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: mechanism and measurement

A clear understanding of the anatomy of accommodative structures, the mechanism of accommodation, and the causes of presbyopia is necessary to understand whether accommodation may be restored to the presbyopic eye. Not withstanding the significant challenges that are faced owing to age-related changes in the eye, theoretically, it may be possible to restore accommodation to a presbyopic eye with an artificial accommodative intraocular lens.     

Scleral expansion surgery does not restore accommodation in human presbyopia.

OBJECTIVE: To determine the efficacy of scleral expansion surgery in the treatment of human presbyopia. DESIGN: Experimental study. PARTICIPANTS: Three preoperative presbyopic subjects, three postoperative presbyopic subjects, and three young control subjects. METHODS: Accommodative responses were recorded by an infrared dynamic optometer while subjects viewed an accommodative stimulus that stepped from 0 to 4 diopters in 1-diopter steps. MAIN OUTCOME MEASURES: Dynamic infrared optometer recordings of accommodation. RESULTS: Presbyopic patients showed no evidence of accommodation after scleral expansion surgery. CONCLUSIONS: If presbyopic patients read smaller letters at near after scleral expansion surgery than they were able to read prior to the surgery, then an explanation other than the restoration of accommodation needs to be found.     

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。     

Polymer refilling of presbyopic human lenses in vitro restores the ability to undergo accommodative changes

PURPOSE: Because presbyopia is thought to be accompanied by increased lens sclerosis this study was conducted to investigate whether refilling the capsule of the presbyopic human lens with a soft polymer would restore the ability of the lens to undergo accommodative changes. METHODS: Accommodative forces were applied to natural and refilled lenses by circumferential stretching through the ciliary body and zonular complex. Nine natural lenses and 10 refilled lenses from donors ranging in age from 17 to 60 years were studied. Two refill polymers with a different Young's modulus were used. The lens power was measured by a scanning laser ray-tracing technique, and lens diameter and lens thickness were measured simultaneously while the tension on the zonules was increased stepwise by outward pull on the ciliary body. RESULTS: In the natural lenses the older lenses were not able to undergo power changes with stretching of the ciliary body, whereas in the refilled lenses, all lenses showed power changes comparable to young, natural lenses. The refilled human lenses had a higher lens power than the age-matched natural lenses. The Young's modulus of the polymers influenced the lens power change when measured with the ciliary body diameter increased by 4 mm. CONCLUSIONS: Refilling presbyopic lenses with a soft polymer enabled restoration of lens power changes with mechanical stretching. Because sclerosis of the lens is an important factor in human presbyopia, refilling the lens during lens surgery for cataract could enable restoration of clear vision and accommodation in human presbyopia.     

Functional presbyopia in a rural Kenyan population: the unmet presbyopic need

Background: Presbyopia is the most common reason for requiring spectacles in low‐income regions, although the unmet need for presbyopic spectacles in these regions is very high. The aim of this study was to estimate the prevalence of presbyopia, and the functional impairment and spectacle use among persons with presbyopia in a rural Kenyan population. Methods: A cross‐sectional study was carried out in the Rift Valley, Kenya. Clusters were selected through probability‐proportionate to size sampling, and people aged ≥50 years within the clusters were identified through compact segment sampling. Within the context of this survey, 130 eligible participants were selected for interview and underwent near‐vision testing. Functional presbyopia was defined as requiring at least +1.00 dioptre in order to read the N8 optotype at a distance of 40 cm in the participant's usual visual state. Participants were corrected to the nearest 0.25 dioptre in order to see N8. Unmet and met presbyopic need, and presbyopic correction coverage were calculated. Results: Functional presbyopia was found in 111 participants (85.4%). Mean age was lower in those with presbyopia (64.1 years vs. 71.5 years, P = 0.004). Increasing degree of addition required to see N8 was significantly associated with increased difficulty with reading (P = 0.04), sewing (P = 0.03), recognizing small objects (P = 0.02) and harvesting grains (P = 0.05). Among participants with functional presbyopia, 5.4% wore reading glasses and 25.2% had prior contact with an eye care professional. The unmet presbyopic need was 80.0%, met presbyopic need was 5.4% and presbyopic correction coverage was 6.3%. Cost was cited as the main barrier to spectacle use in 62% of participants with presbyopia. Conclusion: In low‐income regions, there is a high prevalence of uncorrected presbyopia, which is associated with near‐vision functional impairment. Provision of spectacles for near vision remains a priority in low‐income regions.     

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.     

Relationship between age and presbyopic addition using a sample of 3,645 examinations from a single private practice.

BACKGROUND: This study uses information collected in a private optometric practice to describe the relationship between age and the add power needed to correct presbyopia. METHODS: Computer-assisted data analysis with a database management program, Q&A, and Microsoft Excel was used to assess the relationship between age and presbyopic addition. Data collected from 3,645 examinations by one practitioner in a single private practice--over a period of approximately 23 years--were entered into the database. The patient base was primarily white and about equally divided between the sexes. The practitioner generally used the fused cross cylinder for the tentative presbyopic addition and refined this by patient preference and best visual acuity at near, all using a carefully determined near working distance. RESULTS: The presbyopic addition increased rapidly in patients from ages 40 to 50 years, the rate at age 40 being about 0.22 diopters per year and the average rate during the 40- to 50-year-old decade being about 0.12 diopters per year, or approximately 0.25 diopters every 2 years. After the patient reaches 50 years of age, the presbyopic addition increased more slowly, at the rate of approximately 0.03 diopters per year--or approximately 0.25 diopters in 8 years. CONCLUSIONS: Quantitative data taken from more than 3,600 refractions showed a nearly parabolic relationship between age and presbyopic addition from approximately the age of 40 to 75 years.     

A new method of cornea modulation with excimer laser for simultaneous correction of presbyopia and ametropia

Purpose

To investigate the outcomes of simultaneous correction of presbyopia and ametropia by a bi-aspheric cornea modulation technique, based on the creation of a central area hyperpositive for near vision and leaving the pericentral cornea for far vision in hyperopic, emmetropic, and myopic presbyopic patients.

Setting

Sixty eyes of 30 patients were treated with the PresbyMAX technique by one surgeon (D.U.) at the Eye Hospital Bellevue, Kiel, Germany.

Methods

Twenty eyes with hyperopic presbyopia, 20 eyes with emmetropic presbyopia, and 20 eyes with myopic presbyopia underwent Femto-Lasik, and were assessed up to 6?months postoperatively. All eyes underwent cornea treatment using the PresbyMAX? software, delivering a bi-aspheric multifocal ablation profile developed by SCHWIND eye-tech-solutions (Kleinostheim, Germany). All flaps were created by Ziemer LDV Femtolaser (Port, Switzerland).

Results

The mean binocular distance of uncorrected visual acuity (DUCVA) improved in the hyperopic group from 0.28?±?0.29 logMAR to ?0.04?±?0.07 logMAR, in the emmetropic group from ?0.05?±?0.07 logMAR to 0.02?±?0.11 logMAR, and in the myopic group from 0.78?±?0.27 logMAR to 0.09?±?0.08 logMAR. The mean binocular near uncorrected visual acuity (NUCVA) increased in the hyperopic group from 0.86?±?0.62 logRAD to 0.24?±?0.23 logRAD, and in the emmetropic group from 0.48?±?0.14 logRAD to 0.18?±?0.11 logRAD. The myopic presbyopes showed a decrease of the mean binocular NUCVA from 0.04?±?0.19 logRAD to 0.12?±?0.18 logRAD. The mean postoperative spherical equivalent for distance refraction was ?0.13?±?0.61 D for the hyperopic presbyopia, ?0.43?±?0.35 D for the emmetropic presbyopia, and ?0.68?±?0.42 D for the myopic presbyopia group, whereas the software took aim at ?0.50 D in all groups.

Conclusions

In presbyopic patients without symptomatic cataracts, but refractive errors, PresbyMAX? will decrease the presbyopic symptoms and correct far distance refraction in the same treatment, offering spectacle-free vision in daily life in most of the treated patients. Further investigation is necessary to evaluate the overall benefit of this procedure.     

Presbyopia compensation with a quartic axicon.

PURPOSE: The purpose of this study was to evaluate the performance of quartic axicons for presbyopia compensation. The working principle relies on profiting the high depth of focus of the axicons to supplement the reduced accommodation amplitude of presbyopes. METHODS: We present the design equations of a particular kind of axicon to compensate a general presbyopia condition using simultaneous vision. A rotationally symmetric polynomial of fourth-order, corresponding to the well-known Seidel spherical aberration term, was chosen as its refractive profile. To validate its performance, we computed the retinal images with Stiles-Crawford apodization for a presbyopic eye compensated with this quartic axicon and compared them with those obtained without compensation or with other available solutions based on the simultaneous vision principle. RESULTS: The quartic axicon provides an important improvement of the image quality for intermediate distance vision in comparison with conventional bifocal and trifocal solutions. The image quality, however, is still not optimum for all distances. CONCLUSIONS: The results show the usefulness of the proposed approach and point out the need for developing further adapted optimizations.     

Soft multifocal simultaneous image contact lenses: a review

Soft multifocal simultaneous image contact lenses have boomed in recent years due to the growing number of presbyopic patients demanding visual solutions, allowing them to maintain their current standard of living. The concept of ‘simultaneous image’ is based on blur interpretation and/or blur tolerance of superimposed multiple images on the retina formed by various powers of a contact lens. This is the basis for a specific type of multifocal contact lens developed for the compensation of presbyopia. Manufacturers have released a great variety of soft simultaneous image lens designs to meet different patient needs but their fitting is still unsatisfactory in some cases. Some presbyopes discontinue wearing contact lenses due to some limitations in visual quality and comfort that can be overcome with an appropriate contact lens selection based on a comprehensive pre‐fitting evaluation. This paper aims to review the different types of soft multifocal contact lenses that are currently available for presbyopic correction and to define the steps and factors crucial for their fitting, such as pupil, aberrations, accommodation and centring. A discussion about useful tools to achieve a customised fitting leading to a successful outcome, such as the defocus curve, power profile and questionnaires, is performed.     

老视屈光手术的个体化途径

老视手术是矫治老视的有效方法之一。随着手术技术的不断提高,临床经验不断积累,老视屈光手术的有效性及安全性得到了明显提升,但远期稳定性仍需改善。目前,激光矫正术是老视屈光手术的主要途径,屈光晶状体植入术、Inlay植入术成为激光手术的重要补充。个体化的手术术式是今后的发展方向。     

Bifocal adds in Nigeria

A total of 447 female and 915 male presbyopic patients were examined in the Benin-City, Nigeria optometry clinic. Comparison of bifocal adds with published data from other areas of the globe suggests that climatic temperature has less effect on the age of onset of presbyopia than other authors have claimed.     

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.     

An international survey of contact lens prescribing for presbyopia

Purpose: The aim was to determine world‐wide patterns of fitting contact lenses for the correction of presbyopia. Methods: Up to 1,000 survey forms were sent to contact lens fitters in each of 38 countries between January and March every year over five consecutive years (2005 to 2009). Practitioners were asked to record data relating to the first 10 contact lens fittings or refittings performed after receiving the survey form. Results: Data were received relating to 16,680 presbyopic (age 45 years or older) and 84,202 pre‐presbyopic (15 to 44 years) contact lens wearers. Females are over‐represented in presbyopic versus pre‐presbyopic groups, possibly reflecting a stronger desire for the cosmetic benefits of contact lenses among older women. The extent to which multifocal and monovision lenses are prescribed for presbyopes varies considerably among nations, ranging from 79 per cent of all soft lenses in Portugal to zero in Singapore. There appears to be significant under‐prescribing of contact lenses for the correction of presbyopia, although for those who do receive such corrections, three times more multifocal lenses are fitted compared with monovision fittings. Presbyopic corrections are most frequently prescribed for full‐time wear and monthly replacement. Conclusions: Despite apparent improvements in multifocal design and an increase in available multifocal options in recent years, practitioners are still under‐prescribing with respect to the provision of appropriate contact lenses for the correction of presbyopia. Training of contact lens practitioners in presbyopic contact lens fitting should be accelerated and clinical and laboratory research in this field should be intensified to enhance the prospects of meeting the needs of presbyopic contact lens wearers more fully.     

Dynamic aspects of accommodation: age and presbyopia

There has been no comprehensive study involving each of the primary dynamic components of accommodation in the same cohort as related to age and presbyopic onset; furthermore, the current findings are equivocal. Dynamic monocular components of accommodation (latency, time constant, peak velocity/amplitude relationship, and microfluctuations) were assessed objectively using an infrared optometer within the linear region of accommodation in 30 visually-normal human subjects aged 21-50 years. The time constant and the peak velocity/amplitude relationship did not change with age. However, latency progressively increased, and microfluctuation amplitude and frequency progressively decreased, with increasing age. The invariance in time constant suggests that the gross biomechanical aspects of the lens and related structures in the remaining linear region are relatively unaffected by age. In contrast, the decrease in microfluctuation activity with age suggests more subtle alterations in the biomechanical aspects of the lens to these very small perturbations, such as a response amplitude non-linearity. With respect to neurologic control, the progressive latency increase suggests a processing delay of the blur input, and this is consistent with age-related changes in reaction time measures. The lack of any age-related changes in the peak velocity/amplitude relationship implies normalcy of central and peripheral neuromotor control, as well as grossly normal first-order lens biomechanics, in this linear response region. The results are consistent with the Hess-Gullstrand theory of presbyopia.     

Presbyopic contact lenses

The year 1999 will be remembered as the one in which a very successful bifocal soft contact lens was finally available for the millions of presbyopic and emerging presbyopic Baby Boomers. As a result, soft bifocal fits almost tripled in 1 year. The introduction in 1999 of new daily disposable and new high oxygen permeable extended wear soft contact lenses will give practitioners more options to be successful with monovision. Tips from several practitioners on being successful with bifocal soft lenses are given. It cannot be stressed enough, however, that for patients with presbyopia to be successful with these lenses, they must be willing to compromise somewhat on the quality of vision they remember as a 30-year-old.     

Traditional methods for the treatment of presbyopia: spectacles, contact lenses, bifocal contact lenses

Today, many options are available for the correction of presbyopia. New technology perpetually surfaces to offer better ideas and designs to meet the visual demands of the presbyopic population. This article provides information on various modalities for spectacle and contact lens correction of presbyopia. It is based on current information at the time of publication and is not intended to be a fitting guide.     

Presbyopic fitting strategies: Fitting lenses to patients,not patients to lenses

Eighty-six presbyopic patients who were interested in contact lens wear but had no history of using contact lenses for the correction of presbyopia were entered into a study performed across five independent contact lens practices. Patients were fit utilizing a fitting strategy flowchart that included monovision, diffractive, and aspheric simultaneous and alternating vision presbyopic corrections. At the conclusion of the study, 83% of the patients were successful utilizing the criterion that the patient was still actively wearing the lenses. Fifty-two percent were fit with monovision, 14% were fit in alternating vision lenses, while 6% and 10% were fit with aspheric and diffractive lenses, respectively, including modified monovision.