Accommodation and presbyopia : part 2: surgical procedures for the correction of presbyopia

There are two basic approaches for the surgical correction of presbyopia: increasing depth of focus (e.g. by means of multifocal laser abrasion of the cornea), Or restoring accommodation in the sense of a dynamic change in ocular refraction (accommodative intraocular lenses, scleral expansion). Pseudoaccommodative procedures are able to achieve satisfactory near vision, albeit at the price of lower performance in the intermediate range and decreased image quality. The restoration of accommodation remains problematic, partly because the mechanism of accommodation and the development of presbyopia are still not fully understood. Some surgical procedures are based on concepts, the validity of which is not confirmed or which even contradict experimental evidence. Thus, it is necessary to assess the results and presumed mechanisms critically and objectively.     

老视的角膜矫正手术

老视是随着年龄增长、调节能力丧失出现视近物困难的一种生理现象,发病机制尚不明确。人口老龄化使老视人口及老视矫正的需求逐渐增多,老视的手术矫正方法正成为眼科医师关注的热点。随着技术和材料的不断发展,出现了多样化的老视矫正手术,包括经角膜老视矫正手术、晶状体老视矫正手术和巩膜老视矫正手术。尽管还没有一种完美的老视矫正手术能真正恢复眼的调节功能,现有的手术已取得一些临床效果。现对老视的角膜手术矫正方法做一综述。     

老视理论及治疗进展

老视是一种常见的眼部退行性病变,表现为年龄相关性调节力下降,它影响到每一个老年人。随着全新的Schachar调节理论的提出以及传统理论的发展,近年来出现了多种老视治疗方法。目前除了通过各种框架眼镜和接角镜来矫正老视,还可以应用手术方法如前睫状区巩膜切开样(AGS)以及巩膜扩张(SRP)来恢复调节能力。采用人工晶状体植入形成单眼视,多焦点人工晶状体,可调节型人工晶状体,LASIK手术也都是可行的老视治疗措施。本文总结了目前有关老视的各种机制和治疗方法。     

老視理論及治療進展

老視是一種常見的眼部退行性病燮,表現為年齡相關性調節力下降,它影響到每一個老年人.隨着全新的Schachar調節理論的提出以及傳統理論的發展,近年來出現了多種老視治瘵方法.目前除了通過各種框架眼鏡和接觸鏡來矯正老視,還可以應用手術方法如前睫狀區鞏膜切開術(ACS)以及鞏膜擴張(SRP)來恢復調節能力.采用人工晶狀體植入形成單眼視,多焦黠人工晶狀體,可調節型人工晶狀體,LASIK手術也都是可行的老視治瘵措施.本文總結了目前有關老視的各種機制和治瘵方法.     

准分子激光矫正老视的研究进展

老视是一种随着年龄增长而调节力逐渐下降的自然现象。 目前老视的机制尚未完全阐明,因此多种手术方法用于改善老视眼的调节。其中准分子激光手术成为矫正老视一种重要方法,而且其安全性及有效性不断进步。本文就老视的发生机制、治疗方法以及准分子激光矫正老视的手术方式和切削模式进行综述。     

老视矫正手术方法的现状和发展趋势

老视是因年龄相关性调节幅度的下降使得近阅读渐渐困难的一种生理老化现象。现阶段老视矫正的主流方式是配戴单焦框架眼镜、双焦框架眼镜和渐变多焦点眼镜。目前所有针对老视的手术方法都未能带来持久的真正生理意义上的调节改善,本文就目前各种老视矫正手术方法（包括单眼视方法的、施于角膜的、施于巩膜的与施于晶状体的）的现状与发展趋势做一综述。     

老视矫治手术治疗最新进展

老视是一种年龄相关的生理性老化现象.老视手术治疗已逐渐成为屈光手术最终需要面对的挑战.目前,其手术矫治包括眼外(施于角膜或巩膜)和眼内(晶状体置换或施于晶状体本身)两大策略,如角膜准分子激光手术、热传导成形术、飞秒激光基质内环形切开术、角膜植入物手术、各种多焦人工晶状体植入术、可调节人工晶状体植入术、晶状体软化术、巩膜扩张术等.各种手术方法均存在自身的优势和不足.本文就目前现有和近期即将问世的老视治疗方法及其被关注的问题作一综述.     

The mechanism of presbyopia

Accommodation in humans refers to the ability of the lens to change shape in order to bring near objects into focus. Accommodative loss begins during childhood, with symptomatic presbyopia, or presbyopia that affects one's day to day activities, striking during midlife. While symptomatic presbyopia has traditionally been treated with reading glasses or contact lenses, a number of surgical interventions and devices are being actively developed in an attempt to restore at least some level of accommodation. This is occurring at a time when the underlying cause of presbyopia remains unknown, and even the mechanism of accommodation is occasionally debated. While Helmholtz' theory regarding the mechanism of accommodation is generally accepted with regard to broad issues, additional details continue to emerge. Age-related changes in anterior segment structures associated with accommodation have been documented, often through in vitro and/or rhesus monkey studies. A review of these findings suggests that presbyopia develops very differently in humans compared to non-human primates. Focusing on non-invasive in vivo human imaging technologies, including Scheimpflug photography and high-resolution magnetic resonance imaging (MRI), the data suggest that the human uveal tract acts as a unit in response to age-related increasing lens thickness and strongly implicates lifelong lens growth as the causal factor in the development of presbyopia.     

Surgical correction of presbyopia

There are a lot of surgical procedures to correct refractive errors, but the surgical correction of presbyopia is still a problem. In this paper the authors present surgical procedures, which can be used to correct presbyopia. There are three groups of surgery: the corneal, scleral and intrabulbar procedures.     

Lens Refilling

Cataract surgery has developed into a very safe and highly reproducible procedure but the ultimate goal to also restore physiological accommodation has not yet been achieved. A variety of accommodative intraocular lenses (IOLs) and surgical techniques have been suggested to cure presbyopia but all showed only poor accommodative effects by objective measurements. Complete lens refilling with flexible polymers might be an interesting alternative. Recent investigations on accommodation and presbyopia have given support to the lens refilling method. After development of suitable surgical techniques and filling materials only secondary cataract formation and the unsolved intraoperative control of refraction restrict the clinical use of this technique.     

Physiopathology in accommodation and presbyopia, clinical and surgical approach

Accommodation is a complex of phenomena by which the refracting power of the eye changes for focusing on near vision. Accommodative amplitude declines progressively with increasing age. Until today, this phenomenon called presbyopia was explained by Helmholtz's hypothezis which involves only ciliary muscle. It seems that in accommodation are involved, besides the ciliary muscle, the lens and extraventicular elastic components, biophysical dynamics of the lens capsule, vitreous, iris. According with the role of these factors and theirs pathophysiological implications, new surgical technique has developed to reverse presbyopia in the human eye (Surgical reversal presbyopia, Anterior ciliary sclerotomy) and offers a potential for understanding ocular hypertension and treatment of primary open-angle glaucoma.     

Surgical treatment of presbyopia: scleral, corneal, and lenticular

PURPOSE OF REVIEW: Having solved most of the problems concerning myopia, hyperopia, and astigmatism, it is perfectly understandable that the surgical treatment of presbyopia should be next on the agenda. It is a new challenge where every possible aspect is explored. RECENT FINDINGS: The past five years have been troubled by the debate over von Helmholtz theory on accommodation. Numerous investigations have been carried out on the primate and humans using various procedures. The more we learn about this mechanism, the nearer we will be to finding a solution to presbyopia. It appears essential to refer to recent works confirming von Helmholtz theory. Therefore, understanding presbyopia requires a great deal of optical ingenuity such as monovision, scleral modifications, which still remain controversial, or clear lens exchange or refilling. SUMMARY: In 2003, with all the different techniques available, the surgeon has a wide choice to offer patients that are satisfactory from a practical, theoretical, and ethical point of view. However, these techniques must only be proposed once the patients have been carefully informed.     

Theoretical basis for the scleral expansion band procedure for surgical reversal of presbyopia (SRP)

A new technique, the scleral expansion band procedure, has been developed for the surgical reversal of presbyopia. The effects of scleral expansion band are based on a recently developed theory by Schachar, which states that the crystalline lens is under increased equatorial zonular tension during accommodation. An understanding of demonstrable clinical effects of the scleral expansion band procedure, based on Schachar's theory, requires a revision of historically held views concerning the mechanism of accommodation.     

Corneal surgical correction of presbyopia

A new relaxing-incision surgical procedure was used for the correction of presbyopia and/or hyperopia. The technique consisted of 3 arcuate incisions of 60°, separated by nonincised spaces of 60°, intercalated among themselves. In all 4 reported cases of the total 15, an inferior multifocal cornea was created. Although a larger number of cases are needed, it is clearly possible to correct presbyopia on the cornea without any degree of accommodation.     

Cause and treatment of presbyopia with a method for increasing the amplitude of accommodation.

To understand the mechanism and cause of accommodation and presbyopia, the sclera in the region of the ciliary body of presbyopic patients was expanded. The amplitude of accommodation was increased in all presbyopic patients. A unique hypothesis of accommodation based on increased zonular tension is presented, which when applied clinically, results in a treatment for presbyopia.     

Comparison of the behavior of natural and refilled porcine lenses in a robotic lens stretcher

The mechanism by which the eye dynamically changes focal distance (accommodation), and the mechanism by which this ability is lost with age (presbyopia), are still contested. Due to inherent confounding factors in vivo, in vitro measurements have been undertaken using a robotic lens stretcher to examine these mechanisms as well as the efficacy of lens refilling - a proposed treatment for presbyopia. Dynamic forces, anterior and posterior curvatures, and lens thickness are all correlated for young natural and refilled porcine lenses. Comparisons are made to lenses refilled with a homogeneous polymer system. The amplitude of accommodation of the young porcine lens is very small such that it may be a suitable model for presbyopia. The behavior of refilled lenses was highly dependent on the refill volume. The volume could be tuned to maximize accommodative amplitude in the refilled lens.     

Restoration of accommodation

PURPOSE OF REVIEW: This review examines the current status of accommodation restoration concepts with reference to the recent, published peer-reviewed literature with an emphasis on physiological aspects of accommodation and presbyopia. RECENT FINDINGS: The mechanisms of accommodation and the causes of presbyopia are described. The physiological amenability of the accommodative structures in the presbyopic eye to accommodation restoration is discussed. General theoretical concepts of accommodation restoration are introduced. The methods that have been used to assess accommodation restoration, including the use of animal models, drug stimulated accommodation, subjective near-vision tests and objective measurements, are reviewed. SUMMARY: While physiological and clinical evidence supports the notion that accommodation can be restored to the presbyopic eye, progress in this potentially exciting area is hindered by the scarcity of good, large-scale clinical studies using objective measurement techniques to evaluate the outcomes of accommodation restoration concepts.     

Accommodation and presbyopia : part 1: physiology of accommodation and development of presbyopia

Accommodation is a dynamic change in the dioptric power of the eye. According to the widely accepted and experimentally confirmed theory of Helmholtz, it is achieved by release of zonular tension with contraction of the ciliary muscle and consecutive modelling of the shape of the crystalline lens by the elastic lens capsule. The ability to accommodate is gradually lost with age (presbyopia). Because of difficulties in examining the accommodative apparatus in vivo, many theories, in part contradictory, about the mechanism of accommodation and the origin of presbyopia have been developed. In recent years experimental studies have greatly increased the knowledge about the acommodative apparatus and suggest a multifactorial aetiology of presbyopia. A better understanding of the physiology of accommodation and presbyopia can contribute to the development of effective treatments.     

Presbyopietherapie mit Femtosekundenlaser

Presbyopia is by far the most common refractive error worldwide, with no permanent therapeutic option available. All efforts to restore accommodation by the use of surgery have not led to a generally accepted therapy. However, there is evidence from an animal model that the use of a femtosecond (fs) laser might influence the modulus of elasticity in the lens. Fs-laser impulses can create intralenticular disruption in animal eyes as well as human cadaver lenses and improve elasticity. The concept of treating presbyopia with fs-laser requires a new, complex theory combining the optical and the mechanical aspects of accommodation in the eye. Diagnostic tools for measuring optical change in power and geometrical modification as the eye views from far to near are needed to obtain objective clinical data. A non-invasive treatment of presbyopia to restore accommodation might be possible in the future.     

The effect of incipient presbyopia on the correspondence between accommodation and vergence

PURPOSE: To investigate the accommodation-convergence relationship during the incipient phase of presbyopia. The study aimed to differentiate between the current theories of presbyopia and to explore the mechanisms by which the oculomotor system compensates for the change in the accommodation-convergence relationship contingent on a declining amplitude of accommodation. METHODS: Using a Canon R-1 open-view autorefractor and a haploscope device, measurements were made of the stimulus and response accommodative convergence/accommodation ratios and the convergence accommodation/convergence ratio of 28 subjects aged 35-45 years at the commencement of the study. Amplitude of accommodation was assessed using a push-down technique. The measurements were repeated at 4-monthly intervals over a 2-year period. RESULTS: The results showed that with the decline in the amplitude of accommodation there is an increase in the accommodative convergence response per unit of accommodative response and a decrease in the convergence accommodation response per unit of convergence. CONCLUSIONS: The results of this study fail to support the Hess-Gullstrand theory of presbyopia in that the ciliary muscle effort required to produce a unit change in accommodation increases, rather than stays constant, with age. Data show that the near vision response is limited to the maximum vergence response that can be tolerated and, despite being within the amplitude of accommodation, a stimulus may still appear blurred because the vergence component determines the proportion of available accommodation utilised during near vision.