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At least 145 records · Page 8Linked to original sources
PubMed2002

Signal degradation by multiple scattering in optical coherence tomography of dense tissue: a Monte Carlo study towards optical clearing of biotissues.

Multiple scattering is a major source that limits light penetration into biotissues, thereby preventing visualization of the deep microstructures for high-resolution optical imaging techniques. The optical clearing approach is a new adventure in biomedical optics for manipulating the optical properties of tissue; for example, the scattering coefficient and the degree of forward scattering of photons, by the use of the chemical administration method in order to improve the optical imaging depth, particularly for the recently developed optical coherence tomography (OCT). This paper investigates systematically how the multiple scattering affects signal attenuation and localization in general, and how the alterations of optical properties of tissue enhance the optical imaging depth and signal localization in particular, by the use of Monte Carlo simulations through the separate considerations of the least scattered photons (LSP) and multiple scattered photons (MSP). The LSP are those photons that contribute to the precise OCT signal, i.e. localization, and the MSP are those that degrade the OCT signal. It is shown that with either the reduction of the scattering coefficient or the increase of the degree of forward scattering, signal localization and imaging depth for OCT is enhanced. Whilst the increase of the anisotropic factor of the medium is more efficient in improving signal localization, it introduces more scattering events for the photons travelling within the tissue for both the LSP and MSP. It is also found that the OCT imaging resolution is almost reduced exponentially with the increase of the probing depth as opposed to the claimed system resolution. We demonstrate that optical clearing could be a useful tool to improve the imaging resolution when the light progressively penetrates the high scattering medium. Experimental results are also presented to show intuitively how multiple scattering affects OCT signal profiles by the use of intralipid solution and healthy human whole blood, representing moderately and highly scattering media respectively.

Anisotropy↗
PubMed1998

Optic nerve size in traumatic optic neuropathy.

The assessment of traumatic optic neuropathy in a neurologically impaired patient is difficult, and the size of the optic nerve has been suggested as a potential adjunct in differential diagnosis. This controlled retrospective study was designed to evaluate the size of the optic nerve involved in traumatic optic neuropathy when compared to the optic nerve in the noninjured eye. Maxillofacial computerized tomographs of 22 patients were examined; intraorbital optic nerve diameter was measured on injured and noninjured sides, with the examiner unaware of the side of injury. No statistically significant difference in size was found between the traumatized optic nerves and those that remained intact. The authors have concluded that the size of the optic nerve is not a reliable predicator of the presence or absence of traumatic optic neuropathy when measured with computerized tomograph scans.

Confidence Intervals↗
PubMed1994

Optic nerve injury alters basic fibroblast growth factor localization in the retina and optic tract.

Basic fibroblast growth factor (bFGF) is thought to be a trophic factor for several classes of neurons. Its distribution changes in response to cortical neural injury. We have determined the effect of injury to the optic nerve on localization of bFGF in the rodent retina and visual pathways. Our observations were confirmed by using different antisera and monoclonal antibodies. While photoreceptors normally contain virtually no bFGF, crushing the optic nerve causes a striking increase, over a period of several weeks, in the amount of bFGF in retinal photoreceptors. Since photoreceptors do not synapse directly upon the injured ganglion cells, intermediary cells must participate in the cascade of events that results in the elevated bFGF. In light of the observation that exogenous bFGF protects photoreceptors from photodamage (Faktorovich et al., 1992), this increase in bFGF in photoreceptors may explain, in part, why crushing the optic nerve protects photorecptors against photodamage (Bush and Williams, 1991). Whereas bFGF is constitutively found in glia in the optic nerve, little bFGF is found in glia in the optic tract. However, damage to the optic nerve increases bFGF in astrocytes in the optic tract. This change occurs within days, suggesting that a relatively direct signal may intervene between the injured axon and the adjacent glial cells. Thus, despite the fact that the optic nerve and optic tract are contiguous structures through which axons of retinal ganglion cells project, the glial elements in these structures express distinct properties, because of differences in either glial subclasses or microenvironment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Optic disc morphometry with optical coherence tomography: comparison with planimetry of fundus photographs and influence of parapapillary atrophy and pigmentary conus.

PURPOSE: Optical coherence tomography (OCT) is an established method for visualising macular pathology and for measuring the thickness of parapapillary retinal nerve fibre layer. The purpose of the present study was to compare OCT measurements of the optic disc with those obtained by planimetry of fundus photographs and to investigate whether OCT measurements are influenced by the amount of parapapillary atrophy or pigmentary conus at the disc margin. MATERIALS AND METHODS: Eighty-two eyes of 41 randomly selected Asian-Indian subjects were included. The mean age was 44.2+/-14.3 years (mean+/-SD). All eyes underwent optic disc assessment by OCT (fast optical disc protocol) and digital 20 degree disc photos.. Planimetry of the discs were performed by outlining the disc and the cup. The amount of parapapillary atrophy (zone beta) was quantified as the number of clock-hours around the disc with adjacent parapapillary atrophy. The same procedure was performed to quantify the amount of pigmentary conus around the disc. RESULTS: Mean+/-SD disc size and mean+/-SD cup size in OCT measurements (2.37+/-0.51, 1.29+/-0.55) were significantly smaller than in photographic planimetry (2.83+/-0.62, 1.56+/-0.5: P<0.001, P<0.001). Optic discs with parapapillary atrophy (P=0.2) in their relative difference of disc sizes between OCT and planimetry. Similarly, optic discs with pigmentary conus (n=12) and discs without pigmentary conus (n=70) did not differ significantly (P=0.65). The relative difference in disc size between the two measurement modalities did not correlate with the amount of parapapillary atrophy (r=-0.17, P=0.29) or with the amount of pigmentary conus (r=-0.04, P=0.9). CONCLUSION: OCT analysis of the optic disc produces significantly smaller parameters, compared to the established method of optic disc planimetry. Neither presence, nor extent of parapapillary atrophy zone beta and pigmentary conus seems to produce a systematic error in measurements of disc size with the OCT.

Adolescent↗
PubMedDate not supplied

[Pathogenetic mechanisms of optic nerve lesions in acute vascular optic neuropathies].

The authors analyze the findings of histomorphologic and immunomorphologic studies of 20 cadaver optic nerves from subjects with a history of acute vascular optic neuropathies due to atherosclerosis, eventuating in optic nerve atrophy: 13 atrophic optic nerves and 7 pair nerves from clinically normal eyes of the same patients were examined. The blood sera of 30 patients suffering from acute vascular optic neuropathies were tested. Noteworthy that vascular optic neuropathy associated with atherosclerosis is a bilateral process. Vascular insufficiency due to sclerotic changes in vessels of various diameters undoubtedly contributes to the pathogenesis of the optic nerve impairments in the involved and clinically healthy eyes. The developing immune status disorders and autoimmune processes also contribute to the genesis of sclerotic shifts in the vessels and optic nerve atrophy in both eyes.

Acute Disease↗
PubMed1984

Visual recovery in goldfish following unilateral optic tectum ablation: evidence of competition between optic axons for tectal targets.

Anatomical studies suggest that regenerating optic axons which invade the ipsilateral lobe of the optic tectum following ablation of the contralateral lobe compete with resident optic axons for synaptic sites on tectal neurons. Invader optic axons are initially uniformly distributed over the entire tectal lobe. With time, the invader and resident optic axons progressively segregate so that the invaders are localized in bands or islands separated by areas that are innervated mainly by the residents. When the resident optic axons are destroyed by ablating the eye opposite to the experimental eye, the invader axons remain continuously distributed and the segregation process apparently does not occur. We investigated the relationship between the segregation process and the recovery of visual function by the invader axons. Visual recovery was measured with a behavioral method in which the index of vision was the occurrence of a branchial suppression response to a moving spot of red light that was classically conditioned to an electric shock stimulus. The minimum time to reappearance of vision following ablation of the contralateral lobe of the tectum in two-eye fish was similar to the reported time of onset of the segregation process. Visual recovery occurred sooner when the opposite eye was removed. The restored vision in both groups disappeared following subsequent ablation of the remaining lobe of the tectum. These results suggest that the goldfish optic tectum normally contains no free synaptic sites for anomalous optic afferents and that the invader axons must compete for targets with the resident optic afferents. The invader axons can apparently remain unconnected or non-functional for several weeks following their arrival in the ipsilateral tectal lobe.

Animals↗
PubMed2006

Simple online recognition of optical data strings based on conservative optical logic.

Optical packet switching relies on the ability of a system to recognize header information on an optical signal. Unless the headers are very short with large Hamming distances, optical correlation fails and optical logic becomes attractive because it can handle long headers with Hamming distances as low as 1. Unfortunately, the only optical logic gates fast enough to keep up with current communication speeds involve semiconductor optical amplifiers and do not lend themselves to the incorporation of large numbers of elements for header recognition and would consume a lot of power as well. The ideal system would operate at any bandwidth with no power consumption. We describe how to design and build such a system by using passive optical logic. This too leads to practical problems that we discuss. We show theoretically various ways to use optical interferometric logic for reliable recognition of long data streams such as headers in optical communication. In addition, we demonstrate one particularly simple experimental approach using interferometric coinc gates.

Journal Article↗
PubMed2003

Electro-optic polymer frequency shifter activated by input optical pulses.

We demonstrate electro-optic frequency shifting of 1.55-microm optical pulses by as much as 86 GHz in a polymer traveling-wave phase modulator. The optical pulses were modulated with the linear region of quasi-sinusoidal microwave pulses. In the implemented configuration the electro-optic frequency shifter does not require synchronization with the source of the optical pulses, making it transparent to the optical-pulse repetition rate and increasing its utility. Electro-optic frequency conversion has a number of advantages compared with other methods of all-optical frequency conversion, including no need for a second optical source, high conversion efficiency, and simple control of the output frequency.

Journal Article↗
PubMed2003

Optic disc excavation in the atrophic stage of Leber's hereditary optic neuropathy: comparison with normal tension glaucoma.

BACKGROUND: Abnormal optic disc excavations are reportedly seen in patients with Leber's hereditary optic neuropathy (LHON), a mitochondrial dysfunction disease. We examined the disc morphology in the eyes of patients with LHON at the atrophic stage and compared it to that in eyes with normal-tension glaucoma (NTG). METHODS: We studied 15 LHON patients with the 11778 mutation, 15 patients with NTG, and 25 normal subjects. The optic disc morphology was analyzed by Heidelberg retinal tomography (HRT). Ten parameters of the optic disc obtained by HRT were evaluated, including the diagnostic classification of glaucoma. RESULTS: Six of the nine morphological HRT parameters of the LHON patients, the exceptions being disc area, mean cup depth, and maximum cup depth, differed significantly from those of the normals. NTG patients had a significantly greater mean and maximum cup depth than LHON patients. The HRT glaucoma diagnostic software classified 22 (73%) of the 30 optic discs in LHON patients as glaucomatous. CONCLUSION: The optic discs at the atrophic stage of LHON eyes have glaucoma-like morphological changes. However, the cups were significantly deeper in NTG than LHON. The similarity in the optic disc findings in LHON and NTG suggests that alterations in mitochondrial function may be related to optic disc excavations.

Adolescent↗
PubMed2004

Direct stimulation of optic nerve by electrodes implanted in optic disc of rabbit eyes.

PURPOSE: To determine whether wire microelectrodes implanted in the optic disc can be used to elicit cortical potentials. METHODS: Two or four platinum wire electrodes of two types, viz., the cut-end type and the exposed-tip type, were inserted through the vitreous and fixed in the optic disc of 16 rabbit eyes. Electrically evoked potentials (EEPs) were recorded after bipolar electrical stimulation with the two wire electrodes and by different combinations of the four-electrode system. The optic discs were examined histologically after the experiment. RESULTS: The wire electrodes were successfully implanted and fixed into different positions of the optic disc without serious complications in all 16 eyes. EEPs could be elicited after bipolar electrical stimulation of the optic nerve using either the two-electrode system or different pairs of the four-electrode system. Threshold charge densities to elicit EEPs were 0.32-0.64 mC/cm(2) in eyes using the cut-end type of electrodes and 0.93-6.21 muC/cm(2) in eyes using the exposed-tip type. The amplitude of the EEPs increased with increasing electrical stimulus intensities. Histological evaluation revealed limited damage to the neural tissue adjacent to the electrode track. CONCLUSIONS: The visual cortex can be activated by direct microelectrical stimulation of the optic nerve. The acute implantation of the wire microelectrodes into the optic disc by a transvitreal approach is feasible and results in only limited damage to the optic nerve.

Animals↗
PubMed2005

Optic nerve cyst associated with optic disk pits.

PURPOSE: To report a case with two optic disk pits which were associated with an optic nerve cyst in the same eye. METHODS: Observational case report. RESULTS: A 47-year-old patient noted visual impairment in the right eye. On examination the best corrected visual acuity in the right eye was 20/80 and in the left eye was 20/20. Biomicroscopy revealed, in the right eye, a very pale optic disk with two optic disk pits without macular elevation. Magnetic resonance imaging (MRI) revealed a well circumscribed 6 x 6-mm(2) round cystic lesion within the right optic nerve sheath adjacent to the temporal aspect of the right optic nerve at its retrobulbar segment, which compressed and displaced the nerve. CONCLUSIONS: In the case of an extremely pale optic disk with congenital pits and visual impairment without macular detachment, radiological examination is indicated in order to exclude the possibility of coexisting optic nerve anomalies.

Blood Flow Velocity↗
PubMed2005

Autoantibodies in patients with glaucoma: a comparison of IgG serum antibodies against retinal, optic nerve, and optic nerve head antigens.

PURPOSE: The aim of this study was to analyze and compare the entire IgG autoantibody patterns against different ocular antigens (retina, optic nerve, and optic nerve head) in sera of glaucoma patients and healthy subjects. METHODS: Sixty-six patients were included in this study: healthy volunteers without any ocular disorders (CO, n=30), patients with primary open-angle glaucoma (POAG, n=19), and patients with normal-tension glaucoma (NTG, n=17). The sera were tested for antibodies against retinal, optic nerve, and optic nerve head tissues. Immunodetection was performed using 4-chloro-1-naphthol staining. The autoantibody patterns were digitized and subsequently analyzed by multivariate statistical techniques. RESULTS: All patients showed a complex repertoire of IgG antibodies against retinal, optic nerve, and optic nerve head antigens. The analysis of discriminance revealed a statistically significant differences between the patterns of all three groups. Our multivariate approach could quantify the differences in immunoreactivities of patient sera against the three antigens. The POAG group had the most significant difference against retinal antigens (P=0.0021) compared with the other antigens. In the NTG group the highest reactivity appeared against optic nerve head (P=0.00053) and optic nerve (P=0.0025). CONCLUSIONS: All groups showed different and complex antibody patterns against the three ocular tissues. These autoantibodies are highly specific for each patient group. The analysis of these patterns could provide further information about possible autoimmune mechanisms in the pathogenesis of glaucoma.

Aged↗
PubMed2003

Optic disc structure and shock-induced anterior ischemic optic neuropathy.

PURPOSE: To describe a patient who developed unilateral shock-induced anterior ischemic optic neuropathy (SIAION) after gastrointestinal hemorrhage followed by presumed idiopathic nonarteritic anterior ischemic optic neuropathy (NAION) in the fellow eye. DESIGN: Retrospective, observational case report and literature review. METHODS: The case history of an 80-year-old man who developed SIAION, followed by NAION in the fellow eye, was reviewed. All previously reported cases of SIAION were reviewed. MAIN OUTCOME MEASURES: Neuro-ophthalmic examination, including visual acuity, funduscopy, and automated perimetry. RESULTS: An 80-year-old man, with a history of gastrointestinal bleeding from a duodenal ulcer, was hospitalized and received four units of packed red blood cells after he was found to be severely anemic (hemoglobin 6.7 g/dl). Three days later he complained of loss of vision of the right eye. Neuro-ophthalmic examination 2 weeks later disclosed a visual acuity of counting fingers at 6 inches in the right eye and 20/40 in the left eye, with a right relative afferent pupillary defect and a superior altitudinal visual field defect. Funduscopy revealed optic disc edema with a temporal parapapillary hemorrhage in the right eye and a small optic disc, with no cup, in the left eye. A diagnosis of SIAION secondary to anemia was made. Six weeks later he developed a new inferior altitudinal visual field defect in the left eye and diffuse optic disc swelling. He had no signs or symptoms of giant cell arteritis or polymyalgia rheumatica, his hemoglobin at this time was 11.9 g/dl, and the Westergren erythrocyte sedimentation rate was 6 mm/hour. CONCLUSIONS: Our patient developed optic disc swelling of the right eye after an episode of gastrointestinal hemorrhage (SIAION). The disc swelling in the left eye occurred 8 weeks later, when his hemoglobin had increased to 11.9 g/dl. The timing of the ischemic optic neuropathies suggests that the acute anemia led to involvement of the first but not the second eye. The configuration of the optic disc may have predisposed not only to the second event (NAION) but also to the first episode (SIAION).

Aged↗
PubMed1990

Optic nerve head swelling and optic atrophy in the systemic mucopolysaccharidoses.

The ocular findings in 108 patients representative of all types of mucopolysaccharidoses (MPS) were reviewed. Attention was focused on optic nerve head appearance. Optic nerve head swelling was observed in 8/14 eyes of MPS 1-Hurler (MPS 1-H); 9/21 MPS 1-Hurler-Scheie (MPS 1-H-S); 0/4 MPS I-S; 13/66 MPS II; 1/22 MPS III; 0/58 MPS IV; 5/12 MPS VI; and 2/2 MPS VII eyes. In three patients, optic nerve head swelling was present in one eye and optic atrophy in the fellow eye; in four patients, optic atrophy followed disc elevation; three patients presented with bilateral optic atrophy. It was concluded that optic nerve head swelling precedes the development of optic atrophy in the systemic MPS.

Adolescent↗