Biomedical subjects

E J Casson

Publications and source records attributed to E J Casson.

7 recordsLinked to original sources

PubMed1993

Blue-on-yellow perimetry can predict the development of glaucomatous visual field loss.

OBJECTIVE: The purpose of this investigation was to determine whether blue-on-yellow (B/Y) perimetry is capable of predicting the onset and location of impending glaucomatous visual field loss in patients with ocular hypertension. DESIGN: A Humphrey Field Analyzer (Humphrey Instruments, San Leandro, Calif) was modified to perform B/Y perimetry to isolate and measure the sensitivity of short-wavelength-sensitive mechanisms. Participants were tested annually with standard white-on-white (W/W) and B/Y automated perimetry for a period of 5 years. PATIENTS: The study population consisted of 38 patients with ocular hypertension and 62 age-matched normal control subjects. RESULTS: Initially, all 76 ocular hypertensive eyes had normal W/W automated perimetry results, with 67 eyes having normal and nine eyes having abnormal B/Y test results. Five years later, five of the nine ocular hypertensive eyes with initial B/Y abnormal results developed glaucomatous visual field loss measured by standard W/W automated perimetry, while none of the 67 ocular hypertensive eyes with initially normal B/Y results developed abnormal W/W perimetry results. CONCLUSIONS: Blue-on-yellow perimetry deficits are an early indicator of glaucomatous damage and are predictive of impending glaucomatous visual field loss for standard W/W automated perimetry. To our knowledge, this is the first prospective, long-term longitudinal study that demonstrates the ability to predict the onset of glaucomatous visual field loss in patients with ocular hypertension on the basis of psychophysical testing.

Adult↗

PubMed1993

Progression of early glaucomatous visual field loss as detected by blue-on-yellow and standard white-on-white automated perimetry.

OBJECTIVE: To determine whether blue-on-yellow perimetry reveals progression of glaucomatous damage before it is evident with standard white-on-white perimetry. DESIGN: A Humphrey field analyzer (Humphrey Instruments, San Leandro, Calif) was modified to perform blue-on-yellow perimetry to isolate and measure the sensitivity of short wavelength-sensitive mechanisms. Participants were tested annually with standard white-on-white automated perimetry and blue-on-yellow automated perimetry for 5 years. PATIENTS: Sixteen patients with early glaucomatous visual field loss in one or both eyes and 62 age-matched normal control subjects. RESULTS: At baseline, 25 (78.1%) of the 32 eyes exhibited larger deficits with blue-on-yellow perimetry, five (15.6%) had equivalent loss with both tests, and two (6.3%) had larger deficits with standard white-on-white perimetry. Seven (21.9%) of the 32 eyes demonstrated evidence of progressive visual field loss with standard white-on-white perimetry in 5 years, while the other 25 eyes (78.1%) were relatively stable. Deficits with blue-on-yellow perimetry were twice as large as deficits with white-on-white perimetry in the stable group and were three to four times as large in the group with progressive field loss. CONCLUSIONS: Blue-on-yellow perimetry is effective in predicting which patients with early glaucomatous visual field loss are most likely to have progressive loss. The rate of progressive loss is greater with blue-on-yellow perimetry than with standard white-on-white perimetry.

Adult↗

PubMed1993

Benzodiazepine effects on flicker sensitivity: role of stimulus frequency and size.

1. Benzodiazepines (BZDs) impair sensitivity to temporally modulated visual stimuli (flicker). Critical flicker-fusion frequency (CFF) is commonly used as a measure of this effect, but it only measures sensitivity to a narrow range of frequencies, usually above 25 Hz. Are other frequencies more sensitive to the effects of BZDs? 2. Flicker sensitivity at 1, 2, 4, 8, 16, and 32 Hz was measured for 1 degrees and 5 degrees stimuli before and 50 to 100 minutes after triazolam (0.25 mg), lorazepam (1.0 mg) and placebo. Drug effects on CFF were also measured. 3. Both BZDs significantly impaired overall flicker sensitivity. Triazolam produced 50% more impairment than lorazepam. CFF was significantly impaired by triazolam. BZD effects did not vary with stimulus size. 4. Significantly greater BZD-induced impairment of flicker sensitivity occurred at 16 Hz than at 1, 2, 4, or 32 Hz. 5. The magnitude of BZD effects on flicker sensitivity vary with the temporal frequency of the stimulus. BZD effects are greatest for 8-16 Hz stimuli.

Adult↗

PubMed1993

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.

Color Perception Tests↗

PubMed1993

Temporal modulation perimetry: the effects of aging and eccentricity on sensitivity in normals.

PURPOSE: Temporal modulation perimetry (TMP) is a new test procedure designed to measure sensitivity to sinusoidal flickering stimuli throughout the central 27 degrees visual field. The purpose of this investigation was to determine the effect of age and visual field eccentricity on temporal modulation sensitivity. METHOD: In its present form, TMP is used to determine modulation sensitivity for three temporal frequencies (2, 8, and 16 Hz) at 45 visual field locations. Both eyes of 43 normal observers between 20 and 75 years of age were examined. RESULTS: Our results indicate that sensitivity to all temporal frequencies tested showed a decline with age, particularly in the peripheral visual field. Furthermore, the age-related sensitivity loss was more pronounced for 16 Hz than for 2 or 8 Hz. CONCLUSIONS: These data demonstrate an age-related loss in temporal modulation sensitivity in the peripheral visual field. They also provide a baseline comparison standard for evaluation of clinical patient populations.

Adult↗

PubMed1990

Short-term fluctuation as an estimate of variability in visual field data.

The short-term fluctuation index (SF) is one of several values that provide an indication of a patient's response reliability during an automated perimetry examination. The authors investigated the number of visual field locations used and the number of determinations per location as factors affecting the SF estimate. A computer simulation program for perimetry was used to measure the SF index for 350 normal visual fields with various levels of response fluctuation. As expected, the variability of the SF estimate decreased as the number of locations used to estimate SF increased. There was a more important finding that, for an equal number of threshold estimates, a larger number of determinations at a smaller number of locations produced greater consistency in the SF estimate (eg, ten determinations at two locations instead of two determinations at ten locations). However, it is also important to sample from a representative spatial distribution of visual field locations. These results suggest that five determinations at four locations in the visual field is optimal for most clinical perimetric testing situations.

Computer Simulation↗

PubMed1984

Duration discrimination between weak test lights.

Maloney and Wandell [Vision Res. 24, 633-640 (1984)] describe a model of the response of a single visual channel to weak test signals. In the model an initial continuous visual response is randomly sampled, and each sample gives rise--with a probability that increases with the magnitude of the sample--to a discrete detection event. The authors derive a parameter-free prediction for the upper bound on the discriminability of two lights of different durations. In this paper we describe an experimental test of that prediction. We find that the model accurately distinguishes between discrimination performance under conditions where both test lights are detected by a single channel and conditions where the test lights are detected by different channels.

Discrimination, Psychological↗