Biomedical subjects

Brad Fortune

Publications and source records attributed to Brad Fortune.

22 records · Page 2Linked to original sources

PubMed2002

Immunohistologic evidence for retinal glial cell changes in human glaucoma.

PURPOSE: Glial cells are structurally and functionally linked to neuronal tissues. Pathologically, the cells may be activated and characterized by increased size and number and altered cellular properties. In glaucoma, pathologic mechanisms within the anterior optic nerve may include glial activation. This study examines morphologic changes of glial cells in the retinas of glaucomatous eyes compared with age-matched control retinas. METHODS: Paraffin-processed or flatmounted retinas from 17 human donor eyes [7 normal (donor age, 87.3 +/- 8.3 years) and 10 glaucomatous (donor age, 87.1 +/- 6.9 years)] were examined. With immunohistochemical methods, retinal glial cells were stained with an antibody to glial fibrillary acidic protein (GFAP). The morphology of the glial cells in normal and glaucomatous retinas was evaluated with fluorescence microscopy. RESULTS: Three types of glial cells were identified in flatmounted retinas with differing distributions in the peripapillary region, the nerve fiber layer (NFL), and along the capillaries. Compared with normal eyes, in glaucomatous retinas the glial cells in the peripapillary region showed an increase in density and exhibited a deformation of the end feet. The astrocytes distributed among the NFL showed little difference from normal. The astrocytes accompanying the capillary bed showed a redistribution in the glaucomatous retinas. The quantification of glial cells in paraffin-processed glaucomatous retinas exhibited a profound increase in density and a significant increase of GFAP immunoreactivity in contrast to the lightly stained glial cells in normal retinas. CONCLUSIONS: The activation of glial cells in the glaucomatous retina was characterized in changes of intensity of GFAP immunoreactivity and morphology around the larger blood vessels, compared with age-matched normal retinas. The relationships between glial cells, neuronal cells, and the vasculature, as well as the potential role of glial cells in pathologic mechanisms during different stages of neuronal damage in glaucoma, are discussed.

Aged↗

PubMed2002

Elevated vernier acuity thresholds in glaucoma.

PURPOSE: In 1993, Piltz et al. observed that foveal vernier acuity thresholds for achromatic targets are elevated in patients with glaucoma. This study was undertaken to explore whether such elevated thresholds are present when subject groups are measured with targets of effectively equivalent contrast. Vernier acuity measures were also obtained with short-wavelength and frequency-doubled stimuli, to assess spatial hyperacuity performance in the short-wavelength-sensitive and magnocellular pathways, respectively. METHODS: Twenty patients with glaucoma and 19 subjects with normal vision participated. All subjects had visual acuity of 20/25 or better. Achromatic two-dot vernier thresholds were obtained for 90% contrast dots. In addition, individual contrast thresholds to the achromatic dots were measured for each subject, and vernier thresholds were measured at 4, 8, 12, and 16 times contrast threshold. Short-wavelength vernier acuity thresholds were measured for blue dots presented on a bright yellow background. The stimulus for the frequency-doubling grating vernier acuity task was a 90% contrast, 1-cyc/deg, 25-Hz sinusoidal grating. RESULTS: The glaucoma group demonstrated significantly higher foveal vernier acuity thresholds than control subjects for the blue-on-yellow stimulus (P = 0.002) and frequency-doubling grating stimulus (P < 0.001). No significant difference in vernier acuity between groups was found for the 90% contrast achromatic dots (P = 0.09), however a significant difference was found for the normalized contrast targets (P = 0.04). CONCLUSIONS: Vernier acuity tasks can be used to demonstrate abnormal foveal function in glaucoma. Testing with visual-function-specific stimuli may be effective in identifying such dysfunction. Vernier acuity, or other similar hyperacuity tasks that assess spatial sampling, may be useful in the detection of early glaucomatous damage, before it is detected with traditional perimetric tests.

Aged↗

PubMed2002

Selective loss of an oscillatory component from temporal retinal multifocal ERG responses in glaucoma.

PURPOSE: To evaluate electrophysiologic function in glaucoma by using a new stimulus designed to enhance ganglion cell and optic nerve head component (ONHC) contributions to multifocal electroretinogram (mfERG) responses. METHODS: mfERGs of 16 individuals with glaucoma (POAG) and 18 normal control subjects were recorded and analyzed with a VER imaging system. The stimulus had three frames inserted between each m-sequence step: a full-field dark frame (1.0 cd/m(2)), a full-field flash (200 cd/m(2)), and another dark frame. Multifocal flashes were 100 cd/m(2). The stimulus subtended approximately 40 degrees total diameter and contained 103 scaled hexagonal elements. Signals were obtained using Burian-Allen bipolar electrodes, amplified x10(6), band-pass filtered at 10 to 300 Hz, and sampled at 1200 Hz. RESULTS: Local first-order responses (kernels) consisted of a direct component (DC) followed by an induced component (IC). Nasal-temporal response asymmetries in normal eyes were most easily observed in the IC. A small but distinct oscillation in the ICs of temporal retinal responses distinguished them from nasal IC waveforms. In individuals with glaucoma, there was less asymmetry between nasal and temporal responses, mostly because of the reduction of the oscillation in the temporal retinal ICs. The amplitude of this oscillation was 4.4 +/- 2.1 nV/deg(2) in the control group and 1.8 +/- 1.2 nV/deg(2) in the glaucoma group (P < 0.0001). Amplitude and latency measures of other response features were not significantly different from normal. Amplitude of the IC oscillation was not correlated with age in either the normal or glaucoma groups. In a group of normal subjects retested 3 months later, the average test-retest repeatability was +/-12%. CONCLUSIONS: Selective loss of an oscillatory feature from IC responses in glaucoma may represent abnormalities in the inner plexiform layer of the temporal retina, where classic oscillatory potentials (OPs) are thought to arise. However, evidence suggests that this effect may also be due in part to loss of the ONHC.

Adult↗

PubMedDate not supplied

Origin of electroretinogram amplitude growth during light adaptation in pigmented rats.

We assessed the growth of the rat photopic electroretinogram (ERG) during light adaptation and the mechanisms underlying this process. Full field ERG responses were recorded from anesthetized adult Brown-Norway rats at each minute for 20 min of light adaptation (backgrounds: 1.8, 2.1, 2.4 log scotopic cd m(-2)). The rat photopic b-wave amplitude increased with duration of light adaptation and its width at 33% maximal amplitude narrowed (by approximately 40 ms). These effects peaked 12-15 min after background onset. The narrowing of the b-wave reflected steepening of the b-wave recovery phase, with little change in the rising phase. OP amplitudes grew in proportion to the b-wave. Inhibition of inner retinal responses using TTX resulted in a greater relative growth of b-wave and OP amplitude compared with fellow control eyes, and delayed the change in recovery phase by approximately 5 min. Inhibition of all ionotropic glutamate receptors with CNQX/D-AP7 delayed both rising and recovery phases equally (approximately 12 ms) without altering b-wave width or the time course of adaptation changes. These outcomes suggest that inner retinal light responses are not directly responsible for b-wave amplitude growth, but may contribute to the change in its recovery phase during adaptation. A TTX-sensitive mechanism may help to hasten this process. The cone a-wave was isolated using PDA/L-AP4 or CNQX/L-AP4. A-wave amplitude (35 ms after stimulus onset) also increased with time during light adaptation and reached a maximum (130 +/- 29% above baseline) 12-15 min after background onset. B-wave amplitude growth in fellow control eyes closely followed the course and relative magnitude of cone a-wave amplitude growth. Hence, the increase of the cone response during light adaptation is sufficient to explain b-wave amplitude growth.

2-Amino-5-phosphonovalerate↗