The correction of presbyopia

Effects of accommodation on geometrical parameters of human lens: A systematic review and meta-analysis

Purpose

To investigate the effects of accommodation on the geometrical parameters of human lens.

Methods

Eight databases from inception to November 2023 were used for the literature search: CNKI, CBM, VIP, Wan-Fang, PubMed, Web of Science, EMBASE, and the Cochrane Library. The Methodological Index for Non-randomized Studies was used to assess the risk of bias. The PRISMA were followed and the following outcomes were taken into consideration: lens diameter (LD), lens thickness (LT), anterior curvature radius (ACR), posterior curvature radius (PCR), lens center position (LCP), and total cross-sectional area (TCSA). This systematic review was registered on an international platform for registered systematic reviews and meta-analysis (INPLASY202260085).

Results

A total of 19 studies were included. LT increased by 0.04 mm/D (18 studies; 95% confidence interval [CI], 0.03-0.06; I2 = 96.6%; P < 0.001). At the same time, LD, ACR, and PCR decreased by 0.06 mm/D (6 studies; 95%CI, -0.07-0.05; I2 = 50.1%; P < 0.001), 0.53 mm/D (8 studies; 95%CI, -0.64-0.41; I2 = 96.5%; P < 0.001), and 0.14 mm/D (9 studies; 95%CI, -0.19-0.09; I2 = 94.7%; P < 0.001) during accommodation, respectively. Moreover, LCP shifted forward by 0.01 mm/D (3 studies; 95%CI, -0.02-0.00; I2 = 0.0%; P < 0.001), and TCSA by 0.58 mm2/D (2 studies; 95%CI, 0.41-1.57; I2 = 97.0%; P = 0.457) during accommodation.

Conclusions

Changes in LT, LD, ACR, PCR and LCP supported Helmholtz's theory. Different apparatuses or measurement methods influenced the measurement of lens geometrical parameters.

The evolution of mechanism of accommodation and a novel hypothesis

Myopia and presbyopia are two major optometry problems facing the whole society. The mechanism of accommodation is strongly related to the treatments of myopia and presbyopia. However, the key mechanism of accommodation has puzzled us for over 400 years and is still not clear at present, leading to the stagnation of prevention and treatment of myopia and presbyopia. With the continued development of experimental technologies and equipment, the approaches to elucidate accommodation's intricacies have become more methodological and sophisticated. Fortunately, some significant progress has been made. This article is to review the evolution of the mechanism of accommodation. Helmholtz proposed a classical theory of "zonules relax during accommodation." In contrast, Schachar put forward a theory of "zonules taut during accommodation." Those hypotheses are relatively complete, but either do not fully explain everything about the accommodation mechanism or lack sufficient experimental and clinical evidence to support them. Then, some contentious issues are discussed in detail to find the truth. Finally, we proposed our hypothesis about accommodation based on the anatomy of the accommodative apparatus.

A preliminary study on the visual outcomes after LaserACE for presbyopia

Background

To investigate the visual outcomes over 1 year after laser anterior ciliary excision (LaserACE) procedure for presbyopic subjects.

Methods

A prospective, non-randomized, non-comparative study. Eight emmetropic eyes of four patients with presbyopia were included in this study. All eyes were treated with the LaserACE procedure using the VisioLite erbium-YAG laser (Ace Vision Group, USA). Subjects were assessed preoperatively and at 1 day, 1 week, 1 month, 3 months, 6 months, and 1 year postoperatively. Outcome measures included questionnaires, visual acuity, manifest refraction, pupil size, keratometry, reading prescription, and intraocular pressure.

Results

Binocular distance corrected intermediate visual acuity (DCIVA) had improved from 0.33±0.12 logMAR to 0.12±0.12 logMAR after 6 months (P<0.05) and 0.13±0.12 logMAR after 12 months postoperatively (P<0.01). Binocular distance corrected near visual acuity (DCNVA) improved from 0.41±0.10 logMAR to 0.24±0.12 logMAR after 6 months (P<0.05) and 0.26±0.09 log MAR after 12 months postoperatively (P<0.05). An average decrease of 0.91±0.28 D in the reading prescription at a 40 cm reading distance was observed and remained stable over 12 months (P<0.05). There were no significant differences in manifest refraction, uncorrected distance visual acuity (UDVA), corneal curvature, high order aberrations, pupil size compared with preoperative and 6 months as well as 12 months postoperative visits (P>0.05).

Conclusions

The LaserACE procedure is shown to be safe and efficient for presbyopia correction without influencing distance vision or visual quality. However, its mechanism and long-term effects need further validation.

Scleral surgery for the treatment of presbyopia: where are we today?

Presbyopia corrections traditionally have been approached with attempts to exchange power, either at the cornea or the lens planes, inducing multifocality, or altering asphericity to impact the optical system. Treatments that affect the visual axis, such as spectacle and contact lens correction, refractive surgeries, corneal onlays and inlays, and intraocular lenses are typically unable to restore true accommodation to the presbyopic eye. Their aim is instead to enhance 'pseudoaccommodation' by facilitating an extended depth-of-focus for which vision is sufficient. There is a true lack of technology that approaches presbyopia from a treatment based or therapy based solution, rather than a 'vision correction' solution that compromises other components of the optical system. Scleral surgical procedures seek to restore true accommodation combined with pseudoaccommodation and have several advantages over other more invasive options to treat presbyopia. While the theoretical justification of scleral surgical procedures remains controversial, there has nevertheless been increasing interest and evidence to support scleral surgical and therapeutic approaches to treat presbyopia. Enormous progress in scleral surgery techniques and understanding of the mechanisms of action have been achieved since the 1970s, and this remains an active area of research. In this article, we discuss the historic scleral surgical procedures, the two scleral procedures currently available, as well as an outlook of the future for the scleral surgical space for treating presbyopia.

Developments in the correction of presbyopia II: surgical approaches

PURPOSE

To discuss the various static and dynamic surgical approaches which attempt to give presbyopes good vision at far, intermediate and near viewing distances.

CONTENT

Static methods broadly adopt the same optical techniques as those used in presbyopic contact lens correction and aim to satisfy the needs of the presbyope by increasing binocular depth-of-focus, often using monovision as well as simultaneous-imagery. Dynamic methods generally attempt to make use of at least some of the still-active elements of the accommodation system. They include procedures which are supposed to modify the relative geometry of the ciliary muscle and lens, or which reduce the stiffness of the presbyopic lens either by replacing it with other natural or man-made material or by subjecting it to femtosecond laser treatment. Alternatively the natural lens may be replaced by some form of intraocular lens which changes power as a result of forces derived from the still-active ciliary muscle, zonule and capsule, or other sources.

CONCLUSIONS

At present, multifocal intraocular lenses appear to offer the most consistent and reliable surgical approach to surgical presbyopic correction. They have obvious advantages in convenience and stability over optically-similar, simultaneous-image presbyopic contact lenses but this must be balanced against their relative inflexibility in cases of patient dissatisfaction. Dynamic methods remain largely experimental. Although some approaches show promise, as yet no method has demonstrated a reliable, long-term ability to correct distance refractive error and to appropriately change ocular power in response to changes in viewing distance over the normal range of interest.

Insights into the age-related decline in the amplitude of accommodation of the human lens using a non-linear finite-element model

AIM

To understand the effect of the geometric and material properties of the lens on the age-related decline in accommodative amplitude.

METHODS

Using a non-linear finite-element model, a parametric assessment was carried out to determine the effect of stiffness of the cortex, nucleus, capsule and zonules, and that of thickness of the capsule and lens, on the change in central optical power (COP) associated with zonular traction. Convergence was required for all solutions.

RESULTS

Increasing either capsular stiffness or capsular thickness was associated with an increase in the change in COP for any specific amount of zonular traction. Weakening the attachment between the capsule and its underlying cortex increased the magnitude of the change in COP. When the hardness of the total lens stroma, cortex or nucleus was increased, there was a reduction in the amount of change in COP associated with a fixed amount of zonular traction.

CONCLUSIONS

Increasing lens hardness reduces accommodative amplitude; however, as hardness of the lens does not occur until after the fourth decade of life, the age-related decline in accommodative amplitude must be due to another mechanism. One explanation is a progressive decline in the magnitude of the maximum force exerted by the zonules with ageing.

Presbyopiekorrektur mittels Intraokularlinsen

Modern cataract surgery has advanced tremendously over the past 20 years. Improved surgical techniques, as well as improved implant materials and designs, have enlarged patient profiles and indications not only for cataract surgery, but also for refractive lens exchange surgery. This has also created much higher patient expectations. The loss of accommodation is a loss of quality of life for presbyopic and especially young pseudophakic patients. Multifocal intraocular lenses (MIOL) have been implanted since 1986, starting with 2-3 zone refractive and diffractive designs. Due to the surgical techniques available at that time, MIOL decentration and surgically induced astigmatism were possible complications. In addition, reduced contrast perception and increased glare were common problems of MIOL because of their optical principles. New developments in this field in recent years such as the folding, multizonal, progressive refractive MIOL and aspheric diffractive MIOL in combination with improved surgical techniques have overcome those initial problems. Therefore, modern MIOL (and in the future also accommodative IOL) can be considered not only for the correction of aphakia but also for refractive purposes.

Surgical management of presbyopia

Presbyopia is age-related reduction in amplitude of accommodation and the loss of the ability to change the eye's focus from far to near. It is the one of the most common age-related ailment. Traditional methods such as spectacle glasses or contact lenses are still the most widely used for correction of the problem. This article is an attempt to review the surgical options available for presbyopia.

Accommodation measurements in a prepresbyopic and presbyopic population

PURPOSE

To study the efficacy of several subjective and objective methods of accommodation measurement in normal prepresbyopic and presbyopic populations to identify appropriate methods for measuring the outcome of accommodative restorative procedures.

SETTING

University of Houston, College of Optometry, Houston, Texas, USA.

METHODS

Thirty-one normal subjects with a mean age of 43.7 years (range 31 to 53 years) participated. Accommodation was measured monocularly using 3 subjective approaches--the push-up test, minus lenses to blur, and a focometer--and 2 approaches measured with a Hartinger coincidence refractometer, in which accommodation was stimulated with minus lenses to blur and topical pilocarpine 6%.

RESULTS

The push-up method overestimated accommodative amplitude relative to objective measures in 28 subjects. Two subjective methods, minus lenses to blur and the focometer, produced comparable results, but with lower amplitudes in younger subjects and higher amplitudes in older subjects compared with objective methods. Comparable results were obtained when accommodation was stimulated in 1 of 2 ways and measured with the Hartinger. Pilocarpine elicited stronger accommodative responses than distance blur for subjects with low accommodative amplitudes. Pilocarpine 6% produced stronger responses in subjects with light irides than in those with dark irides.

CONCLUSIONS

Hartinger-measured accommodation provides more realistic measurement of accommodative amplitude than the subjective methods tested, especially in the presbyopic population. In presbyopic subjects, the subjective tests resulted in accommodative amplitudes up to 4.0 diopters greater than those measured with objective tests. Measurements of accommodative amplitude are best achieved with objective methods to stimulate and measure accommodation.