The mean number of missed points on visual field testing in the better eye (using a "better/worse" eye analysis) in each group were measured. The visual field was measured using the Henson semiautomated central field analyser (CFA 3000). Measurements were made by the research team on all patients at baseline before randomisation and again 2 years after randomisation. The mean number of missed points on visual field testing in the worse eye, mean intraocular pressure (mm Hg), and cup disc ratio using a "better/worse" eye analysis in each group at 2 years were also measured. Measurements were made by the research team on all patients at baseline before randomisation and again 2 years after randomisation. An analysis of covariance comparing method of follow up taking into account baseline measurements of outcome variables was carried out. Additional control was considered for age, sex, diagnostic group (glaucoma suspect/established primary open angle glaucoma), and treatment (any/none). RESULTS: From examination of patient notes, 2780 patients with established or suspected glaucoma were identified. Of these, 752 (27.1%) fulfilled the entry criteria. For hospital and community follow up group respectively, mean number of missed points on visual field testing at 2 year follow up for better eye was 7.9 points and 6.8 points; for the worse eye 20.2 points and 18.4 points. Similarly, intraocular pressure was 19.3 mm Hg and 19.3 mm Hg (better eye), and 19.1 mm Hg and 19.0 mm Hg (worse eye); cup disc ratio at 2 year follow up was 0.72 and 0.72 (better eye), and 0.74 and 0.74 for hospital and community follow up group respectively. No significant differences in any of the key visual variables were found between the two groups before or after adjusting for baseline values and age, sex, treatment, and type of glaucoma. CONCLUSIONS: It is feasible to set and run shared care schemes for a proportion of patients with suspected and established glaucoma using community optometrists. After 2 years (a relatively short time in the life of a patient with glaucoma), there were no marked or statistically significant differences in outcome between patients followed up in the hospital eye service or by community optometrists. Decisions to implement such schemes need to be based on careful consideration of the costs of such schemes and local circumstances, including geographical access and the current organisation of glaucoma care within the hospital eye service.

Age Distribution↗
PubMed2000

Simulation of longitudinal threshold visual field data.

PURPOSE: To describe and evaluate a computer model that simulates longitudinal visual field data. METHODS: A computer model was designed using factors that influence thresholds of normal and glaucomatous visual fields. The simulation model was used to quantify the effects of fluctuation on the outcomes of pointwise linear regression by comparison with simulated gold standard data with no variability. RESULTS: Serial sets of 10 stable and 10 progressive visual fields with different fluctuation levels were generated by simulation and were analyzed using pointwise linear regression. Regression outcome measures used were slopes of -1 dB/year or worse and slopes of -1 dB/year or worse that were also statistically significant. In stable visual fields, the number of locations with regression slopes worse than -1 dB/year increased with fluctuation and defect size and was inversely related to the number of fields. The number of locations with statistically significant slopes remained low and appeared unaffected by these variables. In progressive visual fields, analysis of a small number of visual field test results (<8) overestimated the number of locations with regression slopes worse than -1 dB/year and underestimated the number of locations with statistically significant slopes. CONCLUSIONS: Computer simulation may be used to provide a gold standard outcome that permits evaluation of statistical tools for monitoring progressive glaucomatous visual field loss.

Computer Simulation↗
PubMed1999

The Bristol Shared Care Glaucoma Study: reliability of community optometric and hospital eye service test measures.

BACKGROUND/AIMS: Primary open angle glaucoma patients and glaucoma suspects make up a considerable proportion of outpatient ophthalmological attendances and require lifelong review. Community optometrists can be suitably trained for assessment of glaucoma. This randomised controlled trial aims to assess the ability of community optometrists in the monitoring of this group of patients. METHODS: Measures of cup to disc ratio, visual field score, and intraocular pressure were taken by community optometrists, the hospital eye service and a research clinic reference "gold" standard in 405 stable glaucoma patients and ocular hypertensives. Agreement between and within the three centres was assessed using mean differences and intraclass correlation coefficients. Tolerance limits for a change in status at the level of individual pairs of measurements were also calculated. RESULTS: Compared with a research clinic reference standard, measurements made by community optometrists and those made in the routine hospital eye service were similar. Mean measurement differences and variability were similar across all three groups compared for each of the test variables (IOP, cup to disc ratio, and visual field). Overall, the visual field was found to be the most reliable measurement and the cup to disc ratio the least. CONCLUSIONS: Trained community optometrists are able to make reliable measurements of the factors important in the assessment of glaucoma patients and glaucoma suspects. This clinical ability should allow those optometrists with appropriate training to play a role in the monitoring of suitable patients.

Community Health Services↗
PubMed1998

Variability in glaucomatous visual fields: implications for shared care schemes.

The purpose of this study was to establish the extent of variability in the visual fields of patients with glaucoma using a suprathreshold perimetric test strategy. The visual fields of 104 patients (126 eyes) were measured twice, on separate days, with a Henson CFA3000 central visual field analyser. All eyes had a diagnosis of glaucoma and had a minimum of three stimuli missed at 12 dB above their threshold estimate derived at the beginning of the first suprathreshold examination. The perimeter tested 132 locations within the central 25 degrees with a multiple stimulus suprathreshold strategy. Data were analysed on the basis of the difference in the number of recorded missed stimuli between the two visits. Large amounts of variability were found in the visual field results. Variability was largest when all levels of defect were included (> = 5 dB) and was found to be independent of the overall extent of loss. Results from the superior hemifield were found to be more variable than those from the inferior hemifield. The results highlight the problem of differentiating real change in visual field status from the enhanced variability seen in patients with glaucomatous visual field loss. The results from this study can be used to establish return-referral criteria for shared care schemes. The advantages of duplicate measures of the visual field are highlighted.

Glaucoma↗
PubMed1997

The Bristol Shared Care Glaucoma Study--validity of measurements and patient satisfaction.

BACKGROUND: The aims of the study were to determine (1) whether community optometrists are able to make valid measurements of visual parameters in patients with established or suspect primary open angle glaucoma and (2) patient satisfaction with follow-up by community optometrists. METHODS: A randomized study was carried out in the former county of Avon in South West England with patients allocated to follow-up by the hospital eye service or by community optometrists. The subjects were 403 patients with established or suspected primary open angle glaucoma attending Bristol Eye Hospital and meeting defined inclusion and exclusion criteria. The main outcome measures were 91) measurements of key visual parameters (intraocular pressure, visual fields and cup/disc ratio) made by hospital eye service and community optometrists, compared with a research clinic reference standard at baseline, and (2) patient satisfaction at baseline and at six months. RESULTS: Community optometrists were able to make measurements of comparable accuracy to those made in the hospital eye service. Patients were significantly more satisfied with a number of aspects of care provided by community optometrists, particularly those relating to waiting times, compared with those from the hospital eye service. CONCLUSIONS: Community optometrists are able to make measurements of key visual parameters in patients with established or suspect primary open angle glaucoma which are of comparable quality to the hospital eye service. Follow-up by community optometrists is acceptable to patients. The costs of each option are reported elsewhere.

Aged↗
PubMed1997

Comparing costs of monitoring glaucoma patients: hospital ophthalmologists versus community optometrists.

OBJECTIVES: To compare the costs of monitoring stable glaucoma patients by community optometrists and hospital ophthalmologists. METHODS: A cost analysis was conducted alongside a randomised controlled trial which compared the accuracy and acceptability of measurement in each form of care. The viewpoints of the health service and of patients were considered. Costs were assessed using a number of different methods. Sensitivity analysis was conducted for key variables. RESULTS: The baseline analysis reflected heavily the different length of time between follow-up in the two arms of the trial (10 months (average) for hospital, 6 months for optometrists). It showed annual cost per patient for hospital ophthalmologists varied from 14.50 pounds to 59.95 pounds, and community optometrist costs varied from 68.98 pounds to 108.98 pounds. Assuming a 6-month follow-up interval for the hospital ophthalmologists, costs varied from 24.16 pounds to 99.92 pounds. CONCLUSIONS: Recommendations about the least costly form of follow-up must depend on the context in which the decision is being taken and the scale of change envisaged. If the aim is to recoup resources from hospitals in order to pay for monitoring in the community, community monitoring is unlikely to be the least costly option.

Community Health Services↗
PubMed1995

The cost of monitoring glaucoma patients by community optometrists.

Glaucoma patients are currently undergoing monitoring by community based optometrists as part of a randomised controlled trial of shared care. As part of this trial, the costs of monitoring these patients by community optometrists are being calculated. Data were obtained from eight practices for the 1993-1994 financial year. The average 'full' cost of a 40 min appointment was calculated as epsilon 31.56 pounds. The average number of unbooked appointments for the month of October 1994 was 16 per practice, which equated to 12, 40 min appointments. Once the number of unbooked appointments was surpassed for each practice, an average opportunity cost of epsilon 54.00 pounds was experienced per appointment. The participating optometrists were willing to accept a minimum fee of epsilon 26.03 pounds for a small number of patient assessments but this rose to epsilon 43.16 pounds for up to 100 glaucoma patients seen per annum.

Community Health Services↗
PubMed1995

The Bristol Shared Care Glaucoma Study: study design.

The purpose of this study was the evaluation of community based optometric monitoring of stable glaucoma patients and glaucoma suspects compared to the routine Hospital Eye Services (HES) monitoring. Four hundred and five subjects were recruited from routine outpatient clinics at the Bristol Eye Hospital. All eligible participants were seen in the routine hospital clinic and then within two months were given a 'Gold Standard Assessment' (GSA) by an independent research team. Participants then visited one of 12 glaucoma-trained optometrists, for a standard battery of tests. Randomisation resulted in 204 subjects being allocated to community care, with reviews on a six monthly basis, with 201 who remained a control group within the hospital. Referral criteria were established to enable optometric detection of apparent glaucomatous progression. A questionnaire was used to assess patient satisfaction with both care types. Additionally a cost analysis exercise was performed.

Community Health Services↗