Computer generation and quantitative morphometric analysis of virtual neurons.

An important goal in computational neuroanatomy is the complete and accurate simulation of neuronal morphology. We are developing computational tools to model three-dimensional dendritic structures based on sets of stochastic rules. This paper reports an extensive, quantitative anatomical characterization of simulated motoneurons and Purkinje cells. We used several local and global algorithms implemented in the L-Neuron and ArborVitae programs to generate sets of virtual neurons. Parameters statistics for all algorithms were measured from experimental data, thus providing a compact and consistent description of these morphological classes. We compared the emergent anatomical features of each group of virtual neurons with those of the experimental database in order to gain insights on the plausibility of the model assumptions, potential improvements to the algorithms, and non-trivial relations among morphological parameters. Algorithms mainly based on local constraints (e.g., branch diameter) were successful in reproducing many morphological properties of both motoneurons and Purkinje cells (e.g. total length, asymmetry, number of bifurcations). The addition of global constraints (e.g., trophic factors) improved the angle-dependent emergent characteristics (average Euclidean distance from the soma to the dendritic terminations, dendritic spread). Virtual neurons systematically displayed greater anatomical variability than real cells, suggesting the need for additional constraints in the models. For several emergent anatomical properties, a specific algorithm reproduced the experimental statistics better than the others did. However, relative performances were often reversed for different anatomical properties and/or morphological classes. Thus, combining the strengths of alternative generative models could lead to comprehensive algorithms for the complete and accurate simulation of dendritic morphology.

Generation, description and storage of dendritic morphology data.

It is generally assumed that the variability of neuronal morphology has an important effect on both the connectivity and the activity of the nervous system, but this effect has not been thoroughly investigated. Neuroanatomical archives represent a crucial tool to explore structure-function relationships in the brain. We are developing computational tools to describe, generate, store and render large sets of three-dimensional neuronal structures in a format that is compact, quantitative, accurate and readily accessible to the neuroscientist. Single-cell neuroanatomy can be characterized quantitatively at several levels. In computer-aided neuronal tracing files, a dendritic tree is described as a series of cylinders, each represented by diameter, spatial coordinates and the connectivity to other cylinders in the tree. This 'Cartesian' description constitutes a completely accurate mapping of dendritic morphology but it bears little intuitive information for the neuroscientist. In contrast, a classical neuroanatomical analysis characterizes neuronal dendrites on the basis of the statistical distributions of morphological parameters, e.g. maximum branching order or bifurcation asymmetry. This description is intuitively more accessible, but it only yields information on the collective anatomy of a group of dendrites, i.e. it is not complete enough to provide a precise 'blueprint' of the original data. We are adopting a third, intermediate level of description, which consists of the algorithmic generation of neuronal structures within a certain morphological class based on a set of 'fundamental', measured parameters. This description is as intuitive as a classical neuroanatomical analysis (parameters have an intuitive interpretation), and as complete as a Cartesian file (the algorithms generate and display complete neurons). The advantages of the algorithmic description of neuronal structure are immense. If an algorithm can measure the values of a handful of parameters from an experimental database and generate virtual neurons whose anatomy is statistically indistinguishable from that of their real counterparts, a great deal of data compression and amplification can be achieved. Data compression results from the quantitative and complete description of thousands of neurons with a handful of statistical distributions of parameters. Data amplification is possible because, from a set of experimental neurons, many more virtual analogues can be generated. This approach could allow one, in principle, to create and store a neuroanatomical database containing data for an entire human brain in a personal computer. We are using two programs, L-NEURON and ARBORVITAE, to investigate systematically the potential of several different algorithms for the generation of virtual neurons. Using these programs, we have generated anatomically plausible virtual neurons for several morphological classes, including guinea pig cerebellar Purkinje cells and cat spinal cord motor neurons. These virtual neurons are stored in an online electronic archive of dendritic morphology. This process highlights the potential and the limitations of the 'computational neuroanatomy' strategy for neuroscience databases.

Teleophthalmology: the use of real-time telementoring to remove an orbital tumor.

OBJECTIVE: To determine whether current telemedicine technology can support real-time surgical telementoring to remove an orbital tumor. DESIGN: Interventional case report METHODS: An orbital specialist guided a general ophthalmologist in the removal of a lateral orbital tumor from a site 210 miles away on another island. A 3-mm endoscope connected to a three-chip digital video camera attached to a Concorde 4500 Picture-Tel videoconferencing system was used to transmit images at a rate of 384 kb per second over integrated service digital network lines. MAIN OUTCOME MEASURES: Successful performance and outcome of the telementored procedure comparable to hands-on orbital surgery. RESULTS: The surgical procedure was successfully telementored with uncomplicated removal of the orbital tumor. CONCLUSIONS: Current telemedicine technology can support real-time telementoring to remove an orbital tumor.

Uric acid in the aqueous humor and tears of retinoblastoma patients.

PURPOSE: Malignancy can be associated with high levels of catabolic products. We performed a two-part study. Part 1 measured levels of uric acid and xanthine in the aqueous humor of eyes with malignant and nonmalignant diagnoses. Part 2 measured the levels of uric acid in tears of retinoblastoma patients. If compounds in high concentrations inside the eye could be detected outside the eye, via diffusion, in high concentrations in the tears, then a tear screening test for retinoblastoma could be developed. METHODS: High-performance liquid chromatography measured levels of uric acid and xanthine in aqueous humor samples of patients with retinoblastoma, melanoma, Coats' disease, adult cataract, and congenital cataract. Tear sampling was performed on patients with retinoblastoma and on normal eyes, and samples were assayed for uric acid. RESULTS: Part 1--Uric acid was elevated in the aqueous humor of eyes with retinoblastoma, melanoma, and Coats' disease compared with eyes with cataracts. Xanthine was elevated in retinoblastoma and Coats' disease and was lower in adult and congenital cataracts and melanoma. Part 2-No significant difference was found in the concentrations of uric acid in the tears of patients with retinoblastoma and those of normal patients. CONCLUSIONS: High levels of uric acid and xanthine present in the aqueous humor of patients with malignancy are consistent with the destructive nature of these conditions. Although uric acid was not elevated in the tears of retinoblastoma patients, continued investigation into substances that might be measurably different in the tears may yield a useful screening test in the future.

Transformation of a set of slices rotated on a common axis to a set of Z-slices: application to three-dimensional visualization of the in vivo human lens.

A technique that transforms a set of images acquired as a rotating frame about an axis (Z axis) into a set of images along the Z axis in presented. This technique is applied to the three-dimensional visualization of the in vivo human lens. A Scheimpfling slit camera acquired 60 optical images through the in vivo human lens. Between each image acquisition the plane containing the slit beam of light was sequentially rotated. This set of 60 images was transformed into a new stack of images on the Z axis. The transformed stack of Z images was visualized with volume rendering software.

Three-dimensional volume visualization of the in vivo human ocular lens showing localization of the cataract.

An in vivo human lens containing a cataract has been visualized by volume rendering a transformed series of 60 rotated Scheimpflug digital images. The data set was obtained by rotating the Scheimpflug camera about the optic axis of the lens in 3-degree increments. The set of 60 Scheimpflug digital images were mathematically transformed into a new data set in which the images are oriented perpendicular to the optic axis of the eye. The transformed set of optical sections were first aligned to correct for eye movements during the data collection process, then rendered into a three-dimensional volume reconstruction with volume-rendering computer graphics techniques. The viewpoint and the transparency of the volume rendered in vivo human lens were varied in order to observe volume opacities in various regions of the lens. To help visualize lens opacities, the intensity of light scattering was pseudocolor-coded as an integral part of the three-dimensional volume rendering. Three-dimensional, pseudocolored volume rendering of the in vivo human ocular lens represents a new technique to visualize in vivo human cataracts.

Oncogenic mutations in the rb1 gene in retinoblastoma tumors from patients from the kingdom of saudi-arabia.

Five retinoblastoma tumours from patients treated in the King Khaled Eye Specialist Hospital in Riyadh were analysed for mutations in the RB1 gene using single strand conformation polymorphism analysis and mutations were found in all of them. In one tumour the mutation in exon 11 was homozygous demonstrating the role of loss of heterozygosity in tumorigenesis. The mutation in the remaining 4 tumours were heterozygous and in only one case were two independent mutations found. Three mutations were insertions or deletions and the other three were point mutations of which 5 resulted in the generation of premature stop codons within the coding region of the gene and one is predicted to affect the correct splicing of the pre-mRNA. The nature of the mutations found in this series of patients from the Kingdom of Saudi Arabia, therefore, are similar to those found in other populations throughout the world and show no evidence for mutation hotspots within the RB1 gene.

Atypical presentation of Coats disease.

PURPOSE: To highlight the possibility of intraocular calcification in Coats disease and evaluate the ultrasound and computed tomographic findings. METHOD: A 7.5-year-old boy had a 2-week history of unilateral glaucoma and leukocoria with retinal detachment, suggestive of Coats disease. The possibility of retinoblastoma, however, could not be excluded by ultrasound or computed tomographic examination, which revealed a retinal detachment overlying a subretinal mass with calcification. The blind, painful eye was subsequently enucleated. RESULTS: Histopathologically, there were telangiectatic retinal vessels in a fold of the detached retina peripherally and proteinaceous exudate in the subretinal space containing cholesterol clefts and foamy histiocytes, characteristic of Coats disease. There was also a fibro-osseous nodule in the macular area that correlated with intraocular calcification clinically. CONCLUSION: This case provides the first documentation of ancillary corroboration of intraocular bone formation in Coats disease, which, although rare, is an important consideration in the differential diagnosis of retinoblastoma.

Retinoblastoma aqueous humor: aromatic amino acids.

Aqueous humor from children with retinoblastoma obtained at enucleation and from eyes with adult cataracts were assayed with electrochemical liquid chromatography (Model 5500 Coulochem electrode array system) for metabolites of tyrosine, tryptophan metabolic pathways, catecholamine degradation pathways and ascorbate. More than 20 metabolites were identified in human aqueous for the first time. High levels of ascorbate were found in aqueous of eyes with adult cataracts (254, 336 ng/ml). Tyrosine metabolism in both sets of eyes was through dopamine. Vandylmandelic acid (VMA), homovanillic acid (HVA), and 3-methoxy, 4-hydroxyphenylglycol (MHPG) were all detected in retinoblastoma eyes. Although eyes with either adult cataracts or childhood retinoblastoma convert tryptophan through the serotonin pathway, retinoblastoma eyes metabolize tryptophan through the kynurenine pathway to a greater degree than adult cataract eyes.

Cumulative incidence of retinoblastoma in Riyadh, Saudi Arabia.

A survey of all hospitals in the city of Riyadh for retinoblastoma cases presenting during the period 1982-1986 was performed; 22 cases (16 females and six males) were identified. The cumulative live births in the city of Riyadh for the same period numbered 254,780. The authors report the cumulative incidence of retinoblastomas in Riyadh, Saudi Arabia as 1:11580 live births per year.

Growth of thalamic afferents into mouse barrel cortex.

We studied thalamocortical afferent (TCA) growth into somatosensory cortex as the whisker barrels emerge in postnatal mice. Ingrowing fibers from the ventrobasal (VB) thalamus were selectively labeled by two means. Under direct vision, individual axons and populations of axons were labeled in vitro with HRP, or in fixed tissue with Dil (1,1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), in pieces of brain containing both the source nucleus in the thalamus and its cortical target. Many simple thalamocortical afferents are already within the upper cortical plate at birth [postnatal day one (PND1)]. Initially, TCAs from each point in the thalamus distribute in the cortex as two-dimensional "Gaussians," which overlap laterally to constitute a uniform projection pattern. The projection is topographic, because adjacent focal injections within VB label adjacent cortical loci. Subsequent development of barreloids (thalamic representations of the whiskers) partitions the TCA projection into a set of whisker-related Gaussians, centered on cortical targets whose collective topography reflects that of the source pattern. After barreloids form on about PND3, but before barrels appear in cytoarchitecture on about PND5, the overlapping TCAs segregate into dense terminal clusters in layer IV, around which barrels later mature. Time series of single fibers traced with camera lucida explain this transformation that is so noticeable at the population level. As early as PND1, individual TCAs emit multiple ascending collaterals on their horizontal run through white matter and oblique ascent into upper cortex. Subsequently, by PND4, and proceeding at least through PND7, there is accelerated terminal arborization of selected appropriate collateral branches and pruning back of other inappropriate ones. The selection mechanism appears to result from within-group reinforcement events that are stronger for branches toward the center of each whisker-related Gaussian distribution.

Computer-aided analyses of thalamocortical afferent ingrowth.

Segregation of thalamocortical afferent (TCA) fibers precedes barrel formation in rodent somatosensory cortex (Killackey and Leshin, 1975; Jeanmonod et al., 1981; Jensen and Killackey, 1987b; Senft, 1989; Erzurumlu and Jhaveri, 1990). Hypotheses about the arborization strategies followed by these ingrowing fibers have been generated from evaluation of labeled terminal fragments of mouse TCAs (Senft and Woolsey, 1991a). Those TCAs were of necessity truncated by the histological processing needed to observe them at high resolution. This fragmentation, along with biological variability, forces conclusions about single intact axons to be derived from populations of parts of arbors. To evaluate the hypotheses critically, we designed a computer program to quantify morphological aspects of labeled TCAs drawn with a camera lucida. We constructed algorithms to abstract, from fiber populations, properties minimally affected by truncation. Our program analyzes, and displays as histograms, fiber and branch densities and orientations. To represent these features by additional graphical means, "average" ingrowing TCAs were generated, based on the accumulated statistics of the traced fiber fragments. Quantitative descriptions of TCA populations from postnatal day 1 (PND1) through PND7 are presented. These analyses show that fibers and their branches accumulate with age within the cortical plate (emergent layer IV), and to a lesser extent within developing layer VI. Simultaneously, the distributions of these afferents within cortical laminae transform from uniform to patchy in the plane of the cortex. Peaks exhibit the periodicity typical of mature barrels. Branches become more numerous focally as and where layer IV barrels emerge. Individually traced arbors show reduced total widths consistent with progressive pruning of branches extending into territories of inappropriate barrels, both in layer IV and deeper in the cortex.

Mouse barrel cortex viewed as Dirichlet domains.

Barrels are patterned groups of neurons in rodent somatosensory cortex that correspond one to one with the animal's facial whiskers. Dirichlet domains are a class of convex polygon found frequently in nature, often arising by nucleation from center points. Analytic and graphical methods were devised to verify the hypothesis that Dirichlet domains accurately describe the adult barrel fields of normal mice. We found that normal barrel fields and abnormal barrel fields caused by supernumerary whiskers or lesions to the whisker pad are closely approximated by this mathematical formalism. This implies that each developing cortical barrel organizes about a center point. Experiments in neonatal animals (Senft and Woolsey, 1991a) demonstrate foci in the thalamocortical afferent (TCA) distributions. These results support an hypothesis in which TCAs are the nucleating agents causing barrels to organize as Dirichlet domains. This is made possible because TCA terminals from each barreloid (a whisker-related group of cells in the ventrobasal complex of the thalamus) initially colonize somatosensory cortex with an approximately "Gaussian" distribution. These peaked groups of related TCAs behave as Dirichlet domain centers. They generate barrel structures competitively, in animals with normal or with perturbed whisker patterns, via statistical epigenetic interactions within and between distinct TCA Gaussians associated with separate whiskers. This leads to selective axon outgrowth and pruning of single TCA branches, regulated by the TCA population, and creates beneath each Gaussian the dense knot of related TCA arbors typical of the barrel cortex. Similar parcellation of neuronal processes into contending subgroups having spatially coherent actions could lead to nucleation of other geometric patterns as Dirichlet domains elsewhere in the brain.

Clinical experience with the Molteno implant in advanced infantile glaucoma.

The alternatives in the management of infantile glaucoma refractory to conventional treatment are quite limited and unrewarding. We did a retrospective study of 49 patients (53 eyes) under 12 years of age with advanced, uncontrolled glaucoma who each underwent implantation of a single-plate Molteno implant in one stage. Over the follow-up period ranging from 6 months to 3 years (mean 18 months), 36 of the 53 eyes (68%) had an intraocular pressure less than or equal to 21 mm Hg and were considered a success. Fourteen eyes (26%) required further glaucoma surgery, 2 eyes developed severe chronic hypotony, and 1 eye lost light perception following endophthalmitis. The number of anti-glaucoma medications was decreased from a mean of 2 (+/- 1) to 1 (+/- 1). The probability for success of the Molteno implant in controlling glaucoma increased with the age of the patient. Six eyes (11%) were late failures, most probably due to fibrous encapsulation of the bleb. Complications observed were: prolonged hypotony and flat anterior chamber, retinal detachment, migration of the tube, erosion of the tube through the conjunctiva, and an ingrowth of fibrous tissue in the anterior chamber. We consider the Molteno implant to be a reasonable option in the management of difficult cases of infantile glaucoma.

Neodymium-YAG laser goniotomy vs surgical goniotomy. A preliminary study in paired eyes.

Goniotomy and trabeculotomy are two widely accepted modalities of treatment for primary congenital/infantile glaucoma. Both procedures may be associated with complications. We treated 10 patients with bilateral, symmetrical congenital/infantile glaucoma and clear corneas. One eye of each patient underwent surgical goniotomy under general anesthesia, and the other was treated by neodymium-YAG laser goniotomy under oral chloral hydrate sedation (average energy, 76.6 mJ). Mean pretreatment intraocular pressure in the surgical goniotomy group was 28.4 mm Hg and in the laser goniotomy group it was 29.5 mm Hg, decreasing to 23.6 and 23.1 mm Hg, respectively, following treatment. There was a strong positive correlation (r = .81) between the percent of intraocular pressure change after laser treatment (mean, -14.4%) and that after surgery (mean, -14.3%). Our preliminary results indicate that neodymium-YAG laser goniotomy is an effective, noninvasive alternative to surgical goniotomy.

Retinoblastoma: the Saudi Arabian experience.

During the period March 1983-May 1987, 74 cases of retinoblastoma were evaluated at the King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia. 60% of the cases were unilateral with a female preponderance of 59.4% noted for this series. Additionally, the mean age at diagnosis was 22 months, and delay of retinoblastoma diagnosis since the first symptoms were observed ranged from two days to 36 months. Fifty-seven eyes were enucleated, and in 21 of these patients, this was the sole form of therapy. The remainder of patients were treated with radiotherapy alone or combined with chemotherapy, cryotherapy/photocoagulation. Overall, two-year survival statistics of this group of Saudi patients is 80% which compares favorably to other reports in the West. Emphasis is placed on management of the retinoblastoma patients by a multi-disciplinary group, and public educational efforts are imperative.

Aqueous misdirection and flat chamber after posterior chamber implants with and without trabeculectomy.

Three patients developed flat anterior chamber and were ultimately diagnosed as having aqueous misdirection after trabeculectomy with extracapsular cataract extraction and posterior chamber lens implantation (glaucoma triple procedure). A fourth patient developed aqueous misdirection after posterior chamber lens implantation only (without trabeculectomy). This latter was cured by repeated pars plana vitrectomy, not requiring removal of the pseudophakos. In only one of the three eyes with the triple procedure did the lens have to be removed and anterior vitrectomy performed, whereas the remaining two were cured by neodymium-YAG laser disruption of the anterior hyaloid. In these two cases, the posterior capsule remained intact. Neodymium-YAG laser vitreolysis should be the first step in the management of these cases because of its safety compared with open surgery.

Optical sectioning of HRP-stained molluscan neurons.

The use of high-resolution differential interference contrast(DIC) microscopy on cleared whole-mounts of the circumesophageal nervous system from Hermissenda crassicornis permits visualization of neuronal morphology in detail without the need for physical sectioning. Such optical sectioning, when preceded by intracellular iontophoresis of horseradish peroxidase (HRP) permits rapid and accurate examination of the arborization of electrically characterized neurons. Details such as varicosities and terminal swellings can readily be resolved. This method has revealed new morphological features of neurons implicated in training-specific behavioral modification in Hermissenda, and promises to be of further general use for the quantitative morphometry of electrically identified neurons.