Biomedical subjects

G L Trick

Publications and source records attributed to G L Trick.

At least 19 recordsLinked to original sources

PubMed2001

Optic disc topography in pseudopapilledema: a comparison to pseudotumor cerebri.

OBJECTIVES: To determine if confocal scanning laser (CSL) tomography can quantify optic disc topography in patients with pseudopapilledema (PP) and to contrast the regional topography of the optic disc in PP and pseudotumor cerebri (PTC). MATERIALS AND METHODS: Three-dimensional optic disc images from 10 PP patients PP and 17 PTC patients were obtained using the Heidelberg Retinal Tomograph (HRT). Two conventional HRT parameters, volume above the reference plane and volume above the surface, were used to quantify global disc elevation. In addition, local topography was determined at 100 microm intervals along eight meridians at 100 to 1700 microm from the disc center. The global and local measures of disc topography in the two groups were compared statistically. RESULTS: Significant between group differences were detected for both global measures. Regional analysis revealed vertical symmetry and horizontal asymmetry in PP and PTC as well as significant between group differences in peripapillary height. CONCLUSIONS: CSL tomography can quantify disc elevation in both PP and PTC and may be useful for differentiating disc morphology in PP and PTC. The volume of the disc above the retinal surface is greater in PTC than in PP. However, most of the difference in elevation between the two groups occurs over the disc rim and peripapillary retina.

Adolescent↗

PubMed1998

Quantitative evaluation of papilledema in pseudotumor cerebri.

PURPOSE: To determine the feasibility of adapting confocal scanning laser (CSL) tomography of the optic disc for quantitative evaluation of papilledema in pseudotumor cerebri (PTC). METHODS: Confocal scanning laser tomography of the optic disc was performed in 11 patients with diagnosed PTC and 12 visually normal control subjects of similar age. In five patients with active papilledema, CSL tomography was performed serially over several months. To quantify optic disc characteristics, surface topography was measured in 0.1-mm steps along the horizontal and vertical meridians and four oblique meridians. Best fit polynomial functions, describing surface topography along each meridian, were derived using linear regression analysis. RESULTS: Third-order polynomials provided excellent fits (significantly better than the second-order functions) to the surface topography for all meridians in the control subjects and patients with PTC. In control subjects and PTC patients an asymmetry in the slope of the optic disc contours was evident along the horizontal but not the vertical meridian. In patients with active papilledema a significant elevation of the center of the disc was accompanied by a change in overall surface topography. Each of the PTC patients followed up serially had a pronounced posterior deformation of the disc (i.e., a reduction in papilledema) that was initially apparent in the temporal meridian and did not proceed uniformly across all meridians. CONCLUSIONS: Confocal scanning laser tomography can quantify the magnitude and monitor the resolution of papilledema in PTC. Studies of optic nerve head topography may provide further insight into optic nerve compliance with elevated intracranial pressure.

Adult↗

PubMed1997

Pattern electroretinogram and spatial contrast sensitivity in primary congenital glaucoma.

OBJECTIVE: The authors investigated the temporal and spatial characteristics of pattern electroretinogram (PERG) and spatial contrast sensitivity (CS) in primary congenital glaucoma (PCG) to determine whether the PERG and CS could be useful tools in the diagnosis of childhood glaucoma, especially PCG. PARTICIPANTS: The PERGs were evaluated in eyes from ten patients with PCG and nine age-matched visually normal subjects. INTERVENTION: All patients received complete ophthalmologic evaluations including visual field testing. MAIN OUTCOME MEASURES: The PERGs were recorded using phase-alternating (2, 4, and 16 reversals per second [rps]) checkerboard patterns (30' and 60' checks). RESULTS: The patients with PCG exhibited decreased CS when compared with that of control subjects. Significant PERG deficits also were detected in these patients. However, PERG amplitude in patients with PCG almost reached control subject levels at high (16 rps) temporal frequency. This was true for both 30' and 60' checks. Taken together, these observations on PERG amplitude suggest a more important deficiency of the neural response of the retinal cells at lower temporal frequency (rps) in patients with PCG. This is unlike primary open-angle glaucoma (POAG) in which significant PERG deficits are observed at high temporal frequencies. CONCLUSIONS: The PERG amplitude is reduced in patients with PCG, and this is consistent with a loss of CS and visual field changes in these patients. However, the spatiotemporal characteristics of the PERG deficits in PCG differ from those of POAG. This could suggest a difference in the mechanisms mediating retinal ganglion cell dysfunction in the two types of glaucoma.

Adolescent↗

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↗