The distribution of toxic metals in the human retina and optic nerve head: Implications for age-related macular degeneration.

OBJECTIVE: Toxic metals are suspected to play a role in the pathogenesis of age-related macular degeneration. However, difficulties in detecting the presence of multiple toxic metals within the intact human retina, and in separating primary metal toxicity from the secondary uptake of metals in damaged tissue, have hindered progress in this field. We therefore looked for the presence of several toxic metals in the posterior segment of normal adult eyes using elemental bioimaging. METHODS: Paraffin sections of the posterior segment of the eye from seven tissue donors (age range 54-74 years) to an eye bank were examined for toxic metals in situ using laser ablation-inductively coupled plasma-mass spectrometry, a technique that detects multiple elements in tissues, as well as the histochemical technique of autometallography that demonstrates inorganic mercury, silver, and bismuth. No donor had a visual impairment, and no significant retinal abnormalities were seen on post mortem fundoscopy and histology. RESULTS: Metals found by laser ablation-inductively coupled plasma-mass spectrometry in the retinal pigment epithelium and choriocapillaris were lead (n = 7), nickel (n = 7), iron (n = 7), cadmium (n = 6), mercury (n = 6), bismuth (n = 5), aluminium (n = 3), and silver (n = 1). In the neural retina, mercury was present in six samples, and iron in one. Metals detected in the optic nerve head were iron (N = 7), mercury (N = 7), nickel (N = 4), and aluminium (N = 1). No gold or chromium was seen. Autometallography demonstrated probable inorganic mercury in the retinal pigment epithelium of one donor. CONCLUSION: Several toxic metals are taken up by the human retina and optic nerve head. Injury to the retinal pigment epithelium from toxic metals could damage the neuroprotective functions of the retinal pigment epithelium and allow toxic metals to enter the outer neural retina. These findings support the hypothesis that accumulations of toxic metals in the retina could contribute to the pathogenesis of age-related macular degeneration.

Structured polarized light microscopy for collagen fiber structure and orientation quantification in thick ocular tissues.

Collagen is a major constituent of the eye and understanding its architecture and biomechanics is critical to preserve and restore vision. We, recently, demonstrated polarized light microscopy (PLM) as a powerful technique for measuring properties of the collagen fibers of the eye, such as spatial distribution and orientation. Our implementation of PLM, however, required sectioning the tissues for imaging using transmitted light. This is problematic because it limits analysis to thin sections. This is not only slow, but precludes study of dynamic events such as pressure-induced deformations, which are central to the role of collagen. We introduce structured polarized light microscopy (SPLM), an imaging technique that combines structured light illumination with PLM to allow imaging and measurement of collagen fiber properties in thick ocular tissues. Using pig and sheep eyes, we show that SPLM rejects diffuse background light effectively in thick tissues, significantly enhancing visualization of optic nerve head (ONH) structures, such as the lamina cribrosa, and improving the accuracy of the collagen fiber orientation measurements. Further, we demonstrate the integration of SPLM with an inflation device to enable direct visualization, deformation tracking, and quantification of collagen fibers in ONHs while under controlled pressure.

Utilizing RNA-Seq to Identify Differentially Expressed Genes in Glaucoma Model Tissues, Such as the Rodent Optic Nerve Head.

Understanding the cellular pathways activated by elevated intraocular pressure (IOP) is crucial for the development of more effective glaucoma treatments. Microarray studies have previously been used to identify several key gene expression changes in early and extensively injured ONH, as well as in the retina. Limitations of microarrays include that they can only be used to detect transcripts that correspond to existing genomic sequencing information and their narrower dynamic range. However, RNA sequencing (RNA-seq) is a powerful tool for investigating known transcripts, as well as for exploring new ones (including noncoding RNAs and small RNAs), is more quantitative, and has the added benefit that the data can be re-analyzed as new sequencing information becomes available. Here, we describe an RNA-seq method specifically developed for identifying differentially expressed genes in optic nerve heads of eyes exposed to elevated intraocular pressure. The methods described here could also be applied to small tissue samples (less than 100 ng in total RNA yield) from retina, optic nerve, or other regions of the central nervous system.

Collagen Architecture of the Posterior Pole: High-Resolution Wide Field of View Visualization and Analysis Using Polarized Light Microscopy.

Purpose: The purpose of this study was to leverage polarized light microscopy (PLM) to visualize the collagen fiber architecture of posterior pole and optic nerve head with micrometer-scale resolution and to identify and quantify major organizational components. Methods: Eight sheep posterior poles were cryosectioned and imaged using PLM. Collagen fiber orientation was determined by using custom scripts, and the resulting orientation maps were inspected and quantified to identify major structural elements and tested for differences in mean fiber orientation and anisotropy, using linear mixed effect models. Results: Images revealed an intricate organization of collagen fibers in the posterior pole. In the lamina cribrosa, interweaving fibers formed large knots and wrapped around nerve fiber pores, with beam insertions into the scleral canal wall that were either narrow and straight or wide. In the peripapillary sclera, three significantly different (P < 0.0001) components were identified: fibers oriented circumferentially proximal to the canal, radially in the innermost sclera, and unaligned with interweaving fibers. The radial fibers were between 60 and 180 µm thick, extending at least 3 mm from the canal. Conclusions: PLM revealed structural aspects of the lamina cribrosa and sclera that may have important biomechanical roles but that were previously unreported or not characterized quantitatively. In the lamina cribrosa, these roles included wide and narrow beam insertions and details of collagen fibers interweaving and wrapping around the pores. In the sclera, we described regions of circumferential, radial, and unaligned "random" fibers. Although there is consensus that circumferential fibers protect neural tissues by resisting canal expansion, the role of the radial fibers remains unclear.

Estimation of the relative amount of hemoglobin in the cup and neuroretinal rim using stereoscopic color fundus images.

PURPOSE: To calculate the relative amount of hemoglobin (Hb) in sectors of the optic nerve head (ONH) from stereoscopic color fundus images using the Laguna ONhE method and compare the results with the visual field evaluation and optical coherence tomography (OCT). METHODS: Healthy eyes (n = 87) and glaucoma eyes (n = 71) underwent reliable Oculus Spark perimetry and Cirrus OCT. Optical nerve head color images were acquired with a nonmydriatic stereoscopic Wx Kowa fundus camera. Laguna ONhE program was applied to these images to calculate the relative Hb amount in the cup and six sectors of the rim. Receiver operating characteristic (ROC) analysis and correlations between parameters were calculated. RESULTS: We did not observe any variations in the relative amount of Hb in relation to age in healthy subjects (R(2) = 0.033, P > 0.05). Maximum ROC area confidence intervals were observed for a combination between perimetric indices and the Laguna ONhE Glaucoma discriminant function (0.970-0.899) followed by rim area (0.960-0.883), and mean deviation (MD; 0.944-0.857). In glaucoma cases, relative Hb amount presented significant reduction in all rim sectors, especially 231° to 270° and 81° to 120° (P < 0.001), except in the temporal 311° to 40° (P = 0.11). Perimetry mean sensitivity by sectors was better correlated with respective Hb levels than with rim areas or the corresponding nerve fiber thickness, especially the superior and inferior sectors (P < 0.05). CONCLUSIONS: Visual field sensitivity was better correlated with Hb levels than with rim sector areas or the corresponding nerve fiber thickness. In many cases the remaining rim show low perfusion, especially in the superior and inferior sectors.

Genome-wide association studies in Asians confirm the involvement of ATOH7 and TGFBR3, and further identify CARD10 as a novel locus influencing optic disc area.

Damage to the optic nerve (e.g. from glaucoma) has an adverse and often irreversible impact on vision. Earlier studies have suggested that the size of the optic nerve head could be governed by hereditary factors. We conducted a genome-wide association study (GWAS) on 4445 Singaporean individuals (n = 2132 of Indian and n = 2313 of Malay ancestry, respectively), with replication in Rotterdam, the Netherlands (n = 9326 individuals of Caucasian ancestry) using the most widely reported parameter for optic disc traits, the optic disc area. We identified a novel locus on chromosome 22q13.1, CARD10, which strongly associates with optic disc area in both Singaporean cohorts as well as in the Rotterdam Study (RS; rs9607469, per-allele change in optic disc area = 0.051 mm(2); P(meta) = 2.73×10(-12)) and confirmed the association between CDC7/TGFBR3 (lead single nucleotide polymorphism (SNP) rs1192415, P(meta) = 7.57×10(-17)) and ATOH7 (lead SNP rs7916697, P(meta) = 2.00 × 10(-15)) and optic disc area in Asians. This is the first Asian-based GWAS on optic disc area, identifying a novel locus for the optic disc area, but also confirming the results found in Caucasian persons suggesting that there are general genetic determinants applicable to the size of the optic disc across different ethnicities.

OPA1 expression in the human retina and optic nerve.

Mutations in the optic atrophy type 1 (OPA1) gene give rise to human autosomal dominant optic atrophy. The purpose of this study is to investigate OPA1 protein expression in the human retina and optic nerve. A rabbit polyclonal antiserum was generated using a fusion protein covering amino acids 647 to 808 of the human OPA1 protein as the immunogenic antigen. Western blot and immunofluorescence staining were performed to examine OPA1 expression in the human retina and optic nerve. In human retina, we found that OPA1 expression was clearly present in retinal ganglion cells and photoreceptors. OPA1 immunoreactivity was also present in the nerve fiber layer, inner plexiform layer and outer plexiform layer. However, OPA1 protein was not detected in the choline acetyltransferase-positive, calretinin-positive, and calbindin-positive amacrine cells, nor in the calbindin-positive horizontal cells. In the human optic nerve, expression of OPA1 was present in the axonal tract that was labeled with neurofilament specific antibody. In conclusion, expression of OPA1 gene is present in the mitochondria-rich regions of the retina and optic nerve. This suggests that OPA1 protein might be involved in the functioning of the mitochondria that are present in both inner and outer retinal neurons.

Androgen receptor and NFkB expression in human normal and glaucomatous optic nerve head astrocytes in vitro and in experimental glaucoma.

For several decades, clinical and experimental observations suggested a relationship between steroids and glaucoma; however, the possibility that androgens are also involved in the glaucomatous changes in the optic nerve heads (ONH) has not been explored. Our previous findings that glaucomatous ONH astrocytes synthesize androgen-metabolising enzymes and overproduce a neuroactive androgen, 5alpha-androstane-3alpha, 17beta-diol (3alpha-diol) led us to propose that ONH astrocytes are androgen target cells. Androgens modulate different cellular processes through androgen receptor (AR). NFkB is a transcription factor that positively regulates AR transcription. Here, we analysed AR and NFkB expression in normal and glaucomatous ONH astrocytes in vitro, and in vivo in a monkey model of experimental glaucoma (ExpG) by quantitative real time RT-PCR, Western blotting and immunohistochemistry. We demonstrated that in vitro human glaucomatous ONH astrocytes express AR mRNA and protein at higher levels than normal astrocytes and that in vivo ONH astrocytes from eyes with ExpG showed increased nuclear and cytoplasmic AR immunostaining compared to control eyes. In the retina, retinal ganglion cells (RGC) demonstrated cytoplasmic staining both in control and in ExpG eyes. NFkB mRNA expression was higher in glaucomatous ONH astrocytes than in normal and more nuclear NFkB protein was detected in glaucomatous ONH astrocytes. In vivo immunopositive NFkB nuclear staining of ONH astrocytes in ONH and in RGC in retina was detected both in control and in ExpG eyes. We conclude that in addition to our published data, increase of AR and NFkB expression in glaucomatous ONH astrocytes provides strong evidence that androgens play a significant role in the pathophysiology of glaucoma.

Glutamate level in optic nerve head is increased by artificial elevation of intraocular pressure in rabbits.

Neurons can be damaged by the activation of glutamate receptors, but whether glutamate is related to the development of glaucomatous optic neuropathy is still controversial. The purpose of this study was to measure the acute changes in the glutamate levels in the optic nerve head (ONH) of rabbits induced by an artificial elevation of the intraocular pressure (IOP). A concentric microdialysis probe was inserted into the ONH of rabbits via the pars plana. The probe was perfused with Ringer's solution, and the levels of glutamate in 10-min dialysate samples were measured repeatedly using high-performance liquid chromatography. After the glutamate level was stabilized for at least 60 min, the IOP was adjusted to three levels; 120 mm Hg (n=11), 60 mm Hg (n=12), and 15 mm Hg (control group; n=11). The IOP was altered by changing the height of a bottle of Ringer's solution, which was connected to the anterior chamber by a 23-gauge needle. The IOP levels were maintained for 60 min, and the glutamate levels were determined every 10 min during the 60 min. The mean basal levels of glutamate in the 10-min dialysate were not significantly different among the three groups. The glutamate levels remained unchanged and stable in the controls, but elevation of the IOP significantly increased the level of the glutamate in the dialysate (IOP60, P=0.012; and IOP120, P=0.005: repeated measures ANOVA). Elevation of the IOP causes an increase in the glutamate levels in the ONH of rabbits. This suggests a possible interaction between glutamate metabolism and the IOP in the ONH.

Cell adhesion glycoproteins in the human lamina cribrosa.

PURPOSE: The distribution of the cell adhesion glycoproteins, laminin, fibronectin, tenascin, vitronectin, thrombospondin, and entactin/nidogen, was examined in the human lamina cribrosa. METHODS: Frozen sections of the optic nerve head from 7 normal human elderly donors were stained by immunohistochemistry. RESULTS: All six glycoproteins were detected in this tissue. While laminin and entactin/nidogen were observed linearly, reflecting the localization of basement membranes, fibronectin was identified diffusely. Marked tenascin immunoreactivity was apparent in the lamina cribrosa, but little or no tenascin staining was detected in the sclera. Vitronectin showed a fine fibrillar staining pattern in the lamina cribrosa, and, to a lesser extent, in the sclera and pial septa. Thrombospondin staining was apparent only in the sclera and the lamina cribrosa, which traversed the optic nerve. CONCLUSIONS: These results indicate that extracellular matrix components in the lamina cribrosa differ from those in the sclera or pial septa. This study is the first report that the human lamina cribrosa includes vitronectin and thrombospondin.

Lack of blood-brain barrier properties in microvessels of the prelaminar optic nerve head.

PURPOSE: To define the blood-brain barrier (BBB) characteristics of microvessels in the optic nerve head (ONH). METHODS: Immunohistochemical staining of different regions of the ONH, retro-laminar optic nerve, and retina of human and monkey eyes was carried out, using antibodies against BBB markers (glucose transporter 1, transferrin receptor, and P-glycoprotein), the non-BBB marker PAL-E, and against plasma proteins fibrinogen and IgG, which serve as endogenous markers of nonspecific microvascular permeability. In the ONH of monkey eyes, the number of transport-related endothelial pinocytotic vesicles and their cellular distribution within the microvessels were determined by electron microscopy. RESULTS: In both human and monkey eyes, only microvessels in the prelaminar region of the ONH were positive for the PAL-E antigen. The prelaminar region microvessels showed either no or weak expression of the transferrin receptor and P-glycoprotein but stained positive for glucose transporter 1. In human ONH, fibrinogen and IgG were present around microvessels in the prelaminar region but not in other parts of the optic nerve or retina. By electron microscopy, endothelial cells of prelaminar region microvessels contained a higher number of pinocytotic vesicles, located at the luminal and abluminal side of the endothelial cell membrane, in contrast to a mainly abluminal localization in microvessels of the retina and other parts of the optic nerve. CONCLUSIONS: Microvessels in the prelaminar region of the ONH lack classical BBB characteristics and display nonspecific permeability, possibly mediated by vesicular transport.

[An immunohistochemistry study on extracellular matrix of lamina cribrosa in optic nerve head of experimental glaucoma].

OBJECTIVE: To observe the change of the macromolecular components of extracellular matrix of lamina cribrosa (LC) in experimental glaucoma. METHODS: Immunoperoxidase (ABC) staining method was used to investigate the changes of collagen type IV and laminin in the lamina cribrosa of 9 monkey eyes with experimental glaucoma. RESULTS: At the late stage of glaucoma, the labeling of collagen type IV and laminin were increased at pre-LC and LC area due to the accumulation of basement membrane-like materials. CONCLUSION: The changes may be a selective response to elevated intraocular pressure. This response may alter the biochemical composition and the biomechanics of the lamina cribrosa.

Age related changes in the non-collagenous components of the extracellular matrix of the human lamina cribrosa.

AIMS: To investigate age related alterations in the non-collagenous components of the human lamina cribrosa. METHODS: Fibronectin, elastin, and glial fibrillary acidic protein (GFAP) staining were assessed in young and old laminae cribrosae. An age range (7 days to 96 years) of human laminae cribrosae were analysed for lipid content (n=9), cellularity (n=28), total sulphated glycosaminoglycans (n=28), elastin content (n=9), and water content (n=56), using chloroform-methanol extraction, fluorimetry, the dimethylmethylene blue assay, and ion exchange chromatography, respectively. RESULTS: Qualitatively, an increase in elastin and a decrease in fibronectin and GFAP were demonstrated when young tissue was compared with the elderly. Biochemical analysis of the ageing human lamina cribrosa demonstrated that elastin content increased from 8% to 28% dry tissue weight, total sulphated glycosaminoglycans decreased, and lipid content decreased from 45% to 25%. There were no significant changes in total cellularity or water content. CONCLUSION: These alterations in composition may be indicative of the metabolic state of the lamina cribrosa as it ages, and may contribute to changes in mechanical integrity. Such changes may be implicated in the susceptibility of the elderly lamina cribrosa and also its response to glaucomatous optic neuropathy.

The similarity of protein expression in trabecular meshwork and lamina cribrosa: implications for glaucoma.

The purpose of the present investigation was to compare protein expression in various ocular cells and tissues including the human trabecular meshwork (TM) and the lamina cribrosa (LC). To conduct the comparisons, we primarily utilized autofluorography of one-dimensional (1D) and high resolution, two-dimensional (2D) polyacrylamide gels of proteins from radiolabelled tissues and cultured cells. Results from the investigations indicated that patterns of protein expression from TM and LC were the most similar among the ocular cells and tissues compared.Specifically, these autofluorographic ' fingerprints' indicated that proteins in TM and LC cultured cells and tissue were exceptionally similar (a) in band position and intensity (1D gels) and (b) in spot congruence (2D gels) as compared to other ocular cells and tissues. We conclude that the TM and the LC, two ocular tissues intimately linked to the pathogenesis of primary open-angle glaucoma, display remarkable similarity in protein expression. This finding may have implications for the molecular etiology of glaucoma.

[Changes in transforming growth factor-beta and platelet-derived growth factor in the optic nerve head in monkey experimental glaucoma].

PURPOSE: Remodeling of the extracellular matrix occurs in the lamina cribrosa in progressed glaucomatous optic nerve damage including disc cupping. We examined immunohistochemical changes in the transforming growth factor (TGF)-beta and platelet derived growth factor (PDGF) in the optic nerve heads in experimentally induced glaucoma. METHODS: We used 3 cynomolgus and 2 Japanese monkey eyes. Glaucoma was induced by repeated argon laser photocoagulation of the chamber angle. Eyes were enucleated after disc cupping had formed 3 to 5 months after treatment. The optic nerve head was examined for expression of TGF beta 1, beta 2, and beta 3, and PDGF A and B in frozen sections and by the biotin-ExtrAvidin-Alkali Phosphatase method. FINDINGS: Normal monkey eyes showed TGF beta 1, beta 2, and beta 3, and PDGF A, and B in the optic nerve head including the nerve fibers, glial cells, and vascular cells. Glaucomatous eyes showed stronger expression of TGF beta 1 and beta 2 in the glial cells around the lamina cribrosa. The staining intensities for TGF beta 3, PDGF A, and PDGF B were the same as in normal eyes. CONCLUSION: Eyes with experimental glaucoma showed higher expressions of TGF beta 1 and beta 2 around the lamina cribrosa. This finding may show upregulation of extracellular matrix production as related to remodeling of the lamina cribrosa in glaucoma.

Pax2 expression and retinal morphogenesis in the normal and Krd mouse.

The Kidney and retinal defects (Krd) mouse carries a 7-cM transgene-induced deletion on chromosome 19 that includes the Pax2 locus. Adult mice heterozygous for the Krd deletion (Krd/+) are haploid for Pax2 and have a variable, semidominant phenotype characterized by structural defects of the kidney, retina, and optic disc. Renal and ocular anomalies present in heterozygous Pax2 mutants in both mice and humans support the hypothesis that haploinsufficiency of Pax2 underlies the Krd phenotype. To understand the embryonic basis of ocular defects observed in adult Krd/+ mice, we used immunohistochemistry, digital three-dimensional reconstructions, and quantitative morphometry to examine Pax2 protein distribution and ocular development in normal and Krd/+ mice from E10.5 to P2. In +/+ embryos, Pax2 immunopositive (Pax2+) cells demarcate the embryonic fissure as it forms in the ventral optic cup and optic stalk. After closure of the embryonic fissure, Pax2 immunostaining disappears from the ventral retina, but persists in a cuff of cells encircling the developing optic disc, the site where ganglion cell axons exit the retina. In Krd/+ embryos, Pax2+ cells in the posterior optic cup and the optic stalk undergo abnormal morphogenetic movements and the embryonic fissure fails to form normally. This results in an abnormal organization of the Pax2+ cells and ganglion cell axons at the nascent optic disc. The abnormal morphogenetic movements of the Pax2+ cells in the embryonic retina and optic stalk and the initial misrouting of the ganglion cell axons give rise to retinal and optic disc defects observed in the adult Krd/+ mice.

Elastosis of the lamina cribrosa in glaucomatous optic neuropathy.

The purpose of this study was to determine whether elastotic degeneration of the elastin component of the lamina cribrosa occurs in optic neuropathy associated with different types of glaucoma. Human optic nerve heads with primary open-angle, neovascular, chronic angle closure and pseudoexfoliation glaucoma, and with varying duration of disease were compared with age-matched normal eyes, using electron microscopy and immunogold labeling of elastin. The percent area occupied by immunogold-labeled elastin material was determined using a digital image analysis system. In all eyes with a history of glaucoma, elastosis was found in the lamina cribrosa and there was a significantly greater percentage of area occupied by elastin compared with age-matched control eyes (P<0.0001). Among the glaucomatous eyes, pseudoexfoliation glaucoma had the largest area of elastosis, followed by primary open-angle and secondary glaucoma (neovascular and chronic angle closure). In all glaucoma samples, large, confluent elastin aggregates of irregular and varied shapes (elastosis) were observed in the lamina cribrosa and insertion region. These results demonstrate that glaucomatous optic neuropathy is associated with elastosis of the lamina cribrosa, which may contribute to the changes in compliance of the optic nerve heads of glaucomatous eyes.

Elastosis of the lamina cribrosa in pseudoexfoliation syndrome with glaucoma.

BACKGROUND: Pseudoexfoliation syndrome is characterized by the presence of glycoprotein fibers in ocular and extraocular tissues, and often is associated with glaucoma. Pseudoexfoliation material may be associated closely with elastic microfibrillar-associated glycoprotein as well as elastin. METHODS: Four optic nerve heads of two patients with pseudoexfoliation syndrome and glaucoma were examined using electron microscopy and immunogold detection of elastin. Optic nerve heads from healthy age-matched individuals and patients with primary open-angle glaucoma were used for comparisons. RESULTS: In all eyes with pseudoexfoliation and glaucoma, there was marked and widespread elastosis in the connective tissue of the lamina cribrosa. Elastotic fibers appeared as large and irregular aggregates of electron-dense material labeled with anti-elastin antibody. Abundant microfibrils were interspersed in the elastotic aggregates, whereas no typical pseudoexfoliation fibers were observed. In contrast, there were less elastotic fibers in the lamina cribrosa from patients with primary open-angle glaucoma compared with pseudoexfoliation glaucoma. Other changes of extracellular matrix were similar to those observed in primary open-angle glaucoma: decreases in collagen fiber density, presence of basement membranes not associated with cell surfaces, and abundant bundles of microfibrils not labeled with elastin antibody. The elastic fibers appeared normal in other locations within the optic nerves of patients with pseudoexfoliation glaucoma, including in the pial septa and blood vessels of the retrolaminar myelinated optic nerve. CONCLUSION: The authors' findings demonstrate marked and site-specific elastosis in the lamina cribrosa of patients with pseudoexfoliation syndrome with glaucoma, suggesting an abnormal regulation of elastin synthesis and/or degradation in the optic nerve of patients with this disease.

Structure and composition of the rodent lamina cribrosa.

To define the architecture and extracellular matrix composition of the lamina cribrosa in rodents, normal, adult pigmented rat and guinea pig eyes were frozen and sectioned for light microscopic immunohistochemistry. Antibodies specific for collagens I, III, IV and VI, laminin, elastin, and chondroitin and dermatan sulfate proteoglycans were exposed to longitudinal and cross-sections of optic nerve heads and their binding distributions observed with the avidin-biotin-peroxidase complex technique. Cross-sections of the intraocular portion of the rat optic nerve head revealed a horizontally oval shape with distinct, vertically oriented, laminar beams. The guinea pig optic nervehead cross-section was circular, with randomly oriented beams. In both animals, collagens I, III and VI were found throughout the laminar beams, along with elastin fibrils. Collagen IV and laminin antibodies deposited along laminar beam margins and within the beams, representing astrocytic and vascular endothelial cell basement membranes. Both animals showed evidence for dermatan and chondroitin sulfate-containing proteoglycans in all connective tissue structures of the nerve head. In the rat, chondroitin-4 sulfate proteoglycans appeared localized to the sclera and laminar beams. The rat and the guinea pig optic nerve head possess an identifiable lamina cribrosa with structural proteins nearly identical to that of the primate. Both animals may provide affordable alternative animal models for in vivo studies on the role of the lamina cribrosa in glaucomatous optic nerve damage.