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A novel swept-laser-based Fourier-domain optical coherence tomography system using an electro-optic phase modulator was demonstrated. The imaging range was doubled by cancellation of the mirror image. The elimination of low-frequency noises resulting from dc and autocorrelation terms increased the sensitivity by 20 dB.
A fiber-optic microphobe was used to analyze the spectral light gradients in benthic cyanobacterial mats with 50-micrometer depth resolution and 10-nm spectral resolution. Microcoleus chthononplastes mats were collected from hypersaline, coastal ponds at Guerrero Negro, Baja California. Gradients of spectral radiance, L, were measured at different angles through the mats and the spherically integrated scalar irradiance, Eo, was calculated. Maximal spectral light attenuation was found at the absorption peaks for the dominant photosynthetic pigments: chlorophyll a at 430 and 670 nm, carotenoids at 450-500 nm, phycocyanin at 620 nm, and bacteriochlorophyll a at 800-900 nm. Scattered light had a marked spectral effect on the scalar irradiance which near the mat surface reached up to 190% of the incident irradiance. The spherically integrated irradiance thus differed strongly from the incident irradiance both in total intensity and in spectral composition. These basic optical properties are important for the understanding of photosynthesis and light harvesting in benthic and epiphytic communities.
After an unilateral destruction of the suprachiasmatic nucleus and with the use of several silver impregnation techniques, degenerating centrifugal fibers were found in both optic nerves. Centrifugal fibers to the retina originate from three different regions of the nucleus and their position in the chiasma are different. In large majority the degenerating fibers were located at the periphery of the optic nerve and were more frequent on the contralateral than on the ipsilateral side to the destroyed suprachiasmatic nucleus. The possibility that our experimental procedure demonstrates the existence of fibers originating not only in the suprachiasmatic nucleus but also in other structures whose efferent fibers pass at this level, is discussed.
BACKGROUND: Schistosomiasis, a parasitic disease, is endemic in many parts of the world. Schistosomal eggs may be found in almost any organ or tissue in the body, including the eye. The presence of schistosomal eggs in the eye can produce granuloma formation and inflammatory sequelae. METHODS: A 63-year-old male had contracted schistosomiasis 40 years earlier while on active military service in the Philippines. Schistosoma japonicum eggs were isolated from his stools and military records indicated that the disease responded well to treatment with antimony potassium tartrate. The patient has gradually lost vision with his left eye over 15 years without the benefit of a complete optometric and medical diagnosis. RESULTS: CT scan suggested the likelihood of "subtle changes in the left optic nerve medially, possibly related to tumor invasion." Further evaluation and coordinated clinical thinking with other eye and medical practitioners led to the suspected diagnosis of schistosomal granuloma in the left optic nerve. In addition, the patient was legally blind from the consequences of glaucoma and its surgical intervention in his fellow eye. CONCLUSIONS: Although over 200 million people are infected with schistosomiasis, the United States is not an area where schistosomiasis is endemic. It is, however, endemic in parts of South America, Africa, Asia and the Caribbean Islands. Patients who have been in endemic areas with unexplained ophthalmic findings or systemic findings that could be related to granuloma formation or inflammatory sequelae of disease should have schistosomiasis included in their differential diagnosis.
Intraocular pressure (IOP), which causes the lamina cribrosa to bulge backward, produces a pressure gradient along the axoplasm of exiting optic nerve axons, and challenges the circulation, interacts with presently unknown physiologic or anatomic factors to harm the optic nerve and causes loss of vision. Present treatment of glaucoma is limited to efforts to lower IOP. Future treatments may be directed at other contributing anatomic or physiologic abnormalities that permit IOP to be harmful, or at some step in the pathway from insult to mortal injury of the axon or cell body.
OBJECTIVE: To investigate the relationship between optic disc changes measured with scanning laser tomography and those measured with conventional perimetry and optic disc photography. METHODS: In a prospective longitudinal study, we followed up 77 patients with early glaucomatous visual field damage. Scanning laser tomography (using the Heidelberg Retina Tomograph) and conventional perimetry (using the Humphrey Field Analyzer) were carried out every 6 months. Disc progression was determined by a procedure recently described by us for scanning laser tomography, with confirmed progression requiring repeatable changes based on probability limits for both the depth (using individual test-retest variability values) and size of change (determined in a group of 37 healthy individuals also followed up prospectively). Field progression was determined with the Statpac Glaucoma Change Probability Analysis. The agreement between scanning laser tomography and conventional disc photography was determined in a subgroup of patients. RESULTS: Patients were followed up for a median of 5.5 years, with a median of 12 sets of examinations with scanning laser tomography and conventional perimetry. Twenty-one patients (27%) showed no progression with either technique. Thirty-one patients (40%) progressed with scanning laser tomography only, while 3 (4%) progressed with conventional perimetry only. Of the 22 patients (29%) who progressed with both techniques, 10 (45%) progressed with scanning laser tomography first (median, 18 month earlier) and 9 (41%) with conventional perimetry first (median, 12 months earlier), while 3 (14%) progressed at the same time. Of the 16 patients with disc photographs that closely overlapped the follow-up, there was concordance between scanning laser tomography and disc photography in 13 patients (81%). CONCLUSIONS: Glaucomatous disc changes determined with scanning laser tomography occur more frequently than field changes. Most patients with field changes also had disc changes; however, less than half of those with disc changes had field changes.
The development of the centrifugal projection to the chick retina in the isthmo-optic tract (IOT) has been studied by the retrograde transport of the enzyme marker horseradish peroxidase (HRP) injected into the eye at various times during the incubation period. Some neurons in the isthmo-optic nucleus (ION--the cells of origin of the IOT) can first be labeled from the eye following injections on the tenth day of incubation; after injections on the twelfth day or later, about 95% of the neurons can be so labeled. It follows from this that the axons of virtually all the neurons in the ION (including the 60% which normally degenerate between the thirteenth and seventeenth days of incubation) reach the contralateral eye. Since in 12-day old embryos the IOT is between six and seven millimeters in length and HRP can be identified in the perikarya of ION neurons within three and one-half hours, the rate of retrograde transport in the system must be of the order of 48 mm/day. A similar time is required for HRP to appear in the perikarya of ION neurons in post-hatched chicks in which the length of the IOT is estimated to be about 14 mm. This suggests that at some time during the latter half of the incubation period there is a significant acceleration in the rate of retrograde transport, similar to that found for anterograde axonal transport in the chick and rabbit visual systems.
The nucleus of the optic tract (NOT) and the dorsal terminal nucleus of the accessory optic tract (DTN) have been recognized to be relevant structures for optokinetic and vestibuloocular reflexes. NOT-DTN neurons relay visual information to the vestibular nuclei via the nucleus prepositus hypoglossi and to the flocculus via the dorsal cap of the inferior olive. It has been previously shown that in carnivores the NOT-DTN receives information from primary visual cortical areas in addition to the direct retinal input. In this study we demonstrate the presence and some functional characteristics such as latency and evicacy of considerable cortical projections to the NOT-DTN in macaque monkeys. In anaesthetized and paralyzed monkeys NOT-DTN neurons were identified physiologically and tested for cortical input by electrical stimulation in various cortical areas. Successful sites of stimulation to activate NOT-DTN neurons orthodromically lie in the primary visual cortex (V1) and in the motion-processing areas in the superior temporal sulcus (STS). In contrast, electrical stimulation in area V4 and in parietal areas in most cases did not yield orthodromic responses. Overall latencies of action potentials elicited by stimulation in V1 were 0.5 ms longer than those elicited from STS. These short latency differences between V1 and STS stimulation suggest a direct projection from both V1 and STS to the NOT-DTN. The physiological results were supported by the results of anatomical experiments by using horseradish peroxidase as anterograde tracer. Both injections into V1 and into the lower bank of STS resulted in anterogradely labelled fibers and terminals around the recording sites of direction-specific NOT-DTN neurons. This paper is a first step in clarifying the significance of corticofugal projections from individual areas involved in the analysis of visual motion for the optokinetic reflex.
PURPOSE: To evaluate manganese (Mn2+)-enhanced MRI in a longitudinal study of normal and injured rat visual projections. MATERIALS AND METHODS: MRI was performed 24 hours after unilateral intravitreal injection of MnCl2 (150 nmol) into adult Fischer rats that were divided into four groups: 1) controls (N = 5), 2) dose-response (N = 10, 0.2-200 nmol), 3) time-response with repeated MRI during 24-168 hours post injection (N = 4), and 4) optic nerve crush (ONC) immediately preceding the MnCl2 injection (N = 7). Control and ONC animals were reinjected with MnCl2 20 days after the first injection, and MRI was performed 24 hours later. RESULTS: In the control group, the optic projection was visualized from the retina to the superior colliculus, with indications of transsynaptic transport to the cortex. There was a semilogarithmic relationship between the Mn2+ dose and Mn2+ enhancement from 4 to 200 nmol, and the enhancement decayed gradually to 0 by 168 hours. No Mn2+-enhanced signal was detected distal to the ON crush site. In the control group, similar enhancement was obtained after the first and second MnCl2 injections, while in the ONC group the enhancement proximal to the crush site was reduced 20 days post lesion (20 dpl). CONCLUSION: Mn2+-enhanced MRI is a viable method for temporospatial visualization of normal and injured ON in the adult rat. The observed reduction in the Mn2+ signal proximal to the ONC is probably a result of retrograde damage to the retinal ganglion cells, and not of Mn2+ toxicity.
The Optic Nerve Head Analyzer (ONHA) calculates by means of computer-assisted analysis of stereo images different parameters of the optic disc: disc diameter, disc size, cup/disc ratio (CDR), neuroretinal rim area, and excavation volume for the disc quadrants and for the total disc. To obtain first indications of the clinical value of ONHA measurements for diagnosis and follow-up in glaucoma we examined the reproducibility of measurement results for different diseases. Furthermore, we studied the mean values of the different disc parameters in healthy eyes. It was investigated: 1) whether the reproducibility is different in the different disc parameters; 2) whether the reproducibility in different eye diseases is different as compared to healthy eyes; 3) by which criteria the reproducibility is influenced; 4) whether there is a correlation between disc size and size of rim area. The reproducibility was studied in 178 eyes of 178 patients, who were all examined twice with the ONHA. The mean difference between the results of first and second measurement was calculated for the different disc parameters. Differences were found in the reproducibility of the parameters: e.g., the mean difference between first and second measurement was 1.8 percent for the disc size, and 5.6 percent for the neuroretinal rim area. For the disc quadrants, the reproducibility of values was worse than for the total disc. No marked differences of reproducibility of disc parameters were found for different diseases. Reproducibility depends, for instance, upon correct determination of the disc margin. In healthy eyes, a significant correlation was found between rim area and disc size: larger discs have a larger neuroretinal rim area than smaller discs. Thus, the rim areas of different eyes are only comparable for equally sized discs. Relative values, as for instance, cup/disc ratio, or the quotient of rim area and disc size, are therefore better suited for comparison of different eyes than absolute values. The recent developments in automatic disc analysis equipment and the clinical relevance of the results for diagnosis and follow-up in glaucoma are discussed.
The authors applied frozen resin cracking after hexamethyldisilazane (HMDS) desiccation on the monkey optic disc region. The cracked face through the central part of the optic disc showed that the inner limiting membrane of the retina continued into the limiting membrane of Elschnig, and this, in turn, continued into the central meniscus of Kuhnt. At the disc margin the membrane was about 70 nm in thickness, due to a large fibrillar component. Elschnig's membrane was about 50 nm in thickness and was composed of both fibrils and flocculent material. The membrane covering the central meniscus of Kuhnt was about 20 nm in thickness. The number of fibrils here was very low, and the membrane consisted of flocculent material. The positive immunohistochemical stainings for GFA and vimentin of Elschnig's membrane and Kuhnt's meniscus were noteworthy. The positive staining disappeared when the membrane continued into the inner limiting membrane of the retina, supporting the different structural composition.
A new sensor for respiratory rate monitoring is described. The sensor uses an optical fibre that detects the evaporated humidity from the mouth and/or nose at each exhalation. The condensed humidity substantially alters the coupling of light from the optical fibre to the surrounding medium, which can be monitored by a photo-detector. The sensing principle is evaluated using ray-tracing simulation and scattering measurements.
Changes in optical attenuation, relevant to cytochrome oxidase, of the rat bone periosteal tissue in explanted culture and human neuronal cells in three-dimensional agarose constructs have been monitored by the use of optical coherence tomography (OCT), with potential applications in tissue engineering and diagnosis. A superluminescent diode (SLD) with a peak emission wavelength (lambda = 820 nm) that is the near-infrared absorption band of the oxidized form of CytOx was employed. The attenuation coefficient was obtained from the depth-resolved reflectance profiles of liquid phantoms (naphthol green B with intralipid), explant culture (periosteum of calvaria from rats) and cells in 3D agarose constructs. The absorption coefficient of naphthol green B can be accurately quantified by the linear relationship between attenuation coefficients and the concentration. The difference in the attenuation coefficient of astrocytoma cells in agarose before and after reduction of CytOx is 0.26 +/- 0.10 mm(-1) ( n = 9), whereas no attenuation is observed with the agarose control. Reduction of the enzyme in periosteal tissue leads to a change in attenuation coefficient of 0.43 +/- 0.24 mm(-1) ( n = 7). For comparison, using a biochemical assay, the absorption coefficient of the oxidized-reduced form of CytOx is measured at approximately 8.3 +/- 1.5x10(-3) mm-1 ( n = 4) and 8.7 +/-2.5x10(-3) mm-1 ( n = 4) at 820 nm for astrocytoma cells and rat periosteum, respectively. The lower value of CytOx concentration using biochemical versus OCT measurements may result from shifts in the scattering profile and the amplifying influences of multiple heme-based oxidases, indicating that conventional OCT is not specific enough to monitor redox changes in cytochrome oxidase. However, qualitative shifts in oxidation state are apparent using the technique. Our results suggest the potential application of OCT in providing high-resolution tomographic imaging of tissues in organ culture and cells grown in three-dimensional constructs in vitro.
An evolutionarily conserved system of small retinotopic neurons in dipteran insects, called bushy T-cells, provides information about directional motion to large collator neurons in the lobula plate. Physiological and anatomical features of these cells provide the basis for a model that is used to investigate requirements for generating optic flow selectivity in collators while allowing for evolutionary variations. This account focuses on the role of physiological tuning properties of T5 neurons. Various flow fields are defined as inputs to retinotopic arrays of T5 cells, the responses of which are mapped onto collators using innervation matrices that promote selectivity for flow type and position. Properties known or inferred from physiological and anatomical studies of neurons contributing to motion detection are incorporated into the model: broad tuning to local motion direction and the representation of each visual sampling unit by a quartet of small-field T5-like neurons with orthogonal preferred directions. The model predicts hitherto untested response properties of optic flow selective collators, and predicts that selectivity for a given flow field can be highly sensitive to perturbations in physiological properties of the motion detectors.
Kainic acid is known to induce characteristic lesions in neurons receiving an intact input with presumed glutamate-mediated neurotransmission. There are indications for glutamate as a transmitter of retinal afferent terminals in the pigeon optic tectum. After tectal injection of kainic acid (0.5-2.0 microgram in 0.5 microliter) the optic tectum was studied by light and electron microscopy and the following changes were observed: (a) within 1-48 h important neuropil vacuolization predominantly in lower part of layer 5. Such vacuoles were sometimes postsynaptic to identified retinal afferent terminals: (b) within 1 h to 21 days progressive neuronal cell loss throughout the tectal layers. These toxic effects were not observed 2-12 weeks after contralateral retinal ablation but could partially be restored by combined glutamate (0.2 mg) and kainate injection. Thus in the pigeon tectum, kainic acid neurotoxicity is dependent upon an intact retinal input, a finding consistent with a special role for glutamate - possibly as a transmitter - in retinal terminals.
Using retrograde HRP labeling from the optic nerve (ON) or optic tectum (OT), we have visualized biplexiform cells in wholemounted retinas of the stichaeid fish Pholidapus dybowskii and studied their morphology and spatial properties. Biplexiform cells labeled from the ON were similar in their morphology to biplexiform cells found in other fishes. Their distribution across the retina was non-random and independent of that of other large ganglion cell types. Biplexiform cells labeled from the OT, too, formed non-random mosaics, whose spatial properties suggested that most or all biplexiform cells project to the OT in this species. We propose that biplexiform cells in Pholidapus are homologous to biplexiform cells in other fishes (lower vertebrates). Pholidapus biplexiform cells may participate in the tectum-mediated visual reactions.
The optic discs of eight normal subjects were photographed on three separate visits under widely varying conditions. Each photograph was scanned by a television camera, converted to digital form, and then analyzed using computer image analysis techniques. The computer was programmed to delineate the boundary around the optic disc and the area of pallor. The percentage of disc pallor was then computed across the entire disc and for each disc quadrant. The reproducibility of the procedure was determined by evaluating several photographic parameters: camera flash intensity, film type, magnification, and centering of the disc in the photograph. The focus adjustment on the television scanner was also varied. Under carefully controlled conditions, results showed that the reproducibility of measuring the total percent of disc pallor was 2%. Results for reproducibility are also given for less than optimal conditions and for manual planimetry on the same set of photographs.
Limited optic nerve crush is a model of diffuse mechanical axon injury, the most prevalent cause of secondary neurodegeneration after closed head neurotrauma. In this report, a protocol is presented which allows for the rapid screening of differential gene expression in the inner retina, as well as the optic nerve, in response to partial nerve crush. To prove the reliability of the method, prototypically, the differential expression profiles of three candidate genes (kinesin light chain, ferritin, RYB-A) were verified. The method seems to be suitable to address the question of how differential gene expression contributes to degeneration, survival and axonal repair after partial nerve crush.