Accommodative intraocular lenses: current status

PURPOSE OF REVIEW: The possibility of using a monofocal IOL with accommodative ability allows refractive cataract surgery with a clearly decreased potential of photic phenomena. Three IOLs of different designs and materials have demonstrated accommodative ability, but the degree of accommodative amplitude has been reported to different extents and variabilities. The plate-haptic CrystaLens has a hinged design that might permit forward movement of the optic as a result of pressure changes in the vitreous cavity. The 1CU has modified haptics that bend in the bag as the lens capsule contracts, which are supposed to cause anterior displacement of the lens optic. With the dual-optic one-piece Synchrony, springlike haptics separate a high-plus anterior lens from a posterior minus lens. With accommodative effort, the capsular bag expands and the springs express kinetic energy, which might allow the optics to separate as the anterior lens moves forward. RECENT FINDINGS: This article seeks to clarify and distinguish the concepts of true accommodation and pseudo accommodation. Current designs of accommodative IOLs are supposed to work by the focus-shift principle to allow true pseudophakic accommodation. Studies that biometrically assessed optic shift found no or only low amplitudes of forward movement. The amount of forward movement, if present, was highly variable between patients. To date, most studies present psychophysical data for the proof of concept, which alone seems insufficient. Capsule bag performance and posterior capsule opacification with accommodative IOLs seem worse than those with standard intraocular lenses. SUMMARY: The potential clinical benefits of accommodative IOL technology for both cataract patients and refractive patients may place accommodative IOLs in a competitive position with multifocal IOL technology.     

Pseudophakic accommodation with translation lenses – dual optic vs mono optic

PURPOSE: To investigate the pseudophakic accommodation effect in dual and mono optic translation accommodative intraocular lenses (AIOL) using linear matrix methods in the paraxial space. METHODS: Dual (anterior optic of power +32 D linked to a compensatory posterior optic of negative power) and mono lens power was determined in the non-accommodated state using linear geometric optics based on the Gullstrand model eye. The position of the AIOL was calculated from a regression formula. Pseudophakic accommodation was assessed with three systems: (1) forward shift of the mono optic lens, (2) anterior translation of the anterior optic in the dual optic lens system with an unchanged position of the posterior minus lens and (3) symmetrical anterior and posterior translation of the anterior and posterior lens. The Gullstrand model eye was modified by changing the axial length (and proportionally changing the phakic anterior chamber depth) to investigate the accommodative effect in myopic and hyperopic eyes. RESULTS: The dual optic lens system (2) yields a nearly constant accommodation amplitude of 2.4-2.5 D mm(-1) movement over the total range of axial lengths. The mono optic lens (1) provides a higher accommodative effect only in extremely short eyes (high refractive power of the lens), whereas for normal eyes (1.4-1.5 D mm(-1) movement) and for long (myopic) eyes the accommodative effect is much less than the dual optic lens. The dual optic lens system under condition (3) yields less accommodation amplitude compared with the dual optic system under condition (2) over the total range of axial length but provides higher accommodation amplitude compared with the mono optic lens system (1) with axial lengths greater than 22.3 mm (lens power 25.5 D). In the accommodated state, with lens translation of 1 mm, the absolute value of the lateral magnification increases with the refractive power of the mono optic lens (1) and decreases in both dual optic lens systems (under conditions 2 and 3). CONCLUSIONS: A mathematical strategy is presented for calculation of the accommodative effect of mono-optic and dual optic AIOL. The dual optic lens yielded a nearly constant accommodation amplitude of about 2.4-2.5 D mm(-1) translation, whereas the mono optic lens yielded an accommodative response of <2 D mm(-1) translation in long myopic or normal eyes. Only in extremely short eyes is the accommodative amplitude of the mono-optic lens higher than the dual optic lens.     

Accommodating intraocular lenses: a critical review of present and future concepts

Background Significant efforts have been made to develop lens implants or refilling procedures that restore accommodation. Even with monofocal implants, apparent or pseudoaccommodation may provide the patient with substantial though varying spectacle independence. True pseudophakic accommodation with a change of overall refractive power of the eye may be induced either by an anterior shift or a change in curvature of the lens optic. Materials and methods Passive-shift lenses were designed to move forward under ciliary muscle contraction. This is the only accommodative lens type currently marketed (43E/S by Morcher; 1CU by HumanOptics; AT-45 by Eyeonics). The working principle relies on various hypothetical assumptions regarding the mechanism of natural accommodation. Dual-optic lenses were designed to increase the dioptric impact of optic shift. They consist of a mobile front optic and a stationary rear optic which are interconnected with spring-type haptics. With active-shift lens systems the driving force is provided by repulsing mini-magnets. Lens refilling procedures replace the lens content by an elastic material and provide accommodation by an increase of surface curvature. Results Findings with passive-shift lenses have been contradictory. While uncorrected reading vision results were initially reported to be favorable with the 1CU, and excellent with the AT-45 lens, distant-corrected near vision did not exceed that with standard monofocal lenses in later studies. Mean axial shift from laser interferometric measurements under stimulation with pilocarpine showed a moderate anterior shift with the 1CU, while the AT-45 paradoxically exhibited a small posterior shift. With the 1CU, the shift-induced accommodative effect was calculated to be less than +0.5 D in most cases, while +1 D was achieved in a single case only. Ranges and standard deviations were very large in relation to the mean values. Under physiological near-point stimulation, however, no shift was seen at all. Prevention of capsule fibrosis by extensive capsule polishing did not enhance the functional performance. Dual optic lenses are under clinical investigation and are reported to provide a significant amount of accommodation. However, possible long-term formation of interlenticular opacifications remains to be excluded. Regarding magnet-driven active-shift lens systems, initial clinical experience has been promising. Prevention of fibrotic capsular contraction is crucial, and it has been effectively counteracted with a special capsular tension ring, or lens fixation technique, together with capsule polishing. Lens refilling has been extensively studied in the laboratory and in primates. Though it offers great potential for fully restoring accommodation, a variety of problems must be solved, such as achieving emmetropia in the relaxed state, adequate response to ciliary muscle contraction, satisfying image quality over the entire range of accommodation and sustained functioning. The key problem, however, is again after-cataract prevention. Conclusions As opposed to psychophysical evaluation techniques, laser interferometry measures what shift lenses are designed to provide: axial shift on accommodative effort. While under pilocarpine some movement was recorded, no movement at all was found under near-point stimulation with any of the lenses currently marketed. In contrast, magnetic-driven active-shift lens systems carry the potential of sufficiently topping up apparent accommodation to provide for clinically useful accommodation while using conventional lens designs with proven after-cataract performance. Dual optic implants significantly increase the impact of axial optic shift. The main potential problem, however, is delayed formation of interlenticular regenerates. Lens refilling procedures offer the potential of fully restoring accommodation due to the great impact of increase in surface curvature on refractive lens power. However, various problems remain to be solved before clinical use can be envisaged, above all, again, after-cataract prevention. The concept of passive single-optic shift lenses has failed. Concomitant poor capsular bag performance makes these lenses an unacceptable trade-off. Magnet-assisted systems potentially combine clinically useful accommodation with satisfactory after-cataract performance. Dual optic lenses theoretically offer substantial accommodative potential but may allow for interlenticular after-cataract formation. Lens refilling procedures have the greatest potential for fully restoring natural accommodation, but will again require years of extensive laboratory and animal investigations before they may function in the human eye. The author has no proprietary interest in any of the materials or equipment mentioned in this study.     

The influence of injection volume and capsular bag contraction on the refractive power of polymer refilled lenses – a finite element modelling simulation study

Purpose: Polymer injection into the capsular bag after phakoemulsification is an interesting and promising approach to lens surgery. Safe clinical application of this technique will require an appropriate estimate of the effect of implantation variables on the lens power. This article details the results of finite element investigations into the effects of the injected polymer volume and capsular bag contraction on the resultant lens power and accommodation amplitude. Methods: An axisymmetric finite element model was created from literature sources. Polymer injection and the capsular contraction were simulated, and their effect on the lens power was calculated. Results and Conclusion: The simulations show that overfilling during polymer injection leads to a refractive power increase of the lens. Capsular bag contraction also results in a power increase. The calculated accommodative amplitude of the lens is minimally affected by capsular bag contraction but decreases significantly with increased capsular bag stiffness as a result of fibrosis.     

Edinger-Westphal and pharmacologically stimulated accommodative refractive changes and lens and ciliary process movements in rhesus monkeys

During accommodation, the refractive changes occur when the ciliary muscle contracts, releasing resting zonular tension and allowing the lens capsule to mold the lens into an accommodated form. This results in centripetal movement of the ciliary processes and lens edge. The goal of this study was to understand the relationship between accommodative refractive changes, ciliary process movements and lens edge movements during Edinger-Westphal (EW) and pharmacologically stimulated accommodation in adolescent rhesus monkeys. Experiments were performed on one eye each of three rhesus monkeys with permanent indwelling electrodes in the EW nucleus of the midbrain. EW stimulated accommodative refractive changes were measured with infrared photorefraction, and ciliary process and lens edge movements were measured with slit-lamp goniovideography on the temporal aspect of the eye. Images were recorded on the nasal aspect for one eye during EW stimulation. Image analysis was performed off-line at 30 Hz to determine refractive changes and ciliary body and lens edge movements during EW stimulated accommodation and after carbachol iontophoresis to determine drug induced accommodative movements. Maximum EW stimulated accommodation was 7.36+/-0.49 D and pharmacologically stimulated accommodation was 14.44+/-1.21 D. During EW stimulated accommodation, the ciliary processes and lens edge moved centripetally linearly by 0.030+/-0.001 mm/D and 0.027+/-0.001 mm/D, with a total movement of 0.219+/-0.034 mm and 0.189+/-0.023 mm, respectively. There was no significant nasal/temporal difference in ciliary process or lens edge movements. 30-40 min after pharmacologically stimulated accommodation, the ciliary processes moved centripetally a total of 0.411+/-0.048 mm, or 0.030+/-0.005 mm/D, and the lens edge moved centripetally 0.258+/-0.014 mm, or 0.019+/-0.003 mm/D. The peaks and valleys of the ciliary processes moved by similar amounts during both supramaximal EW and pharmacologically stimulated accommodation. In conclusion, this study shows, for the first time, that the ciliary processes and lens edge move centripetally, linearly with refraction during EW stimulated accommodation. During pharmacological stimulation, the ciliary processes move to a greater extent than the lens edge, confirming that in adolescent monkeys, lens movement limits the accommodative optical change in the eye.     

Determination of pseudophakic accommodation with translation lenses using Purkinje image analysis

PURPOSE: To determine pseudophakic accommodation of an accommodating posterior chamber intraocular lens (translation lens) using Purkinje image analysis and linear matrix methods in the paraxial space. METHODS: A 2 x 2 system matrix was defined for each Purkinje image I to IV using refraction, translation and mirror matrices. Image size (m) and axial image position (z) was determined as an example for an off-axis object (a 0.2 m off-axis object located 0.5 m in front of the cornea.). First, our method was applied to the phakic relaxed (emmetropic) and accommodated (6.96 D) Le Grand eye. Secondly, for demonstration of the applicability of the calculation scheme to the pseudophakic eye, we provide a clinical example where we determine the accommodation amplitude of the translation lens (1 CU, HumanOptics, Erlangen, Germany) from photographed Purkinje images in the relaxed and accommodated state. From the biometric data: axial length 23.7 mm, corneal power 43.5, corneal thickness 550 microns, implanted intraocular lens (IOL) with a refractive power of 20.5 D (shape equi-biconvex, refractive index 1.46), and refractive indices of the cornea, aqueous and vitreous from the Le Grand model eye, we calculated the refractive state and the sizes of Purkinje images I and III initiated from two off-axis light sources. RESULTS: For the Le Grand model eye, Purkinje image II (z/m = 3.5850 mm/0.0064) is slightly smaller than and directly in front of image I (z/m = 3.8698 mm/0.0077). Purkinje image III (z/m = 10.6097 mm/0.0151) is nearly double the size of image I and during accommodation it moves from the vitreous into the crystalline lens. Purkinje IV (z/m = 4.3244 mm/-0.0059) is inverted, three quarters the size of image I, lies in the crystalline lens and moves slightly towards the retina. For the pseudophakic eye, pseudophakic accommodation of 1.10 D was calculated from the proportion of distances between both Purkinje images I and III in the relaxed (3.04) and accommodated (2.75) state, which is in contrast to the total subjective accommodation of 2.875 D evaluated with an accommodometer. CONCLUSIONS: We present a straightforward mathematical strategy for calculation of the Purkinje images I-IV. Results of our model calculation resemble the values provided by Le Grand. In addition, this approach yields a simple en bloc scheme for determination of pseudophakic accommodation in pseudophakic eyes with accommodative lenses (translation lenses) using Purkinje image photography.     

Accommodation- presbyopia: mechanism etiology

The purpose of the presentation is to elucidate the mechanism of accommodation and etiology of the age‐related decline in accommodative amplitude that results in presbyopia in the fifth decade of life. Multiple physical, mathematical, clinical, in vitro, and in vivo experiments demonstrate that the human crystalline lens develops an unusual shape during accommodation. Central lens thickness increases; the curvatures of the central surfaces of the lens steepen; while the peripheral surfaces of the lens flatten. This ‘steep profile’ also occurs in other biconvex objects that have an aspect ratio ≤ 0.6 (minor axis to major axis ratio) in response to a small equatorial displacement when the volume of the object only minimally changes. The ‘steep profile’ even occurs when the major axis of an ellipse with an aspect ratio ≤ 0.6 is increased and the area enclosed by the ellipse is held constant or permitted to decrease by 2%. The universality of the occurrence of a ‘steep profile’ implies that the lens is under increased tension during accommodation. This hypothesis was confirmed by using high‐resolution anterior segment optical coherence tomography (OCT) to measure the change of stress on the anterior lens capsule in patients who had undergone a phakic refractive intraocular lens (PRL) at least 1 year prior to the study. The PRL served as an internal control. It was found that during a mean of 8‐diopters of in vivo accommodation, the stress on the lens was increased during accommodation, p < 0.001. The increased stress on the lens capsule during accommodation occurs as a consequence of increased equatorial zonular tension. Normal equatorial lens growth predicts both the age‐related decline in accommodative amplitude and the age‐related increase in intraocular pressure (IOP). The rapid decline in accommodative amplitude and rapid increase in IOP that occur during childhood and their slower changes thereafter, both match the logarithmic pattern of equatorial lens growth, R² = 0.90. In summary, the lens is under increased stress during accommodation as a consequence of increased equatorial zonular tension. Normal equatorial lens growth is the etiology of both the age‐related decline in accommodative amplitude that results in presbyopia in the fifth decade of life and the increase in IOP that occurs with age.     

Apparent accommodation of the aphakic eye corrected by an artificial lens

We measured apparent accommodation in 51 pseudophakic eyes (44 patients, after implantation of anterior (15 eyes) or posterior (36 eyes) intraocular lens. Glasses for distant vision were born during the test. The mean apparent accommodation was 1.89 +/- 0.91 dpt. 25 among these 51 pseudophakic eyes who were tested without their glasses showed a mean apparent accommodation that was not different in statistical and clinical terms. The mean accommodative power of 25 phakic and presbyopic eyes used as controls was 1.31 +/- 1.01 dpt. For these 51 pseudophakic eyes the correlation between apparent accommodation and the reciprocal of the pupillary diameter is the most significant (r = 0.79): the smaller the pupil, the greater the apparent accommodation. There was a negative correlation between apparent accommodation and anterior chamber depth (r = -0.64). No correlation was found between pseudo-accommodation and corrected visual acuity, corneal astigmatism and refractive error.     

Magnetic resonance imaging study of the effects of age and accommodation on the human lens cross-sectional area

PURPOSE: To evaluate the effect of age and accommodation on lens cross-sectional area (CSA). METHODS: High-resolution magnetic resonance images of the eye were acquired from 25 subjects ranging in age from 22 to 50 years during accommodation and with accommodation at rest. The images were analyzed to obtain the total lens CSA and the CSAs of the anterior and posterior portions of the lens. RESULTS: The total lens CSA and the CSA of the anterior portion increased with age in both accommodative states. With accommodation, the CSA was larger in these portions of the lens; however, this difference decreased with age. Conversely, the CSA of the posterior portion of the lens remained statistically independent of both age and accommodative state. CONCLUSIONS: This preliminary study documents, in vivo, that the lens grows with age. This growth appears to be confined to the anterior portion. A quite unexpected finding is that both the total lens CSA and the CSA of the anterior portion are greater during accommodation when zonular tension is minimized. This accommodative change in CSA, which decreases with age, may be due to compression of the lens material during relaxed accommodation when zonular tension is greatest. That both age and accommodative changes in CSA appear to be limited to the anterior portion of the lens may be related to properties of the anterior capsule and lens material, the position of the zonular attachments, and the location of the fetal nucleus.     

Accommodative microfluctuations and iris contour

Mechanical interaction between aqueous humor, iris, and intraocular structures can alter the iris profile from its normal curvature. In particular, significant changes to the iris profile occur during accommodation as the anterior lens movement forces the iris into greater posterior bowing. We extended a previous mathematical model of the anterior segment and investigated the response of this coupled fluid-solid system due to accommodative microfluctuations. The results showed that the system response exhibited the same waveform as the stimulus for small-amplitude microfluctuations generally associated with the high-frequency component. Low-frequency microfluctuations with relatively larger amplitudes elicited a response different from the stimulus, indicating that the forces generated by the lens movement significantly affected the aqueous-iris mechanical interaction.     

Accommodation in pseudophakic eyes

PurposeToday, many patients who have undergone cataract surgery want to enjoy good non-spectacle corrected distant vision and nonspectacle corrected near vision with glasses independence. According to the literature, the implantation of an accommodative intraocular lens (AIOLs) can achieve the level of vision after cataract surgery. However, there is a debate regarding the true accommodative capability of the AIOLs (i.e., whether the IOLs can move forward when attempting to accommodate like the natural crystalline lens of a phakic eye). This review aims to answer the following questions: (1) Can pseudophakic eye accommodate? (2) If pseudophakic eyes can accommodate, how long does this accommodation last? (3) Is there pseudoaccommodation?MethodsThis is a systematic review of randomized and nonrandomized controlled trials that have compared different IOLs in accommodation using subjective and objective methods of testing accommodation. All peer reviewed randomized and nonrandomized controlled trials that compared different IOLs in accommodation were included.ResultsThere was evidence of pseudophakic accommodation up to 12 months postoperatively for AIOLs (mostly 1CU): subjective accommodation [95% confidence interval (CI), 0.36–0.98], objective optic shift (95% CI, 0.12–0.76). However, accommodation decreased at 12 months postoperatively (95% CI, 0.55–1.00). In addition, several papers have reported evidence of pseudoaccommodation.ConclusionThere is pseudophakic accommodation up to 1 year post cataract surgery, mostly 1CU AIOL. Pseudoaccommodation may coexist.     

Evaluierung der Wertigkeit objektiver und subjektiver Verfahren zur Messung von pseudophaker Akkommodation

Purpose

The aim of this study was to compare the validity and plausibility of various subjective and objective measurement methods for evaluation of pseudophakic accommodation.

Setting

Eye Clinic Bellevue, Kiel, Germany.

Methods

A total of 21 patients were examined over an average period of 34 months (range 12–51 months) after implantation of a potentially accommodative, model 1CU intraocular lens (IOL, HumanOptics, Germany). The following subjective measurements were taken: near point measurement with the accommodometer (Clement Clarke, Harlow, UK), defocus curve and near visual acuity with far and near reading charts. The IOLMaster (Carl Zeiss Meditec, Germany), ACMaster (Carl Zeiss Meditec, Germany) and Shin-Nippon K 5001 AR (Shin-Nippon, Japan) were employed as objective measurement devices. With this devices information is obtained about the anterior chamber depth (ACD, preoperative and postoperative), the movement of the IOL and the refractive change of eyes during the accommodative process.

Results

Depending on the method utilized there were large variations of the examined IOL in relation to the extent of the measured accommodative effects in their entirety with the objective as well as the subjective measurement method.

Conclusions

A differentiation of pseudophakic accommodation and pseudophakic pseudoaccommodation is not possible with the conventional measurement methods applied and examined in this study. Only the ACMaster is an objective method for measurement of the axial shift of an IOL. However, subjective measurement methods can only record the total of both accommodation portions but do not allow any scientifically-founded statement about the functional principle of a potentially accommodative IOL.     

Magnetic resonance imaging of aging, accommodating, phakic, and pseudophakic ciliary muscle diameters

PURPOSE: To quantify in vivo accommodative changes in the aging human ciliary muscle diameter in phakic and pseudophakic eyes. SETTING: Department of Surgery/Bioengineering, UMDNJ-Robert Wood Johnson Medical School, Piscataway, and the Institute of Ophthalmology and Visual Science UMDNJ-New Jersey Medical School, Newark, New Jersey, USA. METHODS: Images were acquired from 48 eyes of 40 people between the ages of 22 and 91 years, 1 eye of 32 phakic volunteers and both eyes of 8 patients who had monocular implantation of a single-piece AcrySof intraocular lens (IOL) (Alcon Laboratories). Images were acquired during physiological accommodation and with accommodation at rest, and the diameter of the ciliary muscle ring was measured. RESULTS: Results show the ciliary muscle remains active throughout life. The accommodative change in its diameter (mean 0.64 mm) (P<.00001) was undiminished by age or IOL implantation. Preliminary data showed that the accommodative decrease in muscle diameter in phakic and pseudophakic eyes was statistically identical. The phakic eyes had a marked decrease in ciliary muscle diameter with advancing age for both accommodative states (P<.000001 and P<.000001), which did not appear to be altered by IOL implantation. The lens equator was constant with age in the unaccommodated human eye, resulting in decreased circumlental space with advancing age in the phakic eyes. CONCLUSION: Although the undiminished ability of the ciliary muscle to decrease its diameter with accommodation can be relied on in strategies for presbyopia correction, even in advanced presbyopia, the decreasing circumlental space and its potential effects on zonular tension must also be considered.     

植入可调节人工晶状体和多焦点人工晶状体后视功能的对比研究

目的比较超声乳化白内障吸除术后植入可调节人工晶状体和多焦点人工晶状体的视功能。方法32例年龄相关性白内障患者根据自愿原则,采用非随机对照方式分成两组,试验组13例患者（24只眼）植入1CU可调节人工晶状体,对照组19例患者（30只眼）植入Array多焦点人工晶状体。术后3个月使用标准对数视力表检测患者最佳矫正视力及在最佳矫正视力基础上获得的近视力、近点及调节幅度、立体视觉。检查结果以年龄作为协变量,进行成组设计定量资料一元协方差分析。结果随诊期间所有患者均无明显的术后并发症。术后3个月试验组最佳矫正视力为4．96±0．15,对照组为5．02±0．08,两组比较差异无统计学意义（P=0．085）。试验组术后最佳矫正视力基础上获得的近视力为4．65±0．15,对照组为4．60±0．10,两组比较差异无统计学意义（P=0．398）。试验组术后主观近点为（56±9）cm,对照组为（61±11）cm,两组比较差异无统计学意义（P=0．80）。试验组术后调节幅度为（1．30±0．40）D,对照组为（1．20±0．36）D,两组比较差异无统计学意义（P=0．093）。试验组术后立体视觉为43．24”±18．25”,对照组为60．00”±23．09”,两组比较差异无统计学意义（P=0．543）。结论植入1CU可调节人工晶状体的患者术后可在保持最佳远视力的同时获得一定的近视力。两种人工晶状体在矫正远视力、远矫下近视力、主观近点、术后调节幅度及近距矫正基础上的立体视觉检查方面均无统计学意义。     

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.     

Simultaneous measurements of refraction and A-scan biometry during accommodation in humans.

PURPOSE: Accommodation is a dioptric change in power of the crystalline lens resulting from ciliary muscle contraction that leads to an increase in lens surface curvatures and thickness and changes in the position of lens surfaces. Previous studies have used A-scan ultrasound to measure changes in the position of lens surfaces with voluntary accommodation, but have not simultaneously measured the change in refraction. The goal of this study is to simultaneously measure and correlate refractive and biometric changes in the lens during voluntary accommodation in humans. METHODS: Refraction was measured off-axis in the right eye and biometry on-axis in the left eye simultaneously during voluntary accommodation in 22 human subjects between the ages of 21 and 30 years (mean +/- standard deviation: 25.8 +/- 2.3 years). Subjects viewed a distant target and four near targets spanning the full accommodative range available to evaluate refraction and lens surface position at each accommodative state. RESULTS: Maximum objectively measured accommodative amplitude of all subjects was 5.64 +/- 0.21 D (mean +/- standard error of mean). Biometric and refractive changes during accommodation were linearly correlated. The mean +/- standard error of mean decrease in anterior chamber depth was 0.051 +/- 0.008 mm/D, increase in lens thickness was 0.067 +/- 0.008 mm/D, and increase in anterior segment length was 0.017 +/- 0.005 mm/D during accommodation. There was a net anterior movement of the lens center of 0.017 +/- 0.005 mm/D. CONCLUSION: Anterior chamber depth, lens thickness, and anterior segment length change linearly with refraction during accommodation. Per-diopter changes in the lens were greater in the current study compared with previous studies in which only accommodative demand was measured, which overestimates the accommodative response.     

Accommodative lens refilling in rhesus monkeys

PURPOSE: Accommodation can be restored to presbyopic human eyes by refilling the capsular bag with a soft polymer. This study was conducted to test whether accommodation, measurable as changes in optical refraction, can be restored with a newly developed refilling polymer in a rhesus monkey model. A specific intra- and postoperative treatment protocol was used to minimize postoperative inflammation and to delay capsular opacification. METHODS: Nine adolescent rhesus monkeys underwent refilling of the lens capsular bag with a polymer. In the first four monkeys (group A) the surgical procedure was followed by two weekly subconjunctival injections of corticosteroids. In a second group of five monkeys (group B) a treatment intended to delay the development of capsular opacification was applied during the surgery, and, in the postoperative period, eye drops and two subconjunctival injections of corticosteroids were applied. Accommodation was stimulated with carbachol iontophoresis or pilocarpine and was measured with a Hartinger refractometer at regular times during a follow-up period of 37 weeks in five monkeys. In one monkey, lens thickness changes were measured with A-scan ultrasound. RESULTS: In group A, refraction measurement was possible in one monkey. In the three other animals in group A, postoperative inflammation and capsular opacification prevented refraction measurements. In group B, the maximum accommodative amplitude of the surgically treated eyes was 6.3 D. In three monkeys the accommodative amplitude decreased to almost 0 D after 37 weeks. In the two other monkeys, the accommodative amplitude remained stable at +/-4 D during the follow-up period. In group B, capsular opacification developed in the postoperative period, but refraction measurements could still be performed during the whole follow-up period of 37 weeks. CONCLUSIONS: A certain level of accommodation can be restored after lens refilling in adolescent rhesus monkeys. During the follow-up period refraction measurements were possible in all five monkeys that underwent the treatment designed to prevent inflammation and capsular opacification.     

Why we need reading-glasses before a zimmer-frame

Accommodative loss represents the fastest human biological decrement. Why? To examine this, the shape of the eye-lens during accommodation or its relaxation is analysed with special reference to age-related changes. The capsule is viewed as a force transmitter: the distribution of forces along centripetal capsular arcs and the resulting stresses and strains are calculated. The effect of zonular 'shifts' is considered. Age-related accommodative loss can be modelled successfully if changes in mechanical properties are linked to those in lenticular and capsular shape.     

On the relationship between lens stiffness and accommodative amplitude

The purpose of this study was to investigate the relationship between the stiffness of the material comprising the lens and the loss of accommodative amplitude with age. We used a validated mechanical model to determine the changes in the shape of the lens during accommodation and disaccommodation. The relative contribution of lens stiffness to loss of accommodative amplitude with age was determined by varying lens stiffness in the model. The changes in lens stiffness with age were based on the results of two recently published studies. In the first study we showed that lens stiffness increases exponentially with age, and in the second study we showed that there is a considerable stiffness gradient within the lens that changes with age. The results of both studies were incorporated in the mechanical model. The model showed that it is not the increasing stiffness of the lens with age, but rather the changing stiffness gradient that influences accommodative amplitude. The results show that the changing stiffness gradient in the lens may be responsible for almost the entire loss of accommodation with age.