Biomedical subjects

T A McCormick

Publications and source records attributed to T A McCormick.

11 recordsLinked to original sources

PubMed2000

Intraocular pressure and progression of glaucomatous visual field loss.

PURPOSE: To evaluate the relationship between intraocular pressure and visual field progression in patients with primary open-angle glaucoma. METHODS: We prospectively followed 113 patients with early to moderate glaucomatous field damage. Conventional automated static perimetry, high-pass resolution perimetry, and intraocular pressure measurements were carried out at 6-month intervals. The mean and the highest intraocular pressure in the follow-up were compared in stable and progressing patients with each perimetric technique. RESULTS: The mean (+/- SD) follow-up was 4.5 +/- 0.9 years. The mean (+/- SD) intraocular pressure in patients remaining stable with conventional perimetry [18.2 +/- 3.3 mm Hg, n = 81 (71.7%)] was not significantly different (P =.65) from those in whom it progressed (17.9 +/- 3.3 mm Hg, n = 32 [28.3%]). The mean intraocular pressure in patients remaining stable with high-pass resolution perimetry (17. 9 +/- 3.5 mm Hg, n = 63 [55.8%]) was not significantly different (P =.33) from those in whom it progressed (18.5 +/- 3.0 mm Hg, n = 50 [44.2%]). The mean (+/- SD) of the highest (single or three highest) pressure during follow-up for stable and progressing patients with conventional perimetry was not significantly different (22.6 +/- 5.0 and 23.0 +/- 4.6 mm Hg, respectively, P =.76). However, for high-pass resolution perimetry, the difference was highly significant (21.6 +/- 4.5 and 24.1 +/- 4.9 mm Hg, respectively, P <. 01). Furthermore, patients who progressed with high-pass resolution perimetry had more damaged baseline fields compared with those who remained stable (P <.01). CONCLUSIONS: The mean level of intraocular pressure does not differentiate glaucoma patients with progressive visual field loss from ones who remained stable. Baseline visual field status and peak intraocular pressure of patients who progress with high-pass resolution perimetry are significantly different from those who remain stable.

Adolescent↗

PubMed1999

Comparison of conventional and high-pass resolution perimetry in a prospective study of patients with glaucoma and healthy controls.

OBJECTIVE: To determine whether high-pass resolution perimetry detected glaucomatous visual field progression earlier than conventional perimetry. METHODS: In a prospective longitudinal study, we observed 113 patients with open-angle glaucoma and with early to moderate visual field damage and 119 healthy control subjects. Each subject underwent testing at 6-month intervals using conventional and high-pass resolution perimetry (program 30-2 of the Humphrey Field Analyzer [Humphrey Instruments, Inc, San Leandro, Calif] and the Ring program of the Ophthimus perimeter [Hi-Tech Vision, Göteborg, Sweden], respectively). Our predetermined criterion for progression with conventional perimetry was the presence of at least 4 overlapping nonedge locations outside the fifth percentile for test-retest variability of threshold deviations (defined by the Glaucoma Change Probability Analysis of the Statpac 2 program) in 2 of 3 consecutive visual fields. We employed the identical criterion for progression with high-pass resolution perimetry using our own test-retest variability data. We repeated this procedure in the controls to measure the false-positive rate of progression. RESULTS: Patients were observed for a median of 4.5 years and 11 examinations with each technique. Fifty-seven patients (50.4%) did not show progression with either technique. Twenty-four patients (21.2%) showed progression with high-pass resolution perimetry alone, whereas 6 (5.3%) showed progression with conventional perimetry alone. Of the remaining 26 patients (23.0%) who showed progression with both techniques, 14 (54%) showed progression with high-pass resolution perimetry first (median, 12 months earlier); 5 (19%), with conventional perimetry first (median, 6 months earlier); and 7 (27%), with both techniques at the same time. Controls were observed for a median of 5 years and 11 examinations with each technique. One control (0.8%) showed progression with high-pass resolution perimetry. CONCLUSIONS: Our results suggest that high-pass resolution perimetry detects glaucomatous visual field progression earlier than conventional perimetry in most patients with progression.

Adolescent↗

PubMed1997

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.

Adolescent↗

PubMed1997

Intra- and interrater agreement with cumulative defect curves.

PURPOSE: To examine intra- and interrater agreement when analyzing cumulative defect curves. Cumulative defect (Bebié) curves provide a graphical representation of the visual field and allow a subjective classification of diffuse and localized loss. METHODS: We used 75 Humphrey 30-2 visual field tests, randomly chosen from a database of 782 fields of 113 patients with open-angle glaucoma. Cumulative defect curves were generated and randomly arranged into five sets, with each set containing the 75 curves in a unique sequence. Five raters (two experienced and three inexperienced) rated each set and classified each curve as showing diffuse loss, localized loss, both diffuse and localized loss, or no loss. The intra- and interrater agreement in rating the curves was then analyzed. RESULTS: Intrarater agreement ranged from 73.3-88.0% for perfect rater agreement, with 5 identical ratings. Agreement for experienced versus inexperienced raters gave similar results (means: 84.0% and 77.8%, respectively, for perfect agreement). Interrater agreement for each set, evaluated by the kappa statistic, was substantial for all 5 sets (0.65-0.71). Kappa values for each set were comparable for experienced and inexperienced raters (0.72-0.83 and 0.59-0.69 respectively). CONCLUSIONS: Analyzing the nature of visual field loss using the cumulative defect curve is simple to learn and provides high intrarater agreement as well as substantial interrater agreement.

Glaucoma, Open-Angle↗

PubMed1995

Effect of the cardiac cycle on topographic measurements using confocal scanning laser tomography.

BACKGROUND: This study was carried out to investigate the effect of the cardiac cycle on topographic measurements of the optic nerve head and peripapillary retina with confocal scanning laser tomography. METHODS: The sample comprised 25 healthy subjects (mean age 40.44 years, range 23-67 years). Using a random crossover design, we obtained a set of three images using the Heidelberg Retina Tomograph (Heidelberg Engineering GmbH, Heidelberg, Germany) under each of two conditions. In the first, the images were obtained normally, while in the second, image acquisition was pulse-synchronised using an electrocardiographic signal. We compared the variability of topographic measurements under the two conditions in the whole image, in the optic nerve head and in the peripapillary retina free of visible vessels. RESULTS: Nineteen subjects (76%) showed a decrease in variability in the whole image under the pulse-synchronised condition. The respective numbers for the optic nerve head and peripapillary retina were 20 (80%) and 21 (84%). The decrease in variability ranged widely, with a mean of 13.62% in the whole image, 12.26% in the optic nerve head and 18.51% in the peripapillary retina. These decreases were highly significant. There was no relationship between the decrease in variability and age, intraocular pressure, blood pressure, heart rate or the area of the image occupied by blood vessels. CONCLUSION: Detecting structural change depends on the accurate assessment of each subject's variability. Because the cardiac cycle confounds this assessment by varying and unpredictable amounts, it may be necessary to obtain pulse-synchronised images routinely.

Adult↗

PubMed1994

Test-retest variability of topographic measurements with confocal scanning laser tomography in patients with glaucoma and control subjects.

Using confocal scanning laser tomography, we studied the test-retest variability of topographic measurements of the optic nerve head and parapapillary retina in 30 patients with glaucoma and 30 normal control subjects. We obtained three independent images, separated by between one and six hours, centered on the optic nerve head. We condensed each original 256 x 256-pixel image to a 64 x 64-pixel image, thereby allowing a realistic estimate of the empiric 90% confidence interval of testretest variability at each condensed pixel. Confidence interval maps generated for each subject showed highest measurement variability along the cup border and blood vessels. The mean standard deviation equivalents of test-retest variability in the patients and controls were 31.20 and 25.94 microns, respectively. These differences were statistically significant (P = .010). Variability increased with age (P < .001). When the analysis was repeated for discrete parapapillary areas, the group differences were not statistically significant (P = .100).

Adult↗

PubMed1993

Comparison of reliability indices in conventional and high-pass resolution perimetry.

PURPOSE: The purpose of this study is to compare reliability indices in conventional (Humphrey) and high-pass resolution (Ring) perimetry in healthy subjects followed prospectively at 6-month intervals. METHODS: Of the 146 healthy subjects (mean age, 50.24 years; range, 30-84 years) enrolled in the study, 102 have been tested twice and 71 three times. The authors compared the reliability indices, fixation losses, false-positive rate, and false-negative rate between the two techniques, both cross-sectionally and serially. RESULTS: Fixation losses were slightly higher with high-pass resolution perimetry, whereas false-positive errors were higher with conventional perimetry. False-negative errors were uncommon with either technique. Of 319 fields, 30 (9.4%) conventional and 39 (12.2%) high-pass resolution perimetry fields were unreliable using the current suggested reliability criteria. Nearly all unreliable fields were due to high fixation errors. Using alternative criteria derived from baseline 95th percentile values, unreliable fields were attributed more equally to all three reliability parameters. In subjects tested three times, the reliability indices remained constant. CONCLUSION: The results of this study showed that healthy subjects have comparable reliability indices when tested with conventional and high-pass resolution perimetry.

Adult↗

PubMed1993

Characteristics of frequency-of-seeing curves in normal subjects, patients with suspected glaucoma, and patients with glaucoma.

PURPOSE: The authors performed this study to determine factors that affect the characteristics of frequency-of-seeing curves in normal subjects, patients with suspected glaucoma, and patients with glaucoma. METHODS: The sample consisted of 70 subjects (22 normal subjects, 12 patients with suspected glaucoma, and 36 patients with glaucoma). A program was written to interface with the Humphrey Field Analyzer (Humphrey Instruments, San Leandro, CA) to measure frequency-of-seeing curves. The authors presented stimuli 8 dB either side of the estimated threshold in 1-dB intervals with five repetitions at each stimulus intensity. The authors tested four to six locations in each subject, with randomization of the stimulus intensity and location. Fixation was monitored with the Heijl-Krakau method. Using a probit program, the authors calculated the threshold and slope (estimated by the interquartile range) of each curve. RESULTS: The authors obtained 124 curves from the normal subjects, 71 from the patients with suspected glaucoma, and 183 from the patients with glaucoma. In all three groups, the slope of the frequency-of-seeing curve was correlated highly with the threshold or threshold deviation, although the correlation was significantly higher in the normal subjects compared with the patients with suspected glaucoma and patients with glaucoma, even after controlling for the range of the threshold and threshold deviation. For this reason, the authors found considerably different frequency-of-seeing curves, between subject groups and also within the group of patients with glaucoma, in locations with the same threshold. CONCLUSIONS: There may be fundamental differences in areas of normal subjects and patients with glaucoma with similar thresholds or threshold deviations. These differences also may exist within patients with glaucoma.

Adult↗

PubMed1993

Comparison of high-pass resolution perimetry and pattern discrimination perimetry to conventional perimetry in glaucoma.

We compared two new perimetric techniques, high-pass resolution perimetry and pattern discrimination perimetry, to conventional automated static perimetry in an ongoing prospective study. Forty-eight patients with open-angle glaucoma whose median age was 63.4 (range 15.6 to 89.7) years were included in the study. There was a significant correlation between the results obtained with high-pass resolution perimetry and conventional perimetry for both the whole field and the four quadrants (p < 0.001). However, the correlation between pattern discrimination perimetry and conventional perimetry was poor. The differences between the correlations of the newer techniques with conventional perimetry were statistically significant for the whole field and the superior quadrants (p < 0.01) and were borderline significant for the inferior quadrants. Although the three techniques showed very good concordance in both the extent and location of damage of the visual field in some patients, in others it was poor. Our results show that high-pass resolution perimetry and pattern discrimination perimetry may be measuring different components of the visual response.

Adolescent↗

PubMed1993

Correlation between the optic disc and results obtained with conventional, high-pass resolution and pattern discrimination perimetry in glaucoma.

The purpose of this study was to determine whether results obtained with two new techniques, high-pass resolution perimetry and pattern discrimination perimetry, correlated better to the appearance of the optic disc than results obtained with conventional automated perimetry in patients with open-angle glaucoma. Our sample consisted of 28 eyes of 28 patients with early glaucomatous field damage who are part of a prospective follow-up study. We used the second of two sets of baseline perimetric examinations separated by 1 week in the analysis. Neuroretinal rim area was calculated by planimetry of stereophotographs of the disc and was correlated to the visual field sensitivity measured with each of the techniques. We found a poor correlation between the disc and field measurements (correlation coefficients; -0.048 for conventional perimetry, 0.111 for high-pass resolution perimetry and -0.315 for pattern discrimination perimetry). Although the correlation appeared to be higher with the newer techniques, the differences were not statistically significant.

Adolescent↗

PubMed1990

Comprehension of concrete and abstract words in autistic children.

This study employed the Stroop paradigm to examine comprehension of single words in autistic children. The words of interest varied along a concrete-abstract dimension. In the Stroop paradigm, subjects are asked to name the color of ink in which color words are printed. Comprehension is indexed by the degree to which the automatic processing of words interferes with the color-naming task. For both concrete and abstract words, autistic children showed the same degree of interference as reading-matched controls. The findings corroborate and extend previous work suggesting that autistic children understand, and by implication, can mentally represent, at least some word meanings.

Adolescent↗