PURPOSE. To evaluate the degree of inner retinal preservation in the extramacular regions of postmortem retinitis pigmentosa (RP) eyes.METHODS. Eighteen RP retinas and 11 age-matched healthy retinas were sectioned for morphometric analysis by light microscopy. The 18 RP retinas were classified by disease severity and mode of inheritance. Cell nuclei in the outer nuclear layer (ONL), inner nuclear layer (INL), and ganglion cell layer (GCL) were counted in adjacent 125-mu m segments from an area spanning the region between 4 mm and 10 mm from the fovea.RESULTS. A mixed-effects model showed a decrease in mean cell counts for each of the cell layers when the severity groups and inheritance types compared with those of control retinas. There was no statistically significant difference in the number of nuclei preserved in the INL and GCL in the moderate group compared with the severe group. Results from the INL counts for the different inheritance types of RP showed a higher overall mean percentage of cells was preserved for the autosomal dominant RP (ADRP) group when compared with the X-linked (XLRP) and simplex RP groups. Analysis of the GCL counts revealed significantly more counts only in the ADRP group compared with the XLRP group; the other group comparisons were not significant.CONCLUSIONS. Retinitis pigmentosa results in, cell loss in all retinal layers, with the most profound loss in the ONL, followed by the GCL and then the INL. The preservation of the INL and GCL in the extramacular region is less than that previously reported for the macular region of the same retinas.

PURPOSE:In an unpublished study, the authors found that immunoreactivity for basic fibroblast growth factor (bFGF) is increased in rod photoreceptors adjacent to long-standing laser burns in human diabetic retinas. The goal of this study was to determine whether laser photocoagulation produces a similar increase in photoreceptor bFGF and promotes survival of these cells in dystrophic rodent retinas.METHODS:Threshold (whitening) and subthreshold (nonwhitening) laser burns were made in retinas of normal and Royal College of Surgeons (RCS) rats and normal and rds mice. The retinas were processed for immunocytochemical and morphometric analyses.RESULTS:In nonlasered normal rat and mouse retinas, bFGF immunoreactivity was prominent in the nuclei of Müller cells and astrocytes. Photoreceptors were bFGF negative except for a zone of bFGF-immunoreactive rods near the ora serrata. Some photoreceptors in nonlasered retinas of RCS rats and rds mice became bFGF immunoreactive. After laser treatment, bFGF immunoreactivity was markedly increased in all photoreceptors flanking the threshold burns and within the subthreshold burns in normal and mutant rats and mice. In RCS rat retinas, photoreceptor bFGF immunoreactivity remained elevated within subthreshold burns and flanking the threshold burns, and photoreceptor survival was prolonged. In rds mouse retinas, increased bFGF immunoreactivity in photoreceptors was not sustained and their degeneration was not retarded.CONCLUSIONS:Laser treatment of RCS rat retinas produced a sustained increase in bFGF immunoreactivity in photoreceptors and prolonged their survival, but laser treatment of rds mouse retinas did not have a long-term effect on photoreceptor bFGF immunoreactivity or survival. Although species differences in laser effects on photoreceptor bFGF and survival are apparent, the finding that rods flanking laser burns in human retinas have sustained increases in bFGF immunoreactivity suggests that laser treatment may be useful for prolonging survival of mutant photoreceptors in retinas of patients with retinitis pigmentosa.

OBJECTIVE:To determine the extent of preservation in the inner retina in retinitis pigmentosa (RP).METHODS:We analyzed sectioned maculae of 21 postmortem eyes with RP and 19 age-matched, normal, postmortem eyes. Eyes were divided into 2 groups: severe and moderate RP. Cell nuclei were counted in the outer nuclear, inner nuclear, and ganglion cell layers within thirty 100-microns intervals from the foveola to 1500-microns eccentricity.RESULTS:Statistically significant (P < or = .05) loss of both the outer nuclear and ganglion cell layers was present in the groups with moderate and severe RP when compared with the control groups. However, even in the group with severe RP, 30% of the ganglion cells were histologically intact. Similarly, 78% and 88% of the inner nuclear layer cells were preserved in the groups with severe and moderate RP, respectively. Different inheritance modes showed no statistically significant differences in any of the retinal layers.CONCLUSIONS:Despite a statistically significant (P < or = .05) loss of cells found in all retinal layers, a large percentage of the inner retinal neurons remained histologically intact. Current experimental therapies, such as photoreceptor transplantation and implantation of a visual prosthesis, are based on the premise that some inner retinal neurons are preserved after death of photoreceptors in RP. Our observations support this assumption.

Primate cones maximally sensitive to short wavelength light (blue cones) have been previously identified by using indirect methods. We stained 7 wholemounted human retinas obtained from 6 female donors, using an affinity purified antibody to a 19 amino acid peptide sequence at the N-terminus of blue opsin (Lerea et al., '89: Neuron 3:367-376), standard PAP immunocytochemistry, and controls. Cones were counted where all outer segments could be traced to inner segments and were measured where cells were well aligned vertically.We find that: (1) 7% of cones within 4 mm of the foveal center are labeled by antiblue opsin; (2) compared to neighboring red/green cones, blue cone inner segments are 10% taller, have a larger cross-sectional diameter near the junction with the outer segment, and a smaller diameter near the external limiting membrane, resulting in a more cylindrical shape, (3) foveal blue cones are sparse, irregularly spaced, and missing in a zone about 100-mu-m (0.35-degrees) in diameter near the site of peak cone density, (4) the highest densities of blue cones (> 2,000 cells/mm2) are found in a ring at 0.1-0.3 mm eccentricity, and (5) the shortest distances between neighboring cones are between blue and red/green cones, and the blue and red/green mosaics are statistically independent.These findings are consistent with psychophysical reports of foveal tritanopia and maximum sensitivity to blue light at 1-degrees eccentricity. Blue cone spacing may limit resolution of the blue channel out to 20-30-degrees eccentricity. The blue and red/green mosaics appear to be formed by separate processes.

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 α 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 α 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.

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)

Cone but not rod outer segments (OSs) in the retinas of goldfish and carp are diffusely labeled after intravitreal injection of 3H-fucose. Among the different cone types, the OSs are heavily labeled in the long double, short single, and some long single cones. The OSs of short double and the remaining long single cones are consistently more lightly labeled. A correlation thus exists between heavy labeling of OSs maximally sensitive to red and blue light and lighter labeling of OSs with maximum sensitivity to green light, and this may reflect different carbohydrate compositions of the cone visual pigments. New information is presented on OS fine structure of rods and cones, and on differential marking of cone OSs with the extracellular tracers horseradish peroxidase (only green-sensitive cone OSs "stained") and microperoxidase (red- and blue- but not green-sensitive cones OSs "stained").

Radioautographic and cytochemical studies were performed at the ultrastructural level on the optic nerve heads of 21 Macaca fascicularis eyes with normal, elevated, or decreased intraocular pressures (IOP). Orthograde axoplasmic transport was labeled in all eyes by intravitreal injec- tions of a tritiated amino acid (leucine or proline) from 4 hr to 6 days before sacrifice. Retro- grade axoplasmic transport was labeled in most of the same eyes by injection of horseradish peroxidase (HRP) into one or both optic tracts and/or dorsal lateral geniculate nuclei (dLGN) from 12 to 24 hr before sacrifice. Electron microscopic studies were concentrated in the lamina scleralis (LS). Tritiated leucine was confined to axons in the nerve head in both normal and pathologic eyes. In hypertensive eyes both orthograde and retrograde transport appeared blocked initially in the posterior LS, then with increasing severity of injury appeared blocked and intermixed throughout the LS. In hypertensive eyes, collections of HRP were especially prominent within peripherally lying axons in bundles in the LS and on the posterior side of glial-scleral trabeculae in the LS. Hypotensive eyes (with papilledema) had similar, but much less severe, intra-axonal alterations of morphology and also demonstrated accumulations' of HRP in the LS. The morphologic alterations and blockage of axoplasmic transport within the LS in both hypertensive and hypotensive eyes appear to have resulted from mechanical com- pression of axonal bundles.