Behavioral measurements of accommodative amplitude in rhesus monkeys

The extent of voluntary accommodation was investigated behaviorally in two young rhesus monkeys and an adult human using a modified minus-lens technique. Specifically, contrast sensitivity for a high spatial frequency grating was determined as a function of spectacle lens power. Accommodative amplitudes derived from contrast sensitivity vs lens power functions indicate that young monkeys have at least 17 to 18 D of voluntary accommodation and that the accommodative amplitudes of monkeys are larger than those of equivalent-aged humans.     

The lag between effectiveness and cost-effectiveness evidence of new drugs

A new drug is approved for use if its efficacy and safety have been demonstrated. However, healthcare decision makers may also require data on the cost-effectiveness of new drugs if they are to make informed decisions about their place in therapy. Cost-effectiveness evidence may lag behind the effectiveness data in terms of its availability. We explored the timeliness of delivering cost-effectiveness information about new drugs with established effectiveness and significant financial impact. Drugs were identified, based on guidance documents and reports published by the UK National Institute for Clinical Excellence (NICE), and the following data were collected: dates of publication of first effectiveness and cost-effectiveness evidence, methodology of the cost-effectiveness analysis, quality scores of the clinical studies. Eighteen guidance documents on the use of new drugs/drug groups published by NICE by October 2001 covered 30 health technologies, which were included in the analysis. The analysis of the evidence showed that their effectiveness had been demonstrated in the last 12 years, with only two exceptions. However, cost-effectiveness evidence had been published for 21 (70%) of the technologies. The cost-effectiveness was estimated in 52.4% of cases using models. The good quality effectiveness evidence lagged behind the first effectiveness evidence by 1.40 years (95% CI 0.57–2.23), while the mean lag between the first effectiveness evidence and the first cost-effectiveness publications was estimated as 3.20 years (95% CI 1.76–4.65). Cost-effectiveness evidence thus often lags behind the effectiveness evidence. As a result healthcare decision makers are sometimes in a position of having to take decisions without having adequate cost-effectiveness data at their disposal.     

Accommodating intraocular lenses: a critical review of present and future concepts

Background Significant efforts have been made to develop lens implants or refilling procedures that restore accommodation. Even with monofocal implants, apparent or pseudoaccommodation may provide the patient with substantial though varying spectacle independence. True pseudophakic accommodation with a change of overall refractive power of the eye may be induced either by an anterior shift or a change in curvature of the lens optic. Materials and methods Passive-shift lenses were designed to move forward under ciliary muscle contraction. This is the only accommodative lens type currently marketed (43E/S by Morcher; 1CU by HumanOptics; AT-45 by Eyeonics). The working principle relies on various hypothetical assumptions regarding the mechanism of natural accommodation. Dual-optic lenses were designed to increase the dioptric impact of optic shift. They consist of a mobile front optic and a stationary rear optic which are interconnected with spring-type haptics. With active-shift lens systems the driving force is provided by repulsing mini-magnets. Lens refilling procedures replace the lens content by an elastic material and provide accommodation by an increase of surface curvature. Results Findings with passive-shift lenses have been contradictory. While uncorrected reading vision results were initially reported to be favorable with the 1CU, and excellent with the AT-45 lens, distant-corrected near vision did not exceed that with standard monofocal lenses in later studies. Mean axial shift from laser interferometric measurements under stimulation with pilocarpine showed a moderate anterior shift with the 1CU, while the AT-45 paradoxically exhibited a small posterior shift. With the 1CU, the shift-induced accommodative effect was calculated to be less than +0.5 D in most cases, while +1 D was achieved in a single case only. Ranges and standard deviations were very large in relation to the mean values. Under physiological near-point stimulation, however, no shift was seen at all. Prevention of capsule fibrosis by extensive capsule polishing did not enhance the functional performance. Dual optic lenses are under clinical investigation and are reported to provide a significant amount of accommodation. However, possible long-term formation of interlenticular opacifications remains to be excluded. Regarding magnet-driven active-shift lens systems, initial clinical experience has been promising. Prevention of fibrotic capsular contraction is crucial, and it has been effectively counteracted with a special capsular tension ring, or lens fixation technique, together with capsule polishing. Lens refilling has been extensively studied in the laboratory and in primates. Though it offers great potential for fully restoring accommodation, a variety of problems must be solved, such as achieving emmetropia in the relaxed state, adequate response to ciliary muscle contraction, satisfying image quality over the entire range of accommodation and sustained functioning. The key problem, however, is again after-cataract prevention. Conclusions As opposed to psychophysical evaluation techniques, laser interferometry measures what shift lenses are designed to provide: axial shift on accommodative effort. While under pilocarpine some movement was recorded, no movement at all was found under near-point stimulation with any of the lenses currently marketed. In contrast, magnetic-driven active-shift lens systems carry the potential of sufficiently topping up apparent accommodation to provide for clinically useful accommodation while using conventional lens designs with proven after-cataract performance. Dual optic implants significantly increase the impact of axial optic shift. The main potential problem, however, is delayed formation of interlenticular regenerates. Lens refilling procedures offer the potential of fully restoring accommodation due to the great impact of increase in surface curvature on refractive lens power. However, various problems remain to be solved before clinical use can be envisaged, above all, again, after-cataract prevention. The concept of passive single-optic shift lenses has failed. Concomitant poor capsular bag performance makes these lenses an unacceptable trade-off. Magnet-assisted systems potentially combine clinically useful accommodation with satisfactory after-cataract performance. Dual optic lenses theoretically offer substantial accommodative potential but may allow for interlenticular after-cataract formation. Lens refilling procedures have the greatest potential for fully restoring natural accommodation, but will again require years of extensive laboratory and animal investigations before they may function in the human eye. The author has no proprietary interest in any of the materials or equipment mentioned in this study.     

Accommodative function in school children with reading difficulties

Background  Prior findings suggest correlation between reading problems and accommodative function, but few studies have assessed accommodation in children with poor reading skills. Our aim was to characterize monocular accommodative amplitude, relative accommodation and binocular accommodative facility in a population of healthy, non-dyslexic primary school children with reading difficulties. Methods  We conducted a cross-sectional study on 87 poor readers and 32 control children (all between 8 and 13 years of age) in grades three to six recruited from 11 elementary schools in Madrid, Spain. In each subject with best spectacle correction, negative relative accommodation (NRA) and positive relative accommodation (PRA) were measured using a phoropter, monocular accommodative amplitude (MAA) was determined using the minus lenses method, and binocular accommodative facility (BAF) was measured using the Bernell Acuity Suppression Slide (VO/9) and a ± 2.00 D accommodative demand for a period of 1 minute. Results  Monocular accommodative amplitude was significantly lower (p < 0.001) in the group of poor readers (right eye 9.1 D ± 2.3, left eye 9.0 D ± 2.3) than in the control group (right eye 10.5 D ± 1.7, left eye 10.5 D ± 1.7). Binocular accommodative facility values were significantly lower (p < 0.05) in the poor readers (4.9 cpm ± 3.1) than controls (6.3 cpm ± 2.9). Negative and positive relative accommodation values were similar in both groups of children. Conclusions  This study provides data on the accommodative capacity of a population of children with reading difficulties. Our findings suggest a reduced monocular accommodative amplitude and binocular accommodative facility, such that this function should be assessed by an optometric clinician in children whose reading level is below average. Human subjects and informed consent  The authors confirm that this research was performed followed the tenets of the Declaration of Helsinki, and that informed consent was obtained from the subjects after having explained to them in detail the nature of the study. The study protocol was approved by the Clinical Research Ethics Committee of the School of Optometry.     

Analysis of human crystalline lens curvature as a function of accommodative state and age

Slit-lamp photographs from four human subjects, aged 11, 19, 29, and 45 were reanalyzed using computer-based digitization and curve-fitting methods in order to obtain more complete information on internal lens curvature changes during accommodation. All discernible curves (N = 742) could be fit to parabolas with chi 2 less than or equal to 0.001 irrespective of lens age, accommodative state, or curve location within the lens. For each lens, the coefficients of the parabolas, when displayed in graphic form, exhibit a linear relationship between location within the lens and the coefficient of the chi 2 term. The slope of this line remains unchanged over accommodation for a given lens, but is shifted in position. The slope changes as a function of age. The age 45 lens exhibits these characteristics to a limited extent only, the differences possibly related to the development of presbyopia. The further a given curve is located from the lens surface, the smaller the region of its arc that can be considered approximately circular. A roughly hourglass figure is generated by these circular bounds; the waist of the hourglass decreases with increasing accommodation, since changes in radius of curvature with accommodation are more pronounced internally. Calculations of arc lengths as a function of increasing accommodation indicate that these lengths change very little over the entire accommodative range.     

石家庄市PM2.5浓度对居民死亡的急性影响分析

目的 了解石家庄市PM2.5污染特征及其对居民死亡率的影响。方法 收集2013 - 2015年该市逐日大气PM2.5浓度、平均气温、平均相对湿度和居民的死亡数据,利用广义相加模型分析PM2.5日均浓度和居民死亡的关系。结果 研究期间石家庄市日均非意外死亡32人,其中循环系统疾病死亡17人,呼吸系统疾病死亡5人;PM2.5浓度范围为6.3～771.3 μg/m3,平均浓度为118.8 μg/m3。时间序列分析结果表明,该市大气PM2.5浓度每升高10 μg/m3,居民非意外总死亡（lag05）、循环系统疾病死亡（lag05）和呼吸系统疾病死亡（lag1）的风险分别增加0.73%（95%CI:0.42%～1.04%）、1.04%（95%CI:0.64%～1.46%）和0.63%（95%CI:0.07%～1.19%）。结论 石家庄市大气PM2.5浓度的升高可能导致居民非意外总死亡,尤其是循环系统疾病和呼吸系统疾病死亡的增加。     

拟调节人工晶状体在眼内位移与调节力研究

目的 探讨拟调节人工晶状体在眼内位移与调节力的关系.方法 采用病例对照研究方法,将白内障患者20例(20只眼)分成两组:10只眼植入Lestec公司生产的福来视拟调节人工晶状体(TetraflexIOL)(福来视组);另外10只眼植入其他无调节功能的人工晶状体(单焦点组).检测患者术后的裸眼远、中、近视力及矫正远、中、近视力;矫正远视力的近视力;采用前段OCT定量测定1%pilocarpine诱导缩瞳后人工晶状体在眼内前后移动的幅度;同时观察患者调节力的变化.结果 所有患者随访3个月:两组的裸眼、矫正远视力及矫正近视力差异均无统计学意义(P＞0.05);福来视组的裸眼中、近视力及矫正远视力的近视力均优于对照组(P<0.05);福来视组人工晶状体移动度及调节力与对照组比较差异有统计学意义(P<0.05),而且人工晶状体移动度与调节力呈正相关(r=0.977.P=0.000).结论 福来视拟调节人工晶状体是安伞有效的,能使患者术后获得一定的调节力,与人工晶状体的移动度具有正相关性,提供良好的远、中、近视力.     

视标呈现方式和注视方式对调节及调节微波动的影响

背景 研究表明,作为非光学因素,认知对调节系统存在一定的影响,因此客观、准确的实验设计是评价非光学因素对调节系统影响的关键步骤之一. 目的 研究视标呈现方式和注视方式对调节及调节微波动的影响,并进一步探讨认知中专注注视这一高水平注意因素对调节系统影响及近距离工作下专注注视的注视状态与近视发生发展的可能关系.方法 选择健康志愿者30例,平均年龄(24.80±1.98)岁,平均等效屈光度为(-1.92±2.02)D,平均柱镜屈光度为(-0.19±0.58)D.所有测量在屈光全矫下进行.采用开放视野红外自动验光仪测量受试者双眼注视40 cm处随机呈现的不同视标注视状态下右眼的调节反应.视标设计为专注注视状态和放松注视状态. 结果 受试者在专注注视状态下的调节反应均值为(1.86±0.26)D,放松注视状态下的调节反应均值为(1.27±0.39)D,差异有统计学意义(t=-8.052,P=0.000).受试者在专注注视状态下的调节微波动均值为(0.17±0.06)D,放松注视状态下的调节微波动均值为(0.28±0.17)D,差异有统计学意义(t=3.600,P=0.001).结论 视标的呈现方式和注视方式可影响调节反应,专注注视这一高水平注意因素使调节系统的调整更加精确、稳定.     

儿童调节性内斜视临床观察

目的观察儿童屈光性调节性内斜视戴镜后的眼位、屈光度、视力及双眼单视功能情况。方法搜集106例调节性内斜视儿童,准确验光后即时配戴全矫正眼镜,随访观察4年,并进行回顾性分析。结果观察6个月以上,眼位正位者91例,占85.85%;部分性调节性内斜视,带全矫眼镜6个月以上,远视度数由初时的＋6.5 4D,下降为4年后的＋5.0 2D。视力由初诊时的0.36上升到4年后的0.82。结论调节性内斜视的治疗是一个综合治疗过程。既要注重眼位的矫正、又要进行弱视治疗,同时注意建立双眼单视功能。