Two-dot alignment across the physiological blind spot

Three competing hypotheses have been proposed for the cortical representation of the blind spot. These are: (i) the regions surrounding the blind spot maintain their spatial values; (ii) the opposite sides of the blind spot are represented adjacently at the cortex, so that the blind spot is “sewn-up”; and (iii) the blind spot is sewn-up with compensation occurring in the immediate surround of the blind spot, so that spatial values are distorted only in the immediate surround of the blind spot. To distinguish between these hypotheses we used a two-dot alignment task, with the two dots straddling the blind spot at varying dot separations. Thresholds in the two-dot alignment task are limited by the cortical separation of the two dots. When thresholds for alignment across the blind spot are compared with thresholds over intact retina at the same eccentricity, the three hypotheses predict: (i) no change in thresholds; (ii) a lowering of thresholds; and (iii) a lowering of thresholds but only at separations slightly greater than the diameter of the blind spot. Thresoolds across the blind spot were closely similar to thresholds across intact retina. The results do not support a sewing-up (with or without compensation) of the blind spot. Rather, our results are consistent with a preservation of spatial values around the blind spot.     

Distribution and aetiology of blindness and visual impairment in mesoendemic onchocercal communities, Kaduna State, Nigeria. Kaduna Collaboration for Research on Onchocerciasis.

During a field trial of ivermectin in Kaduna State, 6831 people age 5 years and above, living in 34 mesoendemic onchocercal communities in Kaduna State, northern Nigeria, were examined for ocular disease. Visual function assessments included tests of visual acuity and visual fields. A total of 185 individuals (2.7%) were bilaterally blind by acuity criteria with a further 28 blind by field constriction. The overall prevalence of blindness was 3.1%. A further 118 individuals were visually impaired by WHO criteria. Examination for the cause of blindness revealed that 43% of eyes in bilaterally blind patients were blind due to onchocerciasis. A further 11% were blind from optic atrophy much of which was probably onchocercal in origin. Glaucoma was the next most common cause of blindness in the bilaterally blind (11%). Only 6% of eyes were blind from cataract as the primary cause. In the visually impaired population cataract was the most common primary cause of impaired/blind eyes (31%), followed by onchocerciasis (19%) [corrected].     

Correlation of nerve head and blind spot elliptical features

Ellipses were fitted to 129 nerve heads and corresponding blind spots in an attempt to determine how faithfully the elliptical nature of the nerve head is reflected in the blind spot. The blind spots are found to be 2 to 3 times more elliptical (based on the ratio of the long axis to the short axis) than the nerve heads. The correlation between the ratios mentioned above is found to be negligible (Pearson r = 0.07 for Goldmann 1-2 blind spots and 0.18 for Goldmann 1-4 blind spots).     

Historic notices of Louis braille and the development of dot-writing (author's transl)]

Louis Braille is called by his first biographer to be the "Johannes Gutenberg for the blind". Being blind himself--caused by a sympathetic ophthalmia after a perforating hurt to his eye--he invented at the age of 16 years a simple and ingenious method enabling blind people to read and write. His system consisting of six elevated and palpable dots was rejected by the teachers of these days, claiming there could be a distance between blind and fullsighted men. Despite this opposition the Braille system succeeded because of its advantages for the blind: Nowadays this method is used all over the world.     

Filling-in at the natural blind spot contributes to binocular rivalry

The human natural blind spot is usually filled in based on the contextual information. When two sufficiently different images are presented to the two eyes, observers typically perceive an alternation between the two images (binocular rivalry). Both the filling-in process and binocular rivalry have been the subject of considerable research. This study investigates whether filled information in one eye's natural blind spot can contribute to binocular rivalry. A radial grating (D=12 degrees ) was presented to one eye, centered on the natural blind spot. Observers perceived a complete figure in monocular view; the blind spot area was filled-in based on the surrounding information. Simultaneously, a circular grating smaller than the blind spot (D=4 degrees ), was presented to the fellow eye in the region corresponding to the other eye's blind spot. The amount of rivalry as indexed by how often the smaller circular grating remained visible was measured. The results suggest that the filled information in the area of the blind spot does contribute to the rivalry process.     

Vestibulo-ocular reflexes of adventitiously and congenitally blind adults

The vestibulo-ocular reflex (VOR) was measured in congenitally blind, adventitiously blind, and normally sighted adults to determine how it was affected by loss of vision. VOR gain and phase were measured in subjects rotated sinusoidally in total darkness, while concentrating on an imaginary earth-fixed target. Gain was lower in adventitiously blind subjects than in sighted subjects. The gain reduction in blind subjects was accompanied by an increase in the amount of phase lead at low frequencies. The dominant time constant was typically 3 sec for adventitiously blind subjects and 16 sec for sighted subjects. No convincing vestibulo-ocular responses were measured in congenitally blind subjects except at the highest test frequencies. These findings demonstrate that vision is necessary early in life for development of the VOR, and that vision is also necessary throughout life for ongoing maintenance of the VOR.     

生理盲点扩大对开角型青光眼早期诊断价值的探讨

用Humphrey视野分析仪对154眼早期开角型青光眼患者的视野作了检查,发现69眼有生理盲点扩大,占44.8%,认为生理盲点扩大在开角型青光眼的早期诊断中应占一个重要地位。并对生理盲点扩大的判断标准、生理盲点扩大对青光眼的诊断价值及其特异性、假阳性问题作了讨论。     

Childhood visual experience affects adult voluntary ocular motor control.

PURPOSE: To quantify the effects of childhood visual experience/chronic visual deprivation upon adult voluntary ocular motor control. METHODS: Eye movements of blind and sighted adults were elicited and videotaped in total darkness. The videotaped responses were digitized using an eye tracker, yielding data from 10 congenitally blind (infantile onset, blindness before age 1 year), 16 adventitiously blind, and 9 sighted persons. RESULTS: Multivariate analysis of variance, trend analyses and post hoc tests revealed that primary position fixational stability and consistency of return to primary position were lowest in the congenitally blind vs. the adventitiously blind group, and highest in the sighted. Duration of adventitious blindness reduced primary position stability but not consistency of return to primary position. Secondary position maximum amplitudes: congenitally blind mean, 14 degrees; adventitiously blind mean, 40 degrees; sighted mean, 47 degrees. Average velocity (a form of Main Sequence) increased significantly with amplitude in all three groups. CONCLUSIONS: Visual deprivation can greatly attenuate but does not abolish human voluntary eye movement. Adventitious blindness exerts minimal to profound effects, commensurate with age of vision loss.     

Utilization of community-based rehabilitation services for incurably blind persons in a rural population of southern India

PURPOSE: To identify barriers in utilisation of community based rehabilitation (CBR) services for incurably blind persons in rural South India. METHODS: A community-based rehabilitation programme for incurably blind persons was initiated in Theni district of southern Tamil Nadu in south India. After door-to-door enumeration and preliminary ocular screening by trained workers at the village, identified blind persons were categorised as either curable or incurable by an ophthalmologist. Trained workers provided rehabilitation, including mobility training (OM), training to perform activities of daily living (ADL), and economic rehabilitation for the incurably blind in their respective villages. RESULTS: Of the 460,984 persons surveyed, 400 (0.09%) were certified as incurably blind including 156 (39.00%) persons blind from birth. Social rehabilitation was provided for 268 (67.00%) incurably blind persons. Economic rehabilitation was provided to 96 persons, and integrated education to 22 children. Nearly one-fifth (n=68, 17.00%) of incurably blind persons refused the services provided. The major reasons for refusal included old age and other illnesses (41.18%), and multiple handicaps (19.12%). Twenty-seven (6.75%) persons had either migrated or died, and 29 (7.25%) persons were already able to function independently. CONCLUSION: Although CBR programmes provide useful services to the incurably blind, a better understanding of barriers is required to improve service utilisation. Developing a standardised data collection format for every CBR programme can result in the creation of a national database of ophthalmic diseases.     

深圳市低视力和盲患者的生活质量分析

目的通过对深圳市低视力和盲人群进行问卷调查,了解低视力和盲患者的生活质量及影响生活质量的因素。为科学的制定低视力和盲康复方案提供一定的依据。方法对低视力和盲的患者进行低视力康复调查问卷一般检查评估表和生存质量的问卷调查,根据得分评估低力和盲对患者生存质量的影响。主要指标：低视力患者生活质量得分;盲患者生活质量得分。结果共联系了100名低视力和盲患者,完成问卷调查100份。其中低视力患者50例,盲50例。低视力患者生活质量得分为36．78±5．02。影响生活质量的因素主要有：经济状况、社交能力、活动能力。均P ＜0．01。盲患者生活质量得分为25．25±3．65;影响生活质量的因素主要有：经济状况、心理状况、自理能力。均P ＜0．01。结论低视力和盲患者都处于低质量生活水平,影响低视力和盲患者生活质量的相关因素大致相同,又不尽相同,要提高低视力和盲患者的生活质量水平,需要针对不同的主要影响因素。     

Features of the development of a welfare system for visually disabled people in Denmark

PURPOSE: To describe the development of a formal system of welfare for blind and partially sighted people in Denmark. METHODS: The principal laws in Denmark relating to a formal system of welfare for blind and partially sighted people are noted and commented on. No such collection of laws has been found in the literature. The history of aid to visually disabled people in Denmark is described, as are the Danish classifications of visual impairment. DEVELOPMENT: Formalized welfare for blind and partially sighted people was started in Denmark in 1811, as a private initiative by the Kjaede Order. Later, the Danish state took over responsibility, and in 1858 the Royal Danish Institute for the Blind was established. Since then a series of laws concerning welfare for blind and partially sighted people have been issued in accordance with economic and social development in Denmark. In 1858 the Braille writing system for blind people was introduced. The Danish Association of the Blind was founded in 1911 and has profoundly influenced subsequent legislation. During the last 10 years, several visual centres have been established. Since 1968 prevention of blindness has also played a prominent role in Denmark. CONCLUSION: Great steps have been taken towards improving the welfare of blind and partially sighted people. However, being blind is still very difficult. Modern technologies and hectic lifestyles have created new problems for blind people. The obligations of the Danish state towards visually disabled people have, therefore, increased in recent years.     

盲眼患者视神经和视放射磁共振扩散张量成像观察

目的 观察盲眼患者视觉传导通路中视神经和视放射磁共振扩散张量(MR-DTI)扫描像特征.方法 对20例盲眼患者(盲眼组)和20名正常健康者(对照组)行视神经和视放射MR-DTI扫描.应用Volume-one 1.72软件进行后处理,获得黑白各向异性(FA)和方向编码彩色(DEC)图.观察视神经和视放射在FA和DEC图中的信号表达.在DEC图上分别测量并对比分析盲眼组和对照组受检者双侧视神经和视放射的FA、平均扩散率(MD),本征矢量λ∥及λ⊥值.结果 对照组双侧视神经在FA和DEC图均呈高信号,盲眼组双侧视神经在FA和DEC图均呈明显低信号.盲眼组视神经FA和λ∥值均较对照组明显降低,差异有统计学意义(t=16.294,14.660;P值均=0.000);MD和λ⊥值均较对照组明显升高,差异也有统计学意义(t=8.096,8.538;P值均=0.000).两组受检者双侧视放射在FA和DEC图均呈高信号.盲眼组与对照组双侧视放射FA和MD值比较,差异均无统计学意义(左侧:t=1.456、1.811,P=0.152、0.076;右侧:t=0.779、0.073,P=0.440、0.942).结论 盲眼患者双侧视神经MR-DTI呈低信号,双侧视放射MR-DTI呈高信号.     

Blindness and glaucoma: a comparison of patients progressing to blindness from glaucoma with patients maintaining vision

PURPOSE: To compare patients becoming legally blind from glaucoma with those who did not go blind. DESIGN: Retrospective, cohort, and case-control study. METHODS: A retrospective community-based longitudinal study of residents of Olmsted County, Minnesota, who were newly diagnosed with open-angle glaucoma between 1965 and 1980 and followed through 1998. A case-control study was performed comparing patients progressing to legal blindness from glaucoma with aged-matched and visual field-matched patients not progressing to blindness. RESULTS: Fifty-six of 290 patients progressed to legal blindness in at least one eye over the 34-year period of the study. Most who progressed to blindness had moderate to advanced visual field loss at the time of diagnosis of glaucoma. Those becoming legally blind had mean intraocular pressures (IOP) on therapy lower than or similar to patients who did not go blind, although the variability of IOP was higher in the blind group. Different susceptibilities to IOP were apparent, as some eyes with initially normal disks and visual fields became blind at an IOP of 20 mm, while others did not worsen. Changes in medical therapy after progression of visual field damage were less effective in lowering IOP in the group becoming blind than in the nonblind group. CONCLUSIONS: Patients at greatest risk of blindness had visual field loss at the time of diagnosis of glaucoma. Different susceptibilities to IOP were apparent, with some patients becoming blind at pressures that others tolerated without significant progression. This suggests that continued monitoring of visual fields and reassessment of target IOP levels when field damage occurs are fundamental in the management of glaucoma.     

Characteristics of the filled-in surface at the blind spot

Our visual system can restore information missing within the portion of the retinal image corresponding to the blind spot where the optic nerve exits the eye. Previous studies of the properties of filled-in surfaces at the blind spot have found similarities and dissimilarities between filled-in and real surfaces and have therefore not provided a consistent view of the characteristics of the filled-in surface. First, we investigated whether filling-in utilizes a contour integration mechanism. Gratings with collinear lines filled in the blind spot more effectively than those both with orthogonal lines and without any line, suggesting that collinear facilitation underlies the filling-in of the blind spot. Second, the dynamics of binocular rivalry was examined by comparing the dominance duration distributions of filled-in and real surfaces. The results indicated that the strength of the filled-in surface was attenuated compared to that of the real surface during rivalry. Lastly, we tested whether travelling waves of dominance in rivalry could occur at the blind spot. The travelling waves could propagate through a hole only at the blind spot, suggesting that the filled-in surface helps perceptual waves to travel across the blind spot. These results suggest that the filled-in surface shares a common mechanism via a horizontal connection but that it has weak strength to suppress the opposite eye during binocular viewing.     

Four different ways of philanthropic aid to the blind in medieval Eastern Christendom

The care of the blind, either as medical treatment or as divine therapy, has probably been the most ancient form of help for ill people. However, it was during the Byzantine Empire (325 – 1453 AD) that the state organized a 'blindness relief' plan as part of a widespread public health system. Our sources for the subject include medical writings, state decrees, Saint's 'vitae' and representations of relevant works of art. Based on the above data we classify the health care for the blind in Byzantium as: (a) support of ophthalmological education as evidenced by an abundance of medical writings on the subject; (b) establishment of charitable institutions exclusively or partially for the blind, where there was not only medical care but also provision for a wide range of social aid – the most advanced being specially trained escorts for each blind person; and (c) support by the state of an extended chain of religious institutions where miraculous help for the blind was promised. We conclude that the public health policy in Byzantium made adequate and very early provision for the blind.     

安阳县40岁以上农民白内障筛查及治疗

目的了解安阳县≥40岁自觉视力障碍的农民盲与低视力的患病率及致盲原因。方法安阳县各行政村中,≥40岁自觉视力障碍的农民为筛查对象。采用WHO盲与低视力标准和白内障诊断标准。由眼科医生作眼部检查。对所有视力<0.3的患眼进行主要病因诊断,确诊所有白内障患者,并筛选出需手术治疗者。结果共检查853例,盲目患者23例,患病率2.70%,低视力患者99例,患病率4.27%,致盲的主要眼病依次为白内障、角膜病、青光眼、视网膜病等。共筛查出533例白内障,行白内障手术治疗301人次,脱残率98%,脱盲率99.34%。结论白内障仍是盲和低视力的首要病因,防盲治盲的重点仍是白内障复明手术。     

Extrascleral malignant melanoma.

We present two cases of anterior extrascleral extension of malignant melanoma in eyes previously blind from other causes. In both cases, the tumor was not detected by the physician but rather by the patient himself (case 1) or his wife (case 2). In one case, the tumor became manifest more than 60 years after the eye became blind from trauma. Although blind eyes may harbor lethal tumors and, therefore, need regular examinations, this simple part of the physical examination frequently remains neglected by ophthalmologists as well as by primary care physicians. We wish to emphasize the potential life-saving importance of regular examinations of blind eyes.     

Scotoma mapping by semi-automated kinetic perimetry: the effects of stimulus properties and the speed of subjects' responses

PURPOSE: The study aimed firstly to determine the effects of stimulus variables on the detection of a scotoma border and, secondly, to study the reproducibility of the method during semi-automated kinetic perimetry. METHODS: The size of the physiological blind spot in 18 young normal subjects was measured with a video-campimetric device, the Tübingen computer campimeter (TCC). Kinetic stimuli of two different sizes and at four different levels of luminance were presented. Examinations were repeated within 2 weeks. Measurements were corrected for individual response times and the area of the blind spot was computed. The effects of stimulus strength and size and the repeatability of blind spot measurements were evaluated by an analysis of variance. RESULTS: The physiological blind spot showed significant inter- and intraindividual variations in size (least square means ranging from 17 to 49 square degrees), with a standard deviation of 6.8 square degrees. The measured size of the blind spot increased as a function of decreasing stimulus value, by reducing either the relative brightness or the size of stimuli. Use of a correction for each subject's speed of responses nearly halved the level of random variance. The temporal sequence of measurements (the order in which they were performed) had no apparent effect on the calculated values of blind spot size. CONCLUSIONS: Semi-automated kinetic perimetry can determine the size of the physiological blind spot with good repeatability in young, normal subjects. Determination of each individual's speed of response and inclusion of this variable in the calculations reduced variance of the measure significantly. This study confirmed the presence of considerable interindividual differences in the size of the physiological blind spot.     

Motion reveals spatial visual defects

The question of how we can be unaware of the deficit in our (monocular) visual field, equivalent in size to 76 full moons, is examined. A new method of investigating the response to moving images on and near the blind spot has been found. The image of a computer-generated line, which is made to lengthen with time and pass over the blind spot, is seen as shorter than that of a similar, parallel line which passes outside the blind spot. This perceived difference in length corresponds to the actual width of the blind spot. Our unawareness of blind spots and scotomata is often described as involving some form of 'filling in' process. The rapid variation in cortical receptive field size, recently found to occur in response to stabilized images, may provide a general filling-in mechanism for the removal from perception of otherwise-distracting, stabilizing image regions (such as the shadows of blood vessels and clinical scotomata).     

Differential impact of partial cortical blindness on gaze strategies when sitting and walking - an immersive virtual reality study

The present experiments aimed to characterize the visual performance of subjects with long-standing, unilateral cortical blindness when walking in a naturalistic, virtual environment. Under static, seated testing conditions, cortically blind subjects are known to exhibit compensatory eye movement strategies. However, they still complain of significant impairment in visual detection during navigation. To assess whether this is due to a change in compensatory eye movement strategy between sitting and walking, we measured eye and head movements in subjects asked to detect peripherally-presented, moving basketballs. When seated, cortically blind subjects detected ∼80% of balls, while controls detected almost all balls. Seated blind subjects did not make larger head movements than controls, but they consistently biased their fixation distribution towards their blind hemifield. When walking, head movements were similar in the two groups, but the fixation bias decreased to the point that fixation distribution in cortically blind subjects became similar to that in controls - with one major exception: at the time of basketball appearance, walking controls looked primarily at the far ground, in upper quadrants of the virtual field of view; cortically blind subjects looked significantly more at the near ground, in lower quadrants of the virtual field. Cortically blind subjects detected only 58% of the balls when walking while controls detected ∼90%. Thus, the adaptive gaze strategies adopted by cortically blind individuals as a compensation for their visual loss are strongest and most effective when seated and stationary. Walking significantly alters these gaze strategies in a way that seems to favor walking performance, but impairs peripheral target detection. It is possible that this impairment underlies the experienced difficulty of those with cortical blindness when navigating in real life.