功能磁共振成像在弱视中的应用

功能性磁共振基于血管内血氧浓度的变化,可以无损伤地反映活体大脑功能,其在脑功能相关的视觉问题中的应用,使人们有机会从整体水平了解弱视患者脑功能的损害特点,还能通过它观察眼优势柱转移,比较不同类型弱视的脑功能改变,以及药物治疗的监测等。本文就功能性磁共振成像基本原理特点、实验设计、技术要求及其在弱视中应用作一综述。     

功能性磁共振成像在视觉科学研究中的应用进展

磁共振成像是目前较为普及的影像学检查手段之一,传统的磁共振成像及增强成像在眼科临床诊疗中已得到广泛应用.功能性磁共振成像技术包括血氧水平依赖的功能磁共振成像、磁共振波谱成像和弥散张量成像在内,在视觉皮层定位、视神经炎、弱视、青光眼、眼眶肿瘤以及视觉中枢白质纤维重建研究中显示了独特的价值.本文就功能性磁共振成像技术在上述方面的研究进展作一综述.     

共同性斜视患者的大脑功能性核磁共振成像特征

fMRI是一项可用于定位和量化大脑功能区域的检测技术,已被大量应用于多个方面的视觉研究。共同性斜视发病原因至今尚不完全明确,目前认为其发病不仅与眼外肌有关,也与大脑处理视觉信息相关脑区的结构和功能紊乱有关。此外,斜视所引起的视觉损害、视功能障碍及眼球运动异常等在脑部也有相应的表现。本文系统性综述了共同性斜视患者大脑视觉相关脑区的改变在fMRI成像中的特征。     

功能磁共振成像在弱视研究中的新进展

近年来功能磁共振成像（FMRI）技术基于血管内血氧浓度的变化,可以无损伤地反映活体大脑功能,在视觉系统的研究中得到了迅速的发展,尤其在弱视的研究中已取得重要成果。FMRI可用来从整体水平研究弱视患者的皮层损害特点,还能通过它观察眼优势柱转移、视觉运动觉能力的缺陷,比较不同类型弱视的脑功能变化,尤其屈光参差性弱视和斜视性弱视。就FMRI在弱视研究中的新进展进行综述。     

功能性磁共振成像在视觉研究中的应用

fMRI是利用磁共振成像技术探测大脑在不同条件及不同区域与神经活动相关生理变化的实验方法。它可以无损伤、直观地反映活体大脑功能，是研究与脑功能相关视觉系统问题的一项新技术。本对fMRI的基本原理、技术特点及其在视知觉领域的应用作一综述。     

视觉正常人简单图形视觉刺激的视皮层功能定位及定量研究

目的 利用功能磁共振成像的方法定位、定量研究视觉正常人简单图形视觉刺激时的视皮层反应模式,为视皮层假体的刺激位置和强度提供参考.方法 对3名视觉正常成年志愿者进行圆环形棋盘格视觉任务的功能磁共振成像实验,同一任务对每位志愿者重复3次,以SPM2脑功能专业分析软件包作后期处理,显示视皮层反应模式.结果 3名受试者均较好完成视觉任务,平均体素反应总数为5217.3±1110.6.反应最强点坐标 x值为(-4.3±8.7)mm,y值为(-83.3±3.7)mm,z值为(-4.0±4.7)mm.平均最大反应强度为15.99±1.58,最大反应脑区为双侧的Brodmann 18区即初级视皮层V2区.解剖上的舌回附近.结论 利用功能磁共振成像的方法可以定位、定量的研究视皮层反应模式,这些反应模式信息可以为视皮层假体的刺激位置、强度等参数提供参考.     

DIT与BOLD-fMRI技术对屈光不正性弱视皮层损害机制的研究

目的基于大脑各皮层区的功能动力学特征受到皮层间及皮层外解剖结构连接制约的观点,探讨屈光不正性弱视视觉皮层功能损害与胼胝体、视辐射发育不良的关系。方法利用弥散张量成像(DTI)及纤维跟踪技术(DTT)比较30例屈光不正性弱视患者与30例正常人胼胝体、视辐射各向异性分数(FA)值和平均弥散系数(DCavg)值,及神经纤维投射方式;并对屈光不正性弱视组和正常组各10例行血氧水平依赖的功能性磁共振成像(BOLD-fMRI),分别在平面与立体图刺激下比较视皮层激活水平。结果与正常组比较,屈光不正性弱视组背侧视皮层区域激活范围与强度显著低于正常组,胼胝体体部DCavg值显著高于正常组,视辐射FA值显著低于正常组,连接枕叶与顶枕联合皮层的胼胝体纤维数与视辐射纤维数明显减少。结论胼胝体后部和视辐射发育不良,视皮层神经元活动减少或神经元同步化活动减少可能是弱视视皮层功能损害的主要机制。     

视感知觉训练对间歇性外斜视患者术后双眼视觉重建的研究进展

间歇性外斜视(IXT)是一种发病率高、斜视角度多变、双眼视觉功能不同程度受损的眼科常见疾病。双眼视觉功能缺损与视觉皮层的改变有关,IXT涉及包括双眼融合相关皮质区域在内的多个脑区的功能改变,部分IXT患者在矫正眼位后,大脑皮层的异常改变依然存在,双眼视觉的恢复仍然困难。针对这些问题,视感知觉训练逐渐应用到IXT患者术后双眼视觉功能的重建中,视感知觉训练从大脑层面修复视觉皮质,通过不断刺激视觉中枢,提高大脑视皮层处理信息的能力,进而修复视觉中枢功能,使患者获得良好的双眼视觉功能,稳定眼位,减少复发。本文就IXT患者双眼视觉损伤机制以及视感知觉训练在IXT治疗中的作用做一综述。希冀为视感知觉训练重建IXT患者术后双眼视觉功能、降低复发率提供更多证据。     

旋转光栅视觉刺激生理成分的功能磁共振成像研究

目的：利用功能磁共振成像技术,观察旋转光栅刺激引起的视觉皮层生理反应,探索其反应的组成成分。 方法：在1．5T磁共振扫描仪上,对9例健康志愿者以梯度回波基础上加平面回波（GRE-EPI）成像序列法采集旋转光栅引起的视皮层反应数据,SPM99软件进行数据离线后处理。 结果：旋转光栅的各种刺激成分引起不同视觉皮层中枢的兴奋。枕叶中央区域的强烈反应位于初级视觉皮层区,与白光刺激有关;两侧19区的反应与视觉运动功能有关。枕叶中央微弱反应区与形状察觉功能有关。 结论：旋转光栅包含丰富的视觉信息,作为刺激源可兴奋视觉中枢的不同区域。功能磁共振成像技术可以作为研究视皮层生理的良好工具。     

磁共振技术在视觉系统成像中的应用

磁共振成像技术在评估视觉系统的解剖结构及功能变化方面日益得到广泛的应用,目前研究较多的磁共振技术主要包括：传统磁共振成像、弥散张量成像、功能磁共振、磁共振波谱法、锰增强磁共振等。在这些磁共振成像技术中,传统磁共振主要提供视觉系统形态学的改变,弥散张量成像及锰增强磁共振主要用于观测更微观的视觉系统结构的改变,功能磁共振可以反映视觉系统病变所引起的视觉皮层功能反应的改变,磁共振波谱法对深入研究眼部疾病的脑内代谢改变有很重要的意义。这些技术的单独或联合应用对于视觉系统相关疾病的诊断、随访监测以及疗效评估方面有着重要的价值,在临床应用方面将发挥越来越大的作用。     

Changes in Bruch's membrane in experimental hypercholesteremia in rats

PURPOSE: We investigated the effect of high cholesterol diet for the aging changes in Bruch's membrane of rats. METHODS: After feeding a 4% cholesterol diet for 15 weeks to three young rats 3 months old and four aged rats 23 months old, we observed the morphological changes of Bruch's membrane by electron microscopy, and made a comparison with rats fed an ordinary diet. RESULTS: In one young rat fed a high-cholesterol diet, the endothelial basement membrane of the choriocapillaris formed multiple folds separated from the plasma membrane of the endothelium and showed lamellar thickening and crack in some areas. The elastic fiber layer in Bruch's membrane disappeared partly and some new microfibrils appeared. In one aged rat fed a high-cholesterol diet, the endothelial basement membrane of the choriocapillaris showed more lamellar thickening with lumps in some parts. Compared with rats fed an ordinary diet, rats fed a high-cholesterol diet showed thickening of the basement membrane and the changes were more severe. CONCLUSIONS: Our data indicated that high-cholesterol diet might promote age-related changes of Bruch's membrane.     

Advances in imaging in oculoplastics

Color Doppler imaging, computed tomography (CT) and magnetic resonance (MR) imaging are the most precious imaging tools for the clinician in the field of oculoplastics. Orbital and facial vasculature, with its dynamic changes and flow velocities seen in orbital varices, carotid-cavernous fistulas, and dural cavernous arteriovenous malformations, is best detected by Color Doppler imaging. Computed tomography remains the dominant imaging modality in the evaluation of orbital trauma. Helical CT axial scanning with multiplanar reconstruction and three-dimensional CT imaging are most helpful in assessing iatrogenic, traumatogenic, and teratogenic orbital abnormalities. Despite its poor histologic specificity, MR imaging provides superior soft tissue contrast, and contrast-enhanced MR imaging has an established role regarding soft tissue tumor infiltration. The greatest value of MR studies in the evaluation of orbital and palpebral tumors is that it has the capacity to show the precise relation between lesions and adjacent structures before the clinician contemplates a surgical approach. Finally, contrast-enhanced MR imaging proved to be a valuable vascularization indicator based upon the extent of relative enhancement within porous orbital implant in anophthalmic socket.     

Follow-up studies in pattern VECP in demyelinating diseases in children

Spectral sensitivity functions and the transient decrease of sensitivity to short wavelengths after the offset of yellow light (transient tritanopia) were measured by increment threshold techniques in patients suffering from hereditary macular degenerations. Color vision defects were determined by arrangement tests and the anomaloscope. Central areolar choroidal dystrophy was found to produce a mild protan defect and to reduce foveal spectral sensitivity throughout the visible spectrum by a factor of 100; it also abolishes transient tritanopia. Electroretinogram (ERG) was normal, electrooculogram (EOG) subnormal. Stargardt's disease, despite numerous fluorescent macular spots, does not abolish transient tritanopia nor does it reduce spectral sensitivity, although scotopic matches were performed on the Nagel anomaloscope. Only in severe, advanced cases was transient tritanopia reduced and spectral sensitivity found to follow the absorption spectrum of rods. Routine ERGs and EOGs were normal. Vitelliform macular degeneration, despite the ophthalmoscopically pronounced dystrophic macula, produced only very small changes in spectral sensitivity and transient tritanopia, although a widened matching range on the Nagel anomaloscope and electrophysiological abnormalities were found. Apparently damage of the retinal circuit which connects long and short wavelength-sensitive cones, caused by hereditary conditions, is different from that caused by retinotoxic drugs.     

Refractive error in children in a rural population in India

PURPOSE: To assess the prevalence of refractive error and related visual impairment in school-aged children in the rural population of the Mahabubnagar district in the southern Indian state of Andhra Pradesh. METHODS: Random selection of village-based clusters was used to identify a sample of children 7 to 15 years of age. From April 2000 through February 2001, children in the 25 selected clusters were enumerated in a door-to-door survey and examined at a rural eye center in the district. The examination included visual acuity measurements, ocular motility evaluation, retinoscopy and autorefraction under cycloplegia, and examination of the anterior segment, media, and fundus. Myopia was defined as spherical equivalent refractive error of at least -0.50 D and hyperopia as +2.00 D or more. Children with reduced vision and a sample of those with normal vision underwent independent replicate examinations for quality assurance in seven clusters. RESULTS: A total of 4414 children from 4876 households was enumerated, and 4074 (92.3%) were examined. The prevalence of uncorrected, baseline (presenting), and best corrected visual acuity of 20/40 or worse in the better eye was 2.7%, 2.6%, and 0.78%, respectively. Refractive error was the cause in 61% of eyes with vision impairment, amblyopia in 12%, other causes in 15%, and unexplained causes in the remaining 13%. A gradual shift toward less-positive values of refractive error occurred with increasing age in both boys and girls. Myopia in one or both eyes was present in 4.1% of the children. Myopia risk was associated with female gender and having a father with a higher level of schooling. Higher risk of myopia in children of older age was of borderline statistical significance (P = 0.069). Hyperopia in at least one eye was present in 0.8% of children, with no significant predictors. CONCLUSIONS: Refractive error was the main cause of visual impairment in children aged between 7 and 15 years in rural India. There was a benefit of spectacles in 70% of those who had visual acuity of 20/40 or worse in the better eye at baseline examination. Because visual impairment can have a significant impact on a child's life in terms of education and development, it is important that effective strategies be developed to eliminate this easily treated cause of visual impairment.     

Vitrectomy in traumatic cataracts and in the complications of surgery in congenital cataract in children

Vitrectomies were carried out in 35 children with traumatic cataracts and complications of surgery for cataracts, caused by injury to the posterior lenticular capsule and incorporation of its fragments to the vitreous. Complete removal of lenticular rudiments rapidly eliminated phacogenic iridocyclitis and improved visual acuity. Improvement of visual functions was attained in 66.6% cases; in 33.4% cases visual acuity did not change. Hemorrhages to the vitreous cavity occurred in 4 cases with pronounced iridocyclitis; therefore, a corneal approach is preferable for cases with pronounced iridocyclitis.     

Refractive error in children in an urban population in New Delhi

PURPOSE: To assess the prevalence of refractive error and related visual impairment in school-aged children in an urban population in New Delhi, India. METHODS: Random selection of geographically defined clusters was used to identify a sample of children 5 to 15 years of age. From December 2000 through March 2001, children in 22 selected clusters were enumerated through a door-to-door survey and examined at a local facility. The examination included visual acuity measurements, ocular motility evaluation, retinoscopy and autorefraction under cycloplegia, and examination of the anterior segment, media, and fundus. Myopia was defined as spherical equivalent refractive error of at least -0.50 D and hyperopia as +2.00 D or more. Children with reduced vision and a sample of those with normal vision underwent independent replicate examinations for quality assurance in four of the clusters. RESULTS: A total of 7008 children from 3426 households were enumerated, and 6447 (92.0%) examined. The prevalence of uncorrected, baseline (presenting), and best corrected visual acuity of 20/40 or worse in the better eye was 6.4%, 4.9%, and 0.81%, respectively. Refractive error was the cause in 81.7% of eyes with vision impairment, amblyopia in 4.4%, retinal disorders in 4.7%, other causes in 3.3%, and unexplained causes in the remaining 5.9%. There was an age-related shift in refractive error from hyperopia in young children (15.6% in 5-year-olds) toward myopia in older children (10.8% in 15-year-olds). Overall, hyperopia was present in 7.7% of children and myopia in 7.4%. Hyperopia was associated with female gender. Myopia was more common in children of fathers with higher levels of education. CONCLUSIONS: Reduced vision because of uncorrected refractive error is a major public health problem in urban school-aged children in India. Cost-effective strategies are needed to eliminate this easily treated cause of vision impairment.