Objective comparison of a sit to stand test to the walk test for the identification of unilateral lameness caused by cranial cruciate ligament disease in dogs.

OBJECTIVE: The purpose of this study was to evaluate a sit to stand test with the walk test for the identification of unilateral cranial cruciate ligament rupture in dogs. MATERIALS AND METHODS: Peak vertical force and vertical impulse were measured on a pressure-sensitive walkway, during a sit to stand test and walk test, and in 10 dogs with unilateral cranial cruciate ligament rupture and 18 non-lame dogs. Data collected were used to calculate symmetry indices (SI) of ipsilateral and contralateral hindlimbs (HL), diagonal limb pairs (DLP) and ipsilateral limb pairs (ILP). RESULTS: The symmetry indices of peak vertical force of HL during the walk test and sit to stand test were 100% and 90% sensitive for discriminating lame and non-lame dogs respectively. The symmetry indices of vertical impulse of HLs during the walk test and sit to stand test were 100% and 50% sensitive for discriminating lame and non-lame dogs respectively. Analysis of ipsilateral and diagonal limb pairs did not improve the discrimination in either test. The time taken to collect data from the sit to stand test data was shorter than for the walk test. CLINICAL SIGNIFICANCE: Whilst the sit to stand test required a shorter time for collection of data than the walk test, it did not accurately identify all dogs with lameness associated with CCLR, and thus has relatively limited clinical utility in its tested form.

[Situs inversus of the optic nerve. A case report]. / Situs inversus del nervio optico. A proposito de un caso.

INTRODUCTION: Situs inversus of the optic nerve is a congenital anomaly characterised by the emergence of the vessels in the retina towards the nose rather than in a temporal direction. It is caused by an anomalous insertion of the optic stalks into the optic vesicle that gives rise to dysversion of the head of the optic nerve. It is not an isolated condition and usually appears jointly with tilted disc syndrome and in patients with myopia. It is characterised by the presence of inferior conus atrophy, deficiencies in the temporal visual field, refraction defects and ambliopy. CASE REPORT: A 22 years-old female who attended an ophthalmological examination due to severe frontal headaches accompanied by halos and loss of sharpness in her sight. From the results of the ophthalmetric and ophthalmological examination she was diagnosed as suffering from a condition consistent with this congenital anatomical anomaly. CONCLUSIONS: Situs inversus of the optic nerve is a rare condition that may appear in isolation or accompanied by other pathologies. Application of the visual field test and new diagnostic techniques, such as optical coherence tomography, facilitates the differential diagnosis of this situation. Its prevalence remains unknown, as it is not included in the register of rare diseases. Moreover, the scant number of patients studied and the scarce literature on this anomaly do not allow us to know whether the defects it causes develop over time. It would therefore be important to perform an ophthalmological follow-up of patients with situs inversus of the optic nerve.

TITLE: Situs inversus del nervio optico. A proposito de un caso.Introduccion. El situs inversus del nervio optico es una anomalia congenita caracterizada por la emergencia de los vasos de la retina en direccion nasal en lugar de temporal. Es causado por una anomala insercion del tallo optico en la vesicula optica que da lugar a la variacion de disposicion de la cabeza del nervio optico. No es una condicion aislada y suele aparecer junto con el sindrome del disco inclinado y en pacientes con miopia. Se caracteriza por la presencia de un cono de atrofia inferior, defectos en el campo visual temporal, defectos de refraccion y ambliopia. Caso clinico. Mujer de 22 años, que acude a revision oftalmologica por presentar fuertes cefaleas frontales acompañadas de halos y perdida de nitidez en la vision. Tras un examen optometrico y oftalmologico se llega al juicio clinico de que padece un cuadro compatible con esta anomalia anatomica congenita. Conclusiones. El situs inversus del nervio optico es una condicion rara que puede aparecer aislada o acompañada de otras patologias. La aplicacion de la campimetria y de nuevas tecnicas diagnosticas, como la tomografia de coherencia optica, facilita el diagnostico diferencial de esta situacion. No se conoce su prevalencia, pues no se encuentra en el registro de las enfermedades raras. Ademas, el escaso numero de pacientes estudiados y la exigua bibliografia existente sobre esta anomalia no permiten conocer si los defectos causados progresan en el tiempo, por lo que seria importante realizar un seguimiento oftalmologico de los pacientes con situs inversus del nervio optico.

Substance P and calcitonin gene-related peptide intrinsic choroidal neurons in human choroidal whole-mounts.

To determine the presence in the human choroid of substance P (SP)-and calcitonin gene-related peptide (CGRP) positive intrinsic choroidal neurons (ICNs), choroidal whole-mounts were processed for indirect immunofluorescence. An antibody to a component of the neuronal cytoskeleton, neurofilament 200 kDa (NF-200), was combined with antibodies to SP and to CGRP (neuropeptides proper to the sensory nervous system). The human choroid possesses numerous SP(+) and CGRP(+) ICNs. These neurons were observed in the suprachoroid, both in isolation and forming microganglia. For both types of ICNs studied, neurons were more numerous in the temporal than in the nasal regions. In both locations, SP(+) and CGRP(+) ICNs were more abundant in the central choroid (the choroid underneath the macular area of the retina), with cell density diminishing outwards to the choroidal periphery. There were no appreciable differences between the two populations of ICNs studied in terms of size, morphology or immunostaining characteristics. In conclusion, given that peripheral sensory innervation could be involved in the regulation of both choroidal blood flow and vascular architecture, the SP(+) and CGRP(+) ICNs described for the first time in the present work may be involved in these mechanisms of vascular regulation.

Vimentin isoform expression in the human retina characterized with the monoclonal antibody 3CB2.

The antigen recognized by the monoclonal antibody 3CB2 (3CB2-Ag and 3CB2 mAb) is expressed by radial glia and astrocytes in the developing and adult vertebrate central nervous system (CNS) of vertebrates as well as in neural stem cells. Here we identified the 3CB2-Ag as vimentin by proteomic analysis of human glial cell line U-87 extracts (derived from a malignant astrocytoma). Indeed, the 3CB2 mAb recognized three vimentin isoforms in glial cell lines. In the human retina, 3CB2-Ag was expressed in Müller cells, astrocytes, some blood vessels, and cells in the horizontal cell layer, as determined by immunoprecipitation and immunofluorescence. Three populations of astrocytes were distinguishable by double-labeling immunohistochemistry: vimentin+/GFAP+, vimentin-/GFAP+, and vimentin+/GFAP-. Hence, we conclude that 1) the 3CB2-Ag is vimentin; 2) vimentin isoforms are differentially expressed in normal and transformed astrocytes; 3) human retinal astrocytes display molecular heterogeneity; and 4) the 3CB2 mAb is a valuable tool to study vimentin expression and its function in the human retina.

[A comparative study of choroidal innervation in the human and the rabbit (oryctolagus cuniculus)]. / Estudio comparativo de la inervación coroidea en el hombre y en el conejo (oryctolagus cuniculus).

OBJECTIVE: To analyze morphological differences between the choroidal innervation of the human and the rabbit, the latter being a species frequently used as an experimental model of human ocular diseases. METHODS: Twelve human and 12 rabbit choroidal whole mounts were processed using an indirect immunohistochemical technique, peroxidase-anti-peroxidase and antibodies against 200 kD neurofilament. RESULTS: Choroidal nerve fibers were perivascular and intervascular. Perivascular fibers surrounded all arteries forming a network that was more developed in the rabbit. In humans, intervascular fibers were mainly concentrated at the posterior pole where they formed a denser and more highly organized plexus than in the rabbit, which did not exhibit a preferential location for these fibers. Human choroidal ganglion cells were far more numerous than in the rabbit and were concentrated in a circumferential area corresponding to the entrance of the short posterior ciliary arteries of the submacular area. In the rabbit, these cells were restricted to the peripheral choroid. CONCLUSIONS: Some differences were observed between human and rabbit choroidal innervation. The abundance of ganglion cells and their preferential distribution could be necessary to maintain a constant blood flow in the central area of the human choroid. The lack of organization of rabbit choroidal innervation at the posterior pole could be associated with an absence of the macula. These differences, along with peculiarities of retinal vascularization, should be taken into consideration when using the rabbit as an experimental model to study human eye diseases in which regulation of choroidal blood flow is involved.

[Structural changes of the anterior chamber angle in primary congenital glaucoma with respect to normal development]. / Cambios estructurales del ángulo de la cámara anterior en el glaucoma congénito. Comparación con el desarrollo normal.

PURPOSE: To compare findings of normal angles with those from primary congenital glaucoma in order to clarify the pathogenic mechanisms of the disease and to explain the success of surgical treatment in some of these patients. METHODS: Adult normal eyes from cadavers and fragments of surgical trabeculectomies from patients with primary congenital glaucoma previously treated with goniotomy were studied. Eyes were processed for examination using light microscopy and scanning electron microscopy techniques. RESULTS: The following was evident in congenital glaucoma: 1) high iris insertion; 2) no observable pre-trabecular membrane, but enlarged trabeculae with diminished inter-trabecular spaces; 3) Schlemm's canal (SC) apparently normal, with vacuoles in the wall indicating normal functioning; 4) sectioning of the abnormal trabecular tissue during goniotomy allowed repositioning of the angle structures and hence the appearance of the angular recess. CONCLUSIONS: Anomalies of the trabecular structures in primary congenital glaucoma do not always parallel an abnormal development of the SC and the collector channels. This fact could explain the success of goniotomy in this type of glaucoma.

NPY and TH innervation in human choroidal whole-mounts.

To determine the distribution of NPY and TH human choroidal innervation, choroidal whole-mounts were processed for indirect immunofluorescence. An antibody to a component of the neuronal cytoskeleton, neurofilament 200 kDa (NF-200) was used to identify neurons and axons. A double immunostaining was performed, antibodies against NF-200 being combined with antibodies against neuropeptide Y (NPY) and tyroxine hydroxylase (TH). Fibers containing both NPY and TH were distributed in three plexuses, one in the suprachoroid large-sized vessel layer, and two in the medium-sized vessel layer. Intrinsic choroidal neurons (ICNs) containing NPY and TH were observed in the suprachoroid. The TH(+) ICNs were located in the medium-sized vessel layer. Overall, NPY(+) and TH(+) ICNs were more frequent in the central temporal area, both in isolation and forming microganglia. We also detected small spindle elements intensely immunoreactive to TH(+) and distributed mainly in the suprachoroid from the equator to the periphery. In conclusion, the human choroid contains abundant NPY and TH nerve fibers related to chroroidal vascular structures; it further possesses NPY(+) and TH(+) ICNs which contribute to the choroidal self-regulation persisting after sympathetic denervation. Additionally, these ICNs may at least partially explain why the choroidal blood flow does not respond to the factors that influence systemic vascular control. The preferential location of these cells in the submacular area suggests that dysfunction or degeneration of these cells may be a factor in vascular pathologies found in ocular disease, such as diabetic macular edema or age-related macular degeneration.

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.

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

Changes of astrocytes in retinal ageing and age-related macular degeneration.

Most studies of age-related macular degeneration (AMD) have focused on the outer retina but little has been done on the involvement of astrocytes in this disease. We examined normal (young and old) and pathological (AMD) human retinas for the presence of changes in morphology and distribution of the astrocytes. Electron microscopy and inmunohistochemical techniques (anti-GFAP) were used for this study. Astrocytes in the ageing group showed: (1) higher GFAP immunoreactivity and more cytoplasmic organelles and glial filaments than astrocytes from younger retinas; (2) lipofucsin deposits; (3) a significantly smaller number of cells in the honeycomb astroglial plexus in the ganglion cell layer than in the younger group; and (4) Spaces with no GFAP reactivity in the nerve fiber layer. Changes observed in the AMD group were: (1) the basal membrane of the retinal capillaries was considerably thicker than in normal old individuals; (2) There were numerous non-functional capillaries; (3) There were hypertrophic astrocytes that phagocytosed dead ganglion cells; and (4) There were glial membranes constituted by astrocytes and Müller cells located between the vitreous humour and internal limiting membrane. These observations suggested that the extensive retinal ischaemia that can occur with AMD, together with the loss of astroglial cells accompanying normal ageing, could cause the death of the ganglion cells which cannot be protected from oxidative damage. Extensive ischaemia could cause the astrocytes to migrate to the vitreous humour where there is a metabolic reserve.

A practical method for the radioisotope labeling of rabbit astrocytes with (3)H-thymidine.

A practical method for the radioisotope labeling aimed at the study of the proliferative behavior of astrocytes was described. It consisted in injecting 20 microCi of (3)H-thymidine into the vitreous body and tracing by autoradiography labeled astrocytes located both inside and outside the retina, e.g. optic nerve and neighboring parts of the central nervous system. The paraffin sections were immunostained for glial fibrillary acidic protein (GFAP) previous to autoradiographic processing. The semiquantitative analysis of labeled astrocytes was carried out on autoradiographs of semithin sections of rabbits killed as early as 6 h and as late as 3 months after the single intravitreal injection of (3)H-thymidine. Compared with the technique of labeling astrocytes by systemic administration (single injection or continuous infusion) of (3)H-thymidine into small animals, the method described herein has the following outstanding features: (i) it is much more economical in terms of the amount of labeled precursor used per animal; (ii) the labeling of the astrocytes is obtained as early as 6 h and remains up to 3 months after injection; (iii) the immunolabeling of the astrocytes is compatible with autoradiography; (iv) it is less risky to the experimental animal and to the environment; (v) it can be used in animals much larger than rats or mice.

[Application of confocal microscopy in the study of the relationships between astrocytes and blood vessels in the retina]. / Aplicación de la microscopia confocal al estudio de las relaciones vaso-gliales en la retina.

OBJECTIVE: To study the rabbit retina astrocytes by using immunofluorescence techniques together with the confocal microscopy. MATERIAL AND METHODS: The rabbit retinas were processed with an anti-glial fibrillary acidic protein (anti-GFAP) for astrocyte detection and with propidium lobide for nuclear staining. RESULTS: Confocal microscopy allows for three-dimensional reconstruction of astroglial cells, the performance of double staining procedures with superposition of images corresponding to each chromogen, the exchange of observation axes for each slide and finally the performance of serial optic sections that indicate the exact cell location and their relationship with adjacent structures, eliminating the background signals. CONCLUSIONS: The confocal microscopy provides detailed information about tridimensional morphology and the location of the astrocytes in the rabbit retina. The astrocytes associated with the nerve fiber bundles are located in the nerve fiber layer. The type III perivascular astrocytes are located between the intravitreous capillaries close to the internal limiting membrane of the retina. The type I perivascular astrocytes are found in the retinal face of the intravitreal capillaries, these being the neurons which are the most distant from the retina.

Immunohistochemistry in association with scanning electron microscopy for the morphological characterization and location of astrocytes of the rabbit retina.

The purpose of the present investigation was to establish a method for the morphological characterization and location of the several types of astrocytes in the rabbit retina. Whole retinas were incubated with unlabeled antibody to glial fibrillary acidic protein (GFAP) and, afterwards, treated with secondary antibody labeled according to the requirements for the visualization of the antigen-antibody reaction either with the confocal or transmission electron microscope. Specimens treated similarly to the latter were osmium enhanced and analyzed with scanning electron microscopy (SEM). The different immunohistochemical approaches led to the conclusion that the cells selectively visualized with the SEM are astrocytes. The higher resolution and depth of focus of this instrument allowed a better morphological characterization and a more precise location of the astrocytes in the several levels of the inner portion of the rabbit retina. The method described herein, in which pre-embedding immunohistochemistry for GFAP on rabbit retinas was associated with osmium enhancement and examination with SEM, proved to be reliable and efficient for the morphological characterization and location of astrocytes.

Human retinal astroglia. A comparative study of adult and the 18 month postnatal developmental stage.

The immunohistochemical location of glial fibrillary acidic protein (GFAP) was used to study the state of maturation of retinal astrocytes from an 18-mo-old infant and to compare it with the situation in the adult. Infant astrocytes showed intense GFAP immunoreactivity in the perikarya and possessed spindle-like enlargements in their processes, while in the adult immunoreactivity in the perikarya was scarce and the spindle-like enlargements were not evident. Two types of astrocyte were observed in adult and child retinas: elongated and star-shaped. In the adult, the star-shaped type tend to be more stylised and to have longer processes than in the infant. In the infant, numerous astrocyte cell bodies were observed over vessels, while in the adult these were scarce. In the infant, the star-shaped astrocytes made up a honeycomb plexus, but this was not fully developed. These results suggest that at 18 mo of postnatal development the retinal astrocytes are still increasing and growing into the astroglial structure found in adults.

[Apoptosis in ischemic optic neuropathy]. / Apoptosis en la neuropatía óptica isquémica.

PURPOSE: A study of human eyes with non-arteritic ischaemic optic neuropathy (NAION) to determine whether there is apoptosis and whether this is accompanied by cell necrosis mechanisms. METHODS: Transmission electron microscopy was used to examine the retinas of eyes with NAION. RESULTS: There was a large number of apoptotic ganglion cells. The lesion was not confined to this retinal layer but also affected the inner nuclear layer, where Müller glia with fagocytic capacity were detected. In this layer apoptosis alternated with necrosis in all of the cell types existing in this level: bipolar cells, amacrine cells and horizontal cells. The outer nuclear layer can also suffer lesion, essentially by induction of choroid ischaemia to that level. Again, apoptosis was observed at the photoreceptor level, where there was also death by heterophagy, although this was less frequent. CONCLUSIONS: The behaviour of NAION in humans is similar to that found in experimental models. Apoptosis mechanisms develop, alternating with cell necrosis in the nuclear level.

ras gene mutations in ethmoid sinus adenocarcinoma: prognostic implications.

BACKGROUND: The presence of mutations of the 3 ras proto-oncogenes in 31 cases of ethmoid sinus adenocarcinoma, an uncommon tumor type epidemiologically related to professional exposure to wood dust, was studied. METHODS: The authors studied 31 patients with ethmoid sinus adenocarcinoma. The polymerase chain reaction was used to amplify ras specific sequences of DNA isolated from paraffin embedded tumor samples. ras point mutations were subsequently detected with mutation specific oligonucleotide probes. RESULTS: H-ras was found to be mutated in 5 cases (16%). It is noteworthy that all of these mutations were identical and consisted of a G-for-T transversion at the second base of codon 12. H-ras mutations were related to a worse prognosis, with shorter tumor free survival (P = 0.04) and overall survival (P = 0.008). T classification was a significant clinical factor related to survival (P = 0.01 for disease free survival and P = 0.006 for overall survival). The prognostic value of H-ras mutation was consistent after adjustment for T classification. H-ras mutations showed no association with patients' previous exposure to wood dust. K-ras was found to be transformed in a single case; this was the only patient in the series to develop lymph node metastases. In this case, both the nasal tumor and the lymph nodes showed the GAT-for-GGT mutation at codon 12 of K-ras. No activation of the N-ras gene was detected. CONCLUSIONS: The presence of H-ras point mutations defines a subgroup of patients with ethmoid sinus adenocarcinomas for whom the prognosis is very poor. The finding that all of these mutations are identical emphasizes the peculiarity of this type of tumor.

Immunohistochemical study of rabbit choroidal innervation.

Immunocytochemical methods with antibodies to the light (68 kDa), medium (160 kDa), and heavy (200 kDa) chain subunits of the neurofilament triplet have been used to visualize neuronal structures in rabbit choroids. Choroidal nerve fibers were present in the suprachoroid and vascular laminae and absent in the choriocapillary layer. These fibers may be classified as perivascular and intervascular. Perivascular fibers surround all arterial and venous blood vessels and form a network; these fibers were labeled with the three NF antibodies, although they were more easily visualized with anti NF-160 and anti NF-200 than anti NF-68. Intervascular fibers formed two groups. The first group consisted of fibers situated between the blood vessels and parallel to the blood vessel wall surface (paravascular fibers); these fibers were better observed using anti NF-160 and NF-200 than anti NF-68. The second group consisted of fibers which travel the entire length of the choroid until they reach the nerve plexus of the ciliary body (long tract fibers). The plexus was observed with anti NF-68, anti NF-160 and anti NF-200; however, the long tract fibers were more clearly visualized with anti NF-160 and anti NF-200 than with anti NF-68. Two types of choroidal cell were also labeled: ganglion cells and melanocytes. Ganglion cells are small, scarce neurons situated in the peripheral choroid; they were labeled with anti NF-160 and anti NF-200. The melanocytes were only labeled with anti NF-200 and they were the only non neuronal structure visualized using antibodies against neurofilaments.

Comparative study of astrocytes in human and rabbit retinae.

Immunohistochemical location of Glial Fibrillary Acidic Protein (GFAP) was used to compare the morphology of astrocytes in vascularized and partially vascularized retinae (human and rabbit, respectively). Astrocytes in human and rabbit retinae were found in the same regions as the blood vessels. These cells in partially vascularized retinae differed from those in vascularized retina in several respects. Firstly, there were six morphological types in rabbit retina and only two in human retina. Secondly, in rabbit retinae there were astrocytes only related to blood vessels called "perivascular astrocytes" which were absent in human retinae. Thirdly, the astrocytes were located in the nerve fiber layer and ganglion cell layer in both types of retinae, but in human retinae these cells could also be seen in the internal nuclear layer. These observations demonstrate that there are many differences between astrocytes in human and rabbit retina, suggesting that rabbit retina could be used with caution as an experimental model in comparative studies with human retina.

Immunohistochemical study of human optic nerve head astroglia.

Immunocytochemical localization of glial fibrillary acidic protein (GFAP) has been used to study the distribution of astrocytes and their morphology in sections of the optic nerve (ON) of human eye. Although all ON regions presented GFAP immunoreactivity, immunostained tissue was most common in the posterior prelaminar region (PR) and least common in the laminar region (LR). Two shapes of astrocytes were distinguished: thick and thin bodied astrocytes. Astrocytes with thick cell bodies are located in the superficial nerve fiber layer (SNFL), PR, LR and retrolaminar region (RR). Astrocytes with thin cell bodies were found in the SNFL and anterior PR. Sometimes thin bodied astrocytes presented another shape with a long process running parallel to the axons and these were found in the PR and LR. In the SNFL the thin bodied astrocytes accompany the axons and contact the capillaries derived from the central retinal artery. In the anterior PR the thin bodied astrocytes with a stellate shape lie over the vessels forming a sieve through which the axons pass. In the posterior PR, the thick bodied astrocytes form glial tubes that direct axons towards the LR. These astrocytes form a layer in the LR that lines the pores of the lamina cribrosa and separates the connective septa from the axon bundles in the RR. The limiting glial membranes separate the ON tissues from the adjacent tissues and from the course of the central retinal artery and are composed of many thick bodied astrocytes.