The autonomic control of accommodation and implications for human myopia development: a review

Prolonged nearwork has long been associated with myopia development, however, there is no well described linking mechanism. One theory suggests that if accommodation accuracy during nearwork is not maintained, the defocused retinal image leads to myopia development. Here we review the findings of research aimed at determining whether the autonomic inputs to the ciliary smooth muscle are involved in this type of environmental myopia. We examine whether an autonomic imbalance could be a precursor to axial elongation and the resulting myopia. Accommodation responses, such as tonic accommodation and nearwork-induced accommodative adaptation, as a function of refractive error, are described in relation to an autonomic imbalance model. The collective results of this research point to anomalous accommodation responses, possibly as a result of underlying anomalous autonomic input to the ciliary muscle, being involved in myopia development and progression.     

Steady-state accommodation and ocular biometry in late-onset myopia

The steady-state accommodative responses of emmetropes and late-onset myopes was measured for an array of numbers located at +1, +3 and +5 dioptres using an objective infra-red optometer. Responses were compared for passive (reading numbers) and active (adding numbers) conditions. For the passive condition, the late-onset myopes showed a significantly lower accommodative response than the emmetropic group. No significant differences were found between the two groups for the active condition. Ocular biometric characteristics were also measured in emmetropes, late-onset myopes and early-onset myopes using keratometry and ultrasonography. No significant differences in corneal curvature, anterior chamber depth and crystalline lens thickness were found between the groups. Late-onset myopes exhibited significantly deeper vitreous chambers than emmetropes, which more than accounted for the difference in refractive error between the two refractive groups. We conclude that, while significant differences exist in the accommodative responses of late-onset myopes and emmetropes, late-onset myopia is due predominantly to elongation of the vitreous chamber.     

Near retinoscopy and refractive error

Tonic accommodation (TA) was measured in 100 optometry students using near retinoscopy. Subjects were divided into three refractive groups comprising 42 myopes, 48 emmetropes and 10 hyperopes. The myopic group was found to have the lowest values of TA (mean = 0.47 D; s.d. = 0.38 D), the hyperopes the highest (mean = 0.89 D; s.d. = 0.50 D) and the emmetropes intermediate values (mean = 0.65 D; s.d. = 0.42 D). No significant difference was found between subjects exhibiting myopia which was early in onset (prior to the age of 15 years) and those exhibiting late-onset myopia (after the age of 15 years). The results are discussed with respect to theories of refractive error development.     

Impact of accommodative insufficiency and accommodative/vergence therapy on ciliary muscle thickness in the eye

Purpose

Recent evidence suggests that the ciliary muscle apical fibres are most responsive to accommodative load; however, the structure of the ciliary muscle in individuals with accommodative insufficiency is unknown. This study examined ciliary muscle structure in individuals with accommodative insufficiency (AI). We also determined the response of the ciliary muscle to accommodative/vergence therapy and increasing accommodative demands to investigate the muscle's responsiveness to workload.

Methods

Subjects with AI were enrolled and matched by age and refractive error with subjects enrolled in another ciliary muscle study as controls. Anterior segment optical coherence tomography was used to measure the ciliary muscle thickness (CMT) at rest (0D), maximum thickness (CMTMAX) and over the area from 0.75 mm (CMT0.75) to 3 mm (CMT3) posterior to the scleral spur of the right eye. For those with AI, the ciliary muscle was also measured at increasing levels of accommodative demand (2D, 4D and 6D), both before and after accommodative/vergence therapy.

Results

Sixteen subjects with AI (mean age = 17.4 years, SD = 8.0) were matched with 48 controls (mean age = 17.8 years, SD = 8.2). On average, the controls had 52–72 μm thicker ciliary muscles in the apical region at 0D than those with AI (p = 0.03 for both CMTMAX and CMT 0.75). Differences in thickness between the groups in other regions of the muscle were not statistically significant. After 8 weeks of accommodative/vergence therapy, the CMT increased by an average of 22–42 μm (p ≤ 0.04 for all), while AA increased by 7D (p < 0.001).

Conclusions

This study demonstrated significantly thinner apical ciliary muscle thickness in those with AI and that the ciliary muscle can thicken in response to increased workload. This may explain the mechanism for improvement in signs and symptoms with accommodative/vergence therapy.     

眼调节各因素与眼屈光不正的相关性

目的 :评价与眼屈光不正状态可能相关的各项眼调节功能状况 ,探讨眼屈光不正与眼调节之间的相关性。方法 :分别对 4 7名学生 94只眼进行屈光不正、调节幅度、调节灵敏度、调节准确度 (双眼交叉柱镜FCC法 )检查。然后将各项结果与屈光不正状况进行相关性统计分析。结果 :被检者的屈光不正度平均值为 (- 2 .4 6± 2 .2 8)D ,调节幅度均值为(7.90± 2 .95 )D ,调节灵敏度为 (17.2 8± 4 .92 )次 /min ,调节准确度均值为 (0 .5 8± 0 .6 0 )D ,其中调节幅度与眼屈光度有显著相关性 (r=0 .377,P≤ 0 .0 5 ) ;调节准确度与眼屈光度有显著相关性 (r=- 0 .4 71,P≤ 0 .0 5 )。结论 :眼的屈光不正与眼调节幅度和眼调节滞后量有显著相关 ;眼的调节灵敏度与屈光不正无明显关系。提示我们可通过训练调节幅度和准确度来减缓近视加深。     

初发近视儿童调节反应与近视屈光度的关系

目的 探讨初发近视儿童调节反应与近视屈光度的关系。设计 回顾性病例系列。研究对象 北京同仁验光配镜中心视力下降在6个月内的8～10岁儿童96例,复方托吡卡胺散瞳测双眼近视低于-1.00 D。方法 散瞳前采用综合验光仪进行调节反应、调节灵活度以及正、负相对调节检查。选取双眼中较低度数眼的参数进行统计学分析。主要指标 屈光度、调节反应、调节灵活度、正负相对调节。结果 受试者屈光度为（-0.66±0.25）D,调节反应为（0.25±0.36）D;调节灵活度为（6.31±2.54）cpm;负相对调节为（2.20±0.40）D;正相对调节为（-1.96±1.32）D。调节反应与近视屈光度呈负相关（r=-0.34,P=0.001）;调节反应与调节灵活度、负相对调节无相关性（r=0.027,P=0.798,r=-0.140,P=0.174）;调节反应与正相对调节呈正相关（r=0.231,P=0.023）。结论 初发近视儿童已存在调节反应滞后,调节反应滞后和正相对调节的降低,可能是近视发生发展的原因。（眼科, 2014, 23: 319-322）     

虹膜固定型有晶状体眼人工晶状体植入对高度近视患者睫状肌调节性微波动及调节力的影响

目的通过测量睫状肌调节性微波动高频成分(high frequency component,HFC)来分析有晶状体眼人工晶状体(phakic intraocular lens,P-IOL)植入对高度近视患者睫状肌收缩能力及调节力的影响。方法收集2004年12月～2006年3月在我院进行虹膜固定型有晶状体眼人工晶状体Verisyse植入的患者54例(54眼)。采用NIDEK ARK-730A红外验光仪中调节性微波动分析软件,分别在术后1周、3个月对该54例患者(54眼)进行睫状肌调节性微波动高频成分检查。并与患者术后调节力进行相关性分析。结果HFC与Verisys植入术后1周及3个月的调节力均正相关(术后1周r=0.628,P<0.01;术后3个月r=0.835,P<0.01);Verisyse植入术后3个月的HFC及调节力均较术后1周的HFC及调节力有明显提高。结论高度近视患者有晶状体眼人工晶状体植入有利于术后睫状肌收缩能力及调节力的提高。     

Peripheral refraction and the development of refractive error: a review

It has been suggested that emmetropic and low‐hyperopic eyes in which the refractive error in the periphery of the visual field is relatively hyperopic with respect to the axial refraction may be at greater risk of developing myopia than eyes with similar refractions but relatively myopic peripheral refractive errors. The animal and human evidence to support this hypothesis is reviewed. The most persuasive studies are those in which emmetropization has been shown to occur in infant rhesus monkeys with ablated foveas but intact peripheral fields, and the demonstration that, in similar animals, lens‐induced relative peripheral hyperopia produces central axial myopia. Evidence for emmetropization in animals with severed optic nerves suggests that emmetropization is primarily controlled at the retinal level but that the higher levels of the visual system play a significant role in refining the process: there appear to be no directly equivalent human studies. Since any contribution of the higher centres to the control of refractive development must depend upon the sensitivity to defocus, the results of human studies of the changes in depth‐of‐focus across the field and of the contribution of the retinal periphery to the accommodation response are discussed. Although peripheral resolution is relatively insensitive to focus, this is not the case for detection. Moreover accommodation occurs to peripheral stimuli out to a field angle of at least 10 deg, and the presence of a peripheral stimulus can influence the accommodation to a central target. Although the basic hypothesis that a relatively hyperopic peripheral refractive error can drive the development of human myopia remains unproven, the available data support the possibility of an interaction between the states of focus on axis and in the periphery.     

The repeatability and validity of dynamic retinoscopy in assessing the accommodative response

Dynamic retinoscopy (DR) is an objective technique that has been used successfully to examine accommodative function of non-communicative patients. However, there are few studies examining its repeatability and validity. This paper addresses the repeatability and validity of a form of DR (a modified Nott technique), by comparing results to the Shin-Nippon SRW-5000 Autorefractor whose validity and repeatability have previously been demonstrated. Accommodative responses of 41 subjects (aged 6-43 years) were assessed using DR and the Shin-Nippon SRW-5000 Autorefractor. Three different target demands were used (10, 6 and 4 D). DR was shown to be repeatable for all target demands (paired t-test, p > 0.05). The results demonstrated good agreement between the autorefractor and DR. The results of the present study suggest that DR is a repeatable and valid objective technique for assessing accommodative function.     

The relationship between pupillary baseline manipulated by mental effort or luminance and subsequent pupillary responses

Measuring pupillary response is a prevalent technique to evaluate mental states. It is indispensable to conduct a correction procedure for the pupillary baseline to get a meaningful conclusion from the pupillary response. However, the relationship between pupillary baseline and subsequent stimulus-evoked pupillary response varies among studies. In this study, we used the subtractive and proportional baseline corrections to analyze the results. Furthermore, we manipulated the pupillary baseline through mental effort or luminance in the baseline period and investigated whether the subsequent stimulus-evoked pupillary responses were affected. We found that the mental effort–evoked pupillary response was attenuated with a larger pupillary baseline manipulated by a higher mental effort, whereas it was unaffected with the baseline manipulated by luminance. Also, the luminance-evoked pupillary response was attenuated with a smaller pupillary baseline manipulated by a brighter disk, whereas it was unaffected with the baseline manipulated by mental effort. The results could be obtained from subtractive and proportional baseline corrections. Our results suggest that mental effort manipulated pupillary baseline interacts with the subsequent mental effort elicited pupillary response, but not with the luminance elicited pupillary response; the luminance manipulated pupillary baseline interacts with the subsequent luminance elicited pupillary response, but not with the mental effort elicited pupillary response. It is important to consider the ways of controlling the pupillary baseline and subsequent pupillary response simultaneously.     

儿童远视和近视眼睫状肌麻痹前后各屈光成分的变化

目的通过测量比较儿童远视和近视眼睫状肌麻痹前后各屈光成分的变化,探讨调节对其屈光成分的影响。方法对520例3～12岁儿童使用1%阿托品散瞳验光,睫状肌麻痹前后均采用光学相干生物测量仪（Zeiss IOL Master）测量眼轴长度、角膜屈光力（K1、K2）、前房深度。对其中远视646眼、近视221眼的睫状肌麻痹前后各屈光成分测量值进行统计对照分析。结果①儿童远视眼睫状肌麻痹后眼轴变短（P=0.01）,角膜屈光力变小（K1P=0.01;K2P=0.04）,前房深度加深（P=0.00）。②儿童近视眼睫状肌麻痹后前房深度加深（P=0.00）,眼轴长度、角膜屈光力无变化。结论儿童远视眼睫状肌麻痹后眼轴变短,角膜屈光力变小,前房加深;儿童近视眼睫状肌麻痹后前房加深,而眼轴长度、角膜屈光力无变化。     

The prevalence of vision impairment and refractive error in 3654 first year students at Tianjin Medical University

AIM: To determine the prevalence of vision impairment (VI) and refractive error in first year university students at the Tianjin Medical University. METHODS: This is a cross-sectional observational cohort study of VI and refractive error among first year university students at the Tianjin Medical University. The first year university students were involved in this study and were given a detailed questionnaire including age, birth date, and spectacle wearing history. A standardized ophthalmologic examination including visual acuity (VA), slit-lamp examination, non-cycloplegic auto-refraction, objective refraction, fundus photography, and examination of their spectacles were recorded. RESULTS: A total of 3654 participants were included in this study. Totally 3436 (94.03%) individuals had VI in this population. Totally 150 (4.10%) individuals had VI due to ocular disease, including amblyopia, congenital cataract, retinal atrophy or degeneration, strabismus, congenital nystagmus, refractive surgery orthokeratology. Totally 3286 (89.93%) subjects had VI due to refractive error. Only 218 (5.97%) students were emmetropia. Moreover, refractive error was the main cause for the VI (95.63%). Totally 3242 (92.52%) students were myopia and the prevalence of mild, moderate, and high myopia subgroup was 27.05%, 44.35%, and 21.26% respectively. Totally 44 (1.29%) subjects were hyperopic. The rates of uncorrected visual acuity (UCVA), presenting visual acuity (PVA) and best corrected visual acuity (BCVA) which better than 20/20 in both eyes were 5.65%, 22.32% and 82.13% respectively. The rates of correction, under correction and well correction in myopia subjects were 82.73%, 84.39% and 15.61%, respectively. CONCLUSION: We present a high prevalence of refractive errors and high rates of under correction refractive error among first year university students. These results may help to promote vision protection work in young adults.     

Higher order aberrations,refractive error development and myopia control: a review

Evidence from animal and human studies suggests that ocular growth is influenced by visual experience. Reduced retinal image quality and imposed optical defocus result in predictable changes in axial eye growth. Higher order aberrations are optical imperfections of the eye that alter retinal image quality despite optimal correction of spherical defocus and astigmatism. Since higher order aberrations reduce retinal image quality and produce variations in optical vergence across the entrance pupil of the eye, they may provide optical signals that contribute to the regulation and modulation of eye growth and refractive error development. The magnitude and type of higher order aberrations vary with age, refractive error, and during near work and accommodation. Furthermore, distinctive changes in higher order aberrations occur with various myopia control treatments, including atropine, near addition spectacle lenses, orthokeratology and soft multifocal and dual-focus contact lenses. Several plausible mechanisms have been proposed by which higher order aberrations may influence axial eye growth, the development of refractive error, and the treatment effect of myopia control interventions. Future studies of higher order aberrations, particularly during childhood, accommodation, and treatment with myopia control interventions are required to further our understanding of their potential role in refractive error development and eye growth.     

The prevalence of uncorrected refractive error in urban, suburban, exurban and rural primary school children in Indonesian population

Uncorrected refractive error (URE) is a major health problem among school children. This study was aimed to determine the frequency and patterns of URE across 4 gradients of residential densities (urban, exurban, suburban and rural). This was a cross-sectional study of school children from 3 districts in Yogyakarta and 1 district near Yogyakarta, Indonesia. The information regarding age, sex, school and school grader were recorded. The Snellen’s chart was used to measure the visual acuity and to perform the subjective refraction. The district was then divided into urban, suburban, exurban and rural area based on their location and population. In total, 410 school children were included in the analyses (urban=79, exurban=73, suburban=160 and rural=98 school children). Urban school children revealed the worst visual acuity (P<0.001) and it was significant when compared with exurban and rural. The proportion of URE among urban, suburban, exurban and rural area were 10.1%, 12.3%, 3.8%, and 1%, respectively, and it was significant when compared to the proportion of ametropia and corrected refractive error across residential densities (P=0.003). The risk of URE development in urban, suburban, exurban, and rural were 2.218 (95%CI: 0.914-5.385), 3.019 (95%CI: 1.266-7.197), 0.502 (95%CI: 0.195-1.293), and 0.130 (95%CI:0.017-0.972), respectively. Urban school children showed the worst visual acuity. The school children in urban and suburban residential area had 2 and 3 times higher risk of developing the URE.