Biomedical subjects

G R Dunkelberger

Publications and source records attributed to G R Dunkelberger.

11 recordsLinked to original sources

PubMed1991

Retinal ganglion cell loss is size dependent in experimental glaucoma.

Thirty-two areas located in the temporal midperipheral retina were evaluated in whole-mount preparations from four monkeys with monocular experimental glaucoma. Diameter frequency distributions of remaining ganglion cells in the glaucomatous eye were compared with corresponding areas in the normal fellow eye. Large cells were significantly more vulnerable at each stage of cell damage as determined by linear-regression analysis. The magnitude of size-dependent loss was moderate at an early stage (20% loss), peaked at 50% total cell loss, and decreased in advanced damage (70% loss). In glaucomatous eyes, the lower retina had significantly more large cell loss than the corresponding areas of the upper retina. In optic nerve zones that matched the retinal areas studied, large axons selectively were damaged first. Psychophysical testing aimed at functions subserved by larger ganglion cells is recommended for detection and follow-up of early glaucoma; however, assessment of functions unique to small cells is more appropriate for detecting change in advanced glaucoma.

Animals↗

PubMed1990

Optic nerve head extracellular matrix in primary optic atrophy and experimental glaucoma.

Unilateral glaucomatous optic neuropathy and optic nerve transections were produced in cynomolgus monkeys, and the optic nerve heads were examined by light and electron microscopic immunohistochemistry. Glaucomatous nerve heads showed increased labeling for collagen type IV along the margins of beams in the lamina cribrosa, due to accumulation of basement membrane-like materials. We also noted material in the pores of the laminar beams that labeled with antibodies to collagen types I, III and IV, but not elastin. In transected eyes, increased type IV labeling of laminar beam margins resulted solely from redundant astrocyte basement membranes. Extracellular matrix deposition within laminar pores was not observed following optic nerve transection; hence this may be a selective response to elevated intraocular pressure. This response may alter the biochemical composition of the lamina cribrosa and its function in patients with elevated intraocular pressure.

Animals↗

PubMed1990

Aging changes of the rhesus monkey optic nerve.

The authors counted axons in one optic nerve from each of 28 juvenile and aged rhesus monkeys using an automated image analysis system. All nerves were fixed immediately after death and treated identically. Animals ranged in age from 1 1/2 to 29 yr, which correlates with a human age range of 4 1/2-87 yr. Mean axonal number for all specimens was 1,117,859. Large variations in axonal numbers were found, even within a subgroup of ten animals aged 1 1/2-2 yr. Although young nerves had generally more fibers than those from old animals, this difference was not quite statistically significant, translating into a yearly loss of 4319 fibers (0.45% of the total). Age did not have any significant effect on mean axonal diameter.

Aging↗

PubMed1989

Retinal ganglion cell atrophy correlated with automated perimetry in human eyes with glaucoma.

We measured the number and size of retinal ganglion cells from six human eyes with glaucoma. In each, the histologic findings were correlated with visual field results. Five age-matched normal eyes were studied for comparison. In general, there were fewer remaining large ganglion cells in retinal areas with atrophy. In the perifoveal area, however, no consistent pattern of cell loss by size was found. Our estimates suggest that visual field sensitivity in automated testing begins to decline soon after the initial loss of ganglion cells. Throughout the central 30 degrees of the retina, 20% of the normal number of cells were gone in locations with a 5-dB sensitivity loss, and 40% cell loss corresponded to a 10-dB decrease. There were some remaining ganglion cells in areas that had 0-dB sensitivity in the field test.

Atrophy↗

PubMed1989

Pattern-evoked potentials and optic nerve fiber loss in monocular laser-induced glaucoma.

ERG and VEP responses to counterphase checkerboard stimuli were obtained from cynomolgus monkeys with monocular glaucoma induced by laser photocoagulation of the trabecular meshwork. The glaucomatous eyes showed reductions of PERG amplitude that were directly related to the histologically defined nerve damage. VEP amplitudes were also reduced in the glaucomatous eyes, but were more variable and less affected by damage than the PERG responses. An acute increase in eye pressure to 40 mm Hg in eyes without damage had no detectable effect on PERG amplitudes.

Animals↗

PubMed1988

Cellular proliferation after experimental glaucoma filtration surgery.

We used light microscopic autoradiography to determine the time course of cellular incorporation of tritiated thymidine (a correlate of cell division) following glaucoma filtration surgery in seven eyes of four cynomolgus monkeys with experimental glaucoma. Incorporation of tritiated thymidine was detected as early as 24 hours postoperatively. Peak incorporation occurred five days postoperatively and had returned to baseline levels by day 11. Cells incorporating tritiated thymidine included keratocytes, episcleral cells, corneal and capillary endothelial cells, and conjunctival and corneal epithelial cells. Transmission electron microscopy was correlated with the autoradiographic results to demonstrate that fibroblasts were dividing on the corneoscleral margin. These findings have potential clinical implications for the use of antiproliferative agents after filtration surgery.

Animals↗

PubMed1988

Histopathology of the effects of tuneable dye laser on monkey retina.

The tuneable dye laser was used to simulate treatment of choroidal neovascularization and panretinal photocoagulation (PRP) in monkey retina. The histopathologic effects of wavelengths from 560 to 630 nm in juxtafoveal, papillomacular bundle, and nonfoveal areas were investigated. An unexpected observation using high-intensity burns in juxtafoveal and, to a lesser extent, in papillomacular bundle areas was inner retinal damage with 600-nm light. At moderate energy levels, the effect of 600 nm were more comparable with those with other wavelengths and included much less damage to the inner retinal layers. At mild energy levels, the effects were comparable with other wavelengths. During and after the application of the burns, the energy levels and ophthalmoscopic appearances were comparable for each wavelength for the high-, moderate-, and mild-intensity burns. The histopathologic effects of 630-nm light (tuneable dye red) were comparable with those of the standard krypton red (647 nm) laser. Nonmacular and PRP effects were similar with all wavelengths. These results indicate that power levels may need to be reduced when placing 600-nm (orange) laser burns in the macula.

Animals↗

PubMed1988

Chronic human glaucoma causing selectively greater loss of large optic nerve fibers.

Eighteen eyes of 12 persons with chronically elevated intraocular pressure (IOP) were studied histologically to determine the number and diameter of optic nerve fibers. In some eyes, automated perimetry had been performed. Optic nerve fibers larger than the mean diameter were killed more rapidly than smaller fibers, although no fiber size was completely spared at any stage of atrophy. The number of optic nerve fibers varies considerably among normal eyes. The authors confirmed that the death of a substantial proportion of optic nerve fibers precedes detectable visual field loss.

Aged↗

PubMed1987

Chronic glaucoma selectively damages large optic nerve fibers.

To determine whether glaucoma selectively injures a particular size of optic nerve fiber (and its cell body), we induced chronic experimental glaucoma in one eye each of ten monkeys. With automated image analysis, the number and diameter of optic nerve fibers were compared between each glaucomatous eye and its normal fellow eye. Fibers larger than the normal mean diameter atrophied more rapidly in glaucomatous eyes, though no fiber size was spared from damage. The mean fiber diameter for glaucomatous eyes was 0.74 micron, significantly lower than the mean for ten fellow eyes, 0.85 micron (P less than 0.005). There was preferentially greater atrophy of fibers of all sizes in the superior and inferior peripheral nerve sectors, as seen in human eyes with glaucoma. The more rapid atrophy of larger fibers appeared to result from two causes. The areas that suffer most rapid loss of fibers in experimental glaucoma normally contain a high proportion of larger diameter fibers. Furthermore, larger fibers were lost preferentially even in areas of the optic nerve with mild damage, indicating their inherent susceptibility to injury by glaucoma. The tendency for large fibers to be lost in glaucoma has implications for future improvements in testing for early glaucoma damage.

Animals↗

PubMed1986

The number and diameter distribution of axons in the monkey optic nerve.

Using an automated image analysis system, cross-sections from optic nerves of 17 normal cynomolgus monkeys were examined. The number of nerve fibers, their density, and the distribution of their diameters for whole nerves and for various regions of the nerve cross-section were estimated. The mean total number of fibers in the optic nerve was 1.2 million. The mean diameter of axons was 0.8 micron. The method of tissue fixation substantially affected the measurements. Histograms of fiber diameter suggested a trimodal distribution of fiber size with peaks at 0.5, 0.8, and 1.5 micron. The relative proportions of these fiber peaks differed significantly in different regions of the nerve. The highest proportion of large fibers was in the superior nerve periphery. The highest concentration of smallest fibers and the highest density of all fibers were located centrally in the infero-temporal quadrant. The observation that higher fiber density and smaller mean fiber diameter are skewed toward the inferior pole appears to coincide with the inferior position of the fovea with respect to the optic nerve head. This finding has importance for interpretation of pathologic changes in the optic disc.

Animals↗

PubMed1985

Effects of 2.45-GHz microwaves on primate corneal endothelium.

Both eyes of anesthetized cynomolgus monkeys (Macaca fascicularis) were irradiated with 2.45-GHz microwaves, either pulsed or continuous wave. In vivo corneal endothelial abnormalities were observed by specular microscopy and confirmed through histologic techniques after a 16- to 48-hour postexposure period. Pulsed microwaves with an average power density of 10 mW/cm2 (equivalent to a specific absorption rate (SAR) = 2.6 W/kg) produced these effects, while levels of 20-30 mW/cm2 (equivalent to a SAR = 5.3 to 7.8 W/kg) with continuous wave irradiation were required to produce similar changes.

Animals↗