Biomedical subjects

David B Henson

Publications and source records attributed to David B Henson.

5 recordsLinked to original sources

PubMed2004

Test-retest variability of multifocal visual evoked potential and SITA standard perimetry in glaucoma.

PURPOSE: To investigate the test-retest variability of multifocal visual evoked potential (mfVEP) and threshold perimetry in glaucoma, and to examine the relationship between the two techniques. METHODS: Data were recorded using the AccuMap mfVEP and SITA standard program of the Humphrey Field Analyzer. Data were obtained twice within a 4-week period from both eyes of 74 patients with varying amounts of glaucomatous visual field loss. The number of defective test locations (those falling beyond a given probability value of being normal) were calculated for mfVEP and SITA, using databases incorporated within the instruments software. Reliability measures and test times were recorded along with patient test preference. RESULTS: Both tests showed a large degree of test-retest variability in the number of defective test locations (95% limits of agreement for mfVEP and SITA being 13.39 and 9.88, respectively). A "fair to moderate" degree of spatial agreement was found between mfVEP and SITA. The number of mfVEP defective locations was dependent on the signal amplitude. No relationship was found between test-retest variability and the reliability indices for either test. The mean time taken to perform mfVEP and SITA standard was 33 and 20 minutes, respectively, and 73 of the 74 patients preferred the mfVEP test. CONCLUSIONS: Test-retest variability was found to be slightly greater for mfVEP. The processing of mfVEP signals needs to be changed to remove the relationship between the number of defective locations and signal amplitude. The majority of patients preferred mfVEP to conventional perimetry although mfVEP takes longer to perform.

Aged↗

PubMed2003

Age-dependent changes in the basal retinovitreous adhesion.

PURPOSE: To determine the width of the posterior vitreous base in human eyes of different ages and to clarify the nature of the postoral retinovitreous adhesion that underlies the development of juxtabasal retinal tears and retinal detachment after posterior vitreous detachment (PVD). METHODS: The posterior limit of the vitreous base was delineated with indocyanine green after mechanical peeling of the postbasal vitreous cortex from the retina in 58 pairs of donor eyes. The area of residual retinovitreous adhesion was measured by image analysis. Scanning electron microscopy was performed on the undersurface (or retinal aspect) of the inner limiting lamina (ILL) after trypsin digestion of the peripheral retina. RESULTS: An age-dependent increase in the anteroposterior dimension of the posterior vitreous base was revealed that became progressively wider in eyes of male donors than in those of female donors and in the nasal half compared with the temporal half of the globe. Ultrastructural studies showed progressive invasion of the innermost peripheral retina by bundles of collagen fibrils, initially in the form of characteristic braids splaying out beneath the ILL and eventually as a dense sublaminar mat in the elderly. The collagen fibrils penetrated the ILL through localized defects and intertwined with those in the basal gel. CONCLUSIONS: With aging, the posterior border of the vitreous base migrates posteriorly so that an annular band of firm adhesion eventually straddles the ora serrata eccentrically. Intraretinal synthesis of collagen fibrils, their penetration of the ILL, and their splicing with cortical vitreous fibrils, underlie the slowly evolving retinovitreous adhesion.

Adhesiveness↗

PubMed2003

Multisampling suprathreshold perimetry: a comparison with conventional suprathreshold and full-threshold strategies by computer simulation.

PURPOSE: To compare a multisampling suprathreshold strategy with conventional suprathreshold and full-threshold strategies in detecting localized visual field defects and in quantifying the area of loss. METHODS: Probability theory was applied to examine various suprathreshold pass criteria (i.e., the number of stimuli that have to be seen for a test location to be classified as normal). A suprathreshold strategy that requires three seen or three missed stimuli per test location (multisampling suprathreshold) was selected for further investigation. Simulation was used to determine how the multisampling suprathreshold, conventional suprathreshold, and full-threshold strategies detect localized field loss. To determine the systematic error and variability in estimates of loss area, artificial fields were generated with clustered defects (0-25 field locations with 8- and 16-dB loss) and, for each condition, the number of test locations classified as defective (suprathreshold strategies) and with pattern deviation probability less than 5% (full-threshold strategy), was derived from 1000 simulated test results. RESULTS: The full-threshold and multisampling suprathreshold strategies had similar sensitivity to field loss. Both detected defects earlier than the conventional suprathreshold strategy. The pattern deviation probability analyses of full-threshold results underestimated the area of field loss. The conventional suprathreshold perimetry also underestimated the defect area. With multisampling suprathreshold perimetry, the estimates of defect area were less variable and exhibited lower systematic error. CONCLUSIONS: Multisampling suprathreshold paradigms may be a powerful alternative to other strategies of visual field testing. Clinical trials are needed to verify these findings.

Computer Simulation↗

PubMed2002

New developments in supra-threshold perimetry.

PURPOSE: To describe a series of recent enhancements to supra-threshold perimetry. METHODS: Computer simulations were used to develop an improved algorithm (HEART) for the setting of the supra-threshold test intensity at the beginning of a field test, and to evaluate the relationship between various pass/fail criteria and the test's performance (sensitivity and specificity) and how they compare with modern threshold perimetry. Data were collected in optometric practices to evaluate HEART and to assess how the patient's response times can be analysed to detect false positive response errors in visual field test results. RESULTS: The HEART algorithm shows improved performance (reduced between-eye differences) over current algorithms. A pass/fail criterion of '3 stimuli seen of 3-5 presentations' at each test location reduces test/retest variability and combines high sensitivity and specificity. A large percentage of false positive responses can be detected by comparing their latencies to the average response time of a patient. CONCLUSIONS: Optimised supra-threshold visual field tests can perform as well as modern threshold techniques. Such tests may be easier to perform for novice patients, compared with the more demanding threshold tests.

Aged↗

PubMed2002

Response time as a discriminator between true- and false-positive responses in suprathreshold perimetry.

PURPOSE: To report on differences between the latency distributions of responses to stimuli and to false-positive catch trials in suprathreshold perimetry. To describe an algorithm for defining response time windows and to report on its performance in discriminating between true- and false-positive responses on the basis of response time (RT). METHODS: A sample of 435 largely inexperienced patients underwent suprathreshold visual field examination on a perimeter that was modified to record RTs. Data were analyzed from 60,500 responses to suprathreshold stimuli and from 523 false-positive responses to catch trials. RESULTS: False-positive responses had much more variable latencies than responses to suprathreshold stimuli. An algorithm defining RT windows on the basis of z-transformed individual latency samples correctly identified more than 70% of false-positive responses to catch trials, whereas fewer than 3% of responses to suprathreshold stimuli were classified as false-positive responses. CONCLUSIONS: Latency analysis can be used to detect a substantial proportion of false-positive responses in suprathreshold perimetry. Rejection of such responses may increase the reliability of visual field screening by reducing variability and bias in a small but clinically important proportion of patients.

Adolescent↗