Intraocular humidity immediately after fluid–air exchange in pars plana vitrectomy

PURPOSE

To study vitreous cavity humidity during fluid-air exchange in pars plana vitrectomy.

METHODS

Intraocular humidity in the vitreous cavity was recorded for 2 min in six artificial eyes, six enucleated pig eyes, and ten patient eyes, after the eyes had been filled with either humidified air (75% humidity) or dry air (8% humidity).

RESULTS

In artificial eyes the humidity levelled off at a value that was approximately equal to the humidity of the infused air, i.e., a mean of 71.9% when humidified air was used and a mean of 14.4% when dry air was used. In enucleated pig eyes humidity increased slightly with humidified air and remained stable with dry air. In patients intraocular humidity increased to over 90%, regardless of whether humidified or dry air was used.

CONCLUSION

In the living eye, dry air deprives the retinal tissue of humidity, which is lost into the vitreous cavity. This effect can be reduced by using humidified air.

Somatostatin molecular variants in the vitreous fluid: a comparative study between diabetic patients with proliferative diabetic retinopathy and nondiabetic control subjects

OBJECTIVE

There is growing evidence to indicate that somatostatin could be added to the list of natural antiangiogenic factors that exist in the vitreous fluid. In addition, a deficit of intravitreous somatostatin-like immunoreactivity (SLI) has been found in diabetic patients with proliferative diabetic retinopathy (PDR). In the present study, we have determined the main molecular variants of somatostatin (somatostatin-14 and somatostatin-28) in the vitreous fluid and plasma of nondiabetic control subjects and diabetic patients with PDR. In addition, the contribution of cortistatin, a neuropeptide with strong structural similarities to somatostatin, to SLI and its levels in vitreous and plasma in both nondiabetic and diabetic patients has also been measured. RESERCH DESIGN AND METHODS: Plasma and vitreous fluid from 22 diabetic patients with PDR and 22 nondiabetic control subjects were analyzed. Somatostatin-14, somatostatin-28 and cortistatin were measured by radioimmunoassay but separation by high-performance liquid chromatography was required to measure somatostatin-14.

RESULTS

The predominant molecular form of somatostatin within the vitreous fluid was somatostatin-28 (fivefold higher than somatostatin-14 in control subjects and threefold higher in patients with PDR). Cortistatin significantly contributed to SLI and its intravitreous levels were higher than those detected in plasma (nondiabetic control subjects: 147 [102-837] vs. 78 [24-32] pg/ml; patients with PDR: 187 [87-998] vs. 62 [24-472] pg/ml; P = 0.01 for both). Intravitreous somatostatin-14 was similar in both subjects with PDR and the control group (P = 0.87). By contrast, somatostatin-28 concentration was lower in patients with PDR than in nondiabetic control subjects (350 +/- 32 vs. 595 +/- 66 pg/ml; P = 0.004).

CONCLUSIONS

Somatostatin-28 is the main molecular variant in the vitreous fluid. The intravitreous SLI deficit detected in patients with PDR is mainly due to somatostatin-28. Cortistatin is abundant in the vitreous fluid and significantly contributes to SLI. These findings could open up new strategies for PDR treatment.

Experimental observation of intraocular pressure changes during microkeratome suctioning in laser in situ keratomileusis

PURPOSE

To observe changes in intraocular pressure (IOP), the manner in which the eye is suctioned, and the effect of the number of suction ports.

SETTING

Department of Ophthalmology, Tokyo Dental College, Suidobashi Hospital, Tokyo, Japan.

METHODS

Suction rings with single or dual ports were made of transparent acrylic acid resin to facilitate observation with a digital video camera. The IOP and the duration of the IOP increase (time to reach 90% of the maximum IOP) were measured in 6 porcine eyes with an intra-vein pressure-sensor catheter in the vitreous cavity. The IOP changes were recorded using a personal computer.

RESULTS

Suctioning with single- and dual-port suction rings was similar. The IOP increases with single- and dual-port suction rings were similar (99.1 mm Hg +/- 6.1 [SD] and 99.0 +/- 6.5 mm Hg, respectively) (P=.987). The duration of the IOP increase was also similar (4.21 +/- 0.24 seconds and 4.12 +/- 0.33 seconds, respectively) (P=.190).

CONCLUSIONS

The number of ports did not affect suctioning and changes in IOP. This technique is useful in developing the ideal shape and setting of the suction ring.

Regional mapping of molecular components of human liquid vitreous by dynamic light scattering

The distribution of particle sizes was studied in six regions of human liquid vitreous samples. Particle sizes were calculated from dynamic light scattering measurements as hydrodynamic diameter of molecules. In general, particle sizes increased progressively from anterior (near lens) to posterior (near retina). A much weaker trend of increase in particle size was found from nasal to temporal regions. Relative concentrations of particles of certain sizes were calculated from dynamic light scattering parameters. Viscosity coefficients of liquid vitreous samples were measured in a semi-micro viscometer. Hyaluronan concentrations increased from anterior to posterior and the reverse was true for viscosity, implying that the lower concentration of hyaluronan near the lens was offset by increased molecular size. A similar concentration gradient was found with the 6 nm diameter particles, and to a lesser degree with the 15 nm particles. The identities of these proteins must be resolved by techniques of proteomics.

AAV-mediated intravitreal gene therapy reduces lysosomal storage in the retinal pigmented epithelium and improves retinal function in adult MPS VII mice

The beta-glucuronidase-deficient mucopolysaccharidosis type VII (MPS VII) mouse accumulates partially degraded glycosaminoglycans in many cell types, including retinal pigmented epithelial (RPE) cells in the eye. This lysosomal storage in RPE cells leads to progressive retinal degeneration and reduced function as measured by flash electroretinography (ERG). The impact of AAV-mediated intraocular gene therapy on pathology and retinal function was examined in normal and MPS VII mice treated at 4 weeks of age, when lysosomal storage is evident but functional impairment is minimal in affected animals. At 16 weeks, an age at which untreated MPS VII mice have advanced histologic lesions and significantly reduced ERG amplitudes, treated eyes had nearly normal levels of beta-glucuronidase activity, preservation of cells in the outer nuclear layer of the retina, and decreased lysosomal storage within the RPE. The AAV-treated MPS VII mice also had significantly increased dark-adapted ERG amplitudes compared to untreated MPS VII mice. Although retinal function was improved, the efficacy of the treatment depended heavily on parameters related to the injection procedure, such as the injection volume, injection site, and vector dose. These data suggest that intraocular AAV-mediated therapy may be efficacious for treating the retinal disease associated with certain lysosomal storage diseases.

Functional Properties of Hyalocytes under PDGF-Rich Conditions

PURPOSE

To investigate the functional properties and intracellular signaling of hyalocytes under platelet-derived growth factor (PDGF)-rich conditions.

METHODS

The hyalocytes were isolated from bovine eyes and identified by immunocytochemistry and electron microscope. The expression of PDGF receptor alpha/beta and its phosphorylation in response to PDGF-BB was analyzed by Western blot analysis. PDGF-BB-induced proliferation and migration were evaluated by thymidine uptake and Boyden's chemotaxis assay. The expression of the urokinase-type plasminogen activator (uPA) gene and the fibrinolytic activity were assessed by Northern blotting and fibrin zymography. An in vitro type I collagen gel contraction assay was performed to determine the effect of PDGF-BB on cellular contraction.

RESULTS

The hyalocytes were immunocytochemically positive for S-100 and negative for glial fibrillary acidic protein (GFAP) and cytokeratin, as previously described. The electron microscope demonstrated that hyalocytes possess lysosome-like granules, mitochondria, and micropinocytotic vesicles in their cytoplasm. The hyalocytes expressed PDGF receptor alpha and beta, both of which were immediately phosphorylated in response to PDGF-BB. PDGF-BB also activated p85 PI3-kinase, p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase. PDGF-BB induced thymidine uptake and migration in a concentration-dependent (0-10 ng/mL) manner. Inhibitors of the respective kinases prohibited PDGF-BB-dependent thymidine uptake and migration with the exception of the p44/p42 MAP kinase inhibitor, which displayed no inhibitory effects on migration. PDGF-BB increased uPA gene expression and fibrinolytic activity. Collagen gel contraction observed under PDGF-BB-rich conditions was not prohibited by the respective inhibitors investigated.

CONCLUSIONS

The hyalocytes demonstrated macrophage-like characteristics and may have both physiologic and pathologic roles, such as the maintenance of vitreous transparency through fibrinolytic activity and the pathogenesis of proliferative-vitreoretinal diseases through cellular proliferation and vitreous hyper-contraction.

Volume Phase Transition of Bovine Vitreous Body in Vitro and Determination of Its Dynamics

The phase equilibrium property and structural and dynamical properties of bovine vitreous body was studied by macroscopic observation of swelling behavior and dynamic light scattering under various conditions. It was found that the vitreous body collapses into a compact state isotropically or anisotropically depending on the external conditions. The vitreous body collapses while maintaining the shape when the pH (</= 4) and the concentration of calcium ions (</= 1 mol/L) are changed, whereas it collapses along the orbital axis in a mixed solvent of methanol and water. From observations of the dynamics of light scattered by the vitreous body, intensity autocorrelation functions that revealed two independent diffusion coefficients, D(fast) = 7.8 +/- 1.5 x 10 (- 8) cm(2)/s and D(slow) = 3.8 +/- 0.60 x 10 (-9) cm(2)/s, were obtained. The diffusion coefficients were found to be statistically independent of position within a focal depth range of 1-1.5 mm. Divergent behavior in the measured total scattered light intensities and diffusion coefficients was observed as the concentration of calcium ion approached the critical threshold, 1 mol/L. Namely, a slowing down of the dynamic modes accompanied by increased "static" scattered intensities was observed. The divergent behavior in the scattered light intensities and diffusion coefficients was reversible. This is indicative of the occurrence of a phase transition upon calcium ion concentration.

Effects of Optically Imposed Astigmatism on Emmetropization in Infant Monkeys

PURPOSE

Although astigmatism is prevalent during early infancy, the influence of astigmatism on early refractive development is unclear. This study was undertaken to determine the effects of astigmatism on emmetropization in monkeys.

METHODS

Infant rhesus monkeys (n = 39) were exposed to optically simulated astigmatism in one or both eyes from approximately 1 to 4 months of age. With-the-rule, against-the-rule, and oblique astigmatisms were optically simulated by appropriately orienting the principal meridians of the spherocylindrical treatment lenses (+1.50 -3.00 D x 90 degrees, 180 degrees, 45 degrees, or 135 degrees; i.e., +1.50 and -1.50 D powers in the two principal meridians). Refractive development was assessed every 2 to 3 weeks by cycloplegic retinoscopy, keratometry and corneal videotopography, and A-scan ultrasonography. Data from 19 control monkeys, including 3 animals that were reared with binocular plano lenses, were used for comparison purposes.

RESULTS

Most of the cylinder-lens-reared monkeys, regardless of the orientation of the imposed astigmatism, showed clear signs of either hyperopic or myopic growth compared with control monkeys. The distributions of refractive error and vitreous chamber depth both showed bimodal patterns that differed from normal by amounts equivalent to the optical powers of the principal meridians of the treatment lenses. More frequently, refractive development was biased toward the eye's least-hyperopic focal plane. The refractive changes were mainly axial. After lens removal, the lens-reared monkeys recovered and as a group exhibited refractive errors and axial dimensions similar to those in control monkeys.

CONCLUSIONS

In the presence of significant amounts of astigmatism, emmetropization is directed toward one of the two focal planes associated with the astigmatic principal meridians and not the circle of least confusion. These results suggest that the mechanisms responsible for emmetropization are insensitive to stimulus orientation and the global form of the retinal image. It appears that emmetropization seeks out the image plane that contains the maximum effective contrast integrated across spatial frequency and stimulus orientation.

Aqueous Flow through the Iris???Lens Channel: Estimates of Differential Pressure between the Anterior and Posterior Chambers

PURPOSE

To explore the hypothesis that differential pressure between the anterior and posterior chambers arises from the dynamics of aqueous flow across the iris-lens channel.

METHODS

Navier-Stokes equations of fluid dynamics were derived and evaluated numerically for a viscous homogeneous isotropic fluid (aqueous) passing through the iris-lens channel, which is a spherical disc-shaped region conforming to the lens curvature while maintaining a separation distance (channel height) over a certain disc width (channel length). The effect of iridotomy was assessed using Poiseuille flow dynamics.

RESULTS

In the absence of measured values, ranges of anatomic and physiological variables were used for calculations. The magnitude of the posterior to anterior pressure difference was greater with increases in channel length or aqueous flow and with decreases in channel height or pupil diameter. With a nominal channel length of 0.5 mm, aqueous outflow of 2.2 microl/min, and pupil diameter of 1 mm, the pressure difference increased from 0.9 to 10 mm Hg when the channel height decreased from 7 to 3 microm. A channel height of 10 microm or greater reduced the pressure difference below 1 mm Hg for the full range of other channel parameters considered. A 50-microm iridotomy reduced the pressure difference below 1 mm Hg.

CONCLUSIONS

The flow of aqueous through the iris-lens channel is driven by the pressure differential between the posterior and anterior chambers. Viscous forces within the aqueous govern the magnitudes of the flow resistance and the pressure differential. The geometry and dimensions of a specific iris-lens channel will determine whether the pressure differential is of clinical significance.

Modifications of the falciform process in the eye of beloniformes (Teleostei: Atherinomorpha): evolution of a curtain-like septum in the eye

In order to comparatively analyze curtain-like septa in the eyes of visually orientated "close-to-surface-predators" among atherinomorph teleosts, we examined the eyes of 24 atherinomorph species under a binocular microscope with regard to the falciform process and related structures in the vitreous cavity. Additionally, falciform process samples were analyzed by transmission electron microscopy. All the studied representatives of the Cyprinodontiformes and Atheriniformes, and of one of the beloniform suborder, Adrianichthyioidei, possess a "typical" processus falciformis. In the eyes of the representatives of the other beloniform suborder, Belonoidei, however, pigmented structures that originate in the region of the optic disc and protrude into the vitreous cavity were noted. In the Hemiramphidae (halfbeaks) and Exocoetidae (flying fishes) these pigmented structures have a more cone-like shape, whereas in the Belonidae (needlefishes) and Scomberesocidae (sauries) horizontally oriented heavily pigmented curtain-like septa occur that divide the vitreous cavity dorsoventrally. It is suggested that the "typical" processus falciformis represents a plesiomorphic feature within the Atherinomorpha, whereas the pigmented modifications of the falciform process must be seen as a synapomorphic character state of the Belonoidei. The curtain-like septum of the Belonidae and Scomberesocidae might have evolved from the cone-like structures that are found in the Exocoetoidea. The functional significance of the pigmented structures in the eye is as yet not clear, except for the curtain-like septum found in Belonidae. It might play a role in visual orientation near the water surface at Snell's window.

The blood–retinal barriers system. Basic concepts and clinical evaluation

Morphological studies demonstrating the presence in the retinal vessels of 'zonulae occludente' between the endothelial cells and physiological studies examining diffusion gradients in the vitreous after systemic or intravitreal administration of fluorescein, performed under the guidance of David Maurice, established the basis of the Blood-Retinal Barrier (BRB) concept. The BRB system is briefly reviewed as well as its role in health and disease. Regulation of the microenvironment of the retina is fundamental for appropriate retinal function and vision. The diffusional characteristics and transport functions of the BRB system may be evaluated and followed by vitreous fluorometry. Its clinical use has shown the importance of BRB alterations in a variety of retinal diseases but has been restricted by the lack of disease specificity. A recent development, the Retinal Leakage Analyzer, maps BRB alterations and has opened new perspectives for multimodal macula mapping and improved evaluation of newly available drugs that show promise for stabilizing the BRB.

[Vitreous and macular diseases]

We investigated the vitreous in its origin, morphology, metabolism and regeneration, and its role in various vitreomacular diseases. Focal vitreous liquefaction developed anterior to a laser induced chorioretinal scar in rabbit eyes, which suggested that a normal retina is necessary to maintain the integrity of the vitreous. We measured levels of hyaluronic acid and of the precursor of type II collagen in vitreous samples obtained by vitrectomy. Those levels declined with age in women. The precursor of type II collagen was at the same level in the samples from vitrectomy and those obtained by fluid air exchange, which suggested a persistent secretion of type II collagen into the vitreous cavity even after vitrectomy. We found a posterior precortical vitreous pocket in human autopsied eyes whose vitreous was stained with fluorescein. Using the same methods, we confirmed the presence of intravitreal fibrous membranes in the "tractus" in the anterior vitreous. In clinical studies using biomicroscopy, observations during surgery, scanning laser ophthalmoscopy, and optical coherence tomography (OCT), we clarified the role of premacular vitreous cortex which forms the posterior wall of the "pocket" in the premacular membrane and macular hole. The premacular vitreous cortex seems to be the main structure of the premacular membrane and its contraction may cause macular hole. Ring-shaped proliferation tends to develop along the outer margin of the "pocket". OCT demonstrated that some diabetic macular edema is caused by traction of the premacular vitreous cortex. Vitrectomy appear to be effective for diabetic macular edema by eliminating vitreous traction and the accumulated cytokine in the "pocket". The retina appears to have a program for vitreous metabolism throughout life, including the premacular pocket formation.

[Cell biology of hyalocytes]

There is a group of cells, called hyalocytes, in the cortical vitreous. Although hyalocytes were discovered more than a hundred years ago, the molecular and cellular biological characteristics of hyalocytes have yet to be elucidated. In this study, we investigated various aspects of hyalocytes and, also performed triamcinolone acetonide (TA)-assisted vitrectomy to remove the hyalocytes for diabetic macular edema. Immunohistochemical analysis of rat eyes showed that 90% of hyalocytes were negative for ED1 but positive for ED2, indicating that hyalocyte is a tissue macrophage. Chimeric mice were created by transplanting bone marrow from green fluorescent protein (GFP)-transgenic mice into irradiated wild-type mice, showing the origin of hyalocyte to be bone marrow cells. Bovine hyalocytes were cultured successfully. The proliferation of hyalocytes was significantly enhanced by hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), and fibroblast growth factor (FGF-2) and inhibited by transforming growth factor(TGF)-beta. Among these, PDGF-BB stimulated the proliferation most potently through the MEK 1 pathway. Hyalocyte migration assessed by double chamber assay was also stimulated by PDGF-BB and it was mediated by the PI3K and p38 MAPK pathways. Cellular contraction of hyalocyte was significantly enhanced by PDGF-BB and TGF-beta through Rho kinase, p44/42 MAPK, and protein kinase C pathways, as measured by collagen gel contraction assay. Next, the relationship between the vitreous cavity(VC) and the immune system was studied after intravitreous inoculation with ovalbumin (OVA). Injection of OVA into the VC of C 57 BL/6 mice resulted in suppressed systemic cell-mediated immunity to OVA as determined by the ear swelling assay. This aberrant immune responsiveness following VC injection of OVA was termed VC-associated immune deviation or VCAID. The phenomenon of VCAID was mediated by intravitreous antigen-presenting cells. The histological study of chimeric mice showed these cells to be intravitreous residential cells, namely hyalocytes. VCAID was abolished by intravitreous inflammation such as experimental autoimmune uveitis. Finally, TA-assisted vitrectomy for diabetic macular edema was performed to remove cortical vitreous, because it contained many hyalocytes which could secrete inflammatory cytokines including VEGF. Although the number of treated eyes was limited, the surgical results have been favorable so far. The investigation of hyalocytes would open a new avenue for better understanding and development of treatment for various vitreo-retinal diseases.

The relationship between the Stiles-Crawford effect of the first kind (SCE-I) and myopia

The Stiles-Crawford effect of the first kind (SCE-I) was measured on both emmetropic and myopic subjects at six different retinal locations. The results revealed a number of significant discrepancies in receptor alignment between the groups of different refractive errors. In myopic subjects, the receptors in the nasal retina (i.e. between the fovea and the optic nerve head) were found to be aligned nasally towards the optic nerve head, whereas the receptors in the temporal retina were aligned towards the centre of the exit pupil. In emmetropic subjects, the receptors across the retina were finely tuned towards the centre of the exit pupil. The magnitude of the receptor displacement in myopic subjects was found to be directly associated with the length of the eyeball.

Radiation force imaging of viscoelastic properties with reduced artifacts

It is well-known that changes in the mechanical properties of tissues are correlated with the presence of disease. In the eye, for example, the vitreous body undergoes dramatic changes in mechanical properties during age-related degradation. These changes may play a significant role in the formation of retinal detachment or other vitreoretinal diseases. We previously presented a noninvasive method called kinetic acoustic vitreoretial examination (KAVE), which may be used to detect these mechanical changes. KAVE uses acoustic radiation force as a means to produce small, localized displacements within the tissues. Returning echoes are processed using ultrasonic motion tracking so that the response of the tissue to the induced force can be evaluated. By repeating this process at a number of locations, images depicting viscoelastic properties of tissues can be formed. Through the combination of appropriate mechanical modeling and signal processing, we are able to generate images of parameters such as relative mass, relative elasticity, and relative viscosity. These parameters are called relative because they depend on the force applied, which is typically unknown. In this paper, we present new force-free images depicting the time constant tau, the damping ratio xi, and the natural frequency omega of the phantom material. These images are significant in that they lack the artifacts common in the relative property images. Experiments were conducted on a set of three acrylamide-based phantoms with varying gel concentrations. We present images depicting B-mode echogenicity, maximum radiation force-induced displacement, relative material parameters, and force-free characteristics of the series of phantoms. The presented force-free images depict mechanical properties without artifacts from local force variation due to acoustic reflection, refraction, and attenuation. Force-free images should prove particularly useful for in vivo imaging through inhomogeneous tissues.

Intravitreal injections of neurotrophic factors and forskolin enhance survival and axonal regeneration of axotomized beta ganglion cells in cat retina

Some retinal ganglion cells in adult cats survive axotomy for two months and regenerate their axons when a peripheral nerve is transplanted to the transected optic nerve. However, regenerated retinal ganglion cells were fewer than 4% of the total retinal ganglion cell population in the intact retina. The present study examined the effects of intravitreal injections of neurotrophic factors (brain-derived neurotrophic factor, ciliary neurotrophic factor, basic fibroblast growth factor, glial cell-derived neurotrophic factor, neurotrophin 4), first on the survival of axotomized cat retinal ganglion cells within 2 weeks, and then on axonal regeneration of the retinal ganglion cells for 2 months after peripheral nerve transplantation. We tested first enhancement of the survival by one of the factors, and then one or two of them supplemented with forskolin, which increases intracellular cAMP. Single injections of 0.5 microg or 1 microg brain-derived neurotrophic factor, 1 microg ciliary neurotrophic factor, or 1 microg glial cell-derived neurotrophic factor significantly increased total numbers of surviving retinal ganglion cells; 1.6-1.8 times those in control retinas. Identification of retinal ganglion cell types with Lucifer Yellow injections revealed that the increase of surviving beta cells was most conspicuous: 2.5-fold (brain-derived neurotrophic factor) to 3.6-fold (ciliary neurotrophic factor). A combined injection of 1 microg brain-derived neurotrophic factor, 1 microg ciliary neurotrophic factor, and 0.1 mg forskolin resulted in a 4.7-fold increase of surviving beta cells, i.e. 50% survival on day 14. On the axonal regeneration by peripheral nerve transplantation, a combined injection of brain-derived neurotrophic factor, ciliary neurotrophic factor, and forskolin resulted in a 3.4-fold increase of beta cells with regenerated axons. The increase of regenerated beta cells was mainly due to the enhancing effect of neurotrophic factors on their survival, and possibly to a change of retinal ganglion cell properties by cAMP to facilitate their axonal regeneration.

Age-dependent changes in the basal retinovitreous adhesion

PURPOSE

To determine the width of the posterior vitreous base in human eyes of different ages and to clarify the nature of the postoral retinovitreous adhesion that underlies the development of juxtabasal retinal tears and retinal detachment after posterior vitreous detachment (PVD).

METHODS

The posterior limit of the vitreous base was delineated with indocyanine green after mechanical peeling of the postbasal vitreous cortex from the retina in 58 pairs of donor eyes. The area of residual retinovitreous adhesion was measured by image analysis. Scanning electron microscopy was performed on the undersurface (or retinal aspect) of the inner limiting lamina (ILL) after trypsin digestion of the peripheral retina.

RESULTS

An age-dependent increase in the anteroposterior dimension of the posterior vitreous base was revealed that became progressively wider in eyes of male donors than in those of female donors and in the nasal half compared with the temporal half of the globe. Ultrastructural studies showed progressive invasion of the innermost peripheral retina by bundles of collagen fibrils, initially in the form of characteristic braids splaying out beneath the ILL and eventually as a dense sublaminar mat in the elderly. The collagen fibrils penetrated the ILL through localized defects and intertwined with those in the basal gel.

CONCLUSIONS

With aging, the posterior border of the vitreous base migrates posteriorly so that an annular band of firm adhesion eventually straddles the ora serrata eccentrically. Intraretinal synthesis of collagen fibrils, their penetration of the ILL, and their splicing with cortical vitreous fibrils, underlie the slowly evolving retinovitreous adhesion.

Vitreous induces components of the prostaglandin E2 pathway in human retinal pigment epithelial cells

PURPOSE

To investigate the alterations in gene expression when human retinal pigment epithelial (RPE) cells in culture are treated with vitreous as a model for the changes that occur in proliferative vitreoretinopathy.

METHODS

Human RPE cells were cultured with or without human vitreous or collagen. RNA was extracted and reverse transcribed. The RNAs expressed were compared by using DNA macroarrays. Messenger RNA levels were also measured using real-time reverse transcription polymerase chain reaction. Protein expression was examined by immunoblot analysis. Immunoassays were used to determine levels of prostaglandin E(2).

RESULTS

Vitreous treatment of RPE cells resulted in increased expression of two critical enzymes in the synthesis of prostaglandin E(2): membrane-associated prostaglandin E-synthase (mPGES) and cyclooxygenase (COX)-2. Increased levels of mPGES RNA and protein were still present at 48 hours of treatment, but the increase in COX-2 mRNA and protein was transient. The increase in the expression of mPGES was associated with an increase in the production of prostaglandin E(2) that was observed at 12 and 24 hours of treatment but not at 48 hours. Treatment with 100 microg collagen I per ml medium did not cause increased expression of mPGES and COX-2, even though both collagen- and vitreous-treatment caused a morphologic change in the RPE cells to a more fibroblast-like phenotype.

CONCLUSIONS

Treatment of human RPE cells with vitreous induces changes in gene expression that are indicative of an inflammatory response.

Vitreous is a barrier in nonviral gene transfer by cationic lipids and polymers

PURPOSE

To investigate the role of vitreous in nonviral gene delivery into retinal pigment epithelial (RPE) cells.

METHODS

Human RPE cell line D407 was cultured in six-well plates. Bovine vitreous, hyaluronan, or DMEM was added on the cells. Complexes of DNA and cationic carriers (polyethyleneimine, poly-L-lysine, DOTAP liposomes) were pipetted onto the vitreous, hyaluronan, or DMEM. Cellular uptake of DNA was studied with ethidium monoazide DNA and gene expression with GFP-plasmid complexes. FITC-dextrans and FITC-polylysines were used to probe the effects of the size and cationic charge on permeation in the vitreous in a similar experimental setup. Fluorescent cells were analyzed by flow cytometry.

RESULTS

Vitreous decreased the cellular uptake of DNA complexes 2-30 times, and GFP expression was also impaired. In hyaluronan solutions the cellular uptake of the complexes was also decreased significantly in most cases. In vitreous, cellular uptake of all FITC-dextrans decreased slightly, and uptake of poly-L-lysines was decreased substantially, whereas in hyaluronan solutions the effects were mild or nonexistent.

CONCLUSIONS

Polymeric and liposomal gene delivery is substantially limited by the vitreous. This is probably because of the size and charge of the retinal gene delivery after intravitreal injections.

Effect of local hypothermia on the anterior chamber and vitreous cavity temperature: in vivo study in rabbits

BACKGROUND

This study aims to record the variations of the anterior chamber and vitreous cavity temperature after application of local hypothermia.

MATERIAL AND METHODS

Local hypothermia was applied on 20 rabbits' eyes after general anesthesia using a liquid which had been placed in a special plastic container and had been frozen at -20 degrees C. In 10 rabbits (Group A) the frozen container was placed on the eyes without direct contact with the cornea, the hypothermia being applied through the eyelids, for 10 min. In the other 10 rabbits (Group B), the container was in direct contact with the cornea for 10 min. After that time, both the anterior chamber and vitreous cavity temperatures were measured in both groups using a special 20 G tip and were recorded with a digital thermometer (BAT-10, Physitemp Instruments Inc.). Reactions on the fundus were assessed by indirect ophthalmoscopy one day after hypothermia application.

RESULTS

Mean reduction from the body temperature of temperature in the anterior chamber and in the vitreous was 10 +/- 1 degrees C and 4.2 +/- 0.5 degrees C respectively for Group A, and 20 +/- 0.8 degrees C and 8.5 +/- 0.5 degrees C respectively for Group B. All differences were statistically significant.

CONCLUSIONS

Our study shows that local hypothermia application, even without direct contact with the cornea, reduces significantly the temperature in the center of the vitreous in rabbits. This temperature reduction could be beneficial in conditions of intraocular inflammation, where hypothermia could act synergetically with other means to decrease the anterior and/or posterior segment inflammation.

Loss of RPE phenotype affects phagocytic function

BACKGROUND

Cultured retinal pigment epithelial (RPE) cells exposed to vitreous lose their cuboidal epithelial phenotype and transform to a fibroblast-like morphology. This study investigates whether the loss of RPE phenotype will affect the ability of RPE to phagocytize photoreceptor outer segments (ROS).

METHODS

First-passage porcine RPE cells were grown to confluence and exposed to an equal mixture of freshly homogenized vitreous and DMEM (10% FBS) for 48 h to allow transformation to occur. The phagocytic ability of normal epithelial and vitreous-transformed RPE cultures was evaluated by determining the number of ROS bound and ingested. The expression and distribution of alphavbeta5 integrin in control and vitreous-treated RPE were examined by immunoprecipitation coupled with immunoblotting and immunohistochemistry and the contribution of alphavbeta5 integrin to ROS phagocytosis was evaluated using a functional blocking antibody.

RESULTS

Bound ROS on vitreous-transformed RPE decreased to 33% of control and ingested ROS decreased to 47%. The expression of alphavbeta5 integrin was decreased significantly following vitreous transformation as compared with controls and the immunolocalization of alphavbeta5 on control RPE was restricted to apical patches while on vitreous-treated RPE, labeling was diminished and randomly dispersed. Five times less blocking antibody was required to attain maximal phagocytic inhibition in these cultures, but some phagocytic activity remained in both normal and transformed cultures even at saturating concentrations.

CONCLUSION

The decrease in ROS phagocytosis observed in transformed RPE correlated with the down- regulation of alphavbeta5 integrin expression and its random distribution on the RPE.

Rat retinal ganglion cell loss caused by kainate, NMDA and ischemia correlates with a reduction in mRNA and protein of Thy-1 and neurofilament light

Quantification of retinal ganglion cell (RGC) loss/survival following a defined insult to the retina is a prerequisite in order to allow a comparison to be made between the effectiveness of potential neuroprotective drugs. The purpose of the present study was to extend the characterisation of our previously published semiquantitative RT-PCR assay to assess RGC loss/survival. Comparisons were made between the total mRNA levels of the ganglion cell-specific markers Thy-1 and neurofilament light (NF-L) in the retina at specific times after an intravitreal injection of N-methyl-D-aspartate (NMDA) or kainate or after 45 min of ischemia/reperfusion and also between the levels of NF-L mRNA and protein at various times after NMDA injection. Changes in Thy-1 and NF-L immunoreactivities were also observed. NMDA, kainate and ischemia/reperfusion all caused a reduction in the retinal content of Thy-1 and NF-L mRNAs and immunoreactivities. An excellent correlation was observed between the levels of the two mRNAs after these treatments. After NMDA, loss of NF-L mRNA was shown to precede loss of NF-L protein but total loss of each marker was similar after 7 days. The results of the study demonstrate that injury and subsequent death of RGCs, which occurs after ischemia/reperfusion and after intraocular injection of NMDA or kainate, can be followed by measurement of total retinal levels of Thy-1 and NF-L mRNAs and NF-L protein. The assays provides accurate, practical and complementary methods for assessing the potential benefits of neuroprotective drugs on RGCs which have been injured by a variety of experimental modalities.

A direct contact between astrocyte and vitreous body is possible in the rabbit eye due to discontinuities in the basement membrane of the retinal inner limiting membrane

Different from most mammalian species, the optic nerve of the rabbit eye is initially formed inside the retina where myelination of the axons of the ganglion cells starts and vascularization occurs. Astrocytes are confined to these regions. The aforementioned nerve fibers known as medullated nerve fibers form two bundles that may be identified with the naked eye. The blood vessels run on the inner surface of these nerve fiber bundles (epivascularization) and, accordingly, the accompanying astrocytes lie mostly facing the vitreous body from which they are separated only by the inner limiting membrane of the retina. The arrangement of the astrocytes around blood vessels leads to the formation of structures known as glial tufts. Fragments (N = 3) or whole pieces (N = 3) of the medullated nerve fiber region of three-month-old male rabbits (Orictolagus cuniculus) were fixed in glutaraldehyde followed by osmium tetroxide, and their thin sections were examined with a transmission electron microscope. Randomly located discontinuities (up to a few micrometers long) of the basement membrane of the inner limiting membrane of the retina were observed in the glial tufts. As a consequence, a direct contact between the astrocyte plasma membrane and vitreous elements was demonstrated, making possible functional interactions such as macromolecular exchanges between this glial cell type and the components of the vitreous body.

Evaluation of fibroblast growth factor signaling during lens fiber cell differentiation

PURPOSE

Previous studies have implicated members of the fibroblast growth factor (FGF) and insulin-like growth factor (IGF) families as stimulators of lens fiber cell differentiation in rodent and chicken embryo lenses, respectively. In the present study, the role of FGFs in fiber cell differentiation and epithelial cell proliferation in chicken embryos was examined.

METHODS

Lenses were injected on embryonic day (E)3 with replication-defective retroviruses that express full-length or truncated FGF receptor (FGFR)-1 or a secreted form of FGF1. Lens epithelial explants were cultured in defined medium or medium supplemented with FGFs or vitreous humor, in the presence or absence of the FGF receptor antagonist SU5402. Explants were also cultured in vitreous humor that had been depleted of heparin-binding growth factors. Cell elongation was measured optically and protein accumulation by densitometry and Western blot analysis.

RESULTS

Lens fiber cell differentiation was not inhibited in cells infected with virus expressing truncated FGFR1. Epithelial cells infected with virus encoding a secreted form of FGF1 did not differentiate into ectopic fiber cells. Viral transduction of FGFR1, truncated FGFR1, or FGF1 did not appreciably alter the proliferation of lens epithelial cells. Bovine vitreous humor stimulated chicken embryo lens epithelial cells to elongate and express markers of lens fiber cell differentiation. Bovine vitreous humor, but not FGF2, protected lens epithelial cells from apoptosis. Depleting vitreous humor of heparin-binding growth factors or treatment of lens cells with SU5402 did not inhibit the initial, rapid phase of lens cell elongation. Both treatments, used separately or together, reduced but did not prevent the expression of later markers of fiber cell differentiation.

CONCLUSIONS

Fiber differentiation factors that are not members of the FGF family are present in chicken and mammalian vitreous humor. The factors that stimulate fiber cell differentiation in avian and mammalian eyes are similar.