Optic Radiation Damage Research Articles

Optic Radiation Tractography and Visual Field Deficits in Laser Interstitial Thermal Therapy for Amygdalohippocampectomy in Patients with Mesial Temporal Lobe Epilepsy

Background/Aims: Laser interstitial thermal therapy (LITT) has become an alternative to open-resective surgery for refractory mesial temporal lobe epilepsy (MTLE). Occurrence of visual field defects (VFDs) following open surgery for MTLE is reported at 52-100%. We examined the rate of VFDs following LITT for amygdalohippocampectomy (AHE) and correlated the occurrence of VFDs with damage to the optic radiations, assessed by diffusion tensor tractography (DTI). Methods: We performed a retrospective analysis of 5 patients who underwent LITT-AHE for medically refractory MTLE. We examined the association between VFDs and optic radiation damage by correlating postprocedural visual field testing with qualitative assessment of optic radiation fiber tracts. Results: Postoperative assessments showed that 4 patients had normal visual field testing, and 1 had a right superior quadrantanopsia (20%). We performed 3-dimensional reconstruction of the optic radiation, laser probe trajectory, and ablation volume. Damage to Meyer's loop was determined consistent with the VFD. Conclusions: Short-term follow-up in our series suggests that laser ablation AHE may be associated with a lower rate of VFD than has been reported for open AHE. Our results suggest that incorporating optic radiation mapping through DTI may preoperatively help to minimize the risk of VFD following laser ablation AHE.

Optical coherence tomography for retinal imaging in multiple sclerosis.

Visual disturbances caused by inflammatory and demyelinating processes of the visual system, mainly in the optic nerve, are a common symptom in multiple sclerosis (MS). Optical coherence tomography (OCT) is a tool that is increasingly used for quantifying retinal damage in MS and other neurologic diseases. Based on spectral interferometry, it uses low-coherent infrared light to generate high-resolution spatial images of the retina. The retinal nerve fiber layer (RNFL) consists of unmyelinated axons that form the optic nerve, and thus represents a part of the central nervous system. OCT allows for noninvasive measurements of RNFL thickness in micrometer resolution. With the help of OCT, researchers have managed to demonstrate that eyes of MS patients show distinct RNFL thinning after an event of acute optic neuritis in MS, and even subclinical damage in eyes with no previous optic neuritis. OCT is also a useful tool in terms of providing a differential diagnosis of MS toward, for example, neuromyelitis optica, a disease that usually shows stronger retinal thinning, or Susac syndrome, which is characterized by distinct patchy thinning of the inner retinal layers. RNFL thinning is associated with magnetic resonance imaging-derived measurements of the brain, such as whole-brain atrophy, gray and white matter atrophy, and optic radiation damage. These features suggest that OCT-derived retinal measurements are a complement for measuring central nervous system neurodegeneration in the context of clinical trials – for example, with neuroprotective substances.

Optic radiation damage in multiple sclerosis is associated with visual dysfunction and retinal thinning--an ultrahigh-field MR pilot study.

To investigate posterior visual pathway damage in multiple sclerosis using ultrahigh-field magnetic resonance imaging (MRI) at 7 Tesla (7 T), and to determine its correlation with visual disability and retinal fibre layer (RNFL) damage detectable by optic coherence tomography (OCT). We studied 7 T MRI, OCT, functional acuity contrast testing (FACT), and visually evoked potentials (VEP, n = 16) in 30 patients (including 26 relapsing-remitting MS and four clinically isolated syndrome patients) and 12 healthy controls to quantify RNFL thickness, optic radiation lesion volume, and optic radiation thickness. Optic radiation lesion volume was associated with thinning of the optic radiation (p < 0.001), delayed VEP (p = 0.031), and visual disability indicated by FACT (p = 0.020). Furthermore, we observed an inverse correlation between optic radiation lesion volume and RNFL thickness (p < 0.001), including patients without previous optic neuritis (p < 0.001). Anterior visual pathway damage, but also (subclinical) optic radiation integrity loss detectable by 7 T MRI are common findings in MS that are mutually affected. Given the association between optic radiation damage, visual impairment, and increased VEP latency in this exploratory study of a limited sample size, clinicians should be aware of acute lesions within the optic radiation in patients with (bilateral) visual disturbances. • Focal destruction of the optic radiation is detectable by 7 T MRI. • Focal optic radiation damage is common in MS. • Optic radiation damage is associated with RNFL thinning, detectable by OCT. • Optic radiation damage is associated with delayed VEP and visual dysfunction. • RNFL thickness in non-optic neuritis eyes correlates with optic radiation demyelination.

Positive correlation between the degree of visual field defect and optic radiation damage in glaucoma patients

We evaluated optic radiation (OR) damage in patients with glaucoma by using fractional anisotropy (FA) of diffusion-tensor magnetic resonance imaging. We studied 29 patients with glaucoma and 19 healthy controls. Regions of interest were placed over the bilateral anterior and posterior ORs on the FA maps, and the FA value of each region was measured. FA values of the bilateral anterior and posterior ORs were significantly lower in patients with glaucoma (anterior right, P = 0.0002; anterior left, P = 0.00028; posterior right, P = 0.0004; and posterior left, P = 0.0001) than in the healthy controls. In glaucoma patients, significant correlations were observed between the FA values and the average of the total deviation of the contralateral hemifields of both eyes (left hemifield and anterior right OR, correlation coefficient [r] = 0.46 [P = 0.013]; right hemifield and anterior left OR, r = 0.43 [P = 0.021]; left hemifield and posterior right OR, r = 0.54 [P = 0.0027]; and right hemifield and posterior left OR, r = 0.46 [P = 0.012]). FA values of the entire OR were decreased in glaucoma patients and correlated with the degree of visual field defect.

THE PUPIL LIGHT REFEX IN ACQUIRED HOMONYMOUS HEMIANOPIA

AimTo study the characteristics of pupillary responses in patients with homonymous hemianopia following acquired post-geniculate lesion.MethodsEighteen individuals were recruited and were divided into two groups:(1) Eleven patients with acquired homonymous...

Optic radiation damage can be assessed directly by tractography

Abstract Purpose: To verify the clinicoradiological correlation of tractographs of optic radiations (OR) involved by brain tumors and infarcts. Methods: We performed diffusion‐tensor magnetic resonance imaging (DT‐MRI) on 7 patients with brain lesions adjacent to or involving the visual pathway, 5 of whom underwent DT‐MRI before and after surgical excision of the brain lesions. Tractographic findings of OR on coronal reconstruction images, including those in the contralesional hemisphere, were analyzed with respect to their location and size and correlated with existing visual field defects. When the ipsilesional OR appeared to be reduced in craniocaudal height by 70% or more in coronal section than the contralesional OR, we considered the finding abnormal. Results: The contralesional ORs were successfully depicted in all cases. In 8 examinations the ipsilesional ORs were successfully depicted, in 4 they were not. The 8 depicted ORs in the ipsilesional hemisphere were abnormal either in size (n=8) and/or location (n=4). OR defects were noted in either the superior or inferior portions in 8 tractographs. OR deviation due to mass effect from the brain lesions was noted in 4 tractographs. In 5 tractographs with OR defects there was a good correlation with the location of the visual field defect. Conclusions: The tractography demonstrates the ORs all the time on the contralesional side, correlates some of our cases with the visual field defect on the ipsilesional side.

Surgical outcomes of different approaches for mesial temporal lobe gliomas

To analyze the surgical outcomes of different approaches for mesial temporal lobe gliomas. Microsurgery was performed via trans-sylvian, trans-temporal, or subtemporal approaches on 62 patients with mesial temporal lobe gliomas, 33 with localized tumors within the mesial temporal structures (type A), 19 in anterior portion (type A1), and 14 extending to posterior portion (type A2); 19 patients with multicompartmental tumors involving the mesial temporal lobe, insular lobe, and posterior frontorbital gurus (type B); 14 patients with tumors involving the temporal pole and lateral areas of the temporal horn (type C); and 6 patients with tumors infiltrating the brain stem, basal nuclei and thalamus (type D). Trans-sylvian approach was performed in 25 cases of which total tumor removal was achieved in 14 cases, subtotal removal in 6 cases, and gross removal in 5 cases. Primary visual deficits worsened after surgery in 5 cases. Trans-temporal approach was used in 23 cases of which total tumor resection was achieved in 15 cases, subtotal resection in 5 cases, and gross resection in 3 cases. Primary visual deficits worsened after surgery in 5 cases. Four patients in which preoperative vision were good presented with visual deficits postoperatively. Subtemporal approach was used in 14 cases of which total tumor removal was achieved in 10 cases, and subtotal removal in 4 cases. All 14 patients did not develop worsened vision after surgery. Trans-sylvian and subtemporal approaches can reduce possible harm to parenchyma and optic radiation, whereas approaches to the temporal horn through the superior and middle temporal gyri will induce damage to parenchyma and optic radiation.

Unexpected behaviour of polystyrene-based scintillating fibers during irradiation at low doses and low dose rates

The time dependence of the optical radiation damage process was studied for different fibers with polystyrene (PS) core. The fibers were irradiated with X-rays. In the present experiment the light guide BCF-98 (Bicron, clear polystyrene) was compared with the two scintillating fibers SCSF-38 and SCSF-81 (Kuraray). The light transmission through the fiber was investigated before, during and after irradiation. All investigated fibers showed unexpected effects depending on the fiber type: (1) at low doses the scintillating fibers are more sensitive to radiation than at high doses, i.e. the optical absorption rises nonlinearly with dose; (2) shortlived optical absorption centers decaying within several hours were detected in all fibers with PS core investigated up to now. Especially for SCSF-81, the annealing part is large and it totally overlaps the emission spectrum of the fiber.

Loss of relative-motion sensitivity in the monkey superior colliculus after lesions of cortical area MT.

Many cells in the superficial layers of the monkey superior colliculus are sensitive to relative motion. The response to a small stimulus moving through a cell's receptive field is strongly modulated by the relative motion between the stimulus and a textured pattern moving through the surrounding visual field; modulation is independent of absolute direction and speed of the stimulus. To determine whether cortical visual area MT is essential for this type of relative-motion sensitivity, colliculus cells were studied in the anesthetized, immobilized preparation after ablation of area MT. Unilateral MT lesions were made by either aspiration, kainic acid injection, or a combination of both methods. Data from the lesioned animals were compared with those from intact animals. Ipsilateral to the lesions, colliculus cells showed an almost total loss of sensitivity to relative motion. This loss was related neither to inadvertent injury of cortical areas neighboring MT nor to incidental optic radiation damage. Two other forms of motion-dependent, center-surround interactions were still present in the colliculus after the cortical lesions. These were a rudimentary sensitivity to differential motion between stimulus and background, which occurs for only one direction of stimulus movement, and a nonselective center-surround suppression, which is induced by movement of a background stimulus in any direction. Visual responsiveness, ocular dominance, and flash-evoked responses were also unaffected by the cortical lesions. We conclude that input from area MT is crucial for relative-motion sensitivity, but not for other response properties, in the superficial layers of the monkey colliculus.

Effects of fluorinated substituents on the refractive index and optical radiation resistance of methacrylates

AbstractNovel fluorinated methacrylate polymers were synthesized. The purpose was to produce polymers with low refractive indices and increased resistance to optical radiation damage. Six different fluorinated substituents were appended on the monomer before polymerization. Optical‐quality samples were prepared, and their transmission spectra, through 0.8 cm thick samples, were obtained. Each sample was tested for refractive index and glass transition temperature. The samples absorbed 10 MRad gamma radiation from a 60Co source in an air environment; their transmission spectra were recorded immediately after irradiation and again after seven days had elapsed. As expected, increasing the fluorine content in the side chains resulted in decreased refractive indices. Fluorine content also influenced optical radiation stability. One polymer, poly(1H,1H‐heptafluorobutyl methacrylate) retained superior UV/visible transmission after irradiation. © 1993 John Wiley &amp; Sons, Inc.

Optical Radiation and Visual Health

This book provides a focus on the parameters of ultraviolet light, visible, and infrared radiation s which could cause long-term visual health problems in humans. It reviews early research on radiation effects on the eye, and gives detailed attention to the hazardous effects of optical radiation on the retinal pigment epithelium and the photoreceptors. These data are further analyzed with regard to five potential long-term visual health problems; retinal degeneration, visual aging, disorder of visual development, ocular drug phototoxicity, and cataracts. Finally, epidemiologic principles for studying the relationships between optical radiation and long-term visual health problems are reviewed, concluding with the implications for future research and radiation protection. The contents include: historical perspectives; optical radiation and cataracts; the involvement of the retinal pigment epithelium (RPE); optical radiation damage to the ocular photoreceptors; possible role of optical radiation in retinal degenerations; optical radiation and the aged eye; optical radiation effects on aging and visual perception; optical radiation effects on visual development; and index.

Optical radiation damage of SBN materials and pyroelectric detectors at 10.6 μm

Thermal damage of Sr1−xBaxNb2O6 (SBN) crystals and infrared pyroelectric detectors due to 10.6−μm CO2 laser radiation was investigated. Permanent damage in the form of cracking or charring was observed depending on the irradiation conditions. Threshold values of energy density for cracking and charring were determined for SBN crystals of typical detector dimensions as a function of irradiation time. These damage thresholds of SBN are about an order of magnitude larger than the corresponding thresholds previously measured in triglycine sulfate. The energy density thresholds for cracking are independent of irradiation time τ for short times and increase as τ for long times. The time dependence of the cracking thresholds under the particular experimental conditions investigated is described by the empirical equation E0=[3+2400τ/tan−1(82τ)1/2] J/cm2. The charring thresholds are given by the empirical equation E0= (8+470τ1/2) J/cm2. The theoretical models presented for thermally induced damage are in satisfactory agreement with the experimental data. The damage thresholds of commerical SBN pyroelectric detectors were measured and found to correspond to those for SBN crystals.

Critical flicker frequency after unilateral temporal lobectomy in man

Patients with left or right temporal lobectomy were compared with a matched normal group on CFF. Of the patients without field defects, those with left, but not with right, hemisphere removals were impaired (especially in the nasal fields), suggesting that hemispheric specialization may extend even to basic sensory processes. Regardless of the side of the lobectomy, patients with field defects (from optic radiation damage) showed losses not only in the partially anopic quadrant but also in all three “intact” quadrants. This result confirms earlier reports and suggests that interdependence among parts of the visual field is based on interaction between as well as within the hemispheres.