Presbyopia toward the end of the 20th century

Recent advances in our understanding of the anatomy and physiology of accommodation have contributed to current concepts of the possible constituent factors in presbyopia, largely supplanting the long-held belief that presbyopia is due to sclerosis of the crystalline lens. In this review, the author examines epidemiologic, basic scientific, and clinical evidence for a multifactorial decrease in accommodative amplitude with age. Methods of measurement, oculomotor effects of presbyopia, and approaches to correcting it are also considered.     

The aetiology of presbyopia: a summary of the role of lenticular and extralenticular structures

Presbyopia is a condition of age rather than ageing and, as such, is devolved from the lamentable situation where the normal age-related reduction in amplitude of accommodation reaches a point when the clarity of vision at near cannot be sustained for long enough to satisfy an individual's requirements. Most of our facility to accommodate has been lost by 55 years-of-age and subsequent deterioration in visual performance at near is attributable to characteristics of senescent vision familiar to the optometrist. Our understanding of the cause of presbyopia has then to be derived principally from our understanding of the mechanism of accommodation in young eyes. Hermann von Helmholtz did much to clarify these mechanisms, but despite much research in the 100 years since his death, there is still no consensus on their precise nature. This paper presents a summary of issues, past and present, which have figured in the literature on the physiology of accommodation and presbyopia, and confirms that the pathophysiology of presbyopia is likely to result from deterioration in structure and function of a number of inter-related tissues. Changes in crystalline lens dimensions with age, the associated change in geometry of zonular attachments, and changes in viscoelastic properties of the lens capsule and lens matrix would, however, appear to be the principal correlates for the onset of presbyopia. Recent models of the biomechanics of accommodation have drawn attention to the feasibility of extralenticular contributions to presbyopia and have examined properties of the elasticity and leverage provided by posterior, anterior and tensile fibre systems. The stimulus for innovation in the correction and remediation of presbyopia is strong as at least 98% of individuals from the industrialised nations will survive until 45 years-of-age; it is salutary to note that the survival rate 100 years ago was only 60%.     

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.     

Akkommodation und Presbyopie

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.     

Artificial crystalline lens

If presbyopia is caused by hardening of the crystalline lens, replacing it with a material with mechanical properties similar to the young crystalline lens should restore accommodative ability. Such a silicone material has been developed. Refilling the capsular bag with this material results in 3 to 5 D of accommodation in primates in response to pilocarpine.     

Crystalline lens accommodation and anterior chamber depth

Using paraxial equations, the change in dioptric power of the crystalline lens required to image objects at given distances from the eye, on the retina, is calculated. This shows that the depth of the anterior chamber affects crystalline lens accommodation more than other variables. The relationship between anterior chamber depth and presbyopia, and a possible geographical aspect, are discussed.     

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.     

Does sunlight cause premature aging of the crystalline lens?

Premature onset of presbyopia may be an early sign of cataractous lenticular changes. For many years ultraviolet radiation (UVR) has been suspected as a major factor in the degradation of the crystalline lens. Controlled laboratory studies have demonstrated that UVR does cause opacities that closely resemble those naturally occurring in the aging process. Is it true that environmental UVR is also the prime contributor in the deleterious lenticular changes that may begin with premature presbyopia, as has been postulated? This review examines the evidence supporting this and other suggested causes of early presbyopia, including genetics, nutrition, toxins, and environmental temperature. Of all factors reported to affect the onset of presbyopia, UVR has the most scientific support, but further research is necessary to conclusively establish this link.     

Deterioration of amplitude of the accommodation with age and its possible restoration in the intraocular lens implanted eye]

This study aimed to determine whether pseudophakia which have deteriorated amplitude of accommodation with age, i.e., presbyopia and which received implantation of refractively changeable intraocular lenses after cataract extraction are able to regain accommodative function. According surveys on aging in the literature, functional deterioration of the ciliary muscle and the zonular fiber is not so striking compared to the changes of crystalline lens material and capsule. Consequently the artificially pseudophakic eye can be expected to regain accommodative function when the crystalline lens material could be replaced by an appropriately visco-elastic material before 80 years of age when the crystalline lens capsule still retain its elasticity.     

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.     

Presbyopia and cataract: A question of heat and time

Not only are human lenses different in many ways from those of non-primates, they also undergo dramatic changes with age. These age-dependent alterations lead to perturbations in the properties of older lenses, and ultimately to disturbances in visual function, which typically become apparent at middle age. Recent data suggest that many, if not all, of these age-dependent features can be traced to the lack of macromolecular turnover in the lens and to the inexorable modifications to proteins and membrane components over a period of decades. Exposure of lenses to heat can reproduce many of these alterations, suggesting that long-term incubation at body temperature may be an important factor in aging the human lens. Two conclusions flow from this. Firstly, the human lens may be an ideal tissue for studying macromolecular aging in man. Secondly, it will be extremely challenging to examine the origin of human age-related conditions, such as presbyopia and nuclear cataract, using traditional laboratory animals.Characterising the unfolding and decomposition of long-lived macromolecules appears to provide the key to understanding the two most common human lens disorders: presbyopia and age-related nuclear cataract.     

fs-Laser induced elasticity changes to improve presbyopic lens accommodation

Background According to the Helmholtz theory of accommodation, one of the major reasons for the development of presbyopia is the progressive sclerosis of the crystalline lens. However, both the ciliary muscle and the lens capsule stay active and elastic. Thus, the concept for regaining the deformation-ability of the crystalline lens is to create microincisions inside lens tissue to achieve gliding planes. Methods For the preparation of the microincisions, near-infrared femtosecond laser pulses are used, generating laser-induced optical breakdowns. Different cutting patterns were performed, and the elasticity regain of the lenses were measured with Fisher’s spinning test for thickness determination. Results The creation of gliding planes inside lens tissue shows very good results in terms of increasing the deformation-ability. The optimization of laser parameters leads to a minimally invasive surgery with no remarkable side effects like residual gas bubbles. Furthermore, ex vivo elasticity measurements of untreated and treated pig lenses show an improvement in the flexibility of the lens. The deformation-ability increases up to 26% with a very low standard deviation (1.6%) and a high significance (p < 0.05). Conclusion Generating particular cutting patterns inside lens tissue can increase the deformation-ability of the crystalline lens. Thus, it might be one possible way to treat presbyopia. Parts of this work were supported by the German Ministry of Education and Research (BMBF), FKZ 13N8712 and FKZ 13N8709.     

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.     

Non-invasive, spatially resolved determination of tissue properties of the crystalline lens with regard to rheology, refractive index, density and protein concentration by using Brillouin spectroscopy

The confocal Brillouin spectroscopy is an innovative measurement method that allows the non-invasive determination of the rheological properties of materials. Its application in ophthalmology can offer the possibility to determine in-vivo the deformation properties of sections of transparent biological tissue such as the cornea or eye lens with spatial resolution. This seems to be a promising approach concerning current presbyopia research. Due to the spatially resolved detection of the viscoelastic lens properties, a better understanding of the natural aging process of the lens and the influences of different lens opacities on the stiffness is expected. From the obtained spectral data the relative protein levels, the relative refractive index profile and the relative density profile within the lens tissue can be derived in addition. A measurement set-up for confocal Brillouin microscopy based on spectral analysis of spontaneous Brillouin scattering signals by using a high-resolution dispersive device is presented. First in-vitro test results on animal and human lenses are presented and evaluated concerning their rheological significance. These data are compared with known research results.     

Biometric, optical and physical changes in the isolated human crystalline lens with age in relation to presbyopia.

The biometric, optical and physical properties of 19 pairs of isolated human eye-bank lenses ranging in age from 5 to 96 years were compared. Lens focal length and spherical aberration were measured using a scanning laser apparatus, lens thickness and the lens surface curvatures were measured by digitizing the lens profiles and equivalent refractive indices were calculated for each lens using this data. The second lens from each donor was used to measure resistance to physical deformation by providing a compressive force to the lens. The lens capsule was then removed from each lens and each measurement was repeated to ascertain what role the capsule plays in determining these optical and physical characteristics. Age dependent changes in lens focal length, lens surface curvatures and lens resistance to physical deformation are described. Isolated lens focal length was found to be significantly linearly correlated with both the anterior and posterior surface curvatures. No age dependent change in equivalent refractive index of the isolated lens was found. Although decapsulating human lenses causes similar changes in focal length to that which we have shown to occur when human lenses are mechanically stretched into an unaccommodated state, the effects are due to nonsystematic changes in lens curvatures. These studies reinforce the conclusion that lens hardening must be considered as an important factor in the development of presbyopia, that age changes in the human lens are not limited to the loss of accommodation that characterizes presbyopia but that the lens optical and physical properties change substantially with age in a complex manner.     

Involutional changes in the human eye accommodative apparatus as evidenced by ultrasound biometry and biomicroscopy

The paper presents the results of studying involutional changes in the accommodative apparatus of the eye in presbyopia by ultrasound biometry and biomicroscopy. Persons aged 40-70 years who had presbyopia and emmetropic refraction and without concomitant eye disease were examined. In addition to routine studies, all the examinees underwent ultrasound biomicroscopy and ultrasound biometry. The age-related lenticular enlargement was established to be accompanied by a considerable reduction in the orbicular space of the posterior chamber of the eye to the extent of its transformation to a slotted space. The presbyopic patients were found to have a significantly diminished tone in the middle and posterior portions of the lenticular ligamentous apparatus to the extent of its sag, with the altered direction of their passage between the crystalline lenticular equator and the ciliary body crown, i. e. from meridional to radial. The revealed significant age-related topographic and anatomic changes in the orbicular portion of the posterior chamber of eye and in ligamentous tone, which are associated with the involutional increase in the size of the crystalline lens point to the great importance of decreasing the working accommodation distance in the development of presbyopia.     

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.     

Femtosecond laser induced flexibility change of human donor lenses

Background

According to the Helmholtz theory of accommodation the loss of accommodation amplitude is caused by the growing sclerosis of the crystalline lens, whereas the ciliary muscle and the lens capsule are mainly uneffected by age. A permanent treatment method for presbyopia which offers a dynamic accommodation ability is a recent field of study. The concept followed in this paper uses femtosecond laser pulses to potentially overcome the loss of deformation ability of the crystalline lens by creating gliding planes inside the lens tissue to improve its flexibility.

Methods

The aim of the study is to show that the flexibility of human donor lenses can be increased by applying tightly focused near infrared femtosecond laser pulses into the lens tissue. Thereby the tissue is separated by the photodisruption effect. A certain pattern of gliding planes is cut inside the tissue of 41 human donor lenses and the deformation ability of the lenses are compared using the Fisher spinning test before and after laser treatment.

Results

The laser treatment results in an increased deformation ability of the crystalline lens. The lens a-p thickness increases on average by after the treatment. The Fisher spinning test shows an increase of 16% in deformation ability of the lens at a rotational speed of 1620 rpm.

Conclusion

The creation of gliding planes with a fs laser inside the crystalline lens tissue can change the deformation ability of the lens. This might be an indication for a possible method to treat presbyopia in future.     

Grundlagen des refraktiven Linsenaustausches

Removal of the crystalline lens and its replacement by an intraocular lens (IOL) is known as refractive lens exchange (RLE). RLE is performed to correct high ametropia or aniseikonia. Crystalline lens removal always leads to a complete loss of accommodation; therefore, RLE should mainly be used for patients with beginning or existing presbyopia. RLE patients usually have a good best-corrected visual acuity, which is the default value for the postoperative uncorrected visual acuity. To reach this goal, microincisional and astigmatism-neutral implantation techniques as well as special IOL optic designs are available. These optic designs offer each patient individualized best visual performance. In spite of the high requirements for postoperative optical quality, RLE can lead to an effective, safe, predictable, and stable outcome with a low risk of complications.     

Corrección de la presbicia tras cirugía cristaliniana. ¿Dónde nos encontramos en 2020?

IntroductionPresbyopia is the progressive and irreversible loss of accommodation due to aging. It is one of the main causes of loss of quality of life in people from 45 years of age, due to the, often novel, dependence on spectacles. The eagerness to correct it by ophthalmologists impulsed by the desire of millions of people who suffer from it, has become one of the main drivers for the development of intraocular lens (IOL) technology over the last twenty years.Material and methodsThis review briefly presents the different alternatives that have allowed us to improve the crystalline lens surgical approach of presbyopia; from monofocal lenses and monovision technique, accommodative, refractive, and diffractive multifocal lenses, and finally the most recent extended depth of focus/field lenses known as EDOFs.ResultsEach IOL has its advantages, limitations and disadvantages. Furthermore, there is no single lens that suits the needs of all patients.ConclusionsIt is necessary to know the variety of lenses available, and to have an in-depth understanding of their optical properties, as well as the impact that these will have later on their clinical performance and on the visual quality of the patients. This should help us to select the best alternative for each of them.