Retinal oxalosis. A clinicopathologic report.

A 55-year-old woman with chronic renal failure treated with hemodialysis had severe bilateral visual loss develop due to retinal ischemia. Ophthalmoscopy showed crystals in the distribution of the retinal arteries, but not veins, and this led to a diagnosis of systemic oxalosis. Factors contributing to systemic oxalosis in addition to renal failure were ascorbic acid dietary supplementation, pyridoxine deficiency, and ileal resection. Histopathologic findings showed ocular calcium oxalate deposition limited nearly entirely to the walls of retinal blood vessels.

Alpha transducin is present in blue-, green-, and red-sensitive cone photoreceptors in the human retina.

Phototransduction in vertebrate rod and cone photoreceptor cells involves G protein-mediated light stimulation of cGMP hydrolysis. Enzymes of the cGMP hydrolysis cascades of rods and cones are products of different genes. Three different classes of cones in the human retina are maximally sensitive to either blue, green, or red light. Distinct opsin genes are expressed in each type of cone. The distribution of cone types in human retina was determined using anti-peptide antibodies that recognize specific amino acid sequences in green/red opsin and blue opsin. These antibodies together with an anti-peptide antibody against Tc alpha were used in double labeling experiments to demonstrate the presence of the Tc alpha peptide in all types of cones. cDNA clones corresponding to human rod and cone transducin alpha subunit (Tr alpha and Tc alpha) genes were isolated. Southern blot analyses of human genomic DNA suggest that there is only one rod T alpha gene but more than one cone T alpha gene. The multiple Tc alpha genes could be closely related genes or different Tc alpha alleles, or one could be a pseudogene.

Aspergillus necrotizing retinitis. A clinico-pathologic study and review.

The authors describe a case of bilateral acute necrotizing retinitis caused by Aspergillus fumigatus in an immunocompromised host. The patient rapidly lose useful vision and expired from progressive systemic disease while on parenteral amphotericin B. Postmortem aqueous cultures were negative whereas vitreous cultures were positive. Light and electron microscopy demonstrated marked choroidal and retinal vascular occlusion by fungi and thrombi, hyphae extending through vessel walls and the internal limiting membrane of the retina, fungi accumulating in tissue spaces, hyphae on the iris surface, and necrosis of the retina. In view of the extensive vascular occlusion present in this disease, early diagnostic vitrectomy plus intravitreal amphotericin B is recommended to deliver adequate drug levels to infected sites.

Long-term corneal retention of a plant foreign body.

A fragment of sunflower stalk had been retained in the cornea of a 71-year-old man for 58 years. During initial healing of the wound, which included formation of a retrocorneal membrane over the foreign body in the anterior chamber, there was probably loss of endothelial cells. This probably predisposed the cornea to the endothelial decompensation that occurred following cataract extraction and implant of an intraocular lens 56 years after the foreign body first appeared in the cornea.

Standardized intravitreal injections: evaluation of the effect of anesthesia on rapid axonal transport in the optic nerve.

Retinal ganglion cells incorporate intravitreally injected [3H]leucine into proteins that are transported orthogradely in optic axons to the superior colliculus. Since optic projections in the albino rabbit are nearly totally crossed, an agent suspected to alter axonal transport can be applied to one optic nerve after bilateral intravitreal injection of [3H]leucine; any reduction in radioactivity transported to the contralateral superior colliculus can then be quantified. Such studies require symmetric uptake and incorporation of precursor into ganglion cell proteins. A technique is described for intravitreal injections that reproducibly produces symmetric uptake of [3H]leucine. Using this technique, we determined that retrobulbar injected lidocaine in clinically used doses (2-4%) does not affect rapid axonal transport, while colchicine (a known inhibitor of axonal transport) blocks transport in a dose-related fashion.

Distribution of membrane proteins in mechanically dissociated retinal rods.

Solitary rods were isolated from frog retinas by mechanical dissociation. Typically, the rods cleave sclerad to the nucleus and consist of outer segments with attached partial inner segments with either tapered or rounded profiles. Light and electron microscopy reveal that the outer and inner segments of rods with tapered inner segments, like rods in the intact retina, are joined by a single connecting cilium. In contrast, the outer and inner segments of rods with rounded inner segments are fused, with no extracellular cleft between the two segments. Opsin distribution was studied in both unfused and fused rods by light and electron microscopic immunocytochemistry. Extensive surface labeling is restricted to the outer segments of tapered rods, as observed in vivo. In contrast, both inner and outer segments of rods with rounded inner segments (fused) label heavily with anti-opsin. Thus opsin, a mobile membrane protein, diffuses from the outer to the inner segment of fused rods. Segregated distribution of opsin in unfused rods suggests that the connecting cilium and/or its associated structures may normally act as a diffusion barrier between the outer and inner segments to mobile membrane proteins such as opsin. Immunofluorescence studies demonstrate that Na+/K+ ATPase is restricted in distribution to the inner segment and calycal processes of both fused and unfused isolated rods, as observed in vivo. Maintenance of its restricted distribution in fused cells indicates that Na+/K+ ATPase is not mobile and may be tethered in the surface membrane of the inner segment.

Optic nerve head axonal transport in rabbits with hereditary glaucoma.

Rabbits with hereditary glaucoma develop ocular changes that resemble human congenital glaucoma and buphthalmia. The inheritance is autosomal recessive (bu). Previous research was performed primarily on albino bu/bu rabbits that were unhealthy and bred poorly. We have bred pigmented bu/bu rabbits to determine if this would improve hardiness and provide a better model for the disease in humans. First-generation offspring from matings of bu/bu albino with bu/bu pigmented rabbits were all affected, indicating that the bu gene is found at the same locus in both strains. The pigmented bu/bu offspring had a high degree of mortality, as reported previously for albino bu/bu rabbits. Newborn bu/bu rabbits initially had normal intraocular pressure (IOP; 15-23 mmHg); after 1- to 3 months, the IOP increased to 26-48 mmHg. The eyes became buphthalmic and the IOP returned to normal or sub-normal levels after 6-10 months. Since the lamina cribrosa is absent or poorly formed in the rabbit optic nerve head (ONH), this model was used to test the role of mechanical factors in the etiology of ONH pathology caused by increased IOP. Orthograde axonal transport was evaluated in both eyes from eight normal and 24 bu/bu rabbits of different ages, using intravitreal injections of [3H]leucine to mark orthograde axonal transport, followed by light- and electron-microscopic radioautography of the ONHs and superior colliculi. Normal rabbits of all ages showed no blockage of axonal transport in the ONH. All optic axons from young bu/bu rabbits with normal IOP and most axons from older buphthalmic rabbits that previously had elevated IOP were normal morphologically. Small zones of transport blockage occurred in bu/bu eyes while IOP was elevated; most affected axons lay immediately adjacent to ONH connective tissue beams that radiate outward from the central retinal vessels to the optic-nerve sheath. Thus, the rabbit, which lacks a true lamina cribrosa, does not show marked blockage of axonal transport as occurs in the LS of the monkey and cat ONH when IOP is elevated acutely. This anatomic difference appears to be protective against axonal damage, since bu/bu rabbits with chronic IOP elevation did not show significant loss of optic axons. These results are consistent with the proposed 'mechanical' theory of ONH damage resulting from increased IOP. Electron-microscopic radioautography revealed that chronically elevated IOP in bu/bu rabbits, which caused small foci of blocked ONH axonal transport against ONH beams, also caused degeneration of a few optic nerve terminals in the superior colliculi as the disease progressed.(ABSTRACT TRUNCATED AT 400 WORDS)

Congenital iris cysts.

Unilateral, spontaneous, non-pigmented iris cysts appeared before the age of 2 years in four patients. Histopathological specimens obtained in three cases showed stratified to cuboidal, non-pigmented, epithelial lined cysts. Goblet cells were recognised in two of the three specimens. The clinical features and histopathological findings indicate that these cysts are derived from surface ectoderm and may be congenital.

Uveoretinitis in rabbits following immunization with interphotoreceptor retinoid-binding protein.

Interphotoreceptor retinoid-binding protein (IRBP) is a glycoprotein found in the interphotoreceptor matrix between the neurosensory retina and the retinal pigment epithelium and is thought to shuttle retinol among cells that border the interphotoreceptor space. Immunization of rabbits with bovine IRBP caused subsequent photoreceptor degeneration, as documented by light- and electron microscopy. Beginning on post-injection day 18, scattered regions had photoreceptor outer segments that were disorganized and shortened or absent. Macrophages were found between the retinal pigment epithelium and neurosensory retina and within choroidal interstitium and blood vessels. Labeling of these cells with a marker specific for monocytic macrophages (RAM11) and absence of labeling with a marker for retinal pigment epithelium (rabbit anti-bovine cellular retinaldehyde-binding protein) suggest that these macrophages were hematogenous in origin. Staining of retinas with fluorescein isothiocyanate (FITC)-conjugated sheep anti-rabbit IgG revealed leakage of rabbit IgG into the interphotoreceptor matrix on and after day 18 in experimental animals but not in controls, suggesting breakdown of the outer blood-retinal barrier. Indirect immunofluorescence with anti-glial fibrillary acidic protein revealed labeling of Müller cells in experimental retinas on and after day 18, but not in control or shorter survival experimental retinas. There were foci of increased cellularity in the choroid on days 18, 26 and 39. From days 26 through 67, the retinal pathology became more widespread. Varying degrees of outer-segment degeneration were present in all parts of the retina and in many areas there was total loss of outer segments and loss of some photoreceptor-cell bodies. The inner retina appeared unaffected in all experimental and control retinas. These results demonstrate that injection of rabbits with bovine IRBP causes retinal photoreceptor degeneration as anti-IRBP titers increase and breakdown of the outer blood-retinal barrier ensues. Further studies will be required to elucidate factor(s) that control accessibility of the neurosensory retina to circulating antibodies against IRBP and other intrinsic retinal proteins.

Donor corneal endothelial striae.

Excessive traction during excision of donor corneoscleral buttons can result in damage or death to corneal endothelial cells. This damage manifests as multiple peripheral and, less commonly, central striae or stretch marks that correspond to linear opacities at the level of the endothelium. The striae consist of parallel lines of degenerate endothelium, each line three to eight cells wide, and stain readily with trypan blue, which is indicative of cell damage or death. Light and electron microscopy demonstrates cell membrane lysis with abrupt demarcation between abnormal and normal endothelial cells. The number of these striae correlates with the degree of traction or stretch applied during corneoscleral excision. Careful slit-lamp biomicroscopy of corneoscleral buttons discloses endothelial striae in approximately 5% of specimens. Careful excisions of corneoscleral buttons are necessary to decrease the incidence and severity of endothelial striae.

Identification of specific transducin alpha subunits in retinal rod and cone photoreceptors.

Transducin is a guanyl nucleotide-binding protein that couples rhodopsin photolysis to hydrolysis of guanosine 3',5'-monophosphate in rod photoreceptor cells of vertebrate retinas. Several complementary DNA clones encoding transducin subunits have recently been characterized. One clone, isolated from a bovine retina complementary DNA library, encodes a previously unidentified polypeptide with an amino acid sequence 78% identical to the sequence of the alpha subunit of bovine rod outer segment transducin. Antibodies to a synthetic peptide with amino acid sequence derived specifically from this novel polypeptide recognize a 41-kilodalton polypeptide in homogenates of bovine retina. Localization of this polypeptide in bovine retina by indirect immunofluorescence demonstrates that it is expressed only in cone outer segments. Antibodies to specific sequences found only in the rod transducin alpha subunit recognize a polypeptide localized only in the rod outer segment. Therefore, bovine rod and cone cells each express structurally related yet significantly different forms of transducin.

Breakdown of the outer blood-retinal barrier in experimental commotio retinae.

An animal model has been developed in this study to produce commotio retinae (Berlin's edema) by means of standardized, non-penetrating B.B. pistol injury to the cornea. Parameters have been established to ensure uniform blunt injury, enabling study of the retina and blood-retinal barrier by light- and electron microscopy, including use of horseradish peroxidase as a vascular tracer. Retinal whitening and swelling were found in the peripapillary and central regions, as occurs in the human. The earliest damage involved breakage of the connecting cilia of rods and cones, with rapid disorganization of the outer segments. Later changes included swelling of photoreceptor inner segments and breakdown of the outer blood-retinal barrier at the level of the retinal pigment epithelium. The outer blood-retinal barrier was re-established between 7 and 14 days, and at the longest survival (56 days), incompletely regenerated outer segments were present. This model for commotio retinae provides a new approach for the study of outer-segment regeneration in rods and cones after mechanical injury, as well as mechanisms that underlie re-establishment of the blood-retinal barrier following non-penetrating trauma to the eye.

'Leopard spot' retinopathy in Warburg syndrome.

A female infant with brain and muscle abnormalities characteristic of Warburg syndrome had an atypical retinal dysplasia which appeared clinically as a 'leopard spot' retinopathy. The retinal histology is described in detail and is remarkable for periodic thinning of the inner nuclear layers and for isolated rosettes in the periphery. We believe 'leopard spot' retinopathy is yet another ocular manifestation of the Warburg syndrome.

Retinal neovascularization in Potter's syndrome secondary to renal agenesis.

Abnormalities of retinal vascularization were observed in a male stillborn at 33 weeks gestation with Potter's syndrome secondary to renal agenesis. Each eye had a persistent tunica vasculosa lentis and hyaloid artery as well as enlarged intraretinal vessels and a sharply demarcated avascular peripheral retina. Light microscopy revealed marked proliferation of capillaries and mesenchymal spindle cells of the retina. Electron microscopy of the retinal vascular endothelial cells revealed intact tight junctions with no fenestrations. Spindle cells had gap and intermediate junctions that appeared normal in number and morphology.

Zonulae adherentes pore size in the external limiting membrane of the rabbit retina.

The interphotoreceptor space (IPS) of the retina is bordered by the retinal pigment epithelium, photoreceptors, and Müller cells and surrounds the photoreceptor outer and inner segments. It contains a matrix composed of glycosaminoglycans and proteins, including interphotoreceptor retinol-binding protein (IRBP). The matrix does not diffuse sclerad through the tight junctions that link cells of the pigment epithelium or vitread beyond the point at which photoreceptors and Müller cells are linked by zonulae adherentes that comprise the external limiting membrane (ELM). Biotinylated protein probes of known Stokes' radius were used to determine the pore size of the ELM. Following exposure of the photoreceptor side of isolated rabbit retinas to each protein, the extent of diffusion of the probe through the retina was determined by avidin D-horseradish peroxidase histochemistry. Each protein with a Stokes' radius of 30 A or less diffused freely through the neurosensory retina while each protein with a Stokes' radius greater than 36 A was blocked abruptly at the ELM. Thus, the pore radius of the zonulae adherentes of the ELM lies between 30 and 36 A, which is sufficiently small to account for containment of IRBP (55 A) within the IPS. This study emphasizes that in addition to providing structural support, the zonulae adherentes of the ELM serve to define an important extracellular space of the retina. This has clinical relevance, since two serum proteins tested, albumin and gamma-globulin, are too large to diffuse through an intact ELM. This may explain why protein-rich fluid accumulates in the IPS when the outer blood retinal barrier is compromised by disease or injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of retinoid-binding proteins in developing rat retina.

Antibodies to cellular retinol-binding protein (CRBP) and cellular retinal-binding protein (CRALBP) were obtained from rabbits immunized with antigens purified from bovine retina. Antigens were localized on frozen sections of rat retina using indirect FITC immunofluorescence. In the retinal pigment epithelium of rats from postnatal day 1 (the day of birth) to postnatal day 32, specific staining with anti-CRBP was restricted to the cytoplasm; the nuclei were unstained. In the neurosensory retina, Muller cell endfeet were stained with anti-CRBP at all ages examined. No CRBP reactivity was found in the pigment epithelium of the ciliary body at any age examined. On postnatal days 14 and 32, in addition to Muller cell endfeet and radial processes, two fine laminae in the inner plexiform layer were faintly positive for CRBP. Anti-CRALBP stained the cytoplasm of the RPE and Muller cells in the adult rat. In developing rat retina, in addition to Muller cells and the retinal pigment epithelium, the ciliary body pigment epithelium and the outer epithelium of the iris were stained with anti-CRALBP in the first postnatal week. The intensity of staining of the ciliary body pigment epithelium decreased gradually from postnatal day 8 until postnatal day 14, at which point a clear line of demarcation was found between the positively stained retinal pigment epithelium and the adjacent, lightly stained, pigment epithelial cells of the ciliary body.

Immunocytochemical localization of interphotoreceptor retinoid-binding protein in developing normal and RCS rat retinas.

Interphotoreceptor retinoid-binding protein (IRBP) was localized immunocytochemically in developing normal and RCS rat retinas. IRBP was present in normal and RCS neural retinas on the day after birth (postnatal day 2, P2) to P8 in the space between the neuroblastic layer and the retinal pigment epithelium (RPE). The presence of IRBP prior to the development of outer segments (OS) suggests that OS formation is not linked temporally with IRBP secretion. On P10, staining was confined to the interphotoreceptor space with an intense band of label adjacent to the RPE. This staining pattern persisted in normal rats throughout development and until P18 in RCS rats. On P18, anti-IRBP staining in the RCS was spread evenly throughout the OS layer with no intense band of label adjacent to the RPE and after P18, there was decreased staining with anti-IRBP. On P45 and later, no staining of the RCS retina was found with anti-IRBP. Immunoblots of normal and RCS retinas corroborated the results from immunocytochemical staining. These findings suggest that IRBP may be synthesized in the photoreceptors, but is not abnormal in amount or distribution prior to onset of retinal degeneration in the RCS rat.