Pazit Pianka

Early 'visual' cortex activation correlates with superior verbal memory performance in the blind

The visual cortex may be more modifiable than previously considered. Using functional magnetic resonance imaging (fMRI) in ten congenitally blind human participants, we found robust occipital activation during a verbal-memory task (in the absence of any sensory input), as well as during verb generation and Braille reading. We also found evidence for reorganization and specialization of the occipital cortex, along the anterior–posterior axis. Whereas anterior regions showed preference for Braille, posterior regions (including V1) showed preference for verbal-memory and verb generation (which both require memory of verbal material). No such occipital activation was found in sighted subjects. This difference between the groups was mirrored by superior performance of the blind in various verbal-memory tasks. Moreover, the magnitude of V1 activation during the verbal-memory condition was highly correlated with the blind individuals abilities in a variety of verbal-memory tests, suggesting that the additional occipital activation may have a functional role.

Characterization of displaced white matter by brain tumors using combined DTI and fMRI.

In vivo white matter tractography by diffusion tensor imaging (DTI) has become a popular tool for investigation of white matter architecture in the normal brain. Despite some unresolved issues regarding the accuracy of DTI, recent studies applied DTI for delineating white matter organization in the vicinity of brain lesions and especially brain tumors. Apart from the intrinsic limitations of DTI, the tracking of fibers in the vicinity or within lesions is further complicated due to changes in diseased tissue such as elevated water content (edema), tissue compression and degeneration. These changes deform the architecture of the white matter and in some cases prevent definite selection of the seed region of interest (ROI) from which fiber tracking begins. We show here that for displaced fiber systems, the use of anatomical approach for seed ROI selection yields insufficient results. Alternatively, we propose to select the seed points based on functional MRI activations which constrain the subjective seed ROI selection. The results are demonstrated on two major fiber systems: the pyramidal tract and the superior longitudinal fasciculus that connect critical motor and language areas, respectively. The fMRI based seed ROI selection approach enabled a more comprehensive mapping of these fiber systems. Furthermore, this procedure enabled the characterization of displaced white matter using the eigenvalue decomposition of DTI. We show that along the compressed fiber system, the diffusivity parallel to the fiber increases, while that perpendicular to the fibers decreases, leading to an overall increase in the fractional anisotropy index reflecting the compression of the fiber bundle. We conclude that definition of the functional network of a subject with deformed white matter should be done carefully. With fMRI, one can more accurately define the seed ROI for DTI based tractography and to provide a more comprehensive, functionally related, white matter mapping, a very important tool used in pre-surgical mapping.

Normal White Matter Development From Infancy to Adulthood: Comparing Diffusion Tensor and High b Value Diffusion Weighted MR Images

To evaluate the sensitivity of high b value diffusion weight magnetic resonance imaging (DWI) in detecting normal white matter maturation, compare it to conventional diffusion tensor imaging (DTI), and to obtain normative quantitative data using this method.

Hyperhomocystinemia in patients with nonarteritic anterior ischemic optic neuropathy, central retinal artery occlusion, and central retinal vein occlusion

OBJECTIVE This study aimed to determine the prevalence of hyperhomocystinemia among patients with nonarteritic anterior ischemic optic neuropathy (NAION), central retinal artery occlusion (CRAO), or central retinal vein occlusion (CRVO). DESIGN Retrospective, case-control study. PARTICIPANTS The study cohort consisted of 74 consecutive patients with NAION, CRAO, or CRVO who were examined at the Retina or Neuro-ophthalmological Unit of the Tel-Aviv Sourasky Medical Center from 1998 through 1999. The control group consisted of 81 consecutive patients of similar gender and age with no history of these pathologic conditions. MAIN OUTCOME MEASURES Plasma homocystine levels of all study participants were obtained. RESULTS Eighteen of 40 patients (45%) with NAION and eight of 13 patients (61.5%) with CRAO had hyperhomocystinemia compared with three of 21 (14.3%) in the CRVO group (P < 0.001) and eight (9.8%) in the control group (P < 0.0001). Hypertension and ischemic heart disease were significantly more prevalent in the NAION patients with elevated plasma homocystine. CONCLUSIONS Our findings suggest that hyperhomocystinemia is a risk factor for NAION and CRAO.

Effect of sub-Tenon’s and peribulbar anesthesia on intraocular pressure and ocular pulse amplitude

Purpose: To compare the effect of peribulbar and sub‐Tenons anesthesia on intraocular pressure (IOP) and ocular pulse amplitude (OPA) in the injected eye and the fellow noninjected (control) eye. Setting: Tel Aviv Medical Center, Tel Aviv, Israel. Methods: This prospective study measured IOP and OPA at baseline and 1 and 10 minutes after administration of lidocaine anesthesia in 40 consecutive adult patients having elective cataract surgery. Results: The IOP remained stable throughout the study with both modes of anesthesia. One minute after injection of the anesthetic agent, the OPA was significantly decreased in the injected eyes in both the sub‐Tenons (24%; P < .05) and peribulbar (25%; P < .05) groups. The decrease in the OPA in the sub‐Tenons group (14%; P < .05) was detectable after 10 minutes in the control eyes. In the peribulbar anesthesia group, the OPA in the control eyes increased significantly (9%; P < .05) 1 minute after injection of the anesthetic agent, returning to preinjection levels 10 minutes after the injection. Conclusions: The OPA in the eyes in which lidocaine was injected decreased significantly in both the sub‐Tenons and peribulbar groups. These findings have implications for the management of patients whose ocular circulation may be compromised.

Macular hole secondary to branch retinal vein occlusion diagnosed by Retinal Thickness Analyzer.

The Retinal Thickness Analyzer is a laser slit biomicroscopy imaging device that produces accurate measurements of retinal thickness and displays the images in a two-dimensional pattern, superimposed on a fundus image. This article reports a patient with decreased vision following branch retinal vein occlusion in whom the Retinal Thickness Analyzer was used to establish the diagnosis of a macular lamellar hole that was not apparent clinically.

Clonidine provides an allergy-free alternative in glaucoma patients with proven allergy to apraclonidine

Abstract · Purpose: The aim of this study was to determine allergic responses to clonidine hydrochloride 0.25% in glaucoma patients with proven allergic reaction to apraclonidine 0.5%. · Methods: Fifteen consecutive glaucoma patients with allergic reaction to apraclonidine were prospectively challenged with clonidine hydrochloride 0.25% and evaluated for recurrence of allergic reactions and efficacy of treatment. Intraocular pressure (IOP), conjunctival hyperemia, blood pressure and resting pulse rate were determined at baseline and after 1, 3, 6 and 12 months. · Results: None of the patients developed ocular allergic reaction during 12 months on clonidine therapy. Blood pressure and pulse rate did not change significantly with clonidine treatment. Clonidine caused a significant reduction of IOP from baseline. In one patient, topical clonidine caused fatigue, dizziness and dry mouth. · Conclusion: Clonidine did not cause allergic reaction in patients with proven allergy to apraclonidine, indicating that there is no cross-reactivity with apraclonidine. Due to the small series, however, we cannot assume that allergy will not occur with clonidine 0.25% given time and a larger number of patients.

Deviation of Fiber Tracts in the Vicinity of Brain Lesions: Evaluation by Diffusion Tensor Imaging

Diffusion Tensor Imaging (DTI) is used to characterize the diffusion properties of deviated white matter caused by brain tumors. DTI was recently shown to be very helpful in delineating white matter both within brain lesions and surrounding them. Displacement of white matter fibers may be one of the consequences of tumor growth adjacent to white matter. The combination of white matter mapping with DTI and gray matter mapping using functional MRI, in some cases, facilitated assessment of the relation between the shifted cortical areas and the corresponding white matter tracts. We found that the fractional anisotropy extracted from DTI is increased by 38% in areas of non-edematous shifted white matter fibers. By contrast, trace apparent diffusion coefficient (ADC) values in those areas were found to be similar to contralateral side and normal control values. Analysis of the three diffusion tensor eigenvalues revealed that the increase in the fractional anisotropy is a result of two processes. The first is the increase in the diffusion parallel to the fibers—λ1 (by 18%), and the second is the decrease in the diffusion perpendicular to fibers—λ3 (by 34%) as compared with the contralateral side. These opposing changes cause an increase in the diffusion anisotropy but no change in the trace ADC. It is suggested that the pressure caused by the tumor may lead to an increase in white matter fiber tension, thus causing an increase in λ1. On the other hand, the same pressure causes increased fiber density per unit area, leading to a higher degree of restricted diffusion in the extracellular space and, hence, a reduction in λ3.

Preservation of the Photoreceptor Layer Following Subthreshold Laser Treatment for Diabetic Macular Edema as Demonstrated by SD-OCT

PURPOSE Subthreshold laser treatment of diabetic macular edema (DME) may have less deleterious effects on the photoreceptors than regular continuous wave laser. This study aimed to assess whether subthreshold laser causes a long-term damage to the retinal structures, as demonstrated by spectral-domain optical coherence tomography (SD-OCT), and to evaluate the change in the axial diameter of retinal diabetic microaneurysms following treatment. METHODS A retrospective study of eyes that were diagnosed with nonfoveal involving DME and underwent subthreshold laser treatment with the Novus SRT system. Spectral-domain OCT scans of treated retinal areas, performed prior to treatment and approximately 4 months following treatment, were assessed for changes in the continuity of the photoreceptor (PR) layer, the thickness of the PR-RPE layer, the retinal thickness at the treatment sites, and the diameter of the microaneurysms. RESULTS Included in this study were 31 microaneurysms. Following treatment, the continuity of the ellipsoid zone of the inner segments of the photoreceptors was confirmed in all but two cases. The thickness of the PR-RPE layers was 72.32 ± 7.36 and 70.97 ± 7.27 μm prior to and following treatment, respectively (P = 0.061). The retinal thickness at the treatment sites decreased from 398.65 ± 57.89 to 372.74 ± 60.4 μm (P < 0.001). The mean measured diameter of the microaneurysms was 87.32 ± 27.45 and 6.68 ± 26.12 μm, respectively (P < 0.001). CONCLUSIONS In this study, subthreshold laser treatment for DME has been shown to be a safe technology that preserves the photoreceptor layer, as demonstrated by SD-OCT.

T1-Weighted Functional Imaging Based on a Contrast Agent in Presurgical Mapping

To assess the applicability of T1‐weighted images in the presence of a contrast agent for functional mapping free of susceptibility artifacts, in comparison to the blood oxygenation level‐dependent (BOLD) imaging.