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The Buchan Rift, in northeastern Victoria, is a north–south-trending basin, which formed in response to east–west crustal extension in the Early Devonian. The rift is filled mostly with Lower Devonian volcanic and volcaniclastic rock of the Snowy River Volcanics. Although the structure and geometry of the Buchan Rift and its major bounding faults are well mapped at the surface, a discrepancy exists between the surface distribution of the thickest rift fill and its expected potential field response. To investigate this variation, two new detailed land-based gravity surveys, which span the rift and surrounding basement rocks in an east–west orientation, have been acquired and integrated with pre-existing government data. Qualitative interpretation of the observed magnetic data suggests the highly magnetic rocks of the Snowy River Volcanics have a wider extent at depth than can be mapped at the surface. Forward modelling of both land-based gravity data and aeromagnetic data supports this interpretati...

Single-plate Molteno implants were installed in two stages in glaucomatous monkey eyes. This device shunts aqueous from the anterior chamber to periocular orbital tissues. The mechanism of aqueous filtration and absorption was explored using flow studies, fluorescently labeled microspheres and histological examination of tissues. Flow studies indicated that the capsule around the explant functions by a passive mechanism, shunting aqueous into the extracellular space. Outflow is proportional to capsule surface area. Latex microspheres (0.2 mum and smaller) passed freely through the capsule, giving the impression of an open sieve. The presence of microspheres in the episcleral wall of the capsule indicates that all surfaces contribute to filtration. A concentration gradient of particles in the extracapsular space, away from the bleb surface, suggests that the capsule itself limits filtration rate.

Replacement of the entire anterior segment of the eye is a very ambitious and complex endeavor and it is not known whether the retina remains functional when the anterior structures have been removed. We used routine histo-pathologic evaluation and electroretinographic measurements to determine the structural and functional status of rabbit retinas following surgical removal of the internal anterior structures (iris, ciliary body, and lens) and replacement of the vitreous with silicone oil. In some cases, we were able to record both a scotopic and a photopic electroretinographic response as long as 15 weeks after complete removal of the internal anterior segment structures. Although many hurdles remain and more efficacious surgical techniques and biomaterials need to be developed, our results suggest that, in the rabbit, the retina may continue to function in the absence of critical anterior segment structures.

The extracellular matrix of retinal pigment epithelial (RPE) cells is an important component of the fibroelastic membranes formed in proliferative vitreoretinopathy (PVR). These membranes consist of cells intermingled with fibrillar proteins, such as elastin and collagen. Because RPE cells may be exposed to vitreous and serum-derived factors in conditions that lead to PVR, the effects of vitreous and serum on the deposition of fibrillar proteins by RPE cells were studied using radioactive labeling and indirect immunofluorescence techniques. The RPE cells, modulated by combined vitreous and serum into a fibrocytic-like appearance, deposited less fibroelastic proteins per cell. However, as a result of simultaneous cell proliferation, the total deposition of fibroelastic proteins per culture was increased. Indirect immunofluorescence studies suggest that it is type I collagen that is altered in the matrix of these modulated cell cultures. This information is important in pathologic conditions characterized by intraocular cell proliferation and fibroelastic membrane formation; these phenomena are seen in many vitreoproliferative disorders.

The disciform response of age-related macular degeneration and other diseases is determined by the development of subretinal neovascularization (SRN). Experimental animal models of SRN based on disruption of Bruch's membrane have been studied extensively during the past decade. Argon laser photocoagulation-induced SRN in primates is one such model, but this is associated with extensive retinal damage. Because the injured retina could be angiogenic, and is not present in clinical SRN, this model might be more relevant if this factor could be eliminated. The current study was conducted with the primary aim of producing a rabbit model of SRN that minimizes retinal damage. Argon laser endophotocoagulation was applied beneath the retina of albino rabbits to achieve this goal. Although argon photocoagulation does not cause clinically apparent SRN (i.e., associated with leaking and pooling of fluorescein) in the rabbit, all laser lesions produced in the current study contained microscopic SRN. A rabbit SRN model would be highly desirable as a step toward other animal models, perhaps involving nonhuman primates, which might ultimately be clinically more relevant.

The Molteno implant has been increasingly utilized during the last several years as a means of controlling intraocular pressure (IOP) in complicated glaucomas [1]. We have studied the pathophysiology of this device utilizing laser-induced secondary glaucoma in the monkey eye as an experimental model [2]. This report summarizes our experimental animal and human pathologic studies of this device.

Junctional ultrastructure of endothelial cells of the choroid was studied with freeze-fracture electron microscopy. A network of multi-stranded linear aggregates was found on arterial endothelial membrane E faces in association with the apposing arterial membrane P face strands. The complexity of the junctional strands decreased as vessel diameter decreased. The choriocapillaris showed staggered junctional strands exclusively on the membrane P face. Junctions of venules and veins were represented by plasmalemmal folds with sparse intramembrane particles on the P face. Freeze-fracture cytochemistry with the membrane probe, filipin, revealed two dissimilar membrane domains: one, an area of membrane fluidity at the junctional strands; and the other, identified by the incorporation of cholesterol into the membrane lipid bilayer, a stable membrane domain. The latter was present throughout endothelial membranes, but was especially prominent on the rims of fenestrations of the choriocapillaris.

In this paper we examine the use of a symmetric binary random stimulus for eliciting the ERG, and for calculating the first-order and second-order kernels of a nonlinear functional expansion of the response. We show that if the stimulus is represented in a non-dimensional form, then the units in which all kernels are measured are the same as the units used to measure the response, microvolts in the case of the ERG; further, contributions from all kernels to the response can be added without scale factors. We present the first-order and second-order kernels measured for a population of 15 normal subjects in a clinical setting. The measurements were made at various levels of adaptation ranging from photopic to scotopic conditions. The second-order kernels illustrate the processes of rapid adaptation (less than 100 ms) in the retina.

A simple technique is described by which retinal whole mounts or slices of brain can be impregnated by the Golgi procedure in a graded manner. The unfixed tissue is laid on a glass slide and covered with a layer of Telfa gauze which is tied in place. Following fixation, the progress of staining, which begins beneath holes in the gauze, is followed by direct observation through the slide. The tissue is impregnated or reimpregnated until the desired results are obtained.

The organization of the retinal nerve fiber layer of the cynomolgus monkey was studied by electron microscopy. Nerve fiber size spectra were obtained from measurements of every fiber in enlarged montages of selected bundles. Variation in spectra among nasal, arcuate, and papillomacular bundles was examined, and variation of spectra of a given bundle as it crossed the retina was determined. Among the three types of bundles, the papillomacular contained relatively more small fibers, nasal bundles relatively more large fibers. Systematic variation of fiber spectra was observed as the disc was approached by arcuate and papillomacular but not nasal bundles. Arcuate bundles sampled in the peripapillary area contained relatively more small fibers than when sampled at a greater distance from the disc. In contrast, papillomacular bundles sampled near the disc contained relatively more large fibers than near the fovea.

It was recently shown that the injection of autologous vitreous beneath the retina of rabbits leads to retinal degeneration, subretinal cellular proliferation and neovascularization. The current study, using electron microscopy, was designed to determine the cellular processes involved in the breakdown of Bruch's membrane in this model. Bruch's membrane was not mechanically damaged by the injection and appeared intact for the first 1 to 2 days after injection. Subsequently, numerous breaks in Bruch's membrane were found associated with invasion of macrophages and fibroblasts; in addition, budding and penetration of retinal pigment epithelial (RPE) and choroidal endothelial cells into Bruch's membrane were noted. Although it was not proven that these cells, per se, were responsible for the breaks, that these cells actively penetrate Bruch's membrane is a reasonable hypothesis.

The receptive field properties of internal horizontal cells (IHCs) were studied in the frog Rana pipiens. The space constant of each cell was determined by the use of stimulus spots of various sizes or by moving a light slit across the retina, varied from 100-500 microns by the former and 100-720 microns by the latter method. A similar range of values has been reported for Xenopus although its IHCs are much larger than the IHCs of Rana. Apparently, coupling among the IHCs is more efficient in the latter than in the former retina. The large range in values suggests substantial variation in coupling efficiency among cells of the same retina.

The organization of nerve fiber bundles, stained by microelectrode injection of horseradish peroxidase, was examined in the retina of the owl monkey. Fibers were traced across the retina in whole mounts and serial sections to evaluate their retinotopic order. Long nasal fibers showed little tendency to wander among bundles but were distributed randomly within the bundles near the disc. Long arcuate and papillomascular fibers, in sharp contrast, spread laterally among many bundles as they approached the disc, but were segregated within the bundles in a scleral position. These results indicate that horizontal retinotopy among bundles is well developed in nasal but not temporal retina; vertical retinotopy within bundles is well developed in temporal but not nasal retina of the owl monkey. These findings are significantly different from those of a recent study of the macaque monkey.

The outer horizontal cell (OHC) of the frog Rana pipiens was studied by light and electron microscopy of Golgi-stained and horseradish peroxidase-injected cells. Responses of OHCs were recorded with intracellular electrodes. The OHCs are probably axonless cells. Their dendritic terminals are lateral processes at synaptic ribbons and are involved frequently in reciprocal invaginating contacts with receptors, ie, contacts characterized by invagination of receptor membrane deeply into the horizontal cell process. Two classes of OHC were distinguished on the basis of size and receptor contacts. Small OHCs (dendritic area about 5,000 micron2) contact all classes of receptor. These cells were not successfully penetrated with microelectrodes. Giant OHCs (dendritic area about 30,000 micron2) apparently contact only blue-sensitive rods and red-sensitive cones. They generate chromaticity or C-type responses, hyperpolarizing to short and depolarizing to long wavelength light.

The nerve fiber layer of several species of primate has been studied with Golgi silver impregnations and Nissl stains. The morphology, distribution, and density of fibrous astrocytes of the nerve fiber layer are described. Two classes of astrocytes are distinguished: elongated cells whose processes parallel the nerve fiber bundles and cover a rectangular area more than two time longer than wide without vascular contact and stellate cells whose processes conspicuously cross the nerve fiber bundles to cover a slightly oval area and make unspecialized vascular contacts. The density of glial nuclei in the nerve fiber layer is roughly proportional to the thickness of the layer all across the retina, so that higher densities are seen in specialized regions such as the arcuate nerve fiber bundles and near the optic disc.

The transretinal pathway of optic nerve fibers in the retinas of cynomolgus and bonnet monkeys was studied by light microscopy following small intraretinal injections of horseradish peroxidase (HRP). Injections of HRP into nerve bundles at the optic disc labeled a few ectopic ganglion cells, in addition to those in the related retinal sector. Injections into nerve bundles in the retina labeled long (more than 3 mm) fibers of passage, most of which remained close to the vitreal surface as they crossed the retina. These long fibers mingled with short (less than 1 mm) peripapillary fibers at the disc margin and in the prelaminar part of the disc. Axons of intermediate ganglion cells (1-3 mm in length) were added to the fiber layer at its scleral border, beneath long fibers of more peripheral origin. These findings demonstrate a retinotopic organization of macaque nerve fiber bundles with long fibers vitreal and shorter fibers more scleral in position. Intermingling of fibers of disparate origin is extensive at the optic disc where a decussation of long and short fibers occurs.

The inner horizontal cell (IHC) of the retina of Rana pipiens was studied by light and electron microscopy of Golgi stained or horseradish peroxidase injected cells. Responses of IHCs were recorded with intracellular electrodes. Both axon and dendritic terminals of the IHC make synaptic contact with all classes of receptor. The terminals occur as lateral or medial processes at synaptic ribbons. Reciprocal invaginations of receptor into horizontal cell process are common. Different classes of receptor are contacted in about the proportions with which they occur in the retina. No tendency for contacts of one type of receptor to occur on a particular part of the cell was found. The IHC generates L-type S-potentials. Both rod and cone input is evident in the waveform of the response, its spectral sensitivity, and the effect on it of adaptation.