Biomedical subjects

G L Trick

Publications and source records attributed to G L Trick.

At least 19 recordsLinked to original sources

PubMed1996

Diabetes can alter the interpretation of visual dysfunction in ocular hypertension.

PURPOSE: The authors examined the influences of diabetes on the results of visual function testing in patients with ocular hypertension (OHT). METHODS: Color vision (desaturated D-15), contrast sensitivity together with both transient and steady-state pattern electroretinogram (PERG) findings from patients with documented OHT were examined in a historic cohort study. All patients were examined at least four times (mean, 7.8 examinations) during a follow-up period that ranged from 1.5 to 4 years. Only individuals who maintained normal visual fields throughout the follow-up period were included in this analysis. The sample included 158 patients with OHT. Of these patients, 32 were African-American and 23 had a history of noninsulin-dependent diabetes with no evidence of retinopathy (by ophthalmoscopy). Normative data were obtained from a control group that included 65 white subjects with normal vision who did not have diabetes and who were similar in age to the patients in the OHT group. RESULTS: Color vision, contrast sensitivity, and PERG results were reduced significantly in patients with diabetes and OHT relative to control subjects. Patients with OHT who did not have diabetes did not have similar abnormalities. Color vision and PERG results also were reduced significantly in patients with diabetes and OHT relative to those with OHT who did not have diabetes. Only the steady-state PERG was reduced in African-American patients with OHT (relative to both control subjects and white patients with OHT). CONCLUSIONS: Patients with diabetes and OHT have significantly greater color vision, contrast sensitivity and PERG abnormalities than patients with OHT without diabetes. Race factors do not play a major role in these differences. Screening for diabetes is recommended before drawing conclusions from the results of these types of functional tests in patients with OHT.

Black People↗

PubMed1996

Pattern electroretinograms and visual evoked potentials in HIV infection: evidence of asymptomatic retinal and postretinal impairment in the absence of infectious retinopathy.

Retinal microangiopathy associated with HIV infection is usually asymptomatic and escapes detection unless funduscopic examination is performed when evanescent cotton-wool spots are present. The aim of this study was to assess retinal and optic nerve/retrochiasmal function in HIV infection by means of electrophysiologic techniques that are sensitive to the detection of subclinical visual impairment. We studied transient and steady state pattern electroretinograms grams (PERGs) and pattern-reversal visual evoked potentials (PVEPs) in 21 HIV-negative controls and 33 HIV-positive subjects (16 with CD4 > or = 200/mL and 17 with CD4 < 200/mL) without visual symptoms or infectious retinopathy. HIV-positive subjects with CD4 > or = 200/mL had reduced amplitude of the transient PERG P1 potential, but no other latency or amplitude abnormalities. The HIV-positive group with CD4 < 200/mL had reduced P1 transient PERG amplitude, as well as latency delay of the transient PVEP. These findings suggest that HIV infection is associated with subclinical retinopathy and that, when severe immunosuppression occurs, both retinopathy and optic nerve/retrochiasmal dysfunction are present. Transient PERGs are more sensitive measures of visual system disease in HIV infection than are steady state responses.

Adolescent↗

PubMed1995

Motion perception deficits in glaucomatous optic neuropathy.

The mechanisms mediating impaired motion perception in glaucoma were investigated. Direction discrimination thresholds for low (4.2 deg/sec) and high (12.5 deg/sec) velocity random-dot kinematograms were measured in controls and patients with glaucoma or ocular hypertension. Thresholds were elevated significantly in glaucoma patients and individual ocular hypertensives. Threshold elevations were not due to blur or pupil size. After compensating for motion reversals, high but not low velocity thresholds remained elevated. Only high velocity thresholds correlated with differential luminance sensitivity. A hypothesis that different mechanisms mediate glaucoma-induced deficits at high and low velocities is presented.

Adult↗

PubMed1995

Topography of the age-related decline in motion sensitivity.

PURPOSE: We examined whether the decline in motion sensitivity in the elderly is equivalent for different visual field locations. METHODS: High velocity (28 degrees/s) random dot kinematograms (RDK's) were used to measure direction discrimination thresholds for 5 locations in the visual field (1 position centered on fixation and 4 locations each centered 18 degrees from fixation in the nasal, temporal, superior, and inferior quadrants). Differential luminance sensitivity was assessed by automated perimetry. Younger (N = 15, mean age = 22.9 +/- 1.3 years) and older (N = 13, mean age = 66.6 +/- 4.5 years) subjects were studied. RESULTS: Motion sensitivity varied with test location for both younger and older subjects, but sensitivity was significantly lower in older individuals. The largest age-related reduction in sensitivity was in the central location, whereas the smallest decline was in the superior position. No significant correlations between motion and differential luminance sensitivity were evident. CONCLUSIONS: There is a significant age-related deterioration in visual sensitivity to motion which is more pronounced in the central visual field than in some regions of the more peripheral field. Although both motion and differential luminance sensitivity decrease with age, the rate and the magnitude of the loss differ for these two visual functions.

Adult↗

PubMed1995

Visual field loss in senile dementia of the Alzheimer's type.

BACKGROUND: Visual performance is impaired in patients with senile dementia of the Alzheimer's type (SDAT). We investigated the visual field topography of these deficits. METHODS: Humphrey automated perimetry (Program 30-2) was used to measure differential luminance sensitivity within the central 60 degrees of the visual field in SDAT patients (n = 61) and in visually and cognitively normal volunteer subjects of similar age (n = 61). Twenty-three SDAT patients were retested 18 months after the original examination. RESULTS: Reliable visual fields (by manufacturer's criteria) were obtained in 72.1% (44/61) of the control subjects and 55.7% (34/61) of the SDAT group. In the SDAT group, differential luminance sensitivity was significantly reduced relative to the control group. Visual sensitivity was reduced throughout the visual field, but deficits were most pronounced in the inferior visual field, where they presented most commonly as arcuate defects. Patients with more severe dementia exhibited greater reductions in visual sensitivity. On follow-up, 14 of 23 SDAT patients exhibited progression of visual field loss, whereas only two of 23 patients exhibited a regression of the visual field loss. CONCLUSIONS: Although automated perimetry requires considerable patient cooperation, many patients with SDAT can produce reliable visual field results. These patients exhibit significant reductions in global sensitivity. Visual field loss in SDAT is most pronounced in the inferonasal and inferotemporal arcuate regions of the visual field but also involves the central field.

Aged↗

PubMed1994

Visual impairment in Parkinson's disease: deficits in orientation and motion discrimination.

PURPOSE: In order to obtain a better understanding of the pathophysiology of visual impairment in Parkinson's disease (PD), orientation and motion discrimination were investigated in PD patients. METHODS: Orientation and motion discrimination thresholds were assessed psychophysically in PD patients with normal cognition (N = 11) and compared to results for age-matched controls (N = 22). RESULTS: PD patients exhibited a significant deficit in orientation discrimination for horizontal but not for vertical gratings. Also, motion discrimination thresholds were elevated significantly in PD patients. No significant correlations were found between motion and orientation discrimination thresholds. CONCLUSIONS: Our results indicate that PD patients exhibit significant visual dysfunction in the absence of cognitive impairment supporting the contention that neural dysfunction in PD is more generalized than previously realized. The results provide further evidence of an orientation selective visual deficit in PD and show that the ability to discriminate global motion is also attenuated in PD.

Aged↗

PubMed1994

A sensory explanation for visual attention deficits in the elderly.

BACKGROUND: Reduced visual attention has been implicated as a major factor in age-related deficits of real-world functioning such as driving. However, the contribution of sensory factors to visual attention deficits has not been delineated. The magnocellular stream, which is diminished in aging, provides the dominant input to attention, and could provide a direct visual sensory explanation for these attentional losses. METHODS: We measured temporal response curves for transient visual attention in older and younger subjects. Attentional cues stimulated both the magnocellular and parvocellular streams. RESULTS: Older subjects exhibited slower, weaker responses than younger subjects. The time course in younger subjects agreed with that obtained for magnocellular(M)-biased stimuli, whereas that of older subjects agreed with parvocellular(P)-biased responses. CONCLUSIONS: The activation of transient visual attention is slower and weaker for elderly subjects, reflecting a reduced magnocellular input. This marks a primary visual cause for visual attention deficits of the elderly.

Adult↗

PubMed1993

Visual dysfunction in normotensive glaucoma.

Color vision (desaturated D-15), contrast sensitivity (Vistech 6500) and pattern electroretinograms (transient and steady state) were measured in nine patients with diagnosed normotensive glaucoma. Results were compared to those from visually normal controls subjects (n = 73) and patients with primary open-angle glaucoma (n = 51). Patients with normotensive glaucoma exhibited significant contrast sensitivity and pattern electroretinogram deficits similar to those evident in patients with primary open-angle glaucoma. However, patients with normotensive glaucoma exhibited significantly better color vision than did patients with primary open-angle glaucoma. These results indicate that the pattern of visual impairment associated normotensive glaucoma and primary open-angle glaucoma is not identical. Different pathologic mechanisms mediating visual loss in the two diseases could explain these differences.

Aged↗

PubMed1992

The human pattern ERG: alteration of response properties with aging.

The influence of aging on both the amplitude and the latency of transient and steady-state pattern electroretinograms (PERG's) was studied in 80 healthy participants ranging from 25 to 77 years of age (mean age, 55.3 years). Responses to counterphasing checkerboard patterns were recorded for each of 7 test conditions in which the spatial (i.e., check sizes 0.25, 0.50, 1.00, and 2.00 degrees) and temporal characteristics (i.e., counterphasing at either 2, 4, 8, or 16 rps) of the stimuli were varied. For both the transient and steady-state PERG's amplitude was inversely related to age (p less than 0.05 for each test condition). In general, PERG latency directly correlated with age, but this effect was less robust (p less than 0.05 for one transient condition and three of the four steady-state conditions). The influence of age on the spatial tuning of the PERG was minimal; the decrease in PERG amplitude and the increase in PERG latency as a function of age were essentially the same for all test conditions. However, the magnitude of the age-related reduction in PERG amplitude was observed to vary with temporal frequency, being largest for the steady-state condition (16 rps). The results from an experiment in which young subjects were tested while wearing opaque contact lenses with 2-mm artificial pupils suggest that senile miosis is a significant factor contributing to the age-related PERG amplitude and latency changes, but it does not fully account for the observed changes.

Adult↗

PubMed1991

The pattern electroretinogram in retinal and optic nerve disease. A quantitative comparison of the pattern of visual dysfunction.

A retrospective analysis was performed on the transient and steady-state pattern electroretinograms recorded from 42 patients with glaucoma, 13 patients with senile dementia of the Alzheimer's type, 58 patients with diabetes mellitus, and 92 control subjects to evaluate the pattern of electroretinographic changes associated with retinal and optic nerve disease. The amplitudes of both the initial positive component (N1 to P1) and the subsequent negative component (P1 to N2) of the transient (4 rps) responses were measured. From these measurements the (P1 to N2)/(N1 to P1) was derived. The N1 to P1 amplitude of the steady-state pattern electroretinogram also was measured. In the glaucoma patients all three amplitude measures, as well as the amplitude ratio of the components of the transient response, were reduced significantly compared with age-matched controls (p less than 0.05). A similar pattern was detected in the patients with Alzheimer's disease, but in this case the only statistically significant amplitude reduction was in the steady-state pattern electroretinogram. A different pattern was observed among the diabetic patients (both with and without retinopathy). Only minor reductions in the amplitude of the transient pattern electroretinogram, which were not statistically significant, were noted. In addition, the ratio of the amplitudes of the components of the transient response did not differ from age-matched controls. The amplitude of the steady-state pattern electroretinogram was reduced in diabetics, but this was significant only for those patients with retinopathy (p less than 0.01). These findings support the suggestion that an analysis of both the positive and negative components of the pattern electroretinogram may be useful for differentiating the contributions of retinal and optic nerve dysfunction to visual impairment. The results also indicate that in both retinal and optic nerve disease the steady-state pattern electroretinogram can be an earlier sign of dysfunction than the transient pattern electroretinogram.

Adult↗

PubMed1991

Visual sensitivity to motion: age-related changes and deficits in senile dementia of the Alzheimer type.

To determine whether motion sensitivity varies with age, we measured motion discrimination in visual normals 25 to 80 years of age and found that motion thresholds increased linearly with age and were approximately two times higher in those 70 to 80 years old than in participants under thirty. This increase was not attributable to pupil size or retinal image distortion, but probably reflects neurodegeneration in the primary visual pathway. We compared the motion sensitivity of patients with senile dementia of the Alzheimer type (SDAT) with results from a subset of the visual normals of similar age. In SDAT patients, there were significant threshold elevations, which were more pronounced in the patients with more severe dementia. These findings confirm previous reports of visual system involvement in SDAT and indicate motion testing may reveal preclinical visual system involvement in SDAT.

Adult↗

PubMed1990

Steady-state pattern electroretinogram following long term unilateral administration of timolol to ocular hypertensive subjects.

To determine whether long-term reduction of intraocular pressure leads to a corresponding preservation of the pattern electroretinogram (PERG), PERGs were studied in 21 patients with ocular hypertension who had received unilateral timolol therapy for a minimum of 6 years. The mean difference in intraocular pressure (IOP) between the placebo-treated and the timolol-treated eyes (over 6 years) was 2.4 mm Hg. Steady-state PERGs (16.0 rps) were obtained simultaneously in both eyes of each patient, with four check sizes (0.25, 0.5, 1.0 and 2.0 degrees). Significant (p less than 0.05) steady-state PERG deficits (i.e., amplitude more than two standard deviations below the mean value of age-matched controls) were observed in 16 eyes of 12 patients (10 placebo-treated and 6 timolol-treated eyes). The mean PERG amplitude did not differ significantly between the placebo-treated and timolol-treated eyes. However, a significant correlation (r = -0.423) in the IOP differences between the placebo-treated and timolol-treated eyes and the corresponding PERG amplitude differences was noted in three of the four test conditions (i.e. 0.25, 0.5, and 1.0 degrees). These results suggest that reducing IOP may preserve ganglion cell function in some patients with ocular hypertension.

Aged↗

PubMed1990

Visual field defects in patients with insulin-dependent and noninsulin-dependent diabetes.

Automated perimetry (Humphrey 30-2) was used to quantitate visual field sensitivity in diabetic patients with either little or no retinopathy (n = 38) or mild background diabetic retinopathy (n = 19) and in visually normal controls (n = 40). Foveal thresholds were unaffected in the diabetic patients but significant reductions in visual field sensitivity, measured by both the mean deviation and the pattern standard deviation indices of visual field sensitivity, were observed in the diabetic patients. Subgroup analyses showed that this sensitivity reduction primarily occurred in noninsulin-dependent diabetic patients. Among the diabetic patients, 26.3% of the visual fields were flagged as "probably abnormal." This percentage was greatest among the noninsulin-dependent patients with mild background diabetic retinopathy (72.3%). The sensitivity reductions observed in the noninsulin-dependent patients with mild background diabetic retinopathy tended to be localized in the superior quadrants and correlated with the extent of retinal vascular compromise evident from vitreous fluorophotometry (r = 0.603). These findings imply that in diabetic patients visual field defects (1) often can be detected in patients with at most moderate retinopathy, (2) occur more frequently in noninsulin-dependent patients than in insulin-dependent patients, and (3) may result from subclinical microangiopathy.

Adult↗

PubMed1990

Glaucomatous visual field damage. Luminance and color-contrast sensitivities.

Using a modified Humphrey perimeter, we evaluated 16 eyes with primary open-angle glaucoma and visual field loss (defects 0.5-3.0 log units in depth), and 14 normal eyes. Each eye was tested twice in random order with conventional luminance-increment static perimetry and with the perimeter modified to produce a high-luminance yellow adapting background and a blue test stimulus. The background was a broad-spectrum light of 500 nm and above (yellow), while the stimulus was a broad-spectrum light of 500 nm and below (blue). Paired comparisons were made between conventional and blue/yellow sensitivities for every point examined (1184 points in 16 diseased eyes and 1036 points in 14 normal eyes). Defect depths were determined by using the age-corrected norms distributed in the Humphrey Statpac software. In glaucomatous eyes, blue/yellow sensitivity showed greater impairment than did conventional perimetric sensitivity, in which defect depths were less than 1.0 log unit. However, for defects greater than 1.0 log unit in depth, conventional perimetric sensitivity and blue/yellow sensitivity showed equivalent degrees of damage. Receiver operating characteristic (ROC) analysis was used to compare the ability of blue/yellow and of conventional perimetry in distinguishing between glaucomatous and normal eyes. Results indicated that although blue/yellow color-contrast perimetry may be more sensitive for the detection of incipient glaucomatous damage, in the manifest stages of visual field damage blue/yellow color-contrast perimetry is no more sensitive than is conventional (luminance-increment) perimetry for defining the extent of glaucomatous visual field defects.

Adult↗

PubMed1990

The relationship of retrobulbar hematomas to vision in cynomolgus monkeys.

An experimental model has been developed to measure the effect of retrobulbar hematomas on functional vision in cynomolgus monkeys. In this model, functional vision was quantitated using flashed evoked visual potentials in five monkeys following creation of retrobulbar hematomas. In one monkey used as a control, functional vision remained impaired for 180 minutes following induction of retinal ischemia by increased intraorbital pressure. In two monkeys in which increased intraorbital pressure was relieved by anterior chamber paracentesis following 15 minutes of retinal ischemia, flashed evoked visual potential promptly returned to baseline level. In two additional monkeys in which increased intraorbital pressure was relieved following 30 minutes of retinal ischemia, flashed evoked visual potentials improved but never returned to baseline levels. This study demonstrates the usefulness of flashed evoked visual potentials in measuring functional vision in cynomolgus monkeys. This experimental model should prove useful in evaluating the effects of increased intraorbital pressure on functional vision and the effect of intervention on impaired vision due to retrobulbar hematomas. Further studies with larger numbers of animals are needed to clarify these preliminary studies and document longer-term effects of retinal ischemia secondary to retrobulbar hematomas.

Animals↗

PubMed1990

Motion perception is abnormal in primary open-angle glaucoma and ocular hypertension.

Several lines of evidence suggest that the large optic nerve fibers, which form the magnocellular retinocortical pathway, are preferentially susceptible to early glaucomatous damage. It is evident from studies of the functional architecture of the visual system that the magnocellular pathway underlies the global perception of motion. Therefore, we have developed a psychophysical technique for assessing motion detection thresholds in patients with ocular hypertension (OHT) and primary open-angle glaucoma (POAG). For this purpose we employed a dynamic random dot display that contained varying degrees of a coherent motion signal embedded within a background of random motion noise. We used this technique to measure motion thresholds in POAG patients (n = 37), OHT patients (n = 14), and age-matched controls (n = 39). Motion thresholds were elevated by 70% for the POAG group and 44% for the OHT group relative to controls. In the same patients, no significant deficit in form discrimination was found as measured by Pelli-Robson charts. Our results demonstrate that significant motion perception deficits are evident in POAG and OHT. These findings support the suggestion that significant and selective damage to the magnocellular pathway occurs in OHT and POAG and indicate that motion threshold testing may reveal preclinical optic nerve disease in early POAG.

Contrast Sensitivity↗

PubMed1989

Abnormal pattern electroretinograms in patients with senile dementia of the Alzheimer type.

Patients with senile dementia of the Alzheimer type frequently have difficulty performing visual tasks. These difficulties may be due, at least partially, to degenerative changes in both the primary visual pathway and the visual association areas. To determine whether retinal ganglion cell dysfunction contributes to visual loss in senile dementia of the Alzheimer type, we tested a group of patients with this disease (n = 13) using the pattern-reversal electroretinogram to both low (4.0 reversals per second) and high (16.0 reversals per second) temporal frequency checkerboard patterns (1.0 degree checks). Significant amplitude reductions were noted for the patients relative to age-matched control subjects (n = 30). In addition, the observed amplitude reductions were most pronounced for the high temporal frequency condition. Therefore, the results are consistent with retinal ganglion cell dysfunction and support the notion that optic nerve damage induced by senile dementia of the Alzheimer type preferentially affects the larger, faster-conducting retinal ganglion cells along with their retinocortical projections.

Aged↗

PubMed1989

Assessing the utility of reliability indices for automated visual fields. Testing ocular hypertensives.

Monocular (right eye) visual fields were recorded with the Humphrey Visual Field Analyzer (30-2 Program) at baseline as well as 6 and 12 months later in 120 patients with established ocular hypertension. Indices of field reliability (fixation loss, less than 20%; false-positives and false-negatives, less than 33%) and field sensitivity (mean deviation [MD] and pattern standard deviation [PSD]) were examined. At baseline, 35% of patients exhibited low reliability (LR) fields, a figure which decreased to approximately 25% at 6 and 12 months, respectively. During this period, over 50% of patients produced at least one LR field, whereas 8.3% were unable to produce even one reliable field. Exhibition of a LR field appeared to be independent of patient age. Fixation errors, the major cause of LR fields, decreased by approximately 10% over the 12-month period; most patients had between 20 and 32% fixation errors. The incidence of significant defects identified by PSD was greater than that for MD; this was true for both reliable and LR fields. It is suggested that increasing the fixation loss criteria for assessing patient reliability to a 33% cutoff might substantially increase the percentage of fields graded reliable with minimal effect on the sensitivity or specificity of the test.

Adult↗