Adaptive modifications of postural attitude in conditions of weightlessness

Summary Adaptation of static posture was studied before, during, and after a 7-day space flight. Body segment orientations, body stability, and muscle activity underlying the reproduction of several postural attitudes were examined in various visual situations either with the shoes attached to the floor or during free floating. In standing or relaxed subjects whose shoes were attached to the floor, the tonic activity of the ankle flexor was enhanced relative to that in the same posture on earth, whereas the extensor activity disappeared. Errors in attempting to reproduce the normal terrestrial upright posture and a forward-leaning posture were accompanied by major changes in the synergies between neck, hip, knee, and ankle joints. These changes are mainly attributed to cumulative adjustments in response to nonvestibular signals such as tactile, articular, and proprioceptive cues.     

Prevalence of Vision Loss and Associations With Age-Related Eye Diseases Among Nursing Home Residents Aged ≥65 Years

ObjectivesTo examine data from Delaware nursing homes to determine prevalence of age-related eye diseases (AREDs), vision impairment, and blindness and to compare the findings with the results of 11 US investigations of vision and eye health in nursing homes.DesignThis is a cross-sectional, retrospective study of nursing home patients.Setting and ParticipantsTwenty nursing homes in Delaware participated in the study, yielding comprehensive eye examination records for 2019 study participants.MethodsSummary statistics and regression analyses.ResultsThe overall prevalence of vision impairment or blindness was 63.8% and was above 60% for each age, sex, and race category. Prevalence of vision impairment or blindness was 68.4% among patients with cataracts, 69.4% among patients with macular degeneration, 70.5% among patients with glaucoma, and 68.4% among patients with diabetic retinopathy. Prevalence of blindness was 14.1%. Among patients with AREDs, prevalence of blindness ranged from 15.0% for patients with cataracts to 22.6% for patients with diabetic retinopathy. When compared with other investigations, we found wide variation in vision and eye factors reported and wide variation in the prevalence of those factors. Only 4 studies diagnosed both AREDs and visual function. Seven studies reported AREDs, and 7 reported vision impairment and/or blindness. Vision impairment or blindness ranged from 29% to 67%; cataract ranged from 32% to 83%; macular degeneration ranged from 4.6% to 70.7%. Glaucoma ranged from 5.3% to 41.4%; diabetic retinopathy ranged from 1.7% to 3.1%.Conclusions and ImplicationsComprehensive eye examinations showed that vision impairment and blindness affected 63.8% of nursing home residents. Compared with other studies, there was a wide range of vision factors reported and wide variation in the prevalence of vision impairment or blindness and AREDs. This investigation suggests the importance of eye care in nursing homes and the importance of reporting standard vision and eye health factors to inform policy and practice.     

"Fatigue on rest" and associated symptoms (headache, vertigo, blurred vision, nausea, tension and irritability) due to locally asymptomatic, unerupted, impacted teeth.

"Fatigue on Rest", headache, vertigo and the feeling of loss of balance, blurred vision, nausea, tension and irritability, were found to be prevalent amongst patients who had locally asymptomatic, unerupted impacted teeth. A comparative pressure sign was developed, which, when positive, confirmed the relationship between the impacted teeth and the medical symptoms. Removal of the impactions resulted in the alleviation of the symptoms. Stress and psychogenic factors are considered as trigger mechanisms, rather than as basic causes of the symptoms.     

The effects of visual input on open-loop and closed-loop postural control mechanisms

In an earlier posturographic investigation (Collins and De Luca 1993) it was proposed that open-loop and closed-loop control mechanisms are involved in the regulation of undisturbed, upright stance. In this study, stabilogram-diffusion analysis was used to examine how visual input affects the operational characteristics of these control mechanisms. Stabilogram-diffusion analysis leads to the extraction of repeatable center-of-pressure (COP) parameters that can be directly related to the resultant steady-state behavior and functional interaction of the neuromuscular mechanisms underlying the maintenance of erect posture. Twenty-five healthy male subjects (aged 19–30 years) were included in the study. An instrumented force platform was used to measure the time-varying displacements of the COP under each subject's feet during quiet standing. The subjects were tested under eyes-open and eyes-closed conditions. The COP trajectories were analyzed as one-dimensional and two-dimensional random walks, according to stabilogram-diffusion analysis. Using this technique, it was found that visual input affects the performance of the postural control system in one of two different ways — either it significantly modifies the steady-state behavior of the open-loop postural control mechanisms, or it significantly alters the characteristics of the other closed-loop feedback mechanisms that are involved in balance control. This result is interpreted as an indication that the visual system is integrated into the postural control system in one of two different ways. The experimental population was roughly evenly divided between these two schemes. For the first group (13 of 25 subjects), visual input principally caused a decrease in the effective stochastic activity of the open-loop control mechanisms in both the mediolateral and anteroposterior directions. For the second group (12 of 25 subjects), visual input caused an increase in the effective stochastic activity and uncorrelated behavior of the closed-loop control mechanisms in the anteroposterior direction only. On the basis of these results, it is hypothesized that visual input, in both schemes, serves to decrease the stiffness of the musculoskeletal system. In the former case, this may be accomplished by decreasing the level of muscular activity across the joints of the lower limb, whereas, in the latter case, reduced stiffness may be achieved by reducing the gain(s) of the other postural feedback mechanisms, i.e., the proprioceptive and/or vestibular systems. Using stabilogram-diffusion analysis, it was also found that the two groups of subjects behaved similarly under eyes-closed conditions. This result suggests that the open-loop postural control mechanisms and reflex-based feedback systems, respectively, of healthy, young individuals are organized in functionally equivalent ways.     

Marijuana,alcohol, and combined drug effects on the time course of glare recovery

The time course of light adaptation after intense light exposure is significantly delayed by alcohol, marijuana, and a combined dose of alcohol and marijuana. These effects were found in a double blind experiment, using 10 subjects. The experimental treatements were placebo, 0.75 ml/kg of 95% ethanol, 8 and 15 mg of ⁹ tetrahydrocannabinol (THC), and 0.75 ml/kg of 95% ethanol together with 15 mg of THC. The marijuana-induced delay in recovery is doserelated. Both drugs produce delayed recovery for at least 2 h after drug ingestion. The combined alcohol and marijuana treatment produces little more than the effect produced by either drug alone, suggesting some antagonism between the drugs — a suggestion supported by a significantly lower blood alcohol level for the alcohol dose when combined with marijuana than when taken alone.     

视力残疾的病因分析及预防

目的：了解重庆市渝中区近5年来视力残疾的状况、特点及致残病因，提出相应的预防措施。方法：由指定眼科医师进行多次常规及特殊检查，分析403例806只眼的调查资料。结果：0～14岁儿童组人群的主要致残因素是先天遗传、屈光不正／弱视、斜视／弱视、角膜病和视神经病变；60岁以上老年人群为青光眼、白内障、角膜病、视网膜病变和视神经病变；其他人群依次为高度近视网脱及黄斑变性、眼外伤、角膜病、青光眼和视网膜病变。结论：对不同年龄段的人群应制定相应的预防视残措施。重点开展孕期保健工作及遗传咨询，加大眼部疾病预防知识宣传，预防眼部感染和外伤，积极治疗原发病。     

An improved technique for the extraction of stochastic parameters from stabilograms

An improved characterization of the dynamics of postural sway can provide a better understanding about the functional organization of the postural control system as well as a more robust tool for postural pattern recognition. To this aim, a novel parameterization was applied to the stabilogram diffusion analysis formerly proposed by Collins and De Luca [Collins JJ, De Luca CJ. Open-loop and closed-loop control of posture: a random-walk analysis of center-of-pressure trajectories. Exp Brain Res 1993;95:308–18] that considered the act of maintaining posture as a stochastic process. The main purpose of the present technique was to overcome some drawbacks of the model presented by Collins and De Luca that may restrain its potential application in clinical practice. The approach uses a unique non-linear model to describe the center of pressure (COP) dynamics that reduces the number of parameters and decreases their intra-subject variability; consequently, fewer trials are required to perform reliable estimates of stochastic parameters and this is of particular importance for subjects that cannot afford many repeated measurements because of age or pathology. Four new statistical mechanics parameters (NSMP) were computed on the log–log stabilogram diffusion plots and their estimates were compared in terms of reliability and sensitivity to the visual conditions with: (1) a minimal set of four summary statistic scores (SSS); and (2) the six statistical mechanics parameters (SMP) proposed by Collins and De Luca. All four NSMP showed at least a fair-to-good reliability (intraclass correlation coefficient, ICC>0.49) while SMP (ICC>0.20) showed some poor reliability. A better overall reliability was also observed with respect to SSS. Moreover, only NSMP had a similar score for eyes open and eyes closed conditions. Three out of four NSMP were also significantly sensitive to eyes open or closed conditions (P<0.001) while only three out of six SMP were sensitive to operating conditions (P<0.01).     

Chronic cerebral hypoperfusion: loss of pupillary reflex, visual impairment and retinal neurodegeneration

Adult rats underwent permanent bilateral occlusion of the common carotid arteries (2VO) to determine the effect of chronic cerebral ischemia on vision and retina. They were monitored post-surgically for the presence of the pupillary reflex to light. Some rats were tested for 6 months post-surgically on a radial arm maze task and then tested in another water-escape task which explicitly tested visual function. Another group of rats were tested post-surgically for 3 months on a task which simultaneously assessed visual and tactile discrimination ability. The thicknesses of the retinal sub-layers were then measured for some rats. Fourteen of the 25 rats that underwent 2VO lost the pupillary reflex. This seemed to occur within 5 days. Rats that lost the pupillary reflex but not rats whose reflex was intact, were impaired on all visually guided mazes. Tactile discrimination ability was unaffected. Only rats that lost the pupillary reflex showed reduced thickness of the retinal outer nuclear and plexiform layers, reduced cell density in the retinal ganglion cell layer and astrocytosis and degeneration of the optic tract. We conclude that 2VO can eliminate the pupillary reflex. Photoreceptors and retinal ganglion cells degenerate, but it is unclear if these are the cause(s) or result(s) of the loss of the pupillary reflex. These effects are accompanied by impairment of visually guided behavior. The possibility that visual system damage may also occur in acute ischemia merits further investigation.     

巩膜扣带手术后视物变形的原因分析

目的 探讨巩膜扣带手术后视网膜复位患者视物变形的原因。 方法 对巩膜扣带手术后视网膜成功复位的79例79只眼行临床观察，手术后2周、2、6个月及1年时行Amsler表检查，分为视物变形组和无视物变形组；同时行检眼镜、荧光素眼底血管造影（FFA）和光相干断层扫描（OCT）检查。并对手术后2周视物变形10只眼和正常人10只眼行视盘-中心凹角测量。 结果 79只眼手术后2周51只眼（64.56%）视物变形，视物变形眼和正常眼的视盘-中心凹角无明显差异(P=0.880)。79只眼中44只眼(视物变形组35只眼，无视物变形组9只眼) 手术后2周时检查OCT和FFA ，视物变形组OCT发现黄斑结构异常31只眼(88.57%)，有7种类型，主要为神经上皮层脱离（74.29%）；FFA发现黄斑结构异常6只眼(17.14%)，也主要为神经上皮层脱离(66.67%)。无视物变形组OCT发现神经上皮层脱离和色素上皮层脱离各1只眼，FFA未见异常。手术后2、6个月、1年时随访，各有18只眼（18/28）、5只眼(5/9)和3只眼(3/7)异常黄斑结构好转，视物变形减轻或消失；而黄斑前膜形成后未见明显变化，视物变形严重而持续。 结论 巩膜扣带手术后视物变形的主要原因是黄斑结构异常，手术后早期和晚期视物变形的主要原因分别是神经上皮层脱离和黄斑前膜。（中华眼底病杂志，2004，20：94-97）     

渗出型老年性黄斑变性患者光动力疗法治疗前后视功能变化

目的 观察渗出型老年性黄斑变性（AMD）患者光动力疗法（PDT） 治疗前后的视功能变化。 方法 对经临床眼底检查、荧光素眼底血管造影（FFA）、吲哚青绿血管造影（ICGA）和光相干断层扫描（OCT）检查确诊的AMD患者25例34只眼采取PDT治疗，治疗后随访4个月～2年，平均随访观察时间9.2个月。对比分析治疗前以及治疗后定期随诊观察的最佳视力［采用最小分辨角度的对数视力(logMRA)统计平均视力］、视物变形及中心暗点、对比敏感度、双眼单视功能和立体视功能、以及色觉辨认等的变化情况。 结果 PDT治疗前患眼平均视力为logMAR 0.73±0. 37，治疗后不同时期的平均视力较治疗前提高，尤其在3个月时较明显，其平均视力logMAR 0.59±0.45。治疗前后比较，差异无显著性的意义（P＞0.05）；其中视力提高者13只眼 ，占38.24%；无变化15只眼，占44.12%；下降6只眼，占17.65%。Amsler方格表检查视物变形和中心暗点均较治疗前范围缩小，但差异无显著性的意义（P＞0.05）。治疗后各频区的对比敏感度值均较治疗前呈现不同程度提高，低频区（1.5 c/d）差异有显著性的意义（P＜0.05） 。患者的双眼同时视功能、融合功能、立体视功能以及色觉辨认功能均较治疗前有轻度改善 （P＞0.05）。 结论 渗出型AMD患者的视功能变化是多方面的，PDT 治疗可改善患者的部分视功能. （中华眼底病杂志，2004，20：289-291）