Inhibition of microvascular endothelial cell proliferation by vitreous following retinal scatter photocoagulation

Laser photocoagulation of pig retina induced breakdown of the blood-retinal barrier, with the appearance of serum proteins in the vitreous as determined by sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting techniques. Vitreous from lasered eyes inhibited the proliferation of cultured retinal microvascular endothelial cells in comparison with vitreous from non-lasered control eyes, and the inhibitory effect in the lasered eyes persisted for at least seven days. Inhibition was specific for endothelial cells, since no effect was observed when retinal pericytes or Tenon's fibroblasts were the target cells. These results suggest that indirect scatter photocoagulation may induce regression of neovascularisation by causing breakdown of the blood-retinal barrier and thus releasing into the vitreous serum components which result in inhibition of retinal microvascular endothelial cell growth.

[Role of the vitreous in idiopathic preretinal macular fibrosis indicated by visual acuity in follow-up cases]

The vitreous and visual acuity in 103 eyes with idiopathic preretinal macular fibrosis were examined. The vitreous was studied biomicroscopically and the follow-up course was 6 months or more. Twenty-two eyes had no posterior vitreous detachment (group 1), 4 eyes had partial posterior vitreous detachment without traction to the macula (group 2), 17 eyes had partial posterior vitreous detachment with traction to the macula (group 3), and 60 eyes had complete posterior vitreous detachment (group 4). There were significantly more eyes with a visual acuity of 0.4 or worse, decreased acuity, or macular fluorescein leakage in group 3 than in groups 1 or 4. Decreased visual acuity was found in 41% of eyes with macular fluorescein leakage, but in only 11% of eyes without macular fluorescein leakage. It is presumed that the vitreous traction to the macula and macular fluorescein leakage are closely related to the outcome of visual acuity in cases with idiopathic preretinal macular fibrosis.

Accommodation used to determine ultrasound velocity in the human lens

Intraocular distances can be measured by echography. In this determination the velocity of sound in the various media is assumed to be constant and equal to the velocity found by in vitro measurements. However, interindividual variability causes an inaccurate determination of these distances. We present a method to determine the velocity of ultrasound in the lens "in vivo." For this purpose continuous registrations of the transit times for the anterior chamber, lens, and vitreous were made during accommodation. Regression analysis of the variation of transit times provides the velocity of ultrasound in the lens with an accuracy of about +/- 3 m/s.

Vitreous modulation of migration and proliferation of retinal pigment epithelial cells in vitro

Retinal pigment epithelial (RPE) cell migration and proliferation are believed to play a role in the pathogenesis of proliferative vitreoretinopathy (PVR). Since PVR develops in situations where vitreous contacts the RPE, we sought to determine whether human vitreous contains factors that stimulate proliferation and migration of RPE cells. We found that postmortem human vitreous stimulates migration but not proliferation of human RPE cells under serum-free conditions in vitro. Stimulation of proliferation of RPE cells and fibroblasts was observed, however, following admixture of albumin with the vitreous. These findings suggest that vitreous contributes modulators that stimulate some functions of RPE cells that are believed to play a role in the pathogenesis of PVR.

Quantitative analysis of the insulating effect of silicone oil on the electroretinogram

A model of the ERG focusing on the insulation effect of silicone oil replacing the vitreous was used to quantify the ERG. The electrical properties of the structures of the eye, the frequency content of the ERG and the percentage of the silicone oil along with the remaining vitreous were incorporated in the model. The result was that it was not until at least 50 per cent of the vitreous was replaced with silicone oil that there was a small reduction in the ERG. As more silicone oil was put into the vitreous cavity the ERG became smaller. If the replacement were large leaving a layer of vitreous 0.24 mm thick, little ERG would be measured even if the retina were functional.

Intraocular oxygen tension measured with a fiber-optic sensor in normal and diabetic dogs

A new fiber-optic O2 sensor was used to measure the O2 tension in the living dog eye, and the results were compared with simultaneous O2 tension measurements with polarographic electrodes. The fiber-optic sensor and the polarographic electrodes gave similar readings of anterior chamber O2 tension and gave an identical response to elevation of inspired O2 levels. In the preretinal vitreous, the fiber-optic probe measured the O2 tension 26 +/- 5 mmHg (means +/- SD, n = 5), whereas the polarographic electrode showed 23 +/- 7 mmHg (means +/- SD, n = 5) in the contralateral eyes. Breathing 100% O2 raised the preretinal O2 tension similarly with both systems. Preretinal O2 tension was measured with the fiber-optic sensor in seven alloxan diabetic dogs and was 26 +/- 7 mmHg, which is not significantly different from normal dogs. The fiber-optic sensor has some advantages over the polarographic electrodes. The fiber-optic sensor does not consume O2 and is not dependent on the diffusion characteristics of the medium or changes due to stirring or fluid currents.

Glutamatergic separation of ON and OFF retinal channels: possible modulation by glycine and acetylcholine

When intravitreally injected into the frog in vivo, 2-amino-4-phosphonobutyrate (APB) and cis-2,3-piperidine dicarboxylic acid (PDA) showed opposite effects on ON and OFF retinal channels: APB abolished the ON responses in the electroretinogram and in ganglion cell activity, and increased OFF responses. At the same time the receptive field area was enlarged, and the inhibition exerted by the surround was suppressed. A cholinergic/glycinergic loop involving amacrine cells was suggested to be the pathway of the inhibitory ON input upon the OFF channel. PDA abolished the OFF responses in the ERG and in ganglion cell activity, while increasing the ON response in the ERG and decreasing the ganglion cell sensitivity at ON. The receptive field area was not modified, but the inhibition exerted by the surround was suppressed, probably by a blockade of horizontal cell glutamate receptors.

Role of the lens and vitreous humor in the refractive properties of the eyes of three strains of goldfish

Certain strains of goldfish are characterized by large bulging eyes which have been shown to be extremely myopic. Such myopia has been hypothesized to have its origin in enlargement of the posterior chamber of the eye. The focal length of the lens was found to be similar for paraxial and marginal lens zones in common, Chinese Black Moor and Celestial goldfish, thus providing indirect support of that hypothesis. Freeze-sectioning study of intraocular dimensions shows that the axial length of the vitreous chamber of the common goldfish eye is about 37% of total axial length. In contrast, it becomes more than 70% of axial length in Chinese Black Moors and Celestials. An examination of vitreous protein concentration indicates that ocular enlargement in Chinese Black Moors and in Celestials is related to an increase in vitreous quantity, and is accompanied by vitreous dilution. The fact that similar findings are reported in the case of experimental myopia in chicks, suggests the existence of a fundamental mechanism of refractive development for the vertebrate eye.

Human retinal pigment epithelial cell cultures: phenotypic modulation by vitreous and macrophages

In proliferative vitreoretinopathy (PVR), retinal pigment epithelial (RPE) cells migrate into the vitreous, where they may acquire a fibroblast-like morphology. Such cells may eventually form contractile periretinal membranes, resulting in traction retinal detachment. Among the environmental influences that could cause this change in RPE phenotype, exposure to vitreous and to macrophages is most obvious, as macrophages are invariably found in epiretinal membranes and precede membrane formation in experimental traction retinal detachment. We initiated studies to define modulation of cultured RPE cell morphology by exposure to vitreous or to macrophage-conditioned media. Vitreous, serum, and albumin alone had no effect on the epithelial appearance of RPE cells in vitro. However, macrophage-conditioned media and vitreous-serum or vitreous-albumin mixtures induced a reversible fibroblast-like appearance in these cells. These findings show that macrophages produce a morphoplastic substance for RPE cells, and suggest that vitreous also contains a factor(s) that affects RPE cell shape, and that requires mediation by serum components.

Effects of vitreous from photocoagulated eyes on retinal microvascular cells in culture: a preliminary report

Panretinal photocoagulation was carried out in mini pigs in an attempt to elucidate the mechanisms involved in laser therapy. The effect of the vitreous from these eyes on the proliferation of retinal microvascular endothelial cells was then studied. Vitreous removed 4 days after panretinal photocoagulation had no effect on the proliferation of bovine retinal microvascular endothelial cells in basal medium but inhibited proliferation in growth medium. Control vitreous was mitogenic for the microvascular cells in basal medium but this effect was not observed in growth medium.

Cellular proliferation induced by subretinal injection of vitreous in the rabbit

A new experimental model of subretinal cellular proliferation, based on injection of autologous vitreous into the subretinal space of rabbits, was studied by light and electron microscopy. As early as five days after injection, proliferation of retinal pigment epithelial (RPE) and retinal glial cells was observed in the subretinal space. These morphologically distinct proliferating cells were sometimes joined by junctional complexes. Morphologically, the proliferating RPE cells resembled either RPE cells or fibroblasts. Some proliferating RPE cells also retained their epithelial characteristics (ie, basement membranes and cell junctions), while others were partially dedifferentiated and showed some embryonic features. New formation of melanin could be identified within the proliferated RPE cells, which could account, in part, for the hyperpigmentation at the site of the bleb caused by the injection of vitreous. The results demonstrated that injection of autologous vitreous into the subretinal space can lead to subretinal proliferation of retinal glial and RPE cells in the rabbit.

Malignant glaucoma

The term "malignant glaucoma" referred originally to a rare and highly feared form of glaucoma occurring in certain postoperative patients. Over time the concept of the disease was expanded to include a group of angle closure glaucomas unresponsive to traditional miotic or filtering therapy. The haphazard lumping of many disease entities under such an umbrella term has caused confusion, which we attempt to resolve through a mechanistic approach to elucidating the pathogenesis of malignant glaucoma based on the anatomical location of obstruction to normal aqueous flow; surgical treatments are suggested based on the pathogenesis. Attention is drawn to the role of the vitreous and anterior hyaloid in combination with a block to normal aqueous circulation, redirection of its flow, high intraocular pressure and vitreous swelling in precipitating malignant glaucoma and creating a vicious circle to maintain it. Surgical management is directed to correcting the obstruction to normal aqueous flow and removing aqueous accumulated in the posterior chamber, vitreous or suprachoroidal space.

Vitreous macrophage elicitation: generation of stimulants for pigment epithelium in vitro

Vitreous and macrophage samples were tested for the ability to stimulate proliferation and cell migration in cultured rabbit retinal pigment epithelium (RPE). A macrophage invasion was elicited by the intravitreal injection of latex particles in rabbits and after 3 days the vitreal macrophages were collected. The macrophages themselves, macrophage-conditioned culture medium, and macrophage-incubated vitreous had modest effects on RPE proliferation, but significantly stimulated RPE migration. A portion of the migration activity may be due to macrophage-derived proteases acting on normal vitreous. Mitogenic and additional migration-stimulating activity may also arise from adjacent tissues or from a breakdown of the blood-vitreous barrier that accompanies a macrophage invasion. A macrophage ingress into the vitreous may provide part of the stimulation for the migration and proliferation of RPE in conditions such as proliferative vitreoretinopathy.

Phosphorylation of ribosomal protein S6 during lens cell differentiation: correlation with translational efficiency

In vitro differentiation of embryonic chicken lens epithelial explants to form lens fiber cells is accompanied by an increase in protein synthesis without a corresponding increase in mRNA levels. This apparent increase in translational efficiency is correlated with a specific enhancement of phosphorylation of a 32K protein, which we identify as ribosomal protein S6 by two dimensional gel electrophoresis of purified ribosomal proteins. Serum, insulin, and chicken vitreous humor, three agents known to initiate differentiation in this system, all lead to enhanced S6 phosphorylation. Maximal enhancement of phosphorylation is reached within the first hour after the onset of differentiation, and is not blocked by inhibitors of RNA and protein synthesis.

Modulation of human lymphocyte proliferation by normal bovine vitreous

A heat stable antiangiogenic protein (Bovine Vitreal Protein or BVP) isolated from normal bovine vitreous and known to inhibit growth of endothelial and smooth muscle cells was studied for its in vitro effect on human lymphocyte proliferation. Unheated BVP inhibited lymphoproliferation in 12 normal, healthy donors in response to tetanus toxoid (TT) and to Concanavalin A (Con A), but had little effect on responses to irradiated allogeneic peripheral blood mononuclear leucocytes (PBML) or Pokeweed mitogen (PWM). In contrast, heated (95 degrees C/10 min) BVP strongly inhibited (more than 50%) proliferative responses to allogeneic cells, TT, and Con A, and strongly augmented responses to PWM.

Pharmacological dissociation of the b-wave and pattern electroretinogram

Electroretinographic responses to modulation of either luminance (focal ERG) or spatial contrast (pattern ERG) were recorded from the pigeon eye before and after intravitreal injection of glutamate analogues DL alpha amino adipic acid (DL alpha AA) and 2-amino-4 phosphonobutyric acid (APB). Both toxins reversibly abolished the b-wave. The pattern ERG was still present, however, when the b-wave had been abolished by the toxins. This result demonstrates that the b-wave and the pattern ERG can be pharmacologically dissociated and suggests the possibility that in pigeons the b-wave and pattern ERG reflect the activity of different generators.

Flow of water between aqueous and vitreous compartments in the rabbit eye

When fluoresceinated dextran (FD) is injected into the vitreous body of the rabbit, it diffuses out of the eye through the anterior chamber so that the ratio of its concentration in the aqueous to that in the vitreous humor remains constant. The rate of loss of the substance from the eye suggests that the vitreous body is stagnant. After penetrating the vitreous body with a 25-gauge needle through the sclera, the FD fluorescence in the aqueous humor is reduced by a factor of three times on the average. This appears to be because the loss of fluid out of the scleral hole sets up a backward seepage of fluid through the anterior vitreous body, which opposes the diffusion of dextran into the anterior chamber. In contrast, making a needle hole has little effect on the level of sulforhodamine B, a more rapidly diffusing molecule, when it has been injected into the vitreous body, and none at all when it has been introduced into the cornea. The changes in the flow across the aqueous-vitreous interface, as well as the changes in aqueous outflow after an experimental intervention to the eye, may be estimated from a comparison of the changes in fluorescence in the anterior chamber of large and small molecular weight compounds injected into the vitreous body.

The optics of comparative ophthalmoscopy

One factor peculiar to the practice of comparative ophthalmoscopy is the very large variation in ocular size of the animals examined, a factor which is ignored in current textbook treatments of the subject. We have computed values of lateral magnification, axial magnification, angular field of view and linear field of view for 19 species of terrestrial vertebrates. The dimensional value of a 1 diopter change in direct ophthalmoscopic focus was also determined. The anterior focal length of the eye in air and the vitreal refractive index were the intrinsic optical parameters of the animal's eye necessary for these calculations. Where these values were not available from the literature, the vitreal refractive index was assumed to be 1.336 and the anterior focal length was estimated as two-thirds of the axial length using a regression equation we derived from data in the literature. The angular field of view in ophthalmoscopy was shown to be invariant in the emmetropic eye and equal to the angular subtense of the ophthalmoscopic beam. The lateral field of view and retinal depth corresponding to a 1 diopter change in direct ophthalmoscopic focus varied directly with the anterior focal length of the eye. The remaining parameters of lateral and axial magnification varied inversely with the anterior focal length of the animal's eyes. These findings provide a basis for evaluating the relative size and significance of ophthalmoscopically viewed features in terrestrial vertebrate eyes.

Proximal retinal contribution to the intraretinal 8-Hz pattern ERG of cat

We investigated the retinal depth of origin of the pattern ERG (PERG) in cat by recording extracellular responses to contrast reversal grating stimuli and performing a current source-density analysis of the depth profiles. The local ERG (LERG) was recorded within the retina; the waveform varied with grating spatial phase position of the microelectrode. The LERG at any arbitrary single spatial phase was not equivalent to the corneal PERG. To obtain an "intraretinal PERG" equivalent to the corneal PERG, we summed LERGs from many spatial phases over a complete grating cycle. This intraretinal PERG was analogous to the corneal PERG in having only even harmonic components and also in being independent of the grating spatial phase. The absence of the fundamental and odd harmonics appeared to result from the summation of responses across grating spatial phase rather than from an intrinsic generator mechanism. The spatial contrast sensitivity function for the intraretinal PERG at 8 Hz was tuned, with peak sensitivity between 0.5 and 0.75 cycles per degree in the area centralis. The 8-Hz PERG response was maximum in the proximal retina at approximately 23% depth from the internal limiting membrane (ILM). This depth lies within the inner plexiform layer and is proximal to the depth at which the b-wave was maximum (49-61% depth). PERG and flash-elicited ERG responses exhibited different amplitude profiles as a function of retinal depth. Analysis of the 8-Hz PERG depth profiles identified generators in the proximal retina between the ILM and the inner plexiform-inner nuclear boundary. The analysis suggested that at least two generators were present. The proportional contribution to the corneal PERG from each of the two or more proximal generators was not determined. Contributions to the corneal PERG from more distal generators, however, were not specifically excluded. The intraretinal recordings suggest that under some conditions contrast reversal gratings at 8 Hz can elicit current generators in the proximal retina of cat. These generators appear to respond to local retinal illumination, and the intraretinal PERG results from nonlinear elements of at least two generators. Spatial tuning of the intraretinal PERG may reflect properties of the underlying LERG components, including the M-wave.